BMV 712 showing wrong SOC at absorb

[WD56]

Hey Im having trouble with my smart BMV 712 not sowing the correct SOC when my MPPT charge controller is at absorb.

I have tried manually syncing it to 100% when I reach absorb on the MPPT. This seems to work for a couple of weeks but then goes back to about 82% give or take 1%

Im pretty sure I have things wired up correctly.

16 x Battle born batteries wired to 48 Volts

Please see photos and let me know if you have any ideas on this.

Thank you so much, any help would be hugely appreciated.

 

[sunshine_eggo]

BMV absorption voltage MUST be 0.2V BELOW MPPT absorption voltage.

BMV charged % should be ABOVE the MPPT tail current (7% as LFP is fully charged at 5%)

MPPT absorption duration should be fixed, 30 minutes

MPPT tail current should be 20A (0.05C). If 20A is too high set it to as high as it will go.

Your Float is too high. BB recommends 13.6V per 12V or 54.4V.

You may want to turn "Battery starts synchronized" off as a power loss to the BMV means it will show 100% even if every low. Turning it off yields "---" indicating it lost its state. You can manually set it, or it will sync at next full charge.

Recommend you turn off the auxiliary reading unless you actually plan to do something with it. I assume you don't actually have a 48V starter battery.

Per BB, wiring their batteries in series requires that you periodically break down the bank and charge them to full individually. A 48V balancer per string will help you avoid that.

Something is horribly wrong with your voltmeter.

 

[sunshine_eggo]

Have you configured the MPPT and the BMV to be in the same VE.Smart network? If not, you should.

 

[Bud Martin]

Your meter is reading Voltage higher than normal because your meter's battery is low, you can see battery symbol shown on your screen telling you need new battery for it.

 

[WD56]

BMV absorption voltage MUST be 0.2V BELOW MPPT absorption voltage.

BMV charged % should be ABOVE the MPPT tail current (7% as LFP is fully charged at 5%)

MPPT absorption duration should be fixed, 30 minutes

MPPT tail current should be 20A (0.05C). If 20A is too high set it to as high as it will go.

Your Float is too high. BB recommends 13.6V per 12V or 54.4V.

You may want to turn "Battery starts synchronized" off as a power loss to the BMV means it will show 100% even if every low. Turning it off yields "---" indicating it lost its state. You can manually set it, or it will sync at next full charge.

Recommend you turn off the auxiliary reading unless you actually plan to do something with it. I assume you don't actually have a 48V starter battery.

Per BB, wiring their batteries in series requires that you periodically break down the bank and charge them to full individually. A 48V balancer per string will help you avoid that.

Something is horribly wrong with your voltmeter.

Thank you so much for this!! I will re do to your suggestions and get back with an update.

 

[WD56]

Your meter is reading Voltage higher than normal because your meter's battery is low, you can see battery symbol shown on your screen telling you need new battery for it.
View attachment 116172

Yep the meter is way off!! Will change battery

 

[WD56]

Have you configured the MPPT and the BMV to be in the same VE.Smart network? If not, you should.

Did this.

BMV absorption voltage MUST be 0.2V BELOW MPPT absorption voltage.

set the BMV to 57.2 it was at 57.4

BMV charged % should be ABOVE the MPPT tail current (7% as LFP is fully charged at 5%)

Im having trouble with this one, do I set the tail current to 7% ??

MPPT absorption duration should be fixed, 30 minutes

Did this in expert mode

MPPT tail current should be 20A (0.05C). If 20A is too high set it to as high as it will go.

Set to 20.0A in expert mode

Your Float is too high. BB recommends 13.6V per 12V or 54.4V.

Set this to the correct amount in MppT

You may want to turn "Battery starts synchronized" off as a power loss to the BMV means it will show 100% even if every low. Turning it off yields "---" indicating it lost its state. You can manually set it, or it will sync at next full charge.

Turn this off

Recommend you turn off the auxiliary reading unless you actually plan to do something with it. I assume you don't actually have a 48V starter battery.

Yes this was not set up correct, its supposed to be a midpoint connection, Do I set this in the middle of the battery bank ? Do I even need it?

Per BB, wiring their batteries in series requires that you periodically break down the bank and charge them to full individually. A 48V balancer per string will help you avoid that.

I will look into this, Ive also been thinking about setting it up with long copper bus bars either side of the bank.

Something is horribly wrong with your voltmeter.

If possible could you take a quick look at my setting again?? see attached.

 

[sunshine_eggo]

BMV is correct.

I would monitor the single 12V as a starter battery. That would be the 12V connected to the main (-) lead. My thinking is it's more useful to know what a single 12V is doing in a string of 4 rather than 2S 12V in a string of 4.

If you're seeing that one peak at absorption/4 volts. If it doesn't that may mean the 12Vs in the 48V strings are becoming imbalanced.

This is an example balancer.

KiloVault Battery Balancers

KiloVault Battery Balancers help extend the life of a battery bank in your solar power system. 24V and 48V versions are used to maintain battery voltages across a series connection of batteries.

www.altestore.com

You'll need one for every independent 4S string. Victron does have balancers, and in their wiring diagrams, they interconnect each 12V in parallel so that you have a 4P4S bank and use only one set of balancers. IMHO, this would be acceptable in your case using the KiloVault product.



The Victron balancers are very low current, and they aren't cheap.

MPPT Float is still too high. 54.4V.