question

p0lar avatar image

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
2 |3000 characters needed characters left characters exceeded

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

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.

3 comments
2 |3000 characters needed characters left characters exceeded

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

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

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

p0lar avatar image p0lar Matthias Lange - DE ♦ ·

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

martinkeogh2 avatar image
martinkeogh2 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.


.

2 |3000 characters needed characters left characters exceeded

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