Bench Power Supplies?

rsilk
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Re: Bench Power Supplies?

Post by rsilk » Wed Jan 26, 2011 2:14 pm

Sparkfun sells a dongle that plugs into the motherboard connector and breaks out to banana jacks. Something like that would be easy enough to kit up.

As for variable voltage... probably possible, but not easy. And it would probably vary from supply to supply. You'd have to mess about with the feedback loop of the regulator, and those things are notoriously fussy.

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JamesCooper
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Re: Bench Power Supplies?

Post by JamesCooper » Sun Jan 30, 2011 8:56 pm

A few words of warning about using ATX power supplies as bench supplies.

First, make sure you have a fuse on the line! The supply itself should have over-current protection, but most supplies can source dozens of amps. Shorting the 12A line on an ATX supply will make some nice sparks. I've also seen cheap supplies which skip some of the protection, resulting in welded wires or even fires. Not all supplies are created equally!

Another thing to note is that switching mode power supplies are finicky things. Some supplies won't even turn on without a minimum load. Almost all of them will have trouble regulating the voltage if there isn't enough of a load. Even with a proper load, the ATX spec allows for quite a bit of sag and noise on the line. For example, ATX12V v1.3 allows for +/-5% regulation on the 5V and 12V, with noise up to 50mVpp and 120mVpp respectively. This is fine for powering most things, but don't expect to use it as a precision reference (such as in an analog circuit).

Lastly, ATX supplies have large capacitors and coils in them and can continue to supply power for quite some time after the plug has been pulled. Also, if you keep the supply plugged in but remove the power-good jumper, the +5VSB will remain powered. I recommend using an actual switch between the supply and your circuit to make sure power is actually disconnected, just in case.

All that said, if you want a cheap, stable 5V supply for IC projects or a beefy 12V supply for motors, it's hard to beat the cost of a used ATX supply. Just keep the above in mind. Play safe!

Tetragrammatron
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Re: Bench Power Supplies?

Post by Tetragrammatron » Sun Feb 06, 2011 3:19 pm

On a related note, I'm in need of at least a dozen 120VAC to 12V DC power adapters, capable of handling up to 1 amp, though I could possibly make due with 500mA - 1A.

Let me know if you have any laying around your house from old routers, small electronics, etc. or let me know if you know of a cheap place to buy these things. I'm typically looking for something like this that I can cut the end off and have two wires to connect to a devices contacts:

http://i.ebayimg.com/04/!C!8lhCwBmk~$(KGrHqN,!lUEz+yFw(kbBNFZuKdKHw~~0_12.JPG

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Bergo
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Re: Bench Power Supplies?

Post by Bergo » Mon Feb 14, 2011 3:34 pm

bump, ended up buying this on Ebay:
Image

When we have a physical space, it shall make its way there!

Tetragrammatron
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Re: Bench Power Supplies?

Post by Tetragrammatron » Mon Feb 14, 2011 10:35 pm

Fantastic! Better than the power supplies I've been using lately at Vecima...grumble. Then again us software guys get the left overs usually when it comes to equipment.

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Bergo
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Re: Bench Power Supplies?

Post by Bergo » Tue Feb 15, 2011 8:17 am

Tetragrammatron wrote:Fantastic! Better than the power supplies I've been using lately at Vecima...grumble. Then again us software guys get the left overs usually when it comes to equipment.
does vecima still do thier garage sale day thing, I remeber years ago (like, close to 10 years ago, back when they were still vcom, or wavecom, one of those..) going there to buy boxes full of parts for like $5. piles of leftover hd44780 LCD's and cheap CRT monitors and stuff.

Tetragrammatron
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Re: Bench Power Supplies?

Post by Tetragrammatron » Tue Feb 15, 2011 8:27 am

I think so...? I know they usually do a parking lot garage sale where people can set up their own sale downtown (since R&D is in the post office building now), but I'm not sure if the company itself sells anything at the garage sale anymore. I've honestly never attended it :oops:

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Bergo
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Re: Bench Power Supplies?

Post by Bergo » Tue Feb 15, 2011 8:40 am

you'll have to give us a heads up if you hear anything :)

shepting
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Re: Bench Power Supplies?

Post by shepting » Thu Aug 11, 2011 4:13 pm

If you just need a small current people often use a LM317 to supply variable voltages.

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