Turning on an ATX power supply

[apostolakisl]

So, I need to turn on an ATX power supply to use the outputs for something other than an ATX motherboard. As near as I can figure, you short the green wire to ground. This worked, the power supply turned on. However, just want to make sure there isn't more to the story. :huh:

 

[nlaredo]

I would consider using as large a resistor as possible where the power supply still turns on.

 

[standon]

I've had an ATX PSU on for about a year by shorting the green and ground with no issues. I've thought about putting a toggle switch or something but I never turn the PSU off. You should be fine just shorting it.

 

[apostolakisl]

Great. I did a bunch more googling and it seems that shorting green/black is the proper thing to do.

One more issue, I have some 9v items to power. You can use the -5 and 3.3 to get close enough, but the -5 is only able to handle very minimal current.

Any other ideas? I read that using the 12 against 3 won't work (trips the protection circuit breaker). Perhaps using a 9v regulator on the 12v output, but I have never done this. Any recommendations on how to do it best.

 

[standon]

I used a 5v regulator for the first time last week for some fans (off a cctv power distribution unit), it's pretty simple. Most have 3 connections with a shared GND. It will shed the extra 3v into heat, so get a heat sink for it. My heat sink was over kill, but 3 bucks or so at the shack.

 

[apostolakisl]

I used a 5v regulator for the first time last week for some fans (off a cctv power distribution unit), it's pretty simple. Most have 3 connections with a shared GND. It will shed the extra 3v into heat, so get a heat sink for it. My heat sink was over kill, but 3 bucks or so at the shack.

Can I put several of them in parallel to get more amps? I want to have 3 sets of terminal blocks (5,9, and 12v), each of which get bunch of stuff plugged into them. The 9v terminal block needs to handle 3 or 4 amps and all the 9v regulators I see on ebay are 1.5 amps.

 

[mdesmarais]

You might do better to power each run separately, if none of the individual devices are over 1.5A.

Or go to Digikey and search there for regulators- something like AP1084D15G-13 would give you 5A in a linear. Dropping from 12V, you need to account for 15 watts of heat.

 

[standon]

Here's a screenshot of the digi results over 1.A. Looks like your options are 2A or 5A, but the 5A has no price on the site. Newark has a 3A but the minimum quantity is 1200, which may be more than you need

 

[mdesmarais]

Doesn't have to be a fixed- a couple of resistors will let you use a variable, with many more options.

Something like this-

http://search.digikey.com/us/en/products/AP1184T5L-U/AP1184T5L-UDI-ND/1301225

1.98 quan 1, 4 amps.

 

[apostolakisl]

Doesn't have to be a fixed- a couple of resistors will let you use a variable, with many more options.

Something like this-

http://search.digike...-UDI-ND/1301225

1.98 quan 1, 4 amps.

How do you adjust it?

I did just hook up a Linksys router and a Cayman DSL modem to a 5v output on an ATX power supply (both claim to need 5v, the modem at 3amp and the router 2amp). It would seem that the ATX is not quite putting out enough voltage for these guys. The router plain doesn't work (even though a 5v wall wart does), and the modem is being flaky. I only had a cheap volt meter at the office (where I was hooking this up) which is reading 4v on the 5v wires (it only shows whole volts, no fractions). Kind of surprised at this. I'll bring my better meter tomorrow and see more precisely what the v output is.

 

[mdesmarais]

Hm, ok, so maybe that one wasn't the best choice. .. it is a little more complicated than your typical 3 pin.
Try this one-
http://search.digikey.com/us/en/products/LM1084IT-ADJ%2FNOPB/LM1084IT-ADJ-ND/363557
and look at the circuit diagram on the 1st page.

 

[apostolakisl]

Hm, ok, so maybe that one wasn't the best choice. .. it is a little more complicated than your typical 3 pin.
Try this one-
http://search.digike...T-ADJ-ND/363557
and look at the circuit diagram on the 1st page.

Got it. Thanks.

 

[apostolakisl]

Well I mounted the atx power supply and two terminal blocks I picked up off ebay. I have 4 things on each the 12 and 5 v terminal blocks and all is working well. I only have a couple of 9v items so I think I may just let them keep their own power supplies. I still have about 6 items that are either 5 or 12 v to hook up.

I like this. It really is going to clean things up. And I won't have to keep dealing with flaky wall warts.

 

[rismoney]

Is there an issue with all the devices sharing a common ground? Like ground loops?
Also what do you do if a plug is marked 12v but put out an unregulated 12vdc and can peak higher?

I want one and need like 20 custom dongles

 

[apostolakisl]

I did go ahead and do this and now have 13 things plugged into the two terminal blocks I picked up on ebay. It has been working flawlessly for about 2 weeks now. I have a 12v and 5v block. I still have a bunch of 8-9v stuff that are on wall warts and probably will just have to stay that way.

Common ground issues? Hmmm. Not sure on that. Obviously, the wall warts all shared a common ground, but that was on the other side of the transformer. I do have this setup powering my intercom and I am not getting any humms.

The issue about peaking higher I don't think is valid. I have plenty of wall warts that when measured, measure higher than labeled, then you put a load on them and they drop. A wall wart wouldn't spike up in voltage to accomodate a power need on the part of the appliance, it would do the opposite (if anything) and drop the voltage as the appliance increased its current consumption. I think having a nice regulated power supply with high current capacity would allow that appliance to maintain it's proper function since the voltage won't drop when it decides to suck up more current.