Can I connect two power supplies in parallel?

[abdullahseba]

Hi
I have two 12V 10A power supplies mounted on din rails and below them is 3 connector blocks.
Can I connect the two PSU's in parallel to get 20 amps?
If not, can I connect the negative from both PSU's together as there is not enough space for 4 connector blocks?
Thanks in advance 

[macboy]

In general, yes you can parallel two supplies. How well this works depends on how well they end up sharing the load current. This depends largely on a good match in the output voltage of the supplies. If one is at 12.0 V and the other at 12.2 V, then the higher one will supply most of the current and the lower one will be idle.

You need to wire it up properly and neither of your diagrams is right. Do not run a wire from one supply to the other then to the load (terminal block). That will absolutely prevent current sharing. Instead, use two identical sets of wires, one from each supply to the load (terminal block). The wire has some resistance, and this forms a ballast resistor to help to ensure sharing of the load current. For this reason, you should also not use really thick, low resistance wire. Instead use a smaller gauge, but ensure that it can still safely pass the current and doesn't cause excessive voltage drop.

[Wolfie]

I guess it would also depend on the output circuitry of each PSU as to whether its a good idea or not.  If one fails then the power from the other PSU is going to be fed into the output circuitry of the failed supply.  Right now they are black boxes so you don't know what that output circuitry is.

As stated, neither of your diagrams is good either.  For more reasons than what MacBoy stated.  In the second, you are supplying two V+ lines.  You are only supplying a single return therefore your total current supply is limited to that single return.  You should have two return leads AND two V+ leads, one for each PSU.  Not just for current supply but also for repair and maintenance.  If the PSU on the right dies and needs to be pulled out of service, then you are also taking the left PSU out of service because you have jumpered to it.  If both PSUs had leads going to the headers, then you would not affect one while removing another (other than the reduction in PSU capacity).


One thing to keep in mind for power diagrams, for every amp you supply you must return an amp.  So, if you supply two red leads of 10a each you need a total of 20a of black leads coming back.  As long as it adds up.  You could use a par of 16ga red leads but you would need a 12ga black lead.

[IanB]

I have two 12V 10A power supplies mounted on din rails and below them is 3 connector blocks.
Can I connect the two PSU's in parallel to get 20 amps?
If not, can I connect the negative from both PSU's together as there is not enough space for 4 connector blocks?
Thanks in advance 

You have two power supplies where you know exactly the make and model no. So the first thing to do is to look at the manufacturer specification sheet for the power supply and see what advice is given. There will very likely be advice about whether they can be connected in series or in parallel, and if so how many can be connected. There would also be advice about how to make the connections.

The advice you will get from the manufacturer will be much more specific and relevant than general advice you may get from a forum. If you still have questions then that would be a good time to come here for clarification.

[Zero999]

Neither the RS website nor the datasheet, say the power supplies will work with the outputs connected in parallel.

http://uk.rs-online.com/webdocs/0adf/0900766b80adf3ec.pdf
http://uk.rs-online.com/web/p/din-rail-panel-mount-power-supplies/0282518/?searchTerm=282-518&relevancy-data=636F3D3126696E3D4931384E525353746F636B4E756D6265724D504E266C753D656E266D6D3D6D61746368616C6C26706D3D5E283F69292852537C5253207C52532D293F5C647B337D285C73293F5B5C732D2F255C2E2C5D285C73293F5C647B332C347D2426706F3D313426736E3D592673743D52535F53544F434B5F4E554D4245522677633D4E4F4E45267573743D3238322D353138267374613D3032383235313826

In reality it may work but whether it will meed the specifications or share the load adequately is another thing.

Of course, you can just common the negative and treat the two positive rails separately.

[Richard Crowley]

You revealed nothing about the nature of the load(s?)
Do you have a SINGLE load that needs 20A?
Or do you have two loads that each need 10A?
Or do you have multiple loads which total 20A?

As others have observed, there is no generic answer to whether power supplies can be parallel-connected or not.  Even if you have exactly the same make and model, they cannot necessarily be assumed to be safe in a paralleled arrangement.  My working thesis is that it is NEVER SAFE to assume that two power sources (supplies, batteries, generators, etc.) can be parallel-connected unless the manufacturer explicitly says that the source is DESIGNED for that (some are).  And there are certain circuit arrangements using steering diodes and/or load-balancing resistors which are used to make parallel connections more safe.

Unless you have a SINGLE load that needs 20A, then my advice would be to NOT try to parallel-connect the supplies, but to use them separately and balance the loads. 

You can assume it is safe to connect the ground/return/negative sides together, at least for identical conventional supplies.

[danadak]

There are supplies designed to current share, and typically have remote sense
and additional connections to facilitate this.

Some ways/methods -

http://www.keysight.com/main/editorial.jspx?cc=US&lc=eng&ckey=520808&nid=-11143.0.00&id=520808

http://www.eham.net/ehamforum/smf/index.php?topic=19506.0;wap2

http://www.switchpwr.com/parallel.pdf

https://www.quora.com/If-multiple-power-supplies-are-connected-in-parallel-with-diodes-keeping-them-from-short-circuiting-what-will-happen

Regards, Dana.