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Old 03-27-2009, 06:46 PM   #1
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Default EE's - 2x Power Supplies: double the current?

EE's - Two Power Supplies in Parallel - Will this increase available current?

Question for you Electrical Engineer types. If I have an 18A and a 9A power supply, if I hook them both up to something, will I have 27A of power available? Also, will anything special need to be done?

Basically I don't want to buy a new high current power supply if I can use two smaller ones to fill the need.

I liken this to two batteries in parallel, positive to postive, negative to negative, which provides you double the amperage.
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Old 03-28-2009, 06:33 AM   #2
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Nobody knows?
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Old 03-28-2009, 07:09 AM   #3
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I've run two 30 amp bulldogs in parallel with no issues.
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Old 03-28-2009, 10:26 AM   #4
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This is an engineering paper from Texas Instruments treating the subject in depth:

Quote:
Many power supply manufacturers have found it economically feasible to make standard modular power supplies which are easily paralleled for higher current applications. If special provisions are not made to equally distribute the load current among the paralleled supplies, then one or more units will hog the load current leaving the other units essentially idle. This results in greater thermal stresses on specific units and a reduction in the system reliability For example, reliability predictions will indicate that a component operating at 50 degrees above ambient will have one-sixth the lifetime of the same component operating at 25 degrees above ambient [1].
http://focus.ti.com/lit/an/slua147/slua147.pdf

Notice there are many engineering issues involved in this 11 page paper, so I would not try it unless I knew the sources were designed for parallel operation.
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Old 03-28-2009, 12:54 PM   #5
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Originally Posted by kn7671 View Post
Nobody knows?
I wouldnt put 2 PSUs in parallel if I were you. Your problem will probably be that the PSUs dont have the EXACT same voltage, putting them in parallel will create a current running through both supplies, even if you have nothing connected.
Even if they're exactly the same, you cannot tell how many amps is supplied by which PSU...

In short, you do not put powersupplies in parallel, you buy a bigger one
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