Bench-top power supplies.

Felino · Post by **Felino** » Mon Jun 18, 2007 4:21 am

I am in need of one of these badly, but don't seem to want to buy one, accounting for the price. How simple would it be to do this, could i make one using one regulators and a nice 18 volt DC power-pack, and some caps of course?

Would his be efficient? I am only looking for ~ 2 amps max. How are adjustable regulators, never used em before, what are they like, can i use them?

-Fel

Post by **Skyone** » Mon Jun 18, 2007 5:16 am

Why don't you pick up an old computer power supply and use that? Throws out a large range of voltages...

Felino · Post by **Felino** » Mon Jun 18, 2007 5:40 am

I would highly prefer not to I think. I picked up one today and got shocked, the cover was on and everything, and i have been shocked enough times to last me a lifetime...

If i used somthing like this
And some regulaters, how would that work out, does that sort of adapter come in 3 or 4 amp?

Thanks
-The Fel

timmeh87 · Post by **timmeh87** » Mon Jun 18, 2007 8:54 am

that adapter dosent have enough power to build a whole power supply with multiple voltages out of. (IMO)

It also costs $30 : \

you dont even have to take a computer power supply apart to use it, it includes all the common voltages needed for portables (inc. 3.3v), and it has nearly unlimited power. its a really good idea.

totokan · Post by **totokan** » Mon Jun 18, 2007 9:00 am

I made a bench-top with a compy psu, it doesn't shock you if you are:
A) grounded
B) Not jumping cap's contacts
C) Generally careful
I took apart 3 before I got a working one, didn't get shocked once. Easiest mod to do, too. I think you only need a resistor, led's, switch, and some binding posts. If you wanna test the PSU before you open it, run a wire from the green wire in the 20/24 block to any black wire (ground)

blackbox_dev · Post by **blackbox_dev** » Mon Jun 18, 2007 7:20 pm

I've heard that compy PSUs don't work if there isn't a big enough load on it...

How about an adjustable regulator or DC/DC? Replace the resistor that sets the voltage with a variable resistor, so you can change the voltage. Then add a voltmeter (or multimeter if you have one) to the output and you can see the voltage your changing it to.

As for getting power into the regulator or DC/DC, use a wall wart. I personally reccomend a DC/DC, because their more efficient and generally free at TI.

This would be an interesting project to undertake, and it really isn't too hard nor expensive. If you want schematics, I might be able to draw you some this weekend, and give you Digi-Key part numbers. Good luck.

-iam

Post by **gannon** » Mon Jun 18, 2007 7:52 pm

A few years ago I designed a variable bench PSU with voltmeter built in. Unfortunately the meter died and I never got around to finishing it, I did find the parts recently though and was thinking of resurrecting it.
Main Parts:
5x Large Transistors
5x 1 Ohm 15 Watt Resistors
1x LM317 Variable Regulator

Also, the voltmeter needs it's own power source. I tried just making a virtual ground to isolate it, but failed

Felino · Post by **Felino** » Tue Jun 19, 2007 2:42 am

As i said before, i will not be using a computer psu, full stop. I do not want anything to do with the 240 volts ac side, thanks. Not meaning to sound rude...

Mmm, gannon, can i have more info on that? How does one limit ampage by the way?

Thanks.
-Fel

parkie · Post by **parkie** » Tue Jun 19, 2007 3:36 am

I am interested in making one of these, Keep posting what you do in the end

Felino · Post by **Felino** » Tue Jun 19, 2007 3:44 am

Mmm, i just don't feel safe using my current setup..

Iam7805, would you really? Thanks man. I have never made a power suply further than just a reg and some caps.

Addition: I am mainly looking for the following. Nothing extreme.

Ã¸ 5v, 3v 9v and 12 positive rails.
Ã¸ Variable rail.
Ã¸ All at around 1-2 amp, not all used together though.

parkie · Post by **parkie** » Tue Jun 19, 2007 4:59 am

I know you said that you WERE NOT MAKING THE POWER SUPPLY OUT OF A COMPUTER psu. But i thought for the sake of others, i found this link while looking around myself, i plan on making it myself seeing i have an old power supply laying around somewhere.
http://www.wikihow.com/Convert-a-Comput ... wer-Supply
enjoy

totokan · Post by **totokan** » Tue Jun 19, 2007 6:51 am

iam7805 wrote:I've heard that compy PSUs don't work if there isn't a big enough load on it...
-iam

That's what the resistor is for, 10 W 10 Ohm between ground and 5v
(sorry to continue this)

Post by **bicostp** » Tue Jun 19, 2007 7:29 am

Felino wrote:As i said before, i will not be using a computer psu, full stop. I do not want anything to do with the 240 volts ac side

Who says you have to open it? Just splice the wires.

Post by **gannon** » Tue Jun 19, 2007 11:52 am

You can make my design have current regulation by replacing the LM317 with the L200 (and corresponding circuitry)
My design was a standard transistor pass PSU with heatsink/fans for cooling. Similar (but different) to http://www.seits.org/features/pwrsup.htm

blackbox_dev · Post by **blackbox_dev** » Tue Jun 19, 2007 6:31 pm

Felino wrote:Mmm, i just don't feel safe using my current setup..

Iam7805, would you really? Thanks man. I have never made a power suply further than just a reg and some caps.

Addition: I am mainly looking for the following. Nothing extreme.

Ã¸ 5v, 3v 9v and 12 positive rails.
Ã¸ Variable rail.
Ã¸ All at around 1-2 amp, not all used together though.

Sure! That doesn't seem too tough. I have exams to study for, but I'll try to pull it off this weekend. If that fails, then I'll do it for sure on the 28th, when I get out of school.

-iam