6
\$\begingroup\$

For several different projects, I need high current DC power (25-50 Amps). The first project needs roughly 50 Amps at 12 volts, which isn't something one ATX can provide on its own (at least I don't think it is.) So is it possible to wire 3 ATX PSU's 12 volt rails together (each with a diode to prevent back-current) to get this? Or is there an easier way?

The second project requires around 1.5-2.5 volts with as high of a current I can get. I was planning on combining the rails of a few ATX supplies with voltage regulators to get this as well.

I'm still somewhat new to electrical engineering so any advice, knowledge, or other information is greatly appreciated.

\$\endgroup\$

3 Answers 3

4
\$\begingroup\$

You cannot wire ATX power supplies in parallel, see this: Parallel ATX Power Supplies

You can power up multiple power supplies, and this can work for most applications where you can separate devices. The product in the discussion above can help with that.

If you absolutely need 50 A then a 750 W plus supply may fit the bill. You could try any good quality supply like this one that delivers 54 A @ 12 V from a single supply or this one (still 750 W) that delivers 62 A @ 12 V.

Think about how you might control two regulators within a few mV - 10's mV difference in output voltage.
If you want to try this build, use a couple of LM317 regulators and try to combine and balance the output currents. It can be done by introducing balancing resistors in the outputs, but this introduces losses and degenerates voltage regulation with load.
You could start by reading articles such as this. It'll help you understand how it's done, but it's much more complicated with SMPS such as the ATX where regulation (it's called cross-regulation) is implemented across multiple voltage supplies and is typically an optically isolated feedback path. You could start reading this historical but very relevant document.
Note: It is possible to buy computer power supplies that can be paralleled, look on Ebay for redundant server power supplies. They typically have balancing built into the feedback mechanism.

The greatest difficulty is if you want to use PS_ON* to turn your paralleled supplies on/off. The timing will be different (not by much, but enough) so that one supply will take all the load for some mS. In all probability it would shut down on overcurrent. The only way around this is to power up the supplies before connecting to the load ...which then means you need either a manual or electronic switch to connect the load. Yet more complexity!

\$\endgroup\$
4
  • 2
    \$\begingroup\$ Are you sure I couldn't put them in parallel with a diode on each rail? \$\endgroup\$
    – catsock
    Feb 27, 2017 at 7:58
  • 1
    \$\begingroup\$ @NeonWizard You could, but any difference in output voltages would lead to one diode conducting before the other, resulting in poor current sharing between the power supplies. You just can't sensibly parallel ATX power supplies like that. Also, good luck finding two >55 A diodes and cooling them (0.7 V * 55 A = 39 W) \$\endgroup\$
    – jms
    Feb 27, 2017 at 8:18
  • \$\begingroup\$ What if I used a voltage regulator to stabilize the two voltages? \$\endgroup\$
    – catsock
    Feb 27, 2017 at 14:06
  • \$\begingroup\$ You'd have to tell me how that would work? It does not make sense to use a voltage regulator to regulate two voltage regulators....they are already separately regulated. \$\endgroup\$ Feb 27, 2017 at 16:17
1
\$\begingroup\$

I don't know nothing about parallel power supplies, but for example this 750W atx power suppply from corsair allows up to 62A on the 12V channel for 744W of power. This is just my first search result and I am sure you may find cheaper PSUs. Unless you want to reuse what you have, it seems quite feasible to me to power your project with a singe PSU.

P.S.: I stronlgy suspect that a single cable cannot safely conduct such high currents and you certainly would have to wire a bunch of 12V cables from the same PSU to supply 50A. As always you do so at your own risk.

\$\endgroup\$
-1
\$\begingroup\$

I would say if you calibrated two similar supplies to the nearest 50mv or so, the loads should balance out, but I would recommend to just get a server psu which generally have much higher 12v current and are cheaper than at. Many of them also support paralleling (servers with multiple psus)

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.