Power Supplies in Parallel problem

Hi I was wondering if its possible to hook 2 Power Supplies in parallel both 12v 15Amps. Now i read that theres allot of problems when doing this because of Load balancing. I was wondering if I could'nt just build 2 Current limiters and put them at the output of both power supplies.In my mind if I could do this it will mean that both will only go up to 15 amps or less meaning I could get 30Amps out of both without burning my house down? What is the Schottky diode method I have been reading about though? Thanks and regards

In theory you could use 2 low-value resistors (like 0,1 ohm) in series with each power supply and connect then after the resistors to balance the currents through the 2 PSUs... But in practice I don't think it will work and at 15A you will also dissipate a lot of heat in that series resistor ...

Perhaps the attached diagram will work. Make sure you use rectifiers that can handle 20Amps or more, unless the 15A is intermittent enough to not stress a 15A rectifier.

The PS1 +Sense and PS2 +Sense are the power supply’s positive sense lines. Most high current power supplies have sense inputs. Let me know if you don't know what these are, and would like an explanation.

Also, most power supplies have a voltage adjust. Without the loads connected to the supplies, adjust both supplies to as close to the target voltage as possible (i.e. so both supplies are producing as close to the same voltage as you can achieve (but don't go "nuts" Then, connect the loads (via the circuit I supplied), and measure the voltages on the anodes of each Rectifier. They should be close to the same (any variance could be due to dissimilar characteristics between the diodes.

Also, as I think about this, because the rectifiers have a negative tempco, the forward voltage will drop as they heat up, and as is the case in nature, no two parts are exactly the same, so one forward voltage is going to drop before the other, and that one will increase the voltage at the cathodes. This will cause three things to happen (simultaneously):
1. Current flow through the other rectifier will decrease (and if it's temperature is above room temp, it will begin to cool).
2. Current flow through the rectifier whose forward voltage dropped first, will rise, causing the rectifier to get even hotter.
3. The sense lines will detect the increase in voltage and each power supply will reduce it's output voltage.

Unfortunately, the power supplies reduction in voltage output won't be enough to cease the heating of the rectifier that is now getting a higher share of the current and it might go into "thermal runnaway", which is not good. The only thing that would prevent melt down is if the power supply has a current limit feature.

I'm not sure if this will happen, but perhaps a small resister in series with each rectifier will prevent this. Something like 10 milliohms at 5 Watts.

Or, how about this:

http://www.home.agilent.com/agilent/editorial...&lc=eng&ckey=520808&nid=-11143.0.00&id=520808

Basically, if one of the power supplies will go into constant current mode [CC] then if you set it's voltage slightly higher than the other one, the supply that is set to the lower voltage (say 12.0V) will regulate the voltage, and the other supply (set to, say 12.1V) will go into CC mode and simply supply the rest of the current required (because, it will supply it's maximum current (or if it has a current adjust, then it will supply the current it is adjusted to)).

I totally agree with calinoaia answer, you are going to dissipate a lot of heat.. you have to be real careful what you are trying to run ( load)..

I would not advise paralleling power supplies unless they specifically state that you can do this as part of the features of the supply. Voltage mode control power supplies without other circuity to allow this will tend to fight eachother and cause mayhem. you might want to look at some power supplies which allow modular addition in the field of mixing and matching modules in parallel - series to create anything you want to within reason. look at www.excelsys.com they have the ability to do this - the diode idea might work or it might not depending - and you are going to burn some power in the diodes.

The power supplies are connected in parallel manner we should notice that two things. one is that should be satisfied Kirchhoff voltage law or not?, ie, the two should have same voltage .second one is during parallel connection of power supplies control system of each one is working proper or not. most case the parallel connection may disturbing the control system of power supplies.So we make isolate the two power supplies output using a high current schottky diode in following manner.

Kevin is probably right, so it's a matter of how adventurous you are ;)

Also, consider that even with the case I described, where one of the supplies goes into CC mode, it will be running at it's max, so it will be under stress (unless it's designed to run like that for extended periods of time, or if the stress can be reduced by adjusting the current down a bit).. But it sounds like there isn't any "head room". You need 30A and each supply maxs at 15A, so that leaves zero leeway. So, it comes down to just how liberal the manufacturer was with the specifications.

Ohh WHOW guys thanks ALLOT for all the replies its really appreciated.
Will get back to you when im done with the reading

Depends what type of power supply as you could end up with control loops fighting each other, are you able to provide more information on the power supplies including data sheets if at all possible?

Paralleling power supplys is even for the hard core not a easy job.
A month ago i was on a project with 6 power supplys from 3 phase 480V to Current control max 24V 300 Amp.
By a big american company design.
And they keept burning out end result the input PFC (power factor control) started fighting and greated very high voltage peaks and over heating that burnt out the power supplys.

And result it is not only the output as well the input that must accept to work in parallel.

You are asking same question I asked about in another forum.
Here is the link
http://www.diyaudio.com/forums/power-supplies/110640-parallal-smps-get-higher-current.html
I think it will work but both the power supplies will not share equal current.

One more thing You need both power supplies to CVCC type other wise it will not work.