Power supplies

[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.