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.
dc to ac inverter 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.
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.
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. Please Register or Log in to view the hidden image!
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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. ------------------------------------- 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. ------------------------------- *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.
That's correct. But if we are being very careful Please Register or Log in to view the hidden image! 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.
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." Please Register or Log in to view the hidden image!
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."
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 Please Register or Log in to view the hidden image! ) 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.
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.)
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.
