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Old 08-13-2022, 08:29 PM   #1
Mini-Skoolie
 
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AGM Battery bank and voltage cut off

800ah of 12v AGM batteries running a mini split through the night.

What's everyone doing for voltage cut off solutions to avoid going too deep for the depth of discharge?

Looking to avoid permanent damage to the battery bank in the middle of the night from running mini split.

For reference, this is going through a renogy 3000w inverter, which only has a 10.5 voltage alarm, and 10.0 voltage cutoff, which seems too low for AGM batteries.

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Old 08-14-2022, 09:55 AM   #2
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One of the high amp versions of this product may do what you need:

https://www.victronenergy.com/batter...attery-protect

Just be aware that deep cycling your bank nightly, even if it's not as deep as 10.5 (which is way lower than you'd ever want to go , btw), is significantly shortening your battery life.
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Old 08-14-2022, 12:39 PM   #3
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Quote:
Originally Posted by TheHubbardBus View Post
One of the high amp versions of this product may do what you need:

https://www.victronenergy.com/batter...attery-protect

Just be aware that deep cycling your bank nightly, even if it's not as deep as 10.5 (which is way lower than you'd ever want to go , btw), is significantly shortening your battery life.

my battery data sheet shows that 10.6 is full discharge, and 10.75 is what they label as a soft floor.. are you saying i should never run them to 10.75?



generall I dont think ive ever run them below 11.5 under normal conditions but i also havent tried to run air conditioning on them either for any length of time
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Old 08-14-2022, 02:36 PM   #4
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I have one of the Victron Battery Protect units as well. Haven’t ever engaged it, lowest I’ve discharged was 54% because I didn’t get to charge in like two days and left the inverter on for the fridge. Seems like pretty simple insurance.
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Old 08-14-2022, 04:31 PM   #5
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my battery data sheet shows that 10.6 is full discharge, and 10.75 is what they label as a soft floor.. are you saying i should never run them to 10.75?

generall I dont think ive ever run them below 11.5 under normal conditions but i also havent tried to run air conditioning on them either for any length of time
The actual numbers are manufacturer dependent, but @ ~12.0v (no load, resting) you're near 50% discharge, which is a commonly accepted figure for the max you'd want to drain them to on a regular basis if longevity is a concern. Granted there's no black or white answer, but the cycle life to discharge depth curve is similar to an exponential curve... As you (routinely) discharge deeper & deeper, your battery life shortens at a much greater rate. 11.5v is about 80% discharge, which is pretty much the max you'd ever want to discharge any to even on rare occasions. If you're routinely discharging to that level as a 'norm' you're murdering them slowly. 10.5 is dead, and hitting that level even once will result in damage you're unlikely to fully reverse. Me... I'd set up the battery protect to open at that 11.5 / 80% figure. I'd never go lower.
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