12 volt battery monitor that will switch a relay off - Electronic Circuits Projects Diagrams Free

ron roberts · 7th May 2008, 10:26 AM

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 · 7th May 2008, 11:35 AM

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.?

rjvh · 8th May 2008, 04:06 AM

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

sucsess
Robert-Jan

ron roberts · 8th May 2008, 03:46 PM

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 · 8th May 2008, 03:48 PM

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

ericgibbs · 8th May 2008, 04:25 PM

Quote:

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.

rjvh · 9th May 2008, 01:18 AM

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 · 9th May 2008, 02:38 PM

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.

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7th May 2008, 10:26 AM
ron roberts New Member	12 volt battery monitor that will switch a relay off 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 Last edited by ron roberts : 7th May 2008 at 10:30 AM.

8th May 2008, 03:46 PM
ron roberts New Member	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.

8th May 2008, 03:48 PM
ron roberts New Member	Hi ericgibbs thanks for the diagram looking in to that one many thanks.

9th May 2008, 01:18 AM
rjvh Experienced Member	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 Last edited by rjvh : 9th May 2008 at 01:21 AM.

9th May 2008, 02:38 PM
jtexas New Member	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.