question

cajun1958 avatar image

BMV 712 Smart resetting to 100%

I have installed two LiFePO4 batteries in my Polaris EV and wired the BMV-712 Smart as per the wiring instructions for two batteries. As I am not the sharpest tool in the shed understanding some of the terminology, I am struggling to find the correct setting on the BMV which tells me how much juice I have left in these two batteries. For example, the monitor is currently set on State-of-Charge and is at 100%. When I take the EV for a run it ticks down % as I am driving along. As soon as I turn the 'ignition' off, it returns to 100%. I have tried to comprehend the 'Synchronizing' section of the manual but what I really want to know is how much juice is left!!!! The only way I can tell the SOC of the two batteries ATM is to physically look at the little LED monitors on the front of them... a pain in the a... as they are under the EV seat.

Anyway, can one of you gurus advise me how to get the BMV to not reset to 100% and to tell me what the batteries are at percentage wise, just like the now redundant one that came in the Polaris (but was for 8 x LA batteries).

BMV Battery Monitor
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2 Answers
seb71 avatar image
seb71 answered ·

There are 3 BMV (or SmartShunt) settings which control when the SOC is synchronized to 100%:

- Charged voltage

- Tail current (which is not set directly in Amps, but set as a percentage of battery capacity)

- Charged detection time


The SOC gets synchronized to 100% when these 2 conditions are met at the same time:

- the battery voltage is higher than "charged voltage"

- the current into the battery is lower than "tail current"

for the duration set at "charged detection time".


"Synchronizing to 100%" means the SOC jumps to 100% when the above conditions are met.


So if it happens too early, you have to do one, two or all three of these:
- increase "charged voltage" value;

- decrease the "tail current" percentage;

- increase the "charged detection time".

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gro avatar image
gro answered ·

I suspect it has something to do with the power going off the measurement components when you turn the ignition off. Can you elaborate on how your system is wired?

The other thing it could be is that when drawing power from your battery the voltage drop is significant and once your battery recovers the voltage jumps back up such that it resets the SOC counter.

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