Over discharge with SBMS0 and MPP Solar 1012LV-MS

cdnbiker

New Member
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Mar 11, 2021
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2
Not nearly as dramatic as some of the other posts here but maybe some other can learn from my mistake of over discharging my cells.

I've got 4x 280ah EVE cells in series, SBSM0 from electrodacus just doing balancing and cutting off DC loads via a solid state relay (SSR-60 DD), then I have the MPP Solar 1012LV-MS, all installed in my van. 2x 195W eco-worthy panels up top.

The MPP Solar has it's own low voltage cutoff, I know Will showed hooking up a FET in parallel with the switch to turn it off but I found that switching it on and off wasn't much different that just using it's own programmable under voltage shutoff. In either case the inverter shuts off but the charger still works.

So I left the van for a 2 week paddling trip, dreaming of the cold beer I would return to, the battery was down to about 60% when I left due to the canoe blocking the panels for the drive to the put in. I assumed where I parked it would get enough sun to keep the fridge running, and if not everything would shut down at the programmed cutoff of 10% in SBMS0 and 10v for the MPP. Instead I came back to nothing working, very warm beer and my cells down at 1v each.

In further testing it seems the SBMS0 seems to draw about 50mA and the MPP pulls another 100 - 130mA (after the under voltage has kicked in) - both currents are from the SBMS0 measurement.

180mA doesn't seem like much but of course 24 hours a day x maybe 10 days = 240hrs x 0.18 = 43Ah being pulled from an already dead battery.

At least that is my post-mortem assessment, interested if others have a different take, or suggestion on how to fully disconnect the SBMS0 and the MPP Inverter Chargers.
 

mrzed001

Voice of reason
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Apr 10, 2020
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Hungary - EU
I am sorry for your cells.
Do you have an idea why the solar panels did not charge the battery?
400W x 5 hour = 2kWh they could charge on a day
The MPP uses 50-60W and the relay 25W ... 85W x24h = 2kWh ... the same.

What I am curious about is how it could deep discharge?
I know relay based BMS full disconnects battery and can not charge while discharge is disabled like a FET based.
But should it not work like when there is a charge then the BMS connects battery again ?
 
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cdnbiker

New Member
Joined
Mar 11, 2021
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I think the parking spot was just too shady, we had to reorganize vehicles at the last minute and it ended deeper in the woods than expected.

the SBMS0 relay only disconnects the 12v loads (which I assume worked fine) but the fridge is on the inverter which is directly connected to the batteries (through a fuse) and that relies on the low voltage cutoff. But even with everything off the BMS itself pulls 50mA, and it turns out the inverter also pulls 100mA even when "off"

The upside is I've been gently reviving the batteries and so far they seem ok, I got 240ah yesterday while testing with a 20A load.. fingers crossed
 

mrzed001

Voice of reason
Joined
Apr 10, 2020
Messages
736
Location
Hungary - EU
I think the parking spot was just too shady, we had to reorganize vehicles at the last minute and it ended deeper in the woods than expected.

the SBMS0 relay only disconnects the 12v loads (which I assume worked fine) but the fridge is on the inverter which is directly connected to the batteries (through a fuse) and that relies on the low voltage cutoff. But even with everything off the BMS itself pulls 50mA, and it turns out the inverter also pulls 100mA even when "off"

The upside is I've been gently reviving the batteries and so far they seem ok, I got 240ah yesterday while testing with a 20A load.. fingers crossed
OK now I understand how could it go so low.
Just be cautious with the cells :) And tell us how they work.
 
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