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p0lar avatar image
p0lar asked

Smart Battery Monitor with BMV/MPPT install problem

I have a working BMV/MPPT system with 2x Trojan 105T 6V batteries. the BMV is set up to monitor the midpoint on the second battery and it has always been around 0-1% deviation. my problem started when I installed the new Smart Battery protect. when I put it in place with the black thin wire to battery bank NEG and on the + Positive side of the battery bank (the - NEG side has the BMV Shunt already) and hooked it up to the + Positive side of the battery and on the IN terminal and the OUT terminal to the RV load I thought everything was working. I got into the Bluetooth and configured it and could see the battery voltage and relay status. THEN my BMV starts beeping. its reporting a midpoint deviation of 99.8%... I grab my voltmeter and the batteries are at 6.9 and 6.8 volts.

Where is the 99% deviation coming from? even weirder I removed the new SBP install and the BMV still shows the same deviation.

One more data point. when I change the midpoint to "starter battery" it shows 0.3v. both BMV red cables fuses are good and upgraded.


Any Ideas?

BMV Battery MonitorBattery Protect
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4 Answers
p0lar avatar image
p0lar answered ·

Thinking some more. which side of the SBP do the MPPT charging cables connect to? when I tried this install I left them ON the battery +POS terminal and ONLY moved the RV load cable to the OUT terminal of the BSP. was that wrong? should I move all the load and charging cables to the OUT terminal and only run a single short cable from the battery +POS to the IN terminal

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Vance Mitchell avatar image Vance Mitchell commented ·

you should only have loads connected to the SBP output they are designed for current to only flow one way through them. Connect any charge sources (alternator, solar, inverter/charger etc) to the battery side.

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Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

I'm not sure if the BMV is designed to monitor the mid-point voltage of two 6V batteries. I think it can only monitor the mid-point voltage of two 12V batteries in a 24V system.

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p0lar avatar image p0lar commented ·

It has worked well up to this point. did this change with new firmware?

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p0lar avatar image
p0lar answered ·

This is going to be hard as the shore power charger is on the far side of the RV and just connects to the "bus bars" near the fuse panel in the back. any ideas on the 99% numbers?

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p0lar avatar image
p0lar answered ·

SO wait... is the smart battery protects only 1 way like a diode? this won't work for me then. I have solar MPPT controllers output wired directly to the POS and NEGs of the battery bank in the front of the RV so I can put this directly connected to the battery terminals and from those terminals I run a short wire to the IN on the Smart Battery Protect. the OUT of the SBP then has POS wire that runs to the fuse panel in the REAR of the RV along with the NEG wire from the BMV shunt. in the rear of the RV, I have the shore power coming into a battery charger and that connection uses the above-mentioned POS/NEG wires to get back to the battery in the front of the RV to change them with Shore power and this would be hitting the OUT side of the SBP expecting to go to the IN side and then to the Battery.

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