Looking for a simple voltage sensitive relay circuit.

[gazzarose]

Hi guys,

Im after some help if I may. My friend does alot of work with campervans and caravans, and installs quite a few second batteries running through split chargers. The commercial available volatge sensitive type retail about the £50 mark, but he has managed to buy a load of 70amp normal tpe relays, so has asked me if theres a way to make these into voltage sensitive ones. I've never done anything with voltage sensing before, withthe only thing close being dark/light sensors in A level electronics using potential dividers and opamps. Is there an easy (read cheap) and relaible way to make a circuit that would do it, but also have a schmitt trigger type switcing to it, so it would turn on at 13.7 voltage (engine running so alternator charging batteries) then off at 12.8. If anyone has got a circuit lying about that would be great. And if theres a way of making it out of single compnents rather than IC that would be brilliant, although if someone has got, or could design a pcb design for one, he could just get a load of pcbs made then solder them up.

Thanks

Gareth

 

[Joe G]

could you use a window comparitor circuit???

 

[Vizier87]

I could only think of uCs here. You'd need to attenuate the voltage for a cheap (reallly cheap) PIC12F to read it, and programming it shouldn't be too hard. As for asking anyone here who's ready to make it, I'm not so sure....

 

[kinarfi]

how about an comparator with hysteresis

 

[kinarfi]

Another idea is use a diodes to feed each battery which would prevent feed back from one to another and use the relay to jumper the batteries together with a momentary switch after your starter battery goes dead