I attempted to google this topic; however, I was unable to find a suitable explanation. If anyone could give me a brief description of the physics behind a DC to AC power inverter, I would really appreciate it.

Caleb

I attempted to google this topic; however, I was unable to find a suitable explanation. If anyone could give me a brief description of the physics behind a DC to AC power inverter, I would really appreciate it.

Caleb

Hello, Caleb,

First, they 'chop' up the DC input electronically which results in something between a true square wave and a sawtooth wave. That is then passed through a step-up transformer with enough turns to produce a higher value than the disered output voltage because the next step is filtering/smoothing. The filter is a L/C network (inductive, capacitive) which forces the output into a more nearly sine wave shape. The purity of the sine wave depends on the cost of the unit. The higher the price, generally the better the filtering will be and a better sine wave output.

That was pretty much a rough overview, anything in specific you'd like to know? I've worked with these things for a number of years.

Just do a search on Oscillator circuits. Although you need to know a bit of electronics to understand them. Basically, the circuit uses an inductor and a capcitor to set up electric oscillations. That's how you get AC from DC. If you know a something about electromagnetism, you can figure out how an inductor (a simple metal coil, really) works.

Please, I have find a module with 4 leads which probably converts dc to ac
it is a module of mitsubishi electric but I can't find its data sheet in the site of mitsubishi. It's code is SF 16DAZ-H1-4, Could you please help me find how it works? and where to buy it or where to find something similar?


Hello, Caleb,

First, they 'chop' up the DC input electronically which results in something between a true square wave and a sawtooth wave. That is then passed through a step-up transformer with enough turns to produce a higher value than the disered output voltage because the next step is filtering/smoothing. The filter is a L/C network (inductive, capacitive) which forces the output into a more nearly sine wave shape. The purity of the sine wave depends on the cost of the unit. The higher the price, generally the better the filtering will be and a better sine wave output.

That was pretty much a rough overview, anything in specific you'd like to know? I've worked with these things for a number of years.

Please, I have find a module with 4 leads which probably converts dc to ac
it is a module of mitsubishi electric but I can't find its data sheet in the site of mitsubishi. It's code is SF 16DAZ-H1-4, Could you please help me find how it works? and where to buy it or where to find something similar?

No, that's just a solid-state relay, not an inverter.

Just do a Google search on Power Inverters or DC Inverters and you should find hundreds of them for sale.

Not often used anymore, but in WWII one converted voltages and dc to ac if you liked by a motor generator - one shaft with motor on one end and generator on other.

I had one cheap army surpluss just after WWII. - It was a PE-103 (why that usless infromaion is still in my accessible menory I do not understand.) Car batteries were 6VDC back then so that was the motor input to spin the shaft. The generator was also DC output at 500V. - just perfect for a transmitter with final stage an 807 vacumn tube driven by a 6L6. I.e. I had a 10m amatuer radio in the car and nearly ran off the road one day when my "CQ" was responded to by a guy in Cuba, while I was driving.

Car batteries were 6VDC back then so that was the motor input to spin the shaft. The generator was also DC output at 500V.
technically not an inverter.
an inverter converts DC to AC.

Not often used anymore, but in WWII one converted voltages and dc to ac if you liked by a motor generator - one shaft with motor on one end and generator on other.


What you've just described is what's commonly called a motor-alternator. And they've been replaced by oscillator driven solid-state switches. Besides the fact that the needed occasional attention (brush replacement, commutator undercutting) the biggest reason for their demise is that it was completely impossible for them to respond to a changing load. Too much lag time in correcting both voltage and frequency.

Incidentally (I'm sure you know this but many won't), the solid-state switches and oscillator is found at the heart of EVERY UPS system on the market today. They're everywhere.

What you've just described is what's commonly called a motor-alternator.
motor - generator. alternators put out AC not DC.

motor - generator. alternators put out AC not DC.

No, precisely a motor-alternator because AC is what you want! That's what he started talking about before he switched to DC-DC and why I cut off that part of his post. ;)

Car batteries were 6VDC back then so that was the motor input to spin the shaft. The generator was also DC output at 500V. -

What you've just described is what's commonly called a motor-alternator.
read it again.

edit:
ah yes, i see what you mean.

read it again.

edit:
ah yes, i see what you mean.

:D ;)

technically not an inverter.
an inverter converts DC to AC.Correct. That is why, in original post, I said: "one converted voltages" or " DC to AC if you liked." Back then, even the big rotating machine that made your 110VAC* was also called a "generator" - I do not know what the electric company's mechanical to AC energy converter is called today, but bet they still have "generators" at the power plant.

With reguard to my calling the output winding a "generator" that is also correct back in WWII era, even if the output were AC. - Like 12V batteries, alternators had not been developed (commercially at least) yet.
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Slightly related, but worth mentioning is that solar cells make DC and an inverter is required - this adds to the cost of solar cell power, as does the capital cost of miles of wire to collect the energy from a large spread out collector system. As it turns out, if you investigate it deeply, unconcentrated solar PV power is not competive against grid power, even if the solar cells were free! I do not mean to imply that concentrated PV power is competive - I think that very likely it is not also. PV cells rapidly lose efficiency as they get hot so you can not concentrate much and the reflectors are not free.) If the cells were free, concentration would mainly save on the cost of the collection wiring and perhaps reduce the number of inverters, but each would need to handle more power so probably not much savings there. Also it is likely that the most economical system has many local inverters and step up transformers to keep the cost of copper wire down.
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*Since we are being careful with terms, I will note that while that big machine at power plant did make your 110VAC, it did not do so directly. - It made much higher voltage to get the power efficient to a transformer closer to your house. (Quite possible via a sub-station' transformers also)

*Since we are being careful with terms, I will note that while that big machine at power plant did make your 110VAC, it did not do so directly. - It made much higher voltage to get the power efficient to a transformer closer to your house. (Quite possible via a sub-station' transformers also)
the voltage is stepped up at the source for transmission.

and since we are being careful with terms it should be noted that the 110VAC is actually the RMS value, not the peak value.

the voltage is stepped up at the source for transmission.

and since we are being careful with terms it should be noted that the 110VAC is actually the RMS value, not the peak value.

That's correct. But if we are being very careful ;) it's interesting to note that there's no longer 110VAC available in North America. For a long time, the standard was 110-115V but for many years now it has been 120-125V.

Also, throughout North America, there are usually (with a few rare exceptions) three different voltage levels used in the transmission grid. As you said, Leo, there is a large "transformer farm" at every generating station to step up the 30KV output pf the "generators (actually, 3-phase alternators) to around 765KV for long-haul transmission. In many cases, the actual number is 1200KV.

As the power gets closer to the consumer end, it typically is reduced in voltage by a transmission substation before finally being sent to the distribution buss substation. Leaving there, is the lines that run up and down the streets and roads and the voltage is 7,200KV. And that's the input to the transformer on the pole (or ground) outside your house.

There are a couple of exceptions to the regular distribution grid and one is the HVDC (high-voltage DC) lines in place in a few areas of North America and other countries. Some of them operate at voltages as high as 500KV while 250-300KV are more common.

The other most common exception is what's called "electrical traction power" and is supplied under contract to city rail and subway systems. In New York, the requirement is 600VDC.

the voltage is stepped up at the source for transmission...Again correct, but i am almost sure it is a lot higher than 110Volts - basically as high as the insulation between winding turns will permit, but standadardized of course - I once knew a typical but now am guessing around 1200 Volts.

BTW, do you know why we designate the RMS voltage instead of the Peak? - Answer goes all the way back to "Stupid Edison" - he was good businness man but never really understood AC. AC is designated by its RMS so it could be compared directly to Edison's DC (same heating value or same light bulbs etc.)

By edit: Just skimmed Read Only's post about transmission. DC is making a comeback in transmission. This is because the crona loss limits the voltage used. with DC you can continusly be just below significant corona loss voltage and over and given line move more power because of this. The conversion at both ends first to and then from DC back to AC, with modern solid state devices is sufficient cheap and efficient to make this interesting (better?). That begins in Sweden about 25 years ago and AEP did at least one line in the US about 20 years ago. - I do not know recent facts as to used of DC transimission. As I recal, there were some worries about inducing corrosion in pipelines, if the Earth was carying any DC return currents.)

Also: peak x (sqrt 2) /2 = RMS or approximately peak = RMS/(0.707) but as never a perfect sine wave, the 0.707 is "good enough for government work." ;)

Again correct, but i am almost sure it is a lot higher than 110Volts - basically as high as the insulation between winding turns will permit, but standadardized of course - I once knew a typical but now am guessing around 1200 Volts.

BTW, do you know why we designate the RMS voltage instead of the Peak? - Answer goes all the way back to "Stupid Edison" - he was good businness man but never really understood AC. AC is designated by its RMS so it could be compared directly to Edison's DC (same heating value or same light bulbs etc.)

By edit: Just skimmed Read Only's post about transmission. DC is making a comeback in transmission. This is because the crona loss limits the voltage used. with DC you can continusly be just below significant corona loss voltage and over and given line move more power because of this. The conversion at both ends first to and then from DC back to AC, with modern solid state devices is sufficient cheap and efficient to make this interesting (better?). That begins in Sweden about 25 years ago and AEP did at least one line in the US about 20 years ago. - I do not know recent facts as to used of DC transimission. As I recal, there were some worries about inducing corrosion in pipelines, if the Earth was carying any DC return currents.)

Also: peak x (sqrt 2) /2 = RMS or approximately peak = RMS/(0.707) but as never a perfect sine wave, the 0.707 is "good enough for government work." ;)

Correct, but it's not only corona losses. There are inductive and capacitive losses also. In addition, there is distortion of the sine wave that necessitates the addition (and it's resulting inherent losses) of phase-correcting networks at points along the transmission path.

Yes, corrosion of pipelines and other buried utilities, like telephone cables, was a MAJOR problem. Because of that, every system that I'm aware of now uses two conductors. No more "earth return."

Correct, but it's not only corona losses. There are inductive and capacitive losses also. ...
Yes, corrosion of pipelines and other buried utilities, like telephone cables, was a MAJOR problem. Because of that, every system that I'm aware of now uses two conductors. No more "earth return."I think corona is byfar the most important limit on transmission voltages. Inductive loses would be current proportional and only in feromagnetic materials (the steel towers - in practical cases) Even this loss would not be present with DC transmission as the losses are from the finite area of the hysteis loop. this also true for the capacitive loses, but they scale with the voltage (probably as at least the square, but I do not know) If you have a really dark night, you can see the bluish corona glow from most long distance transmission lines. If there is no wind or other background noise (and you are not too old :( ) you can hear the hiss.

I think the pipeline corrosion problem was well recognized before the first DC line was made and it had a return wire for that reason; however, any user might "ground" the "cold" side of the two wire supply (many probably would just from habit like the 3 pin AC plugs often do.) If this is done, the Earth carries a small part of the return current in parallel with the intentional return wire.

...there is distortion of the sine wave that necessitates the addition (and it's resulting inherent losses) of phase-correcting networks at points along the transmission path. ...I think, almost sure, that capacitance is added along the line as the natural inductance is dominate. This is not done to keep the sign wave, but the unity power factor - if do not have unity the line transmits less power (actually more accurate to say: loses more in the I^2 R loses while transmitting the energy the users want at that instant). That is the capacitors added, although with loses, actually REDUCE THE NET LOSE.

I think the line inductance if not compensated with capacitors would actually help keep the power more sine like. Certainly it would help smooth out the steps that some simple light dimmers etc. make by switching on and off 120 time a second. Floresent lights may also go off just before zero crossing and restrike after it with the still existing ionization. Any arc-welder can screw up the sine wave with multiple off / on strikes also and as they opperate at atmosphic pressure, the restrike is like first turn on. (Residual ionization dies quickly at one atmosphere.)

I think corona is byfar the most important limit on transmission voltages. Inductive loses would be current proportional and only in feromagnetic materials (the steel towers - in practical cases) Even this loss would not be present with DC transmission as the losses are from the finite area of the hysteis loop. this also true for the capacitive loses, but they scale with the voltage (probably as at least the square, but I do not know) If you have a really dark night, you can see the bluish corona glow from most long distance transmission lines. If there is no wind or other background noise (and you ar not too old :( ) you can hear the hiss.

I think the pipeline corrosion problem was well recognized before the first DC line was made and it had a return wire for that reason; however, and user might "ground" the "cold" side of the two wire supply (many probably would just from habit like the 3 pin AC plugs often do.) If this is done, the Earth carries a small part of the return current in parallel with the intentional return wire.
Sorry, Billy, but I believe you'd be quite surprised at the magnitude of L/C losses in high-tension transmission lines. And you're quite mistaken about the need for the presence of ferromagnetic material to create inductive losses. I'm in no way denying that corona losses are the greatest but the distortion created by the L/C components present in any long distance transmission system is also significant. And that distortion requires the insertion of the phase-correcting stations I mentioned which also adds additional loss.

Yes, there is a tiny amount of return through the earth. It isn't large because the resistance is much higher than that of the return wire. But because it has always been present (way prior to the first HVDC installation) companies that use buried utilties have long been using sacrificial anodes as a part of their installation. Some even employ reverse DC flow supplies - phone companies as well known for that as are some pipelines.

What you've just described is what's commonly called a motor-alternator. And they've been replaced by oscillator driven solid-state switches. Besides the fact that the needed occasional attention (brush replacement, commutator undercutting) the biggest reason for their demise is that it was completely impossible for them to respond to a changing load. Too much lag time in correcting both voltage and frequency.

Incidentally (I'm sure you know this but many won't), the solid-state switches and oscillator is found at the heart of EVERY UPS system on the market today. They're everywhere.

I think the device is more commonly called a dynamotor. That's dynamo plus motor, and dynamo is generally accepted as the term for a DC generator. It is true that this setup would have trouble responding to a changing load, but a good design for a radio has high immunity to swings in B+ voltage. Tube or transistor, in my hobby work I avoid designs that have any great dependence on either the exact supply voltage or the exact characteristics of the components.

Someone mentioned the "ground return." I don't know that anyone, for any large scale power generation, ever used the ground as a return for the power, one wire as one leg, the ground as the other. The "ground return" is used for unbalanced consumption because the current is generated as three-phase and generally consumed as single phase. The three legs of the supplied power from the generating station will never, ever carry anywhere near the same wattage. This is why the center tap on the secondary side of a "pole pig" is grounded and it is also the neutral line. The house ground is for grounding electrical boxes, switches, and outlets. The neutral is not a good substitute for this. The house ground's function is to prevent electrical shock. If a wire comes loose in your appliance the electricity goes to ground, not your fingers.

One problem that I think that people will find in a DC line is that each line acts as a heavy-duty condenser. If you have a wire in the first place that is insulated from the ground its mass will charge up to hundreds or thousands of volts and when you have runs kilometers long that's a lot of stored energy. It's a really good idea to have drains here and there.

I think the device is more commonly called a dynamotor. That's dynamo plus motor, and dynamo is generally accepted as the term for a DC generator. It is true that this setup would have trouble responding to a changing load, but a good design for a radio has high immunity to swings in B+ voltage. Tube or transistor, in my hobby work I avoid designs that have any great dependence on either the exact supply voltage or the exact characteristics of the components.

Someone mentioned the "ground return." I don't know that anyone, for any large scale power generation, ever used the ground as a return for the power, one wire as one leg, the ground as the other. The "ground return" is used for unbalanced consumption because the current is generated as three-phase and generally consumed as single phase. The three legs of the supplied power from the generating station will never, ever carry anywhere near the same wattage. This is why the center tap on the secondary side of a "pole pig" is grounded and it is also the neutral line. The house ground is for grounding electrical boxes, switches, and outlets. The neutral is not a good substitute for this. The house ground's function is to prevent electrical shock. If a wire comes loose in your appliance the electricity goes to ground, not your fingers.

One problem that I think that people will find in a DC line is that each line acts as a heavy-duty condenser. If you have a wire in the first place that is insulated from the ground its mass will charge up to hundreds or thousands of volts and when you have runs kilometers long that's a lot of stored energy. It's a really good idea to have drains here and there.

It's correct that a dynamotor produces DC - but we were talking about AC output and that device is rightly termed a motor-alternator.

HVDC transmission systems are well desigined and a part of that design calls for it to operate at very high voltages to overcome I-square-R losses just as it is with AC transmission facilities. There's no need for "drains" which would also just create additional losses in the system.

Sorry, Billy, but I believe you'd be quite surprised at the magnitude of L/C losses in high-tension transmission lines. And you're quite mistaken about the need for the presence of ferromagnetic material to create inductive losses. I'm in no way denying that corona losses are the greatest but the distortion created by the L/C components present in any long distance transmission system is also significant. And that distortion requires the insertion of the phase-correcting stations I mentioned which also adds additional loss....Until one of us gets some references to back our opinions up, we will just just disagree on much of this. You are correct in that you do not need to have feromagnetic materials to have a loss. There is the eddy current loss in any conductor subjected to an AC (voltage) field, but as noted earlier this loss and the hysterisis loss in the feromagnetic materials does not exist for the DC transmission line which got us speaking about transmission line loses.

I believe the energy loss in high voltage AC line are, in order of importance:
(1) I^2R loss due to current flowing in the line
(2) Corona loss due small wires have sufficient electric field at their surface to exceed the dielectric strength of the air. BTW this is why all high voltage lines do not use one single conductor, but usually 4 with at least 10cm separations so the the field at the wire surface is much less.
(3) Magnetic hysterious Loss in the iron of the towers. (Beats 4 and 5 as parts of tower are much closer to wires.)
(4) Eddy currents in the ground, when wet.
(5) Dielectric losses in the ground when dry
(6) Birds, their nests mainly, kite strings and tree limbs etc. until removed.
(7) Rain drops carring charge to ground after contact with the line.
(8) Shorts, including intentional ones with lightening induced "circuit breakers" briefly operating.

I will estimate the relative importance, annually, using ">" to be "order of magnitue" and >- to be factor of 5.
E.g. >>- is a factor of 50 difference and>>>>- is factor of 5,000. (All just my guesses.)

For AC line:
1 >>>> 2* >>> 3 >- 4 >- 5 > 6 >> 7 ~ 8
For DC line:
1>>>>- 2* >>>>>>> 7 ~8 and 3,4,5,6 are zero loss.

Post you guesses, or better, researched results with source link. If wildly wrong, I will be happy to learn what is correct. I included the conduction losses on surface of the insulators supporting the wires and dielectric loses in them with items 4 & 5 although a small part of these loses might be consider to be more like items 6 & 8. I also note that the monetary losses probably move item 8 ahead of item 6 for both AC and DC lines as repairman may be needed, especailly if the tower is knocked down by wind or some anti- government nut etc.

I still think that it is for "power factor correction" that capacitors are added along the way. I do not even understand how they can reduce the "inductive loses," which are unchanged if the current is unchanged.

However, perhaps we are not in disagreement much as if the power factor is lowered, then the current is increased to deliver the same power to users. That said, it still seems (to me) silly to call the increased losses without capacitors "inductive losses" as the increase in I^2R (item 1) is a 1000 times or more greater than the increase in "inductive loses." If you had said that the capacitors are added to reduce the "resistive loses," then I would agree. So perhaps it is more the names, than the physics, we are discussing on this point.
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*I am assuming each "wire" is actually 4, spaced properly.

Insert # 2.5, magnetic hysteresis losses in the steel wire strands braided together with the aluminum strands of the cable for strength. This may be 1.5, not sure.

Sorry, Billy, but I believe you'd be quite surprised at the magnitude of L/C losses in high-tension transmission lines. And you're quite mistaken about the need for the presence of ferromagnetic material to create inductive losses. I'm in no way denying that corona losses are the greatest but the distortion created by the L/C components present in any long distance transmission system is also significant. And that distortion requires the insertion of the phase-correcting stations I mentioned which also adds additional loss.

Yes, there is a tiny amount of return through the earth. It isn't large because the resistance is much higher than that of the return wire. But because it has always been present (way prior to the first HVDC installation) companies that use buried utilties have long been using sacrificial anodes as a part of their installation. Some even employ reverse DC flow supplies - phone companies as well known for that as are some pipelines.

Is earth-grounding a good idea still?

I would have thought that earth-return-grounding was popular, because the earth is so big, that its resistance would be lower than that of the wire, and so costs of wiring can be reduced. Obviously, at least 1 wire is needed, to avoid obvious short-circuiting and deliver power to where it needs to go. Isn't it a similar concept in grounding in cars?

But, are there strange effects, glows or cows being affected, by electrical currents running through the earth, or are these widely scattered enough to have neglible effects? I have heard of weird stuff like that, but it's probably in that unsubstanciated category like the ridiculous stories about UFOs.

Shouldn't most everybody at least have an inverter?

I have a 500 watt invertor. I figure it to be sort of like "a poor man's generator." I thought about all the stuff in my home that needs electrical power, that no longer works during a power outage. So should I buy a generator? Generators are big, heavy, bulky, expensive, and may not even start when needed. The better, more long-lasting generators aren't portable, but run on natural gas. The cheaper ones often have stale oil and gasoline in them, that may sit neglected for years. In comparison, while an invertor won't adequately power a refrigerator to guard against food spoilage, it will run most anything else, that isn't "power hungry." And for no more cost, than a "toy" battery-powered TV, I could theoretically power up my full size 27" fullscreen HD tube TV. Using my long yard power tool extension cords, and hooking up my invertor to my car battery. But should I? Those invertors in the affordability price-range, I wonder if their power is "pure" enough to power such expensive electronics safely? I saw some demo at an electronics store, with Monster surge suppressors, comparing how "noisy" electrical power is from a typical power strip, as compared to one of their pricy surge suppressors. Lots of noisy hum from the power strip, and very quiet from the speaker when the knob is turned to the Monster surge suppressor. Presumably, they are filtering out the 60 Hertz AC hum, since they both would still have it, leaving the customer to hear all the other garbage "noise" on the power line?

So far, I haven't really powered anything other than a test 60-watt lamp, and an electric cordless/corded shaver during a power outage, that had long since lost its ability to hold a charge.

Insert # 2.5, magnetic hysteresis losses in the steel wire strands braided together with the aluminum strands of the cable for strength. This may be 1.5, not sure.Good point - insert accepted as 1.5 as it may well beat out the corona if simple steel wire, but only as 2.5 if some steel with small hysterisis loop is used.

Is earth-grounding a good idea still?
I would have thought that earth-return-grounding was popular, because the earth is so big, that its resistance would be lower than that of the wire, and so costs of wiring can be reduced....
Shouldn't most everybody at least have an inverter?
I have a 500 watt invertor. I figure it to be sort of like "a poor man's generator." I thought about all the stuff in my home that needs electrical power, that no longer works during a power outage. So should I buy a generator? ...If there is a lethal votage inside a metal box (for example a microwave) I think grounding is a very good idea. Not much corrsion damage from ground currents with AC anyway.

Your inverter would let you watch TV during storm that took down the wires etc, but I would not do it with car battery supply for more than a few minutes at a time. What you need is an electric boat battery which looks just the same, but is structurally very different inside.
Car batteries have many thin plates for high surface area so you can draw several hundred amps for 10 or even 15 seconds before the liquid adjacent to the plates is too depleted of the ions doing the conduction in the liquid (ie before significant "polarization set in") A battery deside for continuous current (but lower) for an hour or so is with relatively few heavy plates than will not warp and short out as they get hot (well warm, as they are in liquid) If you take 500 watts out from you inverter then you are taking from "12V" car battery at least 45 amp from it. (nothing is 100% efficient, perhpas even 50 amps). I bet that will cause an internal short in around 10 minutes or less.
Thus, better to just not open your refrigerator door until the power returns.

What you say about the large cross section, low resistance, of the Earth path is 90% true, but even with a long metal stake driven in the ground that first few feet is a high in-series resistance. In the old days, in rural areas, sometimes a one wire telephone was used, but if you wanted it to work well, you had to pour some salt water on the ground around the "grounding stake," at least in the dry season.

Is earth-grounding a good idea still?
I would have thought that earth-return-grounding was popular, because the earth is so big, that its resistance would be lower than that of the wire, and so costs of wiring can be reduced....
Shouldn't most everybody at least have an inverter?
I have a 500 watt invertor. I figure it to be sort of like "a poor man's generator." I thought about all the stuff in my home that needs electrical power, that no longer works during a power outage. So should I buy a generator? ...If there is a lethal votage inside a metal box (for example a microwave) I think grounding is a very good idea. Not much corrsion damage from ground currents with AC anyway.

I tend to keep things a long time. Several transformers inside various devices I have owned have developed a connetion between their case and the primary winding. I am not sure why, but it has alway been relatively near the one of the two AC line wires. (Pehaps one wire goes straight to the iron core and begins wrapping around and is covered by many turns so it gets hotter as the turns make thermal insulation also and the insulation on the inner most layer of turns fails?) Anyway, I learned to paint with red finger nail polish one side of the AC plug and never plug it in with that side was up. - Sort of primative three wire system with only two wires back when there were no three wire plugs. Then the mild "leakage current" shock, which I had been getting from touching the case, ceased.

Your inverter would let you watch TV during storm that took down the wires etc, but I would not do it with car battery supply for more than a few (<5 ) minutes at a time. What you need is an electric boat battery which looks just the same, but is structurally very different inside.

Car batteries have many thin plates for high surface area so you can draw several hundred amps for 10 or even 15 seconds before the liquid adjacent to the plates is too depleted of the ions doing the conduction in the liquid (ie before significant "polarization" set in). A battery designed for continuous current (but much lower) for an hour or so is with relatively few heavy plates than will not warp and short out as they get hot (well, very warm as they are in liquid).

If you take 500 watts out from you inverter then you are taking from the "12V" car battery at least 45 amp from it. (Nothing is 100% efficient, perhpas even taking 50 amps). I bet that will cause an internal short in around 10 minutes or less.

Thus, better to just not open your refrigerator door until the power returns or at least have the frig load on and then disconnect it for TV and lights on. I doubt, once it is running, that the frig takes 500 W but do not know.

What you say about the large cross section, low resistance, of the Earth path is 90% true, but even with a long metal stake driven in the ground that first few feet is a high, in-series, resistance. In the old days, in rural areas, sometimes a one-wire, party-line*, telephone was used, but if you wanted it to work well, you had to pour some salt water on the ground around the "grounding stake," at least in the dry season.
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*Every one had a different ring pattern (and you though different "ring tones" for you cell phome were new!) It was fun to listen in, but not wise to do so as the current divided and sound got weaker.

However, perhaps we are not in disagreement much as if the power factor is lowered, then the current is increased to deliver the same power to users. That said, it still seems (to me) silly to call the increased losses without capacitors "inductive losses" as the increase in I^2R (item 1) is a 1000 times or more greater than the increase in "inductive loses." If you had said that the capacitors are added to reduce the "resistive loses," then I would agree. So perhaps it is more the names, than the physics, we are discussing on this point.
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*I am assuming each "wire" is actually 4, spaced properly.

Actually, I don't think we're in disagreement at all. Yes, corona losses are by far the largest. Right at the moment I've no references readily available regarding the others but I do know they play contributing roles.

As to the phase-correcting networks, yes they are capacitors and it's merely a choice of wording. Some engineers call them "phase-correcting" while others say "power factor correcting" or "power factor balancing" networks. But no, they cannot do a thing about resistive losses - they correct the phase angle that has been distorted by induction. Exactly the same as where PF correcting capacitors are used in customer installations that have a lot of inductive loading (large electric motors) in their plant.

Incidentally, for the benefit of the few members that may not be aware of it, the skin effect is quite large at these very elevated voltage levels. For that reason, there's been some work done using hollow (tubular) conductors rather than the conventional solid stranded ones. Again, I don't have any references handy but I've read that it seems to be resulting in some degree of success. It reduces the weight loading on the support towers (and stresses on the insulators) and could result in cheaper construction costs. But so far I've not seen where the jury has returned a verdict.

...Incidentally, for the benefit of the few members that may not be aware of it, the skin effect is quite large at these very elevated voltage levels. ...Jeez! We should have stopped when we agreed.:eek:

I hope you only mean that higher voltage drops along a wire correspond to / make higher currents and thus the skin effect loses are higher.

For any given metal, the "skin depth" and curent distribution within the metal volume is a function of frequency alone. Voltage has nothing to do with it. (Actual it is very very slighly more complex as the resistance is a function of temperature, so it is not really "the same metal" when carrying more current. Also the skin may thus has higher resistivity than the interior, if rod is short. If rod is very long - not losing heat to the ends - then interior is at same temperature as surface. No sane person worries about this.)

I do not remember exactly* but roughly, much more than half (90%?) of the AC current will flow in only the first wavelength deep into the conductor; but at 60 hz the current is essentially uniform thru out any reasonable thickness of metal conductor because the wavelength is so much larger than the conductor.
--------------------------
*Skin effect falls out of Maxwell's equations with parallel E field incident on the surface. - A somewhat messy boundary value calculation with real resistivity, even constant, on one side of a plane boundary (infinitely deep) and vaccum on the other, incident E field side. I did it years ago, but can not remember what fraction of the energy lost (not reflected) dies in the first wavelength, but it is surprisingly high.

Jeez! We should have stopped when we agreed.:eek:

I hope you only mean that higher voltage drops along a wire correspond to / make higher currents and thus the skin effect loses are higher.

For any given metal, the "skin depth" and curent distribution within the metal volume is a function of frequency alone. Voltage has nothing to do with it.

Nope, sorry, Billy, but you've slipped another cog. ;) I've very much aware of the skin effect as a result of frequency since I worked with rectangular and circular waveguides in the 4 - 6 MHz range for a good number of years. But the skin effect is also very real at extremely high DC voltages as well. Basically, the effect is due to the large number of electrons present which are naturally trying to repel each other. And since the conductor is "full" of them, they are pushed toward the surface since the surroundings contain almost no charge to repel them.

I see the misunderstanding, though - I failed to mention that I was still talking about HVDC transmission. :)

Resistive losses are fought by running as high a voltage as is practical through the lines.

Corona loss is not such an issue for DC because with DC corona simply makes a larger conductor.

Good point about the skin effect of DC, there.

...the skin effect is also very real at extremely high DC voltages as well. Basically, the effect is due to the large number of electrons present which are naturally trying to repel each other. ...
I see the misunderstanding, though - I failed to mention that I was still talking about HVDC transmission. :)OK I guess we do still agree. I had never heard (or even thought about) what you are calling a skin effect. I have done a little work with a Van de Graph machine so know all about the electrons going to the surface, but never described it a due to the interior being "full", but guess there is nothing wrong with saying that. I think of it as the interior keeps net zero charge (number of protons and electrons essentially equal). All the excess electrons on the surface are free to move and keep as far from each other as possible due the repulsion between like charges. (In the interior only the "valence band" electrons are free to move - slide along the "Fermi surface", if that means anything to you.)

If you could put a bunch of electrons in the interior of a metal, they would immediately flow thru it to the surface. - Hey that is exactly how the Van de Graff works. - they ride up the inside belt, get pulled off by the comb of spikes, and out to the surface they go! :cool:

What if anything can you tell me about the resistance of these excess surface electrons to movement along the surface by electric field (votage drop along the surface? Is it any different that the "free electrons" that are keeping charge neutrality when they flow (very slowly, compared to thermal velociies, drift) under the field. I bet the "excessones" are all entergetically above the fermi surface. I wonder if they could form Cooper Bardine & S? pairs and be high temperature supercnductors under any conditions? - doubt it but interesting thought. I never though about any of this before and it is now time to go to bed.

In a pure metal there are lattice defects that scatter electrons and phonon waves that do the same, both causing the electrical resistance. At room temperatures, in annealed metals at least, I am almost sure the phonons are by far the more important.

I do not know how the phonons behave when nearing the surface, but bet they reflect back into the interior. There is probably a set of "surface confined" waves also, distinct from the thermal phonons. Lot of interesting questions to think about while falling asleep tonight. If I am still so ignorate about all this tommorow, I may need to open a solid state book again. nite-nite.

BTW, do you know why we designate the RMS voltage instead of the Peak? -
110VACRMS is approx 170 VP (peak).
we designate RMS values because a 170 VP gives an equivalent heating value as 110 VDC. this is only accurate for sine wave AC.

edit:
due to read-onlys keen eyeballs i must clarify.
the 170 VP is wrong in both value and nomenclature.
the correct value is app. 155.8 and the nomenclature is peak to peak.

110VACRMS is approx 170 VP (peak).
we designate RMS values because a 170 VP gives an equivalent heating value as 110 VDC. this is only accurate for sine wave AC.

Mmmmm... might want to try the math again, Leo. ;) The peak reading would be about 77.8v and is more commonly expressed as peak-to-peak which is about 155.6v.

Yes, Billy, I still remember Fermi surface, crystal lattice of metals, semiconductors, and all the rest, But it's been a VERY long time and that was simply studying as opposed to very little application work on my part. So most of it has just eroded away over time.

Interesting thoughts, though, but I'd need to locate some old books and notes that I probably don't even have anymore after moving my household many times in the intervening years. <sigh>

Mmmmm... might want to try the math again, Leo. ;) The peak reading would be about 77.8v and is more commonly expressed as peak-to-peak which is about 155.6v.

Try it again yourself, RO. The RMS voltage of a sine wave is .707, one over the square root of two, times the peak voltage. Peak to peak is twice that result. About 155.8 is right for the peak, and 311.6 for the peak to peak.

Try it again yourself, RO. The RMS voltage of a sine wave is .707, one over the square root of two, times the peak voltage. Peak to peak is twice that result. About 155.8 is right for the peak, and 311.6 for the peak to peak.

Incorrect. The original 110V is already peak-to-peak at RMS so the true value of PTP is 155.58698.

Does not a grounding post need to be deep enough to hit the water table ?
If it does not, I fail to see how you get much conduction thru dry, non homogeneous dirt. But if you hit the water table you have a reliable conductor.
Water itself, pure water that is, is an insulator. Its the impurities that make its resistivity lower. In high voltage engineering, we have to deionize the water to use it as a non conducting coolant.

Skin depth at 60Hz; For both copper and aluminum it is surprisingly smaller than one might imagine. As I recall, around 1/3 inch [not sure about that number, but it is close]. Also if your currents are in the 100's of amps, even 4/0 cable is affected and the design must accomodate this.

Also, note that with a simple diode and capacitor, an alternator becomes equivalent to a generator. Much cheaper than the generator or MG set as some call it.

Does not a grounding post need to be deep enough to hit the water table ?
If it does not, I fail to see how you get much conduction thru dry, non homogeneous dirt. But if you hit the water table you have a reliable conductor.
Water itself, pure water that is, is an insulator. Its the impurities that make its resistivity lower. In high voltage engineering, we have to deionize the water to use it as a non conducting coolant.

Skin depth at 60Hz; For both copper and aluminum it is surprisingly smaller than one might imagine. As I recall, around 1/3 inch [not sure about that number, but it is close]. Also if your currents are in the 100's of amps, even 4/0 cable is affected and the design must accomodate this.

Also, note that with a simple diode and capacitor, an alternator becomes equivalent to a generator. Much cheaper than the generator or MG set as some call it.

Hello, Paulfr,

No, it's impractical to try and drive the rod into the watertable. In most locations, that's a depth of 30' and often MUCH more. Nor is it necessary. There's adequate moisture in the top three feet of practically all soils - otherwise grass, trees and other vegetation could not survive.

The soil gains it's conductivity from the salts that are naturally present in abundance.

If you want to fully mimic a generator with an alternator, it's best to use four diodes (a full-wave bridge rectifier) and a fairly large capacitor to filter out the remaining ripples. The latter isn't totally necessary, of course, it just makes the DC output smoother.

Incorrect. The original 110V is already peak-to-peak at RMS so the true value of PTP is 155.58698.

Is that your final answer?

Is that your final answer?

Sure, that's what I've been saying all along. Earlier, I rounded it to 155.6V but it's still the same number.

Sorry Read-Only, you've got it wrong.
vrms~.707*vpeak
vpeak=.5*vptp

so for vrms=110 vpeak~156 and vptp~310

Will hollow wires be good for high voltage transmissions ?

Sorry Read-Only, you've got it wrong.
vrms~.707*vpeak
vpeak=.5*vptp

so for vrms=110 vpeak~156 and vptp~310

What are you guys doing??????

The 110v RMS number IS a peak-to-peak reading. The peak reading is 55v RMS.

To translate the 110 v RMS peak-to-peak to true peak-to-peak, divide 110 by 0.707 and the result is 155.58689. And the true peak voltage is half of that.

Will hollow wires be good for high voltage transmissions ?

They think it might and that's why they're experimenting with it. It might not be working out, though, because I haven't seen it mentioned anywhere in the past couple of years.

What are you guys doing??????

The 110v RMS number IS a peak-to-peak reading. The peak reading is 55v RMS.

To translate the 110 v RMS peak-to-peak to true peak-to-peak, divide 110 by 0.707 and the result is 155.58689. And the true peak voltage is half of that.kevinlam is doing just fine (correct)

the reason a 110Vac lights W light bulb the same as a 110volts of DC is that over the cycle the I^2R heating is the same. At the instant of the peak AC voltage it is of course heating more than DC and at the instant the AC votage is passing thru zero, it is not heating at all, but on the mean, over the cycle, it is the same. That square factor and the mean or average is why it is called the Root Mean Square namely you square the instantous voltage, take the average over the cycle and then the square root to get back to volts, rather than volts squared. I.e. 110 is the RMS value and the peak is higher in the relationship Kevlam gave (and I gave many post ago in this thread. Again:

Vpeak = Vrms/0.707 and Vrms is the effective heating voltage or DC equivalent voltage for heating. In common case the 110Vdc and 110Vac produce the same heating. What the AC fails to provide near the zero crossing instant, it makes up for near the peak voltage instant by at that time providing more than the 110Vdc does.

Is it possible to have another line which taps into the lost current (from the skin for example) and use this line for other purposes (unstable current) like charging batteries etc.

Eg. if the lines have insulator and over that this other line ie. the tap line.

Well u all r experts so i am taking my chances.

This explanation sounds plausible: (http://www.answers.com/topic/electric-power-transmission)

Transmission lines use ACSR (aluminum cable, steel reinforced) and ACAR (aluminum cable, alloy reinforced) conductors. In an ACSR conductor, a stranded steel core carries the mechanical load, and layers of stranded aluminum surrounding the core carry the current. An ACAR conductor is a stranded cable made of an aluminum alloy with low resistance and high mechanical strength. ACSR conductors are usually used for high-voltage lines, and ACAR conductors for subtransmission and distribution lines. Ultrahigh-voltage (UHV) and extrahigh-voltage (EHV) lines use bundle conductors. Each phase of the line is built with two, three, or four conductors connected in parallel and separated by about 1.5 ft (0.5 m). Bundle conductors reduce corona discharge. See also Conductor (electricity).



Truly hollow conductors probably simply couldn't handle the mechanical load. The hollow conductors that I found on Google were mostly experimental superconducting lines that were hollow so that liquid nitrogen could be run through them.

Is it possible to have another line which taps into the lost current (from the skin for example) and use this line for other purposes (unstable current) like charging batteries etc.

Eg. if the lines have insulator and over that this other line ie. the tap line.

Well u all r experts so i am taking my chances.

Skin current isn't lost current. It is a constant and reliable effect that forces the current to ride on the outside of a conductor. This also forces the current to be borne by a much smaller fraction of the mass of that conductor. The problem isn't lost energy. It's the heating effect that forces the utilities company to use a wider conductor, which is more massive and increases its mechanical load on the towers and on the wire.

Thanks for all that great info all of u.

kevinlam is doing just fine (correct)

the reason a 110Vac lights W light bulb the same as a 110volts of DC is that over the cycle the I^2R heating is the same. At the instant of the peak AC voltage it is of course heating more than DC and at the instant the AC votage is passing thru zero, it is not heating at all, but on the mean, over the cycle, it is the same. That square factor and the mean or average is why it is called the Root Mean Square namely you square the instantous voltage, take the average over the cycle and then the square root to get back to volts, rather than volts squared. I.e. 110 is the RMS value and the peak is higher in the relationship Kevlam gave (and I gave many post ago in this thread. Again:

Vpeak = Vrms/0.707 and Vrms is the effective heating voltage or DC equivalent voltage for heating. In common case the 110Vdc and 110Vac produce the same heating. What the AC fails to provide near the zero crossing instant, it makes up for near the peak voltage instant by at that time providing more than the 110Vdc does.

Yes, yes, yes - I'm fully aware of of why the RMS value is a useful number.

But, EGAD!!! Have none of you seemingly highly-techincal people ever looked at the AC power sine wave on an o-scope, as while chasing chasing noise in an audio amp circiuit????????????????? If you had, you would KNOW that the values I gave were correct.

Many times, I'm an etech. The hot lead swings from ~ +156v to -156v referenced to the neutral lead.

Many times, I'm an etech. The hot lead swings from ~ +156v to -156v referenced to the neutral lead.

Best go back and check your setup, then. That's exactly what you'd see if you're looking across a 220v leg.

I fail to see why some of you cannot understand something so simple. Let's try it THIS way and see if you can catch on, OK? Take the 312v peak-to-peak reading YOU are claiming it is and multiply it by 0.707 to get the RMS value. Would that equal 110V? Absolutely not! Sheesh!

That's where you make your mistake. Vrms is .707 of Vpeak _not_ of Vptp. Vpeak is .5 of Vptp.

Can you people tell me why arent all devices made to run on 12 or 24 volts DC ?

But before that tell me if that can save lot of electricity.

Actually, it would tend to waste energy. Say you wanted an electric motor that handled 1200w. (1200w electricity in for somewhat less than 1200w mechanical out, as no motor is 100 percent efficient). At 12v, that's 100amp. At 120v only 10amp. Since joule losses are proportional to I^2, you would likely have a much less efficient motor, unless you used a lot more copper in the motor. And copper is expensive, so there is economics involved as well. Basically you're looking at an engineering trade off. It's very unusual for a single technological solution to work across all applications. This is just one example.

That's where you make your mistake. Vrms is .707 of Vpeak _not_ of Vptp. Vpeak is .5 of Vptp.You are correct, read only is wrong. perhaps he will understand better if a bridge rectifier were used to flip all the negative half cycles to positive. Ie make uni-polararity highly rippled DC. I do not have time to explain in detal and will be away for two days - perhase you will point out that the heating value is unchanged and only voltage only swings thru 156V now. etc.

That's where you make your mistake. Vrms is .707 of Vpeak _not_ of Vptp. Vpeak is .5 of Vptp.

Well, DRAT! :mad: (Angry at myself!) You are exactly right!!

It wasn't until this evening while sitting down during a Mother's Day Dinner that I started thinking about this again (during some quite moments while everyone was busy eating). And I suddenly realized the exact same thing you just said here.

I used to be a very good service bench tech - all sorts of communications gear - but that was over 30 years ago. Since moving on up in the world and my career, the closest I've come to that sort of work after that has been things like locating a faulty relay or limit switch in heating and air conditioning equipment at home.

My utmost and sincere apologies to everyone here! I made a dumb mistake and want to openly own up to it. Very sorry.

No problem. I've made worse mistakes. It's refreshing to see someone admit it on the forum.

In a desperate attempt to bring this thread back on topic:

More interesting than the standard fixed-frequency, fixed-voltage inverter that has already been summarized are designs that produce variable frequencies and voltages. These are useful in applications where a motor must be powered to run at variable speeds.

http://en.wikipedia.org/wiki/Variable-frequency_drive

The design of systems like this gets very hairy for high-power applications, where the input power is usually multi-phase, and the cost and performance of the switches become problematic. Plus, you can't rely on a steep postfilter to reduce harmonics.

My utmost and sincere apologies to everyone here! I made a dumb mistake and want to openly own up to it. Very sorry.
more balls than most.
will definitely earn you some respect.

post title: Power outage protection, on a cheap budget

Is earth-grounding a good idea still?
I would have thought that earth-return-grounding was popular, because the earth is so big, that its resistance would be lower than that of the wire, and so costs of wiring can be reduced....
Shouldn't most everybody at least have an inverter?
I have a 500 watt invertor. I figure it to be sort of like "a poor man's generator." I thought about all the stuff in my home that needs electrical power, that no longer works during a power outage. So should I buy a generator? ...

If there is a lethal votage inside a metal box (for example a microwave) I think grounding is a very good idea. Not much corrsion damage from ground currents with AC anyway.

No, I don't think that was my question. I am talking about using the ground in place of the common conductor, well probably not from the house to the telephone pole, but rather probably from the high voltage transformers somewhere to the electric power station. Obviously most homes need 2 or 3-conductor wiring, as houses aren't commonly made of conducting metal, but they like to use grounding to eliminate expensive current return conductors over long distances, that are apparently quite unnecessary to complete the circuit.

I think I understand the idea that grounding a metal case to some electrical device, helps insure that any ground leakage produces a short circuit rather than a shock hazard, which then hopefully trips the circuit breaker before anybody can get shocked. Ground fault breakers are a huge improvement upon this idea, which can trip at very low current leakage currents, detected by unequal current loads in the hot and common wires. But what applications should avoid ground fault breakers?

I tend to keep things a long time. Several transformers inside various devices I have owned have developed a connetion between their case and the primary winding. I am not sure why, but it has alway been relatively near the one of the two AC line wires. (Pehaps one wire goes straight to the iron core and begins wrapping around and is covered by many turns so it gets hotter as the turns make thermal insulation also and the insulation on the inner most layer of turns fails?) Anyway, I learned to paint with red finger nail polish one side of the AC plug and never plug it in with that side was up. - Sort of primative three wire system with only two wires back when there were no three wire plugs. Then the mild "leakage current" shock, which I had been getting from touching the case, ceased.

Hmmmm. I wouldn't know which way was better on a 2-conductor non-polarized plug. Old transformer plug power adapters don't "wear out" do they? What if they sit around rarely being used? Can they be much of a fire hazard should they stay plugged in for years? Should I go around every now and then, and feel them to make sure they aren't overheating?

Yeah, I am a packrat too. There's a rule of thumb that claims if you haven't used an item in over a year, you probably don't need it and should sell it, give it away, or throw it away. But then "Murphy's Law" probably would claim, the day after you throw it away, will be the day you finally find a use for it. I figure I can keep small stuff, but throw out the large stuff, as the apparent cost of storage (cost per square foot/(cubic foot if heavily invested into efficient shelving systems) of lost house storage space), likely exceeds the expected value of the item once a use for it is eventually found.

I think I have detected some mild "tingle" from touching a simple electric toaster. What's up with that? Does that mean I should have thrown it away? I tossed one out, since I received a replacement for Christmas or something.

Your inverter would let you watch TV during storm that took down the wires etc, but I would not do it with car battery supply for more than a few (<5 ) minutes at a time. What you need is an electric boat battery which looks just the same, but is structurally very different inside.

But who watches TV for just a few minutes? Why not an hour? Are you suggesting that leaving one's headlights on, can ruin a car battery, and not merely result in having to get a jump start? I figure that heavy loads on the car battery, like watching a regular TV, would drain it within what? an hour? But even cranking up the engine to keep the charge, and buying replacement gasoline, is generally cheaper than buying a generator, provided it doesn't occur very often. A car already contains a handy "generator," but for that use, it isn't very efficient, but relies on equipment that most people already have anyway. The invertor is so small I can stick it in a drawer, out of the way. For seldom use, investing in a boat "deep cycle" battery wouldn't be particularly cost-effective, so should I?

Car batteries have many thin plates for high surface area so you can draw several hundred amps for 10 or even 15 seconds before the liquid adjacent to the plates is too depleted of the ions doing the conduction in the liquid (ie before significant "polarization" set in). A battery designed for continuous current (but much lower) for an hour or so is with relatively few heavy plates than will not warp and short out as they get hot (well, very warm as they are in liquid).

Surely just watching TV wouldn't make my car battery get hot, but just mildly warm, if that? Isn't most of the heating in the invertor itself, which does have a fan within it. So are you suggesting that I power only the TV, and not add to the load, plugging up a lamp? Now most likely, during some power outage/storm, I would just go to sleep, or power up a battery radio, and not bother hooking up my invertor. It's more of one of those "just in case" scenarios. Hypothetically, I have guests or family members who say, "We need something to do, can't you get out your invertor and power up some video games or something?" What can I really do with 500 watts that is worthwhile?

I know, power some power tools in a place remote from electrical outlets. Like when the posts broke off my old car battery in the parking lot of the auto parts store. I couldn't put in the new battery, due to the posts being still in the car battery post clamps. My Dad talked some nonsense about leaving my car there and getting it towed. Huh? My Dad used to fix stuff like that. "Can't we just drill out the posts or something?," I asked. So I suggested, let's go to my house and get my invertor, since we had no cordless drills. I thought that better than stringing long extension cords across the parking lot. He tried to power my invertor with his extra "camping" battery from his van, which of course didn't work, because he previously (apparently) flipped off his charge toggle switch too much, and so my invertor "protested" with an audible low voltage alarm. So I suggested, well just start the engine and flip on the charge circuit. Which worked just fine.

And I do have gas logs, for power outage heating. (another excuse not to invest into a generator) Actually, I run my gas logs far more than the furnace anyway, as of course I selected a ventfree model, because my Dad bought me the accessory that almost nobody thinks to get. I have a gas logs wall thermostat, so why pay for natural gas to put heat up the chimney or to heat the basement? (And of course, seeing a small warm flame&glow, rather than hiding it down in the basement, just looks so cozy anyway.) Gas logs zone better, as any room I don't want to heat, I can just close the door. But they don't distribute the heat so well, good thing I don't currently need to heat every room. The wall thermostat works with gas log sets that have the "milivolt system," that provides an electrical connector for an optional regulation switch. The electricity comes from the thermocouple above the pilot light, so there's no batteries, nor any thermostatic remote to sit on. And it never "knows" that there even is a power outage, since its electricity is independent of the power company. It has to be a special thermostat, as ordinary thermostats use too much power to be powered by a pilot light thermocouple. Probably due to that resistor that helps shink the gap between on and off, with an adjustment lever hidden within the thermostat (speaking of the old furnace thermostat). My gas log thermostat is way back on the hallway wall, so that it can't be influenced overly by the heat of the gas logs, as with electric plug-in heaters, that sense their own heat and cut off leaving one cold, then make too much heat on a warm day, due to having to rarely cycle and cycling too much, not feeling their heat due to not having cycled for a while. I have heard that older gas log sets with thermostats on the unit itself, produced similar poor results, unable to maintain temperature from colder to warmer days. Actually, my gas logs thermostat is installed farther away than recommended. Supposedly, the wire should not be over 20 feet? long, lest it might lose too much voltage and fail to activate my gas logs. But come on, it's a sufficient gauge apparently, as wirenutting another extension wire to it, never caused any problems.

My gas logs are rated at 22000 to 32000 BTUs. No wonder they are able to keep me warm by themselves at down to 40 degrees F outside, on low, even in an old poorly insulated house that isn't all that big. That's more heat than running 4 electric heaters. 120V 15A circuits, just aren't all that much energy, thus most every electric hot water heater or air conditioner bigger than a cheap window unit, are all 240V. I usually run them on low, because cranking it up on high, as I might have to do during a power outage, would normally heat too much, cause the thermostat to cut them off, and then I have to see that cold dark hole of a fireplace. I rather they stay on continuously, and let the old furnace come on and push some heat to the extremities of my house, should they need some "help" to keep the house warm on the coldest days of winter. So I set the thermostats to give my gas logs priority in heating, since I think they cost less to operate than my old furnace. Newer high-efficiency gas furnaces capture more of the heat, and don't send as much up the chimney, but the water condensate from newer systems, if not installed exactly correctly, causes yet another reason for the furnace to shut down and require a service visit.

If you take 500 watts out from you inverter then you are taking from the "12V" car battery at least 45 amp from it. (Nothing is 100% efficient, perhpas even taking 50 amps). I bet that will cause an internal short in around 10 minutes or less.

Huh? Are batteries so fragile? And yet they are pushing highly experimental (not ready for the consumer market) hybrid cars as a supposed "green" option? The biggest problem with the old rejected electric cars and the newer trendy hybrid car options, is that the battery technology is nowhere near where it needs to be to power naturally power-hungry cars.

Thus, better to just not open your refrigerator door until the power returns or at least have the frig load on and then disconnect it for TV and lights on. I doubt, once it is running, that the frig takes 500 W but do not know.

Well I looked at the electrical data plate on my old ancient Philco refrigerator, which I think is pretty much on its last legs, as it's gotten more noisy when it starts up, and I have to turn the defrost timer every day to keep it from having defrosting problems. At least I can reach the defrost timer knob hidden behind the plastic front grill. The electrical data plate, suggests its power needs probably slightly exceed my invertors capabilities, so I haven't been brave enough to do a test or anything. If the invertor can't provide enough power, could that damage my refrigerator? I imagine that power-hungry refrigerant compressors, don't much care for low voltage situations. Low voltage might burn such motors up or something by stalling them. The surge voltage rating on my invertor is only 800 watts, which seems a little low. Could it be higher actually, due to manufacturers figuring conservatively what they are sure it can handle for safety or reliability or whatever, or could it be like Consumer Reports report on generators, in which useful load seems to be lacking compared to manufacturers' claimed load capacities? And do compressor motors even "care" that invertors don't produce perfect sine waves? Or is the average RMS all that matters?

Yeah, I know not to dare open the refrigerator door once, any time the power is out? (So how I am supposed to eat perishable food once the power fails? Gee, I guess I should have known the future, and got it out before the power failed?) It's scary how much heat a briefly open door would let in, without the compressor cycling on within a few minutes. But when my power was out for about a day, or many hours, some time ago, fortunately, I didn't have much food in there anyway. Must have been about time for another trip to the supermarket. I had some ice cream, which I took over to my Dad's house, since he still had power. After around 24 hours, my refrigerator was about 60 degree F. So much for "leaving the door closed." Of course during an ice storm, just put one's food in a plastic tote with a lid, and stick it outside. I have figured my car to be a "refrigerator" sometimes in the past. In winter, sometimes I can buy groceries on the way to Church, since it is so cold outside anyway. Cars don't hold heat for long, once the engine is shut off, one reason to, if not actually wearing a coat, at least bring one along, in case of car failure.

If I had a little camper refrigerator, like my Dad used to use when camping, well I then probably could get away with running on invertor power. But then those run on 12V or 120V anyway.

What you say about the large cross section, low resistance, of the Earth path is 90% true, but even with a long metal stake driven in the ground that first few feet is a high, in-series, resistance. In the old days, in rural areas, sometimes a one-wire, party-line*, telephone was used, but if you wanted it to work well, you had to pour some salt water on the ground around the "grounding stake," at least in the dry season.

And who would remember to do that? Isn't it easier to blame the phone company for their lousy service? As much as the local phone monopoly charges for their 50-year-out-of-date slow dial-up service, when we should have had fiber optics run all the way to our homes by now, I think I would rather have the option to go with cheaper party lines. How long must we wait, to get cheap "modern" technology options? I want high-speed internet, but don't want to pay a cent extra for it, since I don't make that much money after taxes, and I mostly get on textbased forums anyway, which do okay even on dial-up.

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*Every one had a different ring pattern (and you though different "ring tones" for you cell phome were new!) It was fun to listen in, but not wise to do so as the current divided and sound got weaker.

Well that's a great benefit to some of these modern 4-handset-in-one cordless phone systems. Since the power comes from the AC power adapter, which has far more power than a low-voltage phone line strung for miles from the phone company, and from multiple handset batteries, I figure they don't weaken the talk volume, when somebody picks up a 2nd handset to join in the conversation. Which seems to sound better than the speakerphone option. But beware, not all cordless phones allow all handsets to be used, simutaneously. The system I bought for my sister, allows only up to 2 out of 4 handsets, to be used at the same time.