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batt load on off on control

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unreal

New Member
ok i have a solar/wind charge controller that charges battery
i have a dc-ac inverter allready, i have the charging controller allready

what i would like help with is this : once batts are charged have a controller turn on a relay that can either turn on my dc-ac inverter and/or turn on a relay that will have a load on it in dc form.
loads will bring batts down , then turn off , let wind/ solar recharge batts and then turn loads back on again.

turn on at batt voltage about 12.2 stay on until batt voltage at 8.5 then turn off
the load to turn on the inverter is very low 3 dc amps or so , the load to turn on dc relay is low as well

thanks for your time
 

MikeMl

Well-Known Member
Most Helpful Member
ok i have a solar/wind charge controller that charges battery
i have a dc-ac inverter allready, i have the charging controller allready

what i would like help with is this : once batts are charged have a controller turn on a relay that can either turn on my dc-ac inverter and/or turn on a relay that will have a load on it in dc form.
loads will bring batts down , then turn off , let wind/ solar recharge batts and then turn loads back on again.

turn on at batt voltage about 12.2 stay on until batt voltage at 8.5 then turn off
the load to turn on the inverter is very low 3 dc amps or so , the load to turn on dc relay is low as well

thanks for your time
I designed a 555 based voltage comparator with independently adjustable upper and lower voltage trip points for a similar application and posted it in this thread in these forums.. Tailoring it for your application should be easy.

Just a couple of comments about your post: What type of batteries? If sealed lead acid, then you are discharging them too deeply; they should not be discharged below 10.5V absolute max, and being conservative, I stop discharging mine at 11.0V.

Terminating the charge of lead-acid batteries (sealed or flooded) by just reaching a fixed cutoff voltage is not a very good way of detecting state of charge. The correct way to do it is to use a voltage regulator which holds the battery voltage constant after it rises to 14.2-14.8V (depends on specific battery SLA, GEL, AGM, VRLA, or flooded), and then use the fact that the battery charging current drops below a preset limit to terminate charging (and switch to float mode, if that is required).

If you just cutoff charging when the battery first reaches a fixed cutoff voltage, say 14.5V, then the battery is only somewhere between 80 and 90% charged.
 
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unreal

New Member
sound about what i am looking for
can i mail you direct ???
how much for a gem like that ????
how many amps will that work with ?
 

MikeMl

Well-Known Member
Most Helpful Member
I would prefer to discuss your circuit here. The voltage trip points can be customized by changing two resistors. I'll talk you through building it yourself. The output can be a relay, so you can switch almost anything.
 

MikeMl

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Most Helpful Member
What type of batteries?
 

MikeMl

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What do you want the load disconnect voltage to be?

What do you want the load connect voltage to be?

Should the voltage detector be powered off the battery bank or do you have another source of power for the detector?
 

MikeMl

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Here is a hack. Load ON is adjustable from 12V to 15V. Load Off is adjustable from 10V to 12V. Battery drain is 12mA in the Load Off state.
 

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unreal

New Member
i would like to use the batts as the power supply as this would make things a lot cleaner. can you sort of give me a parts list of the units involved in your diagram ?
thanks
 

MikeMl

Well-Known Member
Most Helpful Member
i would like to use the batts as the power supply as this would make things a lot cleaner.
As drawn, it runs directly off the battery voltage it is monitoring.

can you sort of give me a parts list of the units involved in your diagram ?
thanks
Parts on the diagram are all standard parts that you can get from Mouser or DigiKey.
 

mmmalmberg

New Member
Mike - Are you still around? It's a year later and I'm here looking for exactly this functionality for a solar-powered robotic sculpture project.

Do you have any update to this circuit, before I run out and buy the parts to build it? I was hoping for a circuit with fewer parts, if you happen to have developed anything simpler. Mainly because I have very limited time to buy the parts and build these (basically tonight after work or tomorrow latest).

If anyone else is listening, I'm looking for a very simple design for a low-voltage cutoff for a 12V sealed lead-acid battery. Thanks!

As drawn, it runs directly off the battery voltage it is monitoring.



Parts on the diagram are all standard parts that you can get from Mouser or DigiKey.
 
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