Power Supply Control Selection

Discussion in 'The Projects Forum' started by Jasieu, Aug 26, 2014.

1. Jasieu Thread Starter New Member

Aug 2, 2014
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I have two separate power sources. Battery A is 12 Volts. Battery B is 12 Volts as supplied from the cigarette lighter. Either battery A or Battery B can supply powe but they can't be connected at the same time. My question is what is the easiest way of doing this?

Aug 23, 2012
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3. Jasieu Thread Starter New Member

Aug 2, 2014
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Thank you, that is an obvious answer. I was so busy thinking of IC chips that I forgot about that

Oct 15, 2009
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5. R!f@@ AAC Fanatic!

Apr 2, 2009
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Diode oring can be done but need correct capacity diode for surge current in mind.
DPDT or SPDT should also be rated for the load

6. crutschow Expert

Mar 14, 2008
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The easiest is to use two Schottky diodes. A large diode should have no more that about 0.4V drop when conducting current.

7. Jasieu Thread Starter New Member

Aug 2, 2014
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So can you provide an example of the Schottky diode circuit. I was under the impression that the high reverse leakage voltage would provide a problem

8. crutschow Expert

Mar 14, 2008
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What's the maximum current?

What amount of leakage current do you consider "high"?

Aug 2, 2014
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Nov 30, 2010
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Aug 2, 2014
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Thanks #12

12. Jasieu Thread Starter New Member

Aug 2, 2014
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Just a quick question # 12. If two power supplies are connected at the same time, how does that circuit prevent them both from supplying the circuit together?

13. IcedFruits Member

Jan 15, 2014
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battery with lower voltage gets blocked at the tri junction.

14. Jasieu Thread Starter New Member

Aug 2, 2014
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So perhaps I didn't explain myself very well. Here is what i would like: If Battery #1 is connected then whether Battery #2 is connected I want only Battery #1, and vice versa. Each battery has a nominal voltage of 12 volts

15. crutschow Expert

Mar 14, 2008
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It's not clear what "vice versa" means for your application. Is the time order of the battery connections important?

16. Jasieu Thread Starter New Member

Aug 2, 2014
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I have 2 batteries, both hooked up to a circuit that lights some LED's. Currently they are connected to a SPDT Center off switch. So one battery powers the lights, flip the switch and the other one does it while not allowing the first battery to power the ;ights. Flip the switch back to battery one and the second battery doesnt supply any power. So, the question is will a Schottky diode or some other chip perform the same function as the switch I am currently using

17. #12 Expert

Nov 30, 2010
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The diode circuit I posted only allows the higher voltage source to take control without having any communication with the lower voltage source. If the higher voltage is disconnected, the other one takes over. I don't think there are any chips that can read your mind for which one you want to turn off or when.

If you want one battery to always be, "dominant", keep talking and maybe we can work something out.

Aug 2, 2014
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ok thanks

19. ISB123 Well-Known Member

May 21, 2014
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Why don't you just keep the switch?No reason to complicate things.

20. Jasieu Thread Starter New Member

Aug 2, 2014
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Thats what I'm gonna end up doing. I just thought it would be a beat idea if I plugged one battery in and it somehow knew to switch to that one and disconnect from the other