How Do Power Inverters Work?

Discussion in 'Physics & Math' started by cb767, Aug 21, 2005.

1. MetaKronRegistered Senior Member

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

5. kevinalmRegistered Senior Member

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

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

7. SingularityBannedBanned

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Will hollow wires be good for high voltage transmissions ?

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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.

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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.

10. Billy TUse Sugar Cane Alcohol car FuelValued Senior Member

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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.

11. SingularityBannedBanned

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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.

12. MetaKronRegistered Senior Member

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This explanation sounds plausible:

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.

13. MetaKronRegistered Senior Member

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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.

14. SingularityBannedBanned

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Thanks for all that great info all of u.

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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.

16. kevinalmRegistered Senior Member

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

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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!

18. kevinalmRegistered Senior Member

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

19. SingularityBannedBanned

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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.

20. kevinalmRegistered Senior Member

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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.

21. Billy TUse Sugar Cane Alcohol car FuelValued Senior Member

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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.

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Well, DRAT!

(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.

23. kevinalmRegistered Senior Member

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