ron roberts

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

ericgibbs

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.?

Attached Images

Limit1.jpg (9.0 KB, 30 views)

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Nigel's site: http://www.winpicprog.co.uk/
Gramo's site: http://www.digital-diy.net/

rjvh

i build this circuit more than a dozen time
simple, effective and cheap

sucsess
Robert-Jan

Attached Files

battery discharge protector.pdf (262.3 KB, 28 views)

ron roberts

Hi rjvh thanks for the diagram it looks interesting but it seems to be in German. The diagram its self is no problem but you say you have built them, so I was just wondering if you can tell me a bit about its performance. How adjustable is it. When it switchers off, will it switch back on a gain when the battery is charged sufficiently. And so on.

ron roberts

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

ericgibbs

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.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Nigel's site: http://www.winpicprog.co.uk/
Gramo's site: http://www.digital-diy.net/

rjvh

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 47k 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

jtexas

Note that discharging a 12-volt lead acid battery below 10.8 volts can damage the battery.

Unless your battery is labelled "deep cycle", repeated discharges beyond 50% (12.23 volts at 70ºF/21.1ºC) will seriously shorten its useful life. For best results limit the depth of discharge to 20% (12.48 volts), and if at all possible avoid discharges of more than 80% (12.02 volts).

A deepcycle battery performs best when the average depth of discharge is between 20% and 90% (11.95 volts).

A wet cell battery with a 20% average depth of discharge can last up to 5 times longer than the same battery with a 50% average DoD.

The battery is fully charged at 12.64 volts.

ron roberts

Thank you all. Still working on it but it looks like I have all the answers on this forum. Thanks