question

cbouch avatar image
cbouch asked

What Shunt Capacity do I need?

I am a little confused which is not that hard to do.. I am buying a bmv700 battery monitor that comes with a 500 amp shunt. My battery bank has a total of approx 665 amps..do I need the 1000amp shunt??the manual says that the 500 amp shunt is satisfactory in most cases. So do you base the shunt size on battery total capacity or what you expect the total maximum amp draw will be at any one time. I would expect that my max draw would not exceed 400 amps and then only when the 2000 watt inverter and bow thruster operating at the same time and then only got a couple of seconds at a time. Thanks

BMV Battery Monitormonitoring
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2 Answers
Murray van Graan avatar image
Murray van Graan answered ·

Hi @Cbouch, the 500A shunt means that that is the amount of current that can flow through it at any time. For a 12V system 500A translates into usage of roughly 6KW, a 24V system 12KW and a 48V system 24KW. Your battery bank rating is 665A/H, that is the total amount of Ah’s it can supply over a period of between 10 and 20 hours.

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cbouch avatar image cbouch commented ·

So does this mean that the provided shunt is ok for my situation??

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Justin Cook avatar image Justin Cook ♦♦ cbouch commented ·

@Cbouch, yes. The only time we've particularly recommended one of the bigger shunts is when the BMV will be monitoring a start battery, under which condition it's easily possible that >500A would be flowing through the shunt. For what you've described, you're absolutely good to go with the shunt you have.

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tedsherrin avatar image tedsherrin Justin Cook ♦♦ commented ·
I start my boat engine with my house battery bank which consists of four 120ah FullRiver batteries. i have a reserved 120ah battery that never gets used. Will the 500 shunt be ok even though I’m starting the engine with the batteries?
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Nev avatar image Nev tedsherrin commented ·

The 500A shunt will be fine.

Our 4 cell 300Ah LiFePO4 battery has started our 3.9l turbo diesel motorhome engine perhaps one or two thousand times over the last 8 years of fullime travel.

Peak starting current current reaches 740A but only for fractions of a second. The Victron 500A SmartShunt and 400A Junctek battery monitor shunt in series still look brand new.

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spirou avatar image
spirou answered ·

It would greatly help the confusion to use correct units. In the US it seems acceptable to use amps when talking about current (amps) and capacity (amp hours). Your battery bank is 665 Ah, capable of delivering xy A. The shunt does not care about capacity.

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tedsherrin avatar image tedsherrin commented ·
If his bank is capable of 665 ah, what amps is it capable of delivering?
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kevgermany avatar image kevgermany ♦♦ tedsherrin commented ·
Check the CCA value in the battery specs. It depends on battery design and not only on capacity.
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