Can a pile of consumer electronics be powered from a single supply?

Reloadron

Joined Jan 15, 2015
5,646
There are some gotcha's with using an ATX PSU - you have to adequately load both the +5 & +3.3V outputs, or the others will sag under load.

When I repaired PSUs for a living, I had a nasty problem with a cheap low rated ATX PSU - not all the 3.3V connector pins actually carried power, one of the pins had the voltage sense wire all to itself. The connector on my test load didn't anticipate this and the unit was powered up with no connection between the 3.3V output and its voltage sense wire - the PSU went bang!

Since then; any time I make up a dummy load, I take the snips and cut the power connector out of the scrap board rather than unsolder the connector - that way, the PCB traces automatically group all the pins that need to be connected together.
Ian, I absolutely agree. I omitted that as all of the newer ATX PSUs I have worked with did not have those problems or require a load. However, it does not hurt to play it safe. You can hack a mating connector from a scrap board or buy an extension connector, 20 or 24 pin depending on what you have. Tie all the orange wires together. If there is a brown wire the supply uses 3.3V sense, include it with the orange wires. On the newer 24 pin connectors it should be Pin #13. Then place a 10 Ohm 5 Watt resistor between all the orange and ground to serve as a load. On a 24 pin connector Pin #16 is PWR_ON and on a 20 pin connector pin #14 is PWR_ON. To turn the PSU on place them at Ground.

Use a good quality PSU which brings us back to all the eggs in one basket. Thanks to Ian for bringing that up.

Ron
 

ian field

Joined Oct 27, 2012
6,539
Ian, I absolutely agree. I omitted that as all of the newer ATX PSUs I have worked with did not have those problems or require a load. However, it does not hurt to play it safe. You can hack a mating connector from a scrap board or buy an extension connector, 20 or 24 pin depending on what you have. Tie all the orange wires together. If there is a brown wire the supply uses 3.3V sense, include it with the orange wires. On the newer 24 pin connectors it should be Pin #13. Then place a 10 Ohm 5 Watt resistor between all the orange and ground to serve as a load. On a 24 pin connector Pin #16 is PWR_ON and on a 20 pin connector pin #14 is PWR_ON. To turn the PSU on place them at Ground.

Use a good quality PSU which brings us back to all the eggs in one basket. Thanks to Ian for bringing that up.

Ron
On the PSU I blew up; there was no brown wire - the sense wire was orange like the power wires, but thinner.
 

tcmtech

Joined Nov 4, 2013
2,867
If it was me I would just pick put a dual output 12V/5V 50 - 100w passively cooled SMPS on eBay for ~$20 and be done with it. Small reliable and easier to work with than modding a old ATX.
 

Thread Starter

strantor

Joined Oct 3, 2010
5,329
Ok, thank you for the responses thus far. I am weighing the "eggs in one basket" aspect and I think I need more incentive to do away with the wall warts. I could just as easily conceal the power strips in a box or build my own plug station as mentioned. The only other incentive I can think of other than space saving, is efficiency. What do you think is more efficient; all devices powered from a single switching supply, or multiple wall warts?
 

MrChips

Joined Oct 2, 2009
21,827
Your idea makes perfectly good sense to me. When AC power goes, just plug in a 12V battery and a solar charger and thar will be musak to ya ears.
 

Thread Starter

strantor

Joined Oct 3, 2010
5,329
Your idea makes perfectly good sense to me. When AC power goes, just plug in a 12V battery and a solar charger and thar will be musak to ya ears.
Yeah good idea. Taking it a step further, maybe I could just leave a 12V SLAB connected in the cabinet permanently. Thars ma UPS, no inverter needed.
 

Hypatia's Protege

Joined Mar 1, 2015
3,226
I am weighing the "eggs in one basket" aspect
Should you indeed choose the single supply route, you are best advised to place a hefty 'crowbar' circuit on the equipment (i.e. load) side of the OC interrupter -- Thence a malfunctioning PS, try as it might, can do no damage:)

Best regards
HP
 

ian field

Joined Oct 27, 2012
6,539
If it was me I would just pick put a dual output 12V/5V 50 - 100w passively cooled SMPS on eBay for ~$20 and be done with it. Small reliable and easier to work with than modding a old ATX.
They're usually pretty easy to tweak for different voltages, but if you increase the 5V output you can quickly run out of headroom on the 12V rail electrolytics.

The usually use the TL431 programmable zener in the regulation control, The Aztec PSUs used a house coded 431, the circuitry around that is usually simple enough - just find the 2 resistors that feed V-ref and calculate a new division ratio.
 

ian field

Joined Oct 27, 2012
6,539
Should you indeed choose the single supply route, you are best advised to place a hefty 'crowbar' circuit on the equipment (i.e. load) side of the OC interrupter -- Thence a malfunctioning PS, try as it might, can do no damage:)

Best regards
HP
Usually the open frame switchers that are easy to find as surplus, tend to self destruct quickly when they fail and rarely damage the load - but crowbar protection included in the original design isn't exactly rare.
 
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