question

milad avatar image
milad asked

Using BMV-712 with solar panels and MultiPlus

Hello everyone!


I am using BMV-712, MultiPlus 12-1600-70 and MPPT SolarSmart 100-50.

I have two 255AH batteries in parallel (AGM LifeLine).

+B1 from shunt is connected to the positive pole of one of my batteries.


I kept everything as default, I just changed the capacity to 510AH.

Also, I have synced the SOC to 100%. But it shows the SOC 99.9 when the voltage dropped to 13.1, and 99.7 when the voltage dropped to 12.85.

Based on the instruction for using solar panels with BMV, I put charged voltage on 14.2V, below the absorption voltage which is 14.4V. I still have the same problem.

I kept everything as default,

Charged detection time 3 min

Charge Efficiency Factor 95%

Tail Current: 4%

Puekert: 1.25


Why the soc is not match with the voltage? 99.7 when the voltage is 12.85.

I would appreciate if you could give me some advice on it.


Thanks in advance,

Milad

BMV Battery Monitor
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

1 Answer
seb71 avatar image
seb71 answered ·

So what is the issue?

SOC is not based on voltage, but on current going out or into the battery.

6 comments
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

milad avatar image milad commented ·

Thanks for the reply.

Sorry I edited the question.

Why the soc is not match with the voltage? 99.7 when the voltage is 12.85.

0 Likes 0 ·
seb71 avatar image seb71 milad commented ·

I already told you that SOC is bassed on current in/out the battery. Not on voltage.

0 Likes 0 ·
seb71 avatar image seb71 milad commented ·

For example, if you have a load which draws 10A from the battery for two hours, you discharged the battery with 10x2=20Ah. This is what the BMV's shunt measures.


As you discharge the battery, the voltage will also decrease. But the voltage also depends on the load you discharge it with (or the amps you charge with, during charging).

A big load will produce a bigger battery voltage drop. Take the big load off and the voltage will rebound (without charging the battery).

0 Likes 0 ·
milad avatar image milad seb71 commented ·

Thanks a lot.

My plan is using the bmv relay to turn the generator on to charge the batteries. So, if I put the soc on 50% to energize the relay, I am not able to run the generator when the voltage drops to 12.2V. Is that correct?

How can I keep the batteries higher than 12.2 (50% dod)?

0 Likes 0 ·
seb71 avatar image seb71 milad commented ·

If you want to activate the BMV relay based on low battery voltage, then set it up based on voltage, not based on SOC.

0 Likes 0 ·
milad avatar image milad seb71 commented ·

Thanks for all your comments and your time. I really appreciate it.

0 Likes 0 ·