How do you use a 12v 10a capacitor as a momentary backup battery for bridge

[Brad Hruska]

I first like to thank everyone for all there help thus far.

I have completed a collapsing circuit it can run on 12VDC, 110/220ac to 12VDC transformer, or 12v Lipo batteries. There is 1 power supply line out. Thus using relays Lipo batteries are the primary power supply, then I can add a lead acid battery, or ac transformer to dc. when I add the AC line it automatically changes from Lipo to AC transformer.

But here is the problem, there is a momentary break when the unit switch between ac transformer and batteries. So on the power out line, I would like to add a capacitor on the power out line, so to continue to supply power to the equipment while it switches over from one source to another.

Thus, How large of a capacitor would I need the system is on 12v, and uses up to 10a for a .5 second break?

Please include a part number or size please.

Please include a schematic of what I need, I was thinking of just cutting the line and solder the 2 ends to the capacitor legs, but something tells me that I will need something to limit the voltage out to 12v on the line to the equipment.

Please let me know.

 

[duke37]

dV/dt = I/C so C = dt/dV * I
C = 0.5 * 10 / 1 if a 1V drop is allowed.
C = 5 F = 5000000μF
This is getting a bit big

 

[TCSC47]

As Duke says!

 

[davenn]

Thus, How large of a capacitor would I need the system is on 12v, and uses up to 10a for a .5 second break?

it would be better to do some delayed switching between the 2 power sources

 

[Brad Hruska]

it would be better to do some delayed switching between the 2 power sources

dV/dt = I/C so C = dt/dV * I
C = 0.5 * 10 / 1 if a 1V drop is allowed.
C = 5 F = 5000000μF
This is getting a bit big

This is my schematic of what I have done, it works well except it needs a make before break connection.
Please remember that all 3 power sources go out on one master wire to the different components.

Daven you said to use delayed switching, I was thinking of using a capacitor and diode on the coil trigger but I don't know how this would work. The relays are Omron ly4 and LY2 12vdc 10a.

Please let me know how to do this. Thank you all

 

[Brad Hruska]

I was thinking of adding a momentary switch to bridge the connections, but I still prefer something automatic incase I forget to press the button.

 

[Alec_t]

Might be simpler to diode-OR the three supplies , if the load can tolerate a supply slightly less than 12V (say 11.4V).

 

[BobK]

He already has them diode or'ed. The only question is which one would dominate if 2 or 3 are connected.

Since they are or'ed, he is correct is saying that all he needs is make before break to make it work.

Bob

Bob