Power supplies

[balsaman]

AC power is a wave varying up and down from about 150 volts to -150 volts. 120 volts ac is actually the average voltage of the wave.

I am not sure if it's actually 150, I can't remember. something like that.

When you convert to DC, the voltage is higher than the average AC voltage...if that makes any sense.

Eric

[Max]

AC is rated at RMS Root Mean Square
The actual voltage peaks above that and looks like a sine wave. The usable power is not at the peaks but rather the average.
I did a google and found this page that explains it better than I could.
http://www.eatel.net/~amptech/elecdisc/voltages.htm

[Max]

an after thought,
that this page isn't discussing power supplies, but does illustrate what I was thinking about with the sine wave of AC

[HuFlungDung]

I thought that the DC voltage was .7071 times the AC voltage, which meant you would need more like 34 volts AC to get 24 vdc rectified.

Rectified AC has no negative component, which means the amplitude of the voltage fluctuates between zero and the postive max. The area of the graph under this sine wave equals the area of the graph representing constant voltage DC under a straight line at .7071 * AC max volts.

But, I'm no engineer so you can set me straight if I'm wrong, but then I'll have to commit suicide because you screwed up my view of the world

[HomeCNC]

Well, like I said before. I'm a Mechanical engineer, not a electrical engineer. I got the formula from Mariss at GeckoDrive. Mariss is very good with electrical formulas. I also have built two power supply's and the formula works.

[Marm]

Originally posted by HuFlungDung I thought that the DC voltage was .7071 times the AC voltage, which meant you would need more like 34 volts AC to get 24 vdc rectified. Rectified AC has no negative component, which means the amplitude of the voltage fluctuates between zero and the postive max. The area of the graph under this sine wave equals the area of the graph representing constant voltage DC under a straight line at .7071 * AC max volts. But, I'm no engineer so you can set me straight if I'm wrong, but then I'll have to commit suicide because you screwed up my view of the world

This is true if you are using a half wave rectifier, it takes only the postive sine wave.

If you have a full wave rectifier then it uses the postive and the negative part of the sine wave. If you look at a full wave rectivier that is made up of idvididual diodes it will look like a square rotated 90 degrees. The AC coming in on the top and bottom point and the rectified is coming out the left and right point. This way you end up with all the sine waves so they are now posivive by still cycling, this is what the capicator is for.

This did not come out all that well but if you do a search on full wave rectifiers you might end up with a picture that shows individual diodes and how it works.

[jimglass]

This is the best buy on an 8 amp power supply I know of

http://www.mpja.com/productview.asp?product=12613+PS

Jim

[CNCadmin]

MFG:TWINFLY
Hey perfect that is just what I need-

P/N: P1-200-24
Input:110/220VAC 50/60Hz Selectable
Specifications/Features:
Enclosed switching supply with internal fan. .5% line, 1% load reg. 1% P/P noise/Ripple. Over load and over voltage protected. Screw terminals. UL Listed.
L: 6-1/2" W: 6" H: 3-3/8" WT: 2.5

[jimglass]

To Hungflung;

You guys got me curious enough to look this up and I have limited books here at work.

.707 converts peak voltage to RMS (root mean squared). With 120 volt AC the peak voltage is more than 60 volts positive then 60 volts negative. These are RMS values. Most likely the .707 would tell you what the peak voltage is of 120 v AC.

Been 10 years since I studied this stuff and without using it, it gone.
Jim

[ToyMaker]

The 120V is the rms value. The peak is 1.414 times that, or about 170V. Or, the other way round, 0.707x170=120 approximately.

robotic regards,

Tom

[JFettig]

Yeah, toymaker and jimglass have it correct, the 24v would be the RMS, not the 30some volts, that would be the Peak ac voltage. I built a 12v 25amp power supply and without a load, It runs at 17v.

Jon