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afk1911 asked

Smart Shunt with batteries in series and 2 bank charger

I just ordered 2 12v 200ah LifePo4 batteries for my trolling motor on my boat. I will be wiring them in series to achieve 24 volts. I understand the wiring to install the shunt with all negatives (except battery negative) connected after it and the 2 small wires from the shunt to each battery positive to be able to monitor both batteries. My question is regarding the charger. I have a multiple bank Minnkota precision charger that is rated for LifePo4 batteries (15 amps per bank). Charger can accommodate charging batteries in series with separate banks. I want to hook up 1 bank per battery so both batteries are maintained properly. Would I hook up the positive wires to the batteries and tie the grounds together on the back side of the shunt? If so I will be using a bus for the negatives. Also would I tie that bus in to the ground circuit on the boat so all grounds are shared?

SmartShunt
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kevgermany avatar image kevgermany ♦♦ commented ·
Not sure how we're supposed to interpret this. A battery bank is a group of batteries wired together to operate as a single battery.

If the two new batteries are the only batteries, then clear, but it seems there are others.

Whatever you do, don't connect the new batteries in series AND tie their grounds. This will create a short circuit.



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afk1911 avatar image afk1911 kevgermany ♦♦ commented ·
Yes I have a total of 4 batteries on the boat. The trolling motor bank is completely separate from the house and starting batteries. The trolling motor bank consists of 2 12v 200ah LifePo4 batteries wired in series to create 24v. I have a 4 bank charger that I want to use for all batteries on the boat. 2 of the banks will go to the start and house batteries and 2 of the banks will go to the trolling motor batteries. I know I can hook the positive wires from each charger bank to each 12v battery in the trolling motor bank. Being that I will be using a shunt and cannot hook any additional negative cables to the batteries upstream of the shunt, can I just hook the negative cables from the 2 charger banks to the downstream side of the shunt. I would not be tying the grounds on the batteries together as they would be wired in series, the 2 charger banks would be sharing a common ground on the downstream side of the shunt. Would that cause as short?
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pwfarnell answered ·

The Minn Kota Precision chargers have isolated charge circuits and the circuits are completely independent. The Minn Kota manual shows how you connect a 2 bank charger to a 24V battery made from 2 12V batteries. You use the same wiring for this, bank 1 output to negative shunt load side and 1st battery positive, bank 2 output negative to 2nd battery negative and 2nd battery positive. The shunt will count the charge going in from bank 1 output and you just have to assume that battery 2 is charging the same as battery 1.

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afk1911 answered ·

Thank you. If I connect charger bank 2 negative to second battery negative will I be able to monitor charge and discharge of both batteries? Will wiring it that way mess with the performance of the shunt?

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pwfarnell avatar image pwfarnell commented ·
To start with, you have no choice of where to put the charger bank 2 output negative because if you put it on the shunt then charger bank 2 output would be trying to charge 24V and it is a 12V charger. See the manual.

If we assume that as the batteries are in series and you use 50Ah the shunt measures this discharge. You then recharge the batteries and charger output on puts 50Ah back into the first battery and this is measured by the shunt and the shunt will go back to 100%. Charger output 2 will also put 50Ah into battery 2 but this is not measured but it does not need to be, output 1 is measured and this is enough.

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afk1911 answered ·

That makes sense. Thank you. I am new to this technology and have been trying to wrap my head around all of the details to ensure everything works as it should.

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