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sheakx avatar image
sheakx asked

Proper Smartshunt Connection

I have 2 100AH lithium batteries on a boat where the negative is parallel jumpered at the batteries with a single negative wire going to the load. The 2 positive terminals run independently to a battery switch about 6 feet away. 99+% of the time, the battery switch is set to use both batteries and the load draws from both. This has never been a issue. Can I just treat this parallel bank as a single battery? From reading other posts, it seems like the long leads to the battery switch may not be a good idea. This was the factory set up and I can’t see a great benefit in trying to manually manage these 2 batteries independently.

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2 Answers
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Kevin Windrem answered ·

It should work as-is as long as ALL loads and charging sources connect to the system side of the shunt. This includes a chassis connection. That is, the ONLY thing that connects to the battery negative is the battery side of the shunt.

As long as all wiring for the two batteries are the same length, what you have now should work fine. In this case, I'd connect both battery negatives to the shunt rather than jumping between two batteries then on to the shunt. That way, it's easy to keep both path lengths the same.

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sheakx avatar image sheakx commented ·

Thanks, That’s what I was hoping to hear. The 3/0 cables to the battery switch are the same length. I read in the install instructions to only connect 1 lead to the battery side of the shunt but using 2 equal length leads makes more sense to me. I also thought I could use both + red wires (one to each battery to view both voltages which should stay the same or very close). Does this make sense?

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Kevin Windrem avatar image Kevin Windrem sheakx commented ·

No, connecting both red wires supplied with the shunt will short the two batteries together though those wires and will blow the fuse(s) if there is any voltage difference.

Unfortunately, you'll need to connect the shunt positive to only one battery.

I don't recommend connecting the shunt's red wire to the battery switch output due to the voltage drop in the wires. This will give you an inaccurate battery voltage measurement and could affect the shunt's calculations.

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sheakx avatar image sheakx Kevin Windrem commented ·

Sounds good. Thanks.

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sheakx avatar image sheakx Kevin Windrem commented ·

Just to make sure, I was talking about using the aux connection to view the second battery voltage and setting it up like a starter battery. Are you saying this will short the connections and blow the fuse? Thanks.

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Kevin Windrem avatar image Kevin Windrem sheakx commented ·

I think that will work without blowing fuses. For some reason I was thinking you were going to tie the shunt end of the wires together.

Keep in mind the shunt relies on the battery capacity to properly calculate SOC. Battery switch in the 1 or 2 position, capacity is half what it is in the 1+2 position.

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sheakx answered ·

Final update results for anyone reading this thread. The 2 parallel 12V 100AH lithium batteries were wired to the shunt with 2 equal length jumpers. One battery positive was plugged into Vbatt+ and the other battery positive was plugged into Aux and set up like a starter battery. Everything works perfectly.

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