Wire Multiple SMPS In Parallel

[Seph.b]

Will anything bad happen if I wire multiple of the exact same 12v SMPS in parallel to increase the current rating?

Will it cause oscillation?

[joeqsmith]

It depends.  The manufacture may offer an application note on how to do this with your particular supply.   Some offer a way to synchronize them.  They may derate the current.  Hard to say without reading the details.   They can go unstable and you can damage a supply/s doing this.   

[Seph.b]

The model on them is FY1205000. I can't find a datasheet on them and it looks like it may be a generic model number for 12v 5a Chinese supplies.

Edit: Tried to open one up and can't find any screws, so the cases are probably ultrasonically welded together. So I can't really even compare the insides to see if they are all really identical.

[joeqsmith]

 Looked up your PC and would assume these are not designed to be paralleled.  If you wanted to try it, just consider they may fail.   If you could live with the loss, say a 0.1ohm on the output of each one.  500mV of loss.  5 Watts dissipated.  May be enough to allow them to share.   Best thing would be to get a larger supply.   

[C]

Most SMPS are not designed to parallel.

Were many supplies are used like in servers the basics is that the parallel circuit sets the voltage and adjusts the voltage of each supply to get a balanced load on each supply.

With out this, you have smoke or problems.

[Seph.b]

Thank you both. We found a 10A supply for now and that should solve our problem.

On a side note, do either of you know a PCB mount barrel plug that will do 20A@12v. I have designed a board with 20 inputs that can switch 20 outputs arbitrarily. My bosses would like the total power to be 20A @ 12v and told me to just put 4 barrel plugs on it. I don't have time right now to look up the plugs, but I know they are not rated for 20A. I thought 4 plugs was silly, but was just going with it because that was the requirement they gave me. Now knowing for sure that that could be a problem, there is no way I will get the board sent to production like that.

[joeqsmith]

I've never seen one that large.  Just check Digi-key. 11A was it.   You may need to consider something other than a barrel style. 

[Seph.b]

I've never seen one that large.  Just check Digi-key. 11A was it.   You may need to consider something other than a barrel style. 

Thanks, I was trying to get away from screw terminals for power. I guess I will have to stick with them.

[james_s]

Take a look at XT60 connectors, I use them in electric RC airplanes and many other applications. They're inexpensive, robust, and can easily carry 40+ Amps.

[Seph.b]

Take a look at XT60 connectors, I use them in electric RC airplanes and many other applications. They're inexpensive, robust, and can easily carry 40+ Amps.

Probably wont find any power supplies that use them and I don't see any PCB mount ones that would allow us to still use a case. I'll keep looking when things aren't so hectic here and I have a bit more time.

[james_s]

It's simple to install one on a power supply, either directly or with a small pigtail. I have a few different 12V 50-60A power supplies with XT60 outputs, they are former hot swap server power supplies. 

I have PCB mounted them too, horizontally by placing rectangular pads at the edge of the board and vertically using large pads with ~6mm holes.

[ocset]

if you put standard voltage output regulated smps's in parallel, one of them will do all the work, and the other will be doing virtually nothing
attached describes parallel smps's
you can buy chips which arrange for certain smps's in parallel to share the load.
Or you can have smps's with transconductance error amplifiers (TEA) and connect all the TEA outputs together, so they act liek one big smps.
Or you can jut s have one error amplifier which controls all the parallel smps's

....otherwise you dont get sharing and one does all the work.

[tooki]

Will anything bad happen if I wire multiple of the exact same 12v SMPS in parallel to increase the current rating?

I feel like this question gets asked every few months…

[Cliff Matthews]

Will anything bad happen if I wire multiple of the exact same 12v SMPS in parallel to increase the current rating?

I feel like this question gets asked every few months…

Agreed, but for those in a pinch (enough to put up with the losses), has anyone ever explained ballast resistor losses?

I haven't seen it discussed, but years ago I saw some pretty big back-feed diodes and resistors on redundant backplanes.
What would one do in such a pinch? count each supply as able to deliver 50 to 75% of its original rating?

[james_s]

Those hot swap server PSUs I mentioned can be wired in parallel, they're designed for it and have a current sharing pin that allows them to coordinate to share the load. With the small ones being capable of around 30 Amps I have not yet found a need to parallel them myself but it's easy to do.

[Seph.b]

Will anything bad happen if I wire multiple of the exact same 12v SMPS in parallel to increase the current rating?

I feel like this question gets asked every few months…

I searched first and found nothing, maybe my search fu was not up to snuff. But I think if there are going to be redundant questions the beginners area is a good place for them.

Either way we found a more appropriate supply to get us out of the pickle we were in. With Joe and James' help I refined the requirements for our 1 power hungry board.

[viperidae]

Xt30 connectors come in right angle through hole PCB mount versions