12v Supply Power Interrupt Protection

[KMorgan]

Hi

I need to be able to switch between two 12v SLA batteries without any interruption to the supply. The max current likely to flowing at the time is 0.5A. The supply only has to stay up for as long as it takes to get the toggle switch from ON through OFF to ON again, say 1 second max (with buttered fingers). I guess a capacitor and a resistor across the supply, but what type and values?

Thanks in advance,

Keith

[game a gogo]

Hello, I'm not an expert here, and I am just starting on the world of electronics :3

But if I am not mistaking, you don't need to use a resistor, just place a capacitor (of at least 12volts of course! but usual capacitor have around 30-50v so that shouldn't be hard to find), and for the capacitance, I'd say somewhere around 2200uF, but that would hold between 1-5 seconds.. It depends I'd suppose but 2200uF is sure to do the job. But you can try to test with different values, since 470uF might give you what you need as well. And for the location to hook up the capacitor, just place the positive (+) lead on the positive energy entry (Wherever the battery are going to be plugged, but must be between the switch and the circuit) and the negative (-) lead on the negative energy entry.. I think that should work.

but remember, I'm not the master in this here.. so I hope this works!

oh, also note that the smaller the value, the more you might notice a power curve that lowers more fast.
And as well, this capacitor will run the circuit for a while when you turn the power completly off as it will discharge itself; so make sure this isn't really a bother, and if it is, make sure the capacitor isn't too big so it can discharge itself more fast, but still able to provide energy between that cut when you flick the switch.
And the good side in all this, is if by any chance, the power was cutted by accident for a short while or something, it won't cut out the power directly either.

[KMorgan]

Thanks for the reply.

The only reason I considered that a resisitor might be needed is the peak current as the capacitor charges might blow the 3A fuse I will be using. Thoughts?

Keith

[game a gogo]

I dunno if the capacitor will do that though... when there is no current it will discharge it's power, the source power won't be added so there shouldn't be a peak, and when there is power coming from the battery, the capacitor will stop discharging itself and recharge... you might wanna do some testing with a probe or something to check