Connecting PSUs in parallel

[Richard]

I want to build a high current 12Vdc PSU for powering a compressor and came across this:

in TinyURL: is an article on how to use an ATX PSU as a lab supply. I have plenty of ATX PSU collecting dust.

My question concerns whether I can connect two ATX PSU in parallel to increase the current o/p.

I seem to remember the need to ensure that both PSUs experience the same load, something which is achieved by introducing very low value but high power resistors in series with the o/p of each PSU before they are connected together.

Is my memory wrong?

TIA

Richard

[The Natural Philosopher]

Not simply, no.

That is one way, but its very fraught.

Must be an easier way.,..

[FKruger]

If your looking for a 12v supply then nearly all PC PSU have more current than that example. Plenty of 300w supplys have 34 Amps.

Althought this is accross 2 lines with suposidly seperate current limiters in effect many dont see:

[Grunff]

If this is a 12V car tyre type compressor, then I'd be very surprised if you couldn't run it off a 300W ATX PSU. They draw around 7A.

However, because it's a brush motor running at a relatively low speed, they're very spikey in their current consumption. As such, I'd add a big capacitor across the 12V output.

[Richard]

I'll work back from the PSUs I have to see if any of them can produce a suitbable current.

Richard

[Richard]

Indeed it is such a device, or rather it is this one:

's cigarette plug is fitted with a 10A fuse.

The search for maximum amps from this PSU is based on the thought that I'll be able to use it to test bits off the cars without having to resort to dreadful contrivances with car batteries.

Richard

[Grunff]

Hmm, I find a portable jump-starter to be very handy for stuff like that. Much easier to carry around than a car battery, and very convenient when you have no mains.

This type of thing:

can even get them with built in compressors:

[The Natural Philosopher]

>>> or in TinyURL: >>> which is an article on how to use an ATX PSU as a lab supply. I have

Hmm. 300w/12v=25A the way they taught ME maths..

Ah. An other peace ov meeningless inglish

[The Natural Philosopher]

Oh..don't piss around. Go to ebay and find a 10A or better ex CB 13.8V power supply.

Regulated and smoothed and do the business.

[Richard]

True, but I have a fair selection of ATX PSUs sitting on a shelf collecting dust. Building a lab PSU with one or some of them will be considerably less expensive than a portable jump starter.

And I like the complicated solution!

Richard

[Dave]

Connect 2 ATX 5 volt outputs in series. 12 volts, or ten. the pump will not notice the difference that much.

You will, of course, have to make sure that the 5 volt 'good' cable is connected up the right way, or the PSU will not start.

Dave

[Dave Plowman (News)]

I got a jump start pack from Lidl for 20 quid. Has a built in compressor. Gets used as a 12 volt source for testing heavy current car bits - my bench top PS is restricted to 5 amps.

I didn't expect the SLA battery to last, but it's some 3 years old and still going strong. Has been used to jump start a few cars too.

[manatbandq]

posted a link to and do some basic maths before posting.

MBQ

[stevelup]

Hi

You would only be able to do that if the units were floating from mains earth. All ATX power supplies I've ever seen are class 1 and would be dangerous to operate with a disconnected earth.

Steve

[meow2222]

will short one of them out nicely via the earth wire, which may get quite hot under the gross overload if it doesnt shut down. Works fine if you disconnect the pcb in one from the case of course.

NT

[Chris Hodges]

You've also got to consider peak vs. contiuous ratings on some of these

[Richard]

I believe that I am still allowed to provide my own entertainment provided it does not interfere with anyone else.

As you may have seen, if had you bothered to read the whole thread, I have surplus ATX PSUs gathering dust. These are, possibly, going to cost me less than anything I can find on Fleabay.

Richard

[Richard]

Good point

[fred]

Class 1 just means that it requires an earth to operate safely, it doesn't mean that the output is necessarily referenced to earth. I didn't have a spare ATX supply to hand but an old AT one I checked has floating outputs so it'd be worth the o/p checking his ATX units.

Note that when you connect the PSU to the mobo in the case the 0V will be connected to earth via the fixings but that is an EMC issue.

[Weatherlawyer]

All very tecnikul. Wossa bindin post innit?