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My school is throwing away some old PCs which are all nearly identical. They happily allowed me to get my hands on a couple of parts including the ATX power supply below. As I see from the spec sticker on the side (picture below), they have a maximum power of 10 amps at 12 volts which makes for 120W

enter image description here

My goal is to power an old 200W (4x50W, so at least 17A at 12V) car stereo so obviously this supply alone isn't going to work on higher volumes. This is a low-budget project more in the form of an experiment so I don't want to spend a lot of money to buy a suitable power supply.

I know that by connecting two of these in parallel, they are going to fight each other and eventually be destroyed because of small voltage differences.

Can I use capacitors to stabilize the output voltage of each supply so that doesn't happen? (And if yes how to find the right capacitance?)

Or maybe I can use diodes to stop the PSUs from fighting entirely. I think there are diodes with tiny voltage loss but I don't remember what they're called. (If they're expensive, I won't buy them but I still want to know)

Is there another way that I can't think of?

Last but not least, will ground loop problems occur in any of these solutions? The stereo has high quality sound and I wouldn't want to ruin it because of a nasty ground loop. I have a ground loop isolator which looks like this but I'm not sure it could help in that case:

enter image description here

This is not the exact one but it looks a lot like this. I am curious whether it could help in case of a such ground loop problem

Παναγιώτης Θ
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  • How safe is parallel wiring two ATX PSUs, if they weren't explicitly sold as dual PSUs? – Andy aka Jan 21 '23 at 10:55
  • Basically you can’t. You need power supplies made for the purpose and/with ORing. – winny Jan 21 '23 at 11:10
  • On a low budget, there is no way to parallel two power supplies to get double the current. There is no specs of the radio but unlikely that you will need the amount of power you think you need for low budget speakers. You will need a complex circuit to OR the power supplies. – Justme Jan 21 '23 at 11:11
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    Also, try with your 120 W one first. Unless you play dubstep at clipping level, you’ll be fine. – winny Jan 21 '23 at 11:20
  • (Hm. At 35 W, efficiency of series connected ATX PSUs need not be any higher than a single supply driving a step-up converter. And even switching them on simultaneously isn't trivial given no common GND, let alone getting +12 V out rise in synchrony: forget series connection.) – greybeard Jan 21 '23 at 14:44
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    @greybeard I know that connecting them in seriues is dangerous, the question says "parallel" – Παναγιώτης Θ Jan 21 '23 at 14:46
  • @winny It kind of does, I checked it out but the answer wasn't 100% clear to me. People answering it focus on a lot of details that have to do with the 20 HDDs he's trying to power. Also, my favorite music genre is dubstep and I love blasting it at high volumes :) – Παναγιώτης Θ Jan 21 '23 at 14:49
  • @Justme the speakers are good, their stereo system is broken and I thought of reusing the old car radio for that. But the amount of complexity you're describing is definitely going to make me search for another solution. Thanks for your help :) – Παναγιώτης Θ Jan 21 '23 at 14:51

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