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BMV-702 with 2 battery banks


Samsed

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Good Morning Learned Friends,

I bought my bmv-702 and now the question is, on the back of the box I see the following schematic.

image.png.90dbd951dce96c32b06455fd6edbeede.png

I got 2 banks of 48V -  200Amp batteries, giving me 400Amps in parallel, now I see that the Battery System 1 connects to the battery side of the shunt and the battery system 2 connects to the load side of the shunt, is this correct and what would the reason be for this.

Do I just go ahead and connect both battery banks to the battery side of the shunt, and can I use the Pos supply cable 2 by connecting that to +B2 for the 2nd bank of batteries?

 

image.png

Edited by Samsed
removed duplicate pic
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I'm not quite sure what you want to do, but the second analog input on the BMV (it can be configured for temperature sensing, midpoint sensing, or another battery) is usually used for a starter battery, eg on a boat/campervan you might have a 24V or 48V house bank, but you also want to watch the voltage of the 12V engine battery.

The second battery is only measured for voltage. No current measurement. No state of charge determination. The negative sides of the batteries are commoned (connected together), but the positive sides remain separate.

Edit: Oh, and when I say the negatives are commoned, it is done after the shunt. Otherwise starter current will flow through the shunt and cause inaccurate measurements on the house bank.

I hope that helps you figure it out.

Edited by plonkster
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57 minutes ago, Samsed said:

is for dual systems in a bakkie or camping

Indeed, but the idea is that the battery systems remain separate. You might have an extra solar charger, or a buck-boost-converter to charge that battery from the alternator, and because the batteries are often of different capacities you may want to keep them separate (so there would usually be some kind of disconnect or charge circuit that charges the "house" battery from the alternator, but disconnects when the engine is not running. This is of course also done to ensure that if the house battery goes dead, you can still start the vehicle.

For such a system with separate batteries, you can use the secondary voltage sense so the BMV can keep track of the voltage of the starter battery, and even provide an alarm if it goes too low and things like that. But the batteries remain (and should remain) separate.

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