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TimDoring avatar image

BMV-712 and MPPT 100/30 configuration

I have installed the BVM-712, and the Smart MPPT 100/30. Currently I have 2 - 170W panels along with 4 Decka DC24 batteries. (specs below, will be replacing them soon)

The issue I am having is the reporting of the BVM, I believe I have the settings correct. And have done the sync SOC to 100 and zero current calibrations. But the readings are not what I think are accurate. the SOC is saying 60% yet the voltage is at sub 10V. I was told the discharge floor setting would adjust your amp hours and display to accommodate but it seems to be in reverse. Did I mess up the settings? How do I make sure its information it reports is accurate?

On the 100/30 I did "User Defined" using the numbers provided by the manufacturer but there is no setting for "Bulk" and I never see the bulk charging above 13.8 any recommendations?






MPPT - Solar Charge ControllerBMV Battery Monitor
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2 Answers
TimDoring avatar image

@Justin Cook - Bay Marine Supply USA

Thanks for your comments, Unfortunately I got them after leaving my trailer, cant wait to go back and double check everything. I am 95% sure there is nothing going to the - side of the battery and that it goes directly to the shunt, but I will confirm.
As for the battery info I will confirm with Deka again I thought 12.6 was a low voltage number and will re-set that.

Thanks again for the help and information, I knew something was not right when voltage was sub 10 volts the inverter was shutting off yet the BVM is telling me 60%. It was almost like the discharge floor was reversed.

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Justin Cook - Bay Marine Supply USA avatar image

@TimDoring, your BMV-712's "charged" voltage is set wayyyy too low... as spec'd in the user manual, on a 12v nominal system the charged voltage should typically be set at 13.2v. Where you have it currently set is well below the battery's resting voltage even, let alone its float voltage.

Secondarily, I strongly suspect that you have a load that's bypassing the shunt somewhere (ie, its ground does not run through the shunt). SOC isn't based on battery voltage, it's based on entered capacity +/- current through the shunt (with of course a lot of other calculations being taken into account, including Puekert exponent and charge efficiency); as such, SOC will only reflect your settings +/- the current measured... but if there's a load that doesn't run through the shunt, it won't be counted against your SOC. This is how you can get a high SOC reading with a low voltage.

I recommend that you go through and make sure that there is nothing connected to your battery bank NEG other than the "battery" side of the shunt. Nothing... no other wires, no chassis grounds, nothing... literally every other system NEG including your chassis ground must go to the "loads and chargers" side of the shunt.

Furthermore, you should almost never do the "zero current calibration" because you've just told the BMV to ignore any current there might have been when you performed it. If there might be a phantom load on the system of, say, 1A and you performed a zero current calibration, you just told the BMV to ignore that... which means that it won't be counted against your SOC.

Bottom line: I recommend that you A. check your installation and make absolutely certain that there is nothing connected to your battery bank NEG other than the "battery" side of the shunt, and B. fully reset the BMV back to factory settings to get rid of your synchronization and your zero current calibration, then go back through (make sure to read the manual on your settings) and re-enter your settings as appropriate.

Then, fully charge your battery bank, ensuring beyond the shadow of a doubt that it is 100% charged, perform your manual synchronization if you like (though you don't need to, it syncs itself at the top of every complete charge cycle) and leave that zero current calibration alone... and you'll probably see much more accuracy.

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