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zubenelgenubi avatar image
zubenelgenubi asked

BMV 702 reading low

Until recently my bmv 702 seemed to be reading the battery voltages correctly.

The setup is a starter battery (74 ah) and a house battery (105 ah). Both are 12V. The house battery is set to be the aux and it is showing a reading on the BMV display of 5.08. When I measure the house battery directly I am getting over 12VDC.

So I performed a factory reset and checked the connections. Still voltages on bmv 702 are reading low (5.08). This also happens to be the lowest voltage recorded in the nvram.

How to start troubleshooting?

BMV Battery Monitor
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2 Answers
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zubenelgenubi answered ·

833-1547720488224.png

This is my setup with the exception that the starter battery is main and aux is my house battery.


833-1547720488224.png (38.2 KiB)
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zubenelgenubi answered ·

OK - Update.

It seems to have magically fixed itself! Aux is reading 12.56V and main is 12.26V. So that is odd.

A couple more questions:

-My starter battery is 74 ah rated and the house battery is 105 ah rated. Is that ill-advised? I entered the correct capacity in the setup for 'main' (74). Is there a similar setting for 'aux' battery?

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wkirby avatar image wkirby ♦♦ commented ·
The main battery, the one with the shunt connected to it can have its current measured by the shunt and so the Ah rating can be entered for it.

The Aux battery current does not go through the shunt, its current is not measured and therefore an Ah rating is irrelevant sine capacity % cannot be tracked.
It's strange to have the start battery connected to the shunt, usually the shunt is connected to the house battery so that capacity % can be tracked.

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kevgermany avatar image kevgermany ♦♦ commented ·
Might have been a poor earth/ground between them. Both batteries must have a good connection to earth.
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