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mjkuhno avatar image
mjkuhno asked

Installing Battery cut-off switch with a SmartShunt or BMV 712

Hi All,


Recently purchased a new RV and am about to add a battery cutoff switch (as there isn't one now). I plan to utilize the cutoff switch to also kill power to either the SmartShunt or BMV 712 so it doesn't draw down the battery over time. So I have two questions here I'm hoping everyone can help:

1. Wiring - my thought is to take the battery negative terminal to the switch, then run the switched 'on' terminal to the Battery Minus connection on the shunt. Of course the Load side would have all other loads etc. My thinking is this will allow the shunt to measure everything when intending to power on the RV without drawing down the batteries. Any drawback to this?

2. (and possibly related to Q1) With the wiring idea above will the BMV 712 and/or SmartShunt retain it's previous settings? Will it essentially 'pick up where it left off' as if in hibernation mode?


I'm thinking I'm OK here - but hoping others who've been down this road before might be able to confirm. Thanks much!

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2 Answers
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

You can do that. The BMV/SmartShunt will keep all settings but will lose the SOC. You have to make a full charging cycle to synchronize the BMV/SmartShunt.

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mjkuhno avatar image mjkuhno commented ·

Did a little more reading in the manual. Am I correct then in assuming in losing the SOC and requiring a resync I should also ensure to NOT select the default setting in the app for Battery Starts Synchronized?

"7.1.10 Battery starts synchronised

The battery state of charge will become 100% after the SmartShunt is powered up. When ON, the SmartShunt will consider itself synchronised when powered-up, resulting in a state of charge of 100%. If set to OFF, the SmartShunt will consider it unsynchronised when powered-up, resulting in a state of charge that is unknown until the first actual synchronisation."

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nick-peck avatar image
nick-peck answered ·

i thought i read that you were only supposed to switch the positive side.

not sure, but its worth looking in to

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Vance Mitchell avatar image Vance Mitchell commented ·

I prefer to switch the negative side as it reduces the risk of shorting to ground when disconnecting terminals.

On trucks and Harvesting equipment it is quite common and I believe John deere isolate negative from factory.

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mjkuhno avatar image mjkuhno Vance Mitchell commented ·

I've read this as well - that switching negative side has less risk of shorts. Did it on a previous RV with a blade switch on the battery terminal which was easily accessible. On this RV not going that route and using a mounted rotary switch.

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