Hi everyone can anyone help.

I have a small 12 volt bulb that I need to run from a 12 lead-acid battery but when the battery goes under 10 volt I would like some kind of circuitry that will switch a changeover relay. This relay will need to disconnect the bulb and switch my solar panel charger to recharge the battery. Now when the battery is charged fully I need the circuitry to switch back to running the bulb and disconnect the solar panel.

So in short I need a 12 volt battery monitor that will switch a relay off when the voltage goes below 10 volt and back on again when the voltage risers above 12 volts.

i know i need a voltage comparator and a current comparator. They set and reset a flip-flop circuit.
The outputs of the flip-flop drive Mosfets that connect the solar panel and disconnect the light bulb.

but i need a diagram only please

can anyone help

hi,
Get the datasheet for the LM393 www.datasheetarchive.com

You require the 'limit' circuit.

Modify the circuit to drive the relay.

Do you follow.?

Originally Posted by ron roberts

Hi ericgibbs
thanks for the diagram looking in to that one many thanks.

hi Ron,
Look at this link:
http://www.national.com/mpf/LM/LM723.html

Get the 723 datasheet.

Its the ic used in Robert-Jan circuit.

Hi Ron Roberts

the text is dutch not german but still not a world language so i don't blame you that you couldn't read it

it switch off at a level around 11.2 volt but this is adjustable

the 47khm: resistor gives hysterisis in the circuit so it means that the voltage has to rise a bit more (+/- 1 volt) to switch back on

if you play a bit with this resistor you can narow or wyden the band of swiching suitable for your aplication

if you change the resister values at the inputes of the comparator you can change the initial switching points up to the value that is suitable for you

Sucsess with building it

Robert-Jan