Amp and watts incorrect

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barbeds asked Feb 22, '20

Amp and watts incorrect

The BMV 700 installed on my narrow boat responds correctly when charging from solar power or shoreline/generator and shows correct volts,amps and watts. When charging from the engines 175amp alternator the volts read correctly at around 14.3 ish but the amps and watts stay in the negative, everything is wired correctly on the right side of the shunt so I'm a little lost although I do have a niggling feeling that the problem could be due to the earth connection linking to the engine starter battery which is obviously being charged at the same time from a separate alternator.

Can anyone confirm (or not) if this could be possible. Many thanks Eddie

BMV Battery Monitor

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Answer 1 · 2020-02-23T07:42:22Z

wkirby answered · Feb 23, 2020 at 07:42 AM

It seems like the charge current from the alternator is bypassing the shunt somehow.
There is very likely a negative strap somewhere. Is there anything else connected to the negative terminal of the battery? The one and only thing that should be connected to the negative battery terminal is the shunt. This is to ensure that all current flows throught the shunt.

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Answer 2 · 2020-02-23T12:20:28Z

barbeds answered · Feb 23, 2020 at 12:20 PM

Yes as I stated in the original post everything feeding from the leasure batteries are indeed connected through the shunt, however the negative of the leasure batteries and the starter battery are linked, therefore I'm thinking that the starter battery and it's individual alternator are a possible cause of my problem.

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