question

simons-solar-studio avatar image
simons-solar-studio asked

How low should AGM go daily and longer nights showing on Voltage graph.

I have a constant 12volt 1.45 amp load (so around 19 watts) 24/7 which does not alter at all.(runing all internet routers/ wifi etc direct DC)

I have a VE 100/30 MPPT powered by x2 250 watt panels in serious working well.

I am noticing my two 12v 110Ah AGM battries (in parallel) are lower each morning just before sun rise, I put this down to longer nights which makes sense. They are reaching float each day easily by lunch so seam nicely charged.(later on cloudy days but still making float)

voltage.png


My question is: what is the lowest we should take these batteries' voltage? I read around 12.00v is considered 50% so best to not go below? Agree?

If so plan to add a boost night time charge once I reach 12.00v pre sun rise.(looks like mid October To Feb this will be needed)

I am surprised though as my load being only 1.5amps (over a 12 hour night ) should only use around 18Ah and I have 220Ah (or 110Ah to get to 50% in theory) so def not getting the capacity expected or am I missing something?


Any advice? thanks


These are the batteries am using: (x2)

batt-type.png

https://www.ebay.co.uk/itm/302554721319

The supplier recommended these odd charge settings: (I ignored the float ones)

number-one-batts.png

I am using MPPT Batt switch postion 2 (Green)

batt-charge-settings.png


Thanks, its fun learning and having atleast something running offgrid.








AGM Battery
number-one-batts.png (10.2 KiB)
batt-type.png (328.4 KiB)
batt-charge-settings.png (114.2 KiB)
voltage.png (343.7 KiB)
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2 Answers
JohnC avatar image
JohnC answered ·

Hi @Simons-Solar-Studio

That downward trend might be partly longer nights, but also battery temperature. Just a light load on cold batteries can show a V sag that frightens. I often see below 12V in winter with similar load, despite rarely dropping my SOC below 80%.

If you're absolutely certain that your load is as you say, then it shouldn't be a worry. The fact that you're getting back to float early the following day also backs this up. Using those broadsweeping guidelines to determine how you operate your system is fraught with unknowns. Take care, but pass on the panic.. :)

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simons-solar-studio avatar image
simons-solar-studio answered ·

Thank you, John, this does comfort me. I will let it creep under 12v next month and see if the slow de-creasing downward graph slows or steadies it self.

I have the batteries inside my warm home office which doesn't drop below 16'C plus they have a VE Battery voltage and temperature sensor. (the limiting factor will be if the 12 Volt fibre router, Wifi mesh unit and Switch like 11volts :)

I might save up for a VE Smart Battery meter BMV-712 and then see what % I am actually reaching instead of guessing from voltage. Thanks

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