Undercharge Protection?

[BigSur]

I have this system on order and a 100ah lead acid battery from MightyMax. This is my first build and I don’t want to ruin the battery!

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Does anyone have experience with this PWM controller to know if you can change the value for when it cuts off power from the battery? I’ve read that 12.1v is where you should disconnect the load. Is there another controller you trust to have this feature?

 

[chrisski]

I don’t have that PWM controller, but the PWM I have, and the ones I looked at do have a low voltage cut off for the load, but the documentation is vague about what the rating on the load is with things like “hook your low power items to the load,” or “Do not hook your inverter to the load.”

So, for higher wattage items like an inverter, this low voltage cutoff is not built in. I have a shunt and a battery monitor that gives me an audible alarm off State of Charge, and has the option of adding a relay which I could set up to power down higher wattage items until my battery could recharge.

I’d like to say download the spec sheet for the PWM to find out, but the PWM I bought, I could not view the manual until I bought it. Even after I got this manual, I felt it was lacking on documentation.

The PWM was for my learning system, and for my RV, I went with an MPPT controller.

 

[BigSur]

I don’t have that PWM controller, but the PWM I have, and the ones I looked at do have a low voltage cut off for the load, but the documentation is vague about what the rating on the load is with things like “hook your low power items to the load,” or “Do not hook your inverter to the load.”

So, for higher wattage items like an inverter, this low voltage cutoff is not built in. I have a shunt and a battery monitor that gives me an audible alarm off State of Charge, and has the option of adding a relay which I could set up to power down higher wattage items until my battery could recharge.

I’d like to say download the spec sheet for the PWM to find out, but the PWM I bought, I could not view the manual until I bought it. Even after I got this manual, I felt it was lacking on documentation.

The PWM was for my learning system, and for my RV, I went with an MPPT controller.

Thank you for your input. This will be running unmonitored in a shed so I’d need to trust the automation since no one would hear a battery monitor alarm.

Which MPPT do you use, and have you observed it cutting off the load at the proper voltage you selected?

Since under voltage protection is supposed to be a feature of using a controller, I’d rather not add more parts to the system. I’m not intending to use an inverter, so there’s no concern about that discharging the battery unmonitored.

 

[Diysolar123]

normally the "load" connections on solar charge controllers are just very low power items, maybe a light...
If you want to protect your battery you have two things you need to consider.
1) overvoltage from whatever is charging the system
2)undervoltage from whatever is draining the system

these are two different activities, that, well, if this was a lifepo4 system the BMS would handle the protection.
In this case the charge controller will do the right thing and not overcharge your battery. Also, as you only have a single solar panel, probably not worth the cost in getting an mppt charge controller.

the undervoltage condition is your main concern here.
as it is completely unattended, even the solar charge controller will be draining power (so a few cloudy days could be an issue)!
You should double check if you can find somewhere in the manual what the drain is for the charge controller in normal, and in low battery voltage mode.
You probably want to consider a low voltage disconnect relay that will complete disconnect the battery from everything..watch out for some disconnects that are uni-directional, you do not want that!!

 

[BigSur]

normally the "load" connections on solar charge controllers are just very low power items, maybe a light...
If you want to protect your battery you have two things you need to consider.
1) overvoltage from whatever is charging the system
2)undervoltage from whatever is draining the system

these are two different activities, that, well, if this was a lifepo4 system the BMS would handle the protection.
In this case the charge controller will do the right thing and not overcharge your battery. Also, as you only have a single solar panel, probably not worth the cost in getting an mppt charge controller.

the undervoltage condition is your main concern here.
as it is completely unattended, even the solar charge controller will be draining power (so a few cloudy days could be an issue)!
You should double check if you can find somewhere in the manual what the drain is for the charge controller in normal, and in low battery voltage mode.
You probably want to consider a low voltage disconnect relay that will complete disconnect the battery from everything..watch out for some disconnects that are uni-directional, you do not want that!!

DIYSolar123 thank you for the input. This will be an unattended Sealed Lead Acid, DC only system - no inverter.

Over Voltage: I trust the SCC not to overcharge the battery.

Under Voltage: I was thinking of using this LVD but would like advice on where to place it and use fuses:

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Would this be correct:
Panels -> SCC -> 20amp fuse -> Battery -> LVD -> Fuse Box -> loads

 

[Bud Martin]

"Would this be correct:
Panels -> SCC -> 20amp fuse -> Battery -> LVD -> Fuse Box -> loads"
That will work.
The relay in that LVD is rated at 20A.
I use the same module from ICSTATION to turn off my inverter when my battery pack goes down to 11VDC, and I set it to come back on at 12VDC.
I bought my from ICSTATION, the one from Amazon will be faster but higher price.

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