[cncadmin]

Who has the best price on a regulated power supply?

[HomeCNC]

Why do you need regulated? I have found that building a un-regulated supply works fine for CNC use.

[cncadmin]

I want a smaller power supply(size wise), and I thought that a regulated PS would provide a more constant voltage.

[balsaman]

For steppers it's not important for the PS to be regulated. I would go with what you can find the cheapest.

Eriv

[kong]

Does anyone have some info on building one of these? I did intend to use a pc supply, but I think i will get better performance from 24v, right?

[HomeCNC]

Kong, are you asking for information on building an Un-regulated power supply? What is your application? We don't know if you would get better performance with 24 Volts!

[kong]

Yeah, sorry, bit vague!
I'm using Pac-Sci 1.85Amp, 65(?)v Max 116oz steppers, like the ones on Xylotex. So I was thinking of getting a 24v 6+Amp psu, but can't seem to find one in the UK at a reasonable price. Hence the question, do you know of some websites where I can get the info to build one? I don't know a great deal about this type of thing, but I am learning!

[kong]

Yeah, sorry, bit vague!
I'm using Pac-Sci 1.85Amp, 65(?)v Max 116oz steppers, like the ones on Xylotex, to use with their 3-axis board. So I was thinking of getting a 24v 6+Amp psu, but can't seem to find one in the UK at a reasonable price. Hence the question, do you know of some websites where I can get the info to build one? I don't know a great deal about this type of thing, but I am learning! And also, would the extra time/money be worthwhile?

[HomeCNC]

To make 24VDC supply you will need to find a transformer that will output at 17-18 VAC. Since you live in the UK this transformer will have to have an AC input of 220. So look for a transformer with 220VAC in and 17-18VAC out with the amps you want. The formula is a follows
VAC * 1.4 = VDC. So if you find a 17VAC * 1.4 = 23.8VDC or you may find 18VAC * 1.4 = 25.2VDC.

You must connect the transformer to a Full Wave Bridge Rectifier. Get a 250 Volt rated one. Like from www.mouser.com a BR250

Next you will need a Capasitor also from mouser. The formula for the minimum Cap is: Cap = Amps * 80,000 / VDC. If you find a 18VAC, 6 amp transformer then you will need at minimum
CAP = 6 * 80,000 / 25 = 19,200 microfarad cap.

[kong]

Excellent! Thanks for the help, hard to find this kind of thing in easy to understand language!

[NeoMoses]

Originally posted by HomeCNC
VAC * 1.4 = VDC. So if you find a 17VAC * 1.4 = 23.8VDC or you may find 18VAC * 1.4 = 25.2VDC.

In this equation, where does the 1.4 come from and why?

[HomeCNC]

I'm a mechanical engineer by profession. I did not come up with the formula, but I do know it works! For some reason when you put the AC power through the Bridge Rectifier and then smooth the signal with the Cap you will get very close to 1.4 * AC input.

[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