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Topic: Parallel power supplies (Read 2381 times) previous topic - next topic


Hey guys,

I need to connect together two power supplies in parallel for more current output. The power supplies are XP Power: ECM40US09, they are rated at 9V 4.5Amps. If someone could check them out and give me a heads up would be great! Im assuming I just need to parallel connect the positive and negative terminals.

I want to enclose the pair inside a box, with an input lead from 240V AC and a two wire(+ -) output with an on/off switch. So basically making it a 9VDC power supply capable of supplying up to 9A. Is it as simple as adding a switch and terminals onto an enclosure or do I need to add some protection circuitry?




Do not to this, it is dangerous.
What will happen is the power will flow from one supply to the other.

If you do want to do this then it is best to connect each power supply through a diode before joining them together. The diode must be rated at twice the maximum current you are going to pull out of each supply. This will give you about 1V loss across each diode.


Or purchase a suitable power supply....


Jul 08, 2011, 01:27 am Last Edit: Jul 08, 2011, 01:34 am by MarkT Reason: 1
Even with diodes one will probably be doing most/all of the work and be overloaded - this is just the wrong approach.

There is a 9V 8.8A supply in that range:
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Thanks for the replies.
The parallel connection is the wrong approach, I was thinking about it wrong.
I am using two power supplies as that is what I was given to use, so I don't have the option to buy another single supply(would save a lot of trouble!).

What I actually want to do is split the load between the two supplies and connect the grounds together.

The project is actually an 8x8 array of ShiftBrite LED's connected to a sensor board. I can use one of the supplies to power the LED array and the other to power the sensor board and control logic.

Also how do I ensure that failure of either supply does not cause my circuit to overload the remaining supply?

Cheers guys,



I'd be very surprised if the supplies didn't have built in overload protection.  I may be imagining your circuit (pictures speak a thousand words...) wrong but you wouldn't have the positives of both supplies connected anywhere would you?  just the "grounds" so if one supply fails - the parts connected to that would lose power but the parts of the circuit connected to the other supply would continue to work.


Be aware that if there are logic signals between different parts of the circuit on different supplies you want to put protection resistors in series on those signal lines to prevent damage - 2k2 or similar.  Otherwise the signal line might try to power the whole of the other circuit...
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It's OK to run two identical supplies in series, though, right?  Been doing that for a week now to test a stepper motor system and get 24V from two 12V supplies I had handy.


It's OK to run two identical supplies in series, though, right?

Not without putting a reverse biased diode across both supplies. The problem is that they can come to to voltage at different rates and so you can get one PSU back powering the other. This will damage the capacitors and eventually destroy them.


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