Shunt in positive or in negative wire?

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hugodevries asked May 28, '19

Shunt in positive or in negative wire?

I've just bought a battery monitor BMV 700. The wiring diagram shows that the shunt should be connected between the battery negative and system ground. I wonder why this is.
The only reason I could imagine is when using a wrench to tighten the bolts the tool can easily hit the surrounding metal housing and this will cause no harm.
Any ideas?

TIA,

Hugo

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Answer 1 · 2019-05-28T13:48:26Z

wkirby answered · May 28, 2019 at 01:48 PM

It is in the negative side so the the Voltage drop measured over the shunt will be a positive value with respect to the negative of the battery.
The Analogue to Digital converters (like what's in the BMV unit) need to measure a positive Voltage with respect to it's digital ground which is referenced to battery negative.

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hugodevries commented · May 28, 2019 at 08:03 PM

Aha, that's a good point.

Thanks!

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