question

p0lar avatar image
p0lar asked

Midpoint Voltage not accurate

my BMV is reporting a 25% midpoint deviation on 2x NEW Trojan T-105 batteries. when I grab the voltmeter and check while connected I show 6.4v and 6.5v. when I disconnect the batteries they show the same 6.5v. The TOP of that spike is when I checked while connected. voltmeter was NOT showing 9V and 5.5v.

Any ideas?screen-shot-2021-04-20-at-115659-am.png

BMV Battery Monitor
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2 Answers
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

The BMV is not designed to measure the midpoint in a 12V system with two 6V batteries in series. It is designed to measure the midpoint in a 24V or 48V system.

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p0lar avatar image p0lar commented ·

Ohh... I didn't get that from the docs so maybe I should disable that and disconnect the second red wire?

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Matthias Lange - DE avatar image Matthias Lange - DE ♦ p0lar commented ·

Since this feature is useless in your system you can deactivate it and remove the 2nd wire.

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p0lar avatar image p0lar Matthias Lange - DE ♦ commented ·

Great to know. Ill take that off my "watch this" list. :)

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Martin Keogh avatar image
Martin Keogh answered ·

This answer does not make since as I was successful measuring the mid point on my 12volt house battery system (2 × 6volt Batterys in series) up until yesterday. Now they are not reading accurately. 2 volts lease than actual. I have also try this on my start battery (24 volts) and this input is measuring 5 volt less than actual.


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