Hi! I want to make a power supply system with rechargeable batteries. I have thougt of four batteries. Two that goes to the device when the other two goes on recharge from the main net. The problem is that the device should never be in contact with the main net.
The device needs +/- 15V DC

I have thougt of a relay as switches between the batteries. I want to have a measure circuit that measures how much power the device get and when it drops below 12 volt the relay should switch to the charged batteries.

The main problem I have is how to solve the measure circuit. I have read about Smitt triggers with hysteresis, but then the Op-amp must have constant V+/V- (feeding voltage?) and the circuit can not be connected to the main net, just to the two batteries that are dropping their voltage level...

I don´t know how to set up this, does anybody have an idea??

Thank´s / Anna

 

Hello,

If your problem is with the feeding of a Op-Amp or a comparator, use a single supply IC as the LM324 quad Op-Amp or the LM339 quad comparator, they can work with just +V in an ample voltage range.

Regards