question

scottrgrewe avatar image

starter battery connection to shunt

On an old battery monitor the start battery was wired to the load/charge side. I installed bmv 700 and kept the connections the same. Is this correct? It seems like it would be best to connect both batteries to battery side, and all load/charging sources to the other.

monitoring
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3 Answers
Paul B avatar image
Paul B answered ·

Yes you are correct. all batteries should go to the battery side, otherwise you cannot see the charge or discharge current coming from or going to the batteries.

3 comments
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You generally want to monitor one battery bank, not 'house battery' and starter battery combined, so you only put shunt between one battery bank and rest of the system.

This will depend on what customer wants and how there system works. Ie in a Boat as a example

there is usually a battery 1, both , battery 2, Off selector switch.

so when both is selected then you want to see total amps going into both batteries.

if 1 is selected then total amps to that battery and select 2 the same.


Voltage will not be afected and you can still see Bank 1 or Bank 2s voltage on a BMV-702 or BMV-712 (unless you have both selected on the selector switch, then voltages are the same)

I have never heard of such in installation..it's a battery monitor to monitor a battery, and some models have an extra input to monitor another batteries - voltage - not SOC

I would never advice to put the starter battery on the same shunt unless you'd just want to use the BMV to measure total current.

mercu1 avatar image
mercu1 answered ·

Everyone is missing the point here. The question here is "why would you connect the cable from the starter to the load side of the shunt". This is the cable that runs from the engine block to the start battery. This cable carries starter current but also carries another very important current which is the charge current from the alternator. This is because most alternators use the alternator case to carry current. In order for the monitor to work correctly all loads and all charging sources must be connected to the load side of the shunt. So if your engine alternator is a charge source for you battery then you have to connect the cable from the engine block to the load side of the shunt. If you don't do this then the charge current from the engine alternator will not be counted by the monitor and you will have a large error.

Here is my question, which I would ask Victron except Victron does not provide support to end users. The question is what happens to the shunt when I put an initial starter surge current of 2000 amps from my big diesel engine? Will anything in the monitor system be damaged?

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pwfarnell avatar image
pwfarnell answered ·

The negative cable from the engine block goes to the load on the shunt AND the negative cable from the starter battery also connects to the load side of the shunt or directly to the engine block. Therefore, when you start the engine, the high current from the starter does not go through the shunt. Your old shunt was wired correctly. As the charge taken out of the starter battery is small there really is no need for monitoring it. If you put the start load through the shunt it will not be able to measure it if it is a 500A shunt so it is therefore of little use and during that period any other current flow will be masked. The twin domestic and starter battery set up is shown in the quick install guide as i have described.

https://www.victronenergy.com/upload/documents/BMV-702-quick-installation-guide.pdf

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