Two batteries one SCC

scott harris · Apr 7, 2024

I have a small boat with two 24 volt homebuilt lifepo4 batteries, each with a separate BMS and each connected to a separate motor. Recently I added 3 solar panels connected in series and a victron SCC. My plan is to use a BlueSeas battery switch to connect the SCC to either battery 1 or 2 for charging. But now I see that BlueSeas has a switch that connects to battery 1 or 2 or 1+2. Is it safe to charge both batteries simultaneously with 1 SCC?

Thanks,

scott

timselectric · Apr 7, 2024

scott harris said:
Is it safe to charge both batteries with 1 SCC?

It is, but the conductors must be sized correctly.
This puts the two batteries and loads in parallel. And the conductors OCP (fuses or breakers) need to be sized to carry any current that can flow through this path.

timselectric · Apr 7, 2024

Also, if this parallel connection is going to be switched on and off.
The batteries on the two sides need to be very close to each others voltage, when switching on.

scott harris · Apr 7, 2024

timselectric said:
It is, but the conductors must be sized correctly.
This puts the two batteries and loads in parallel. And the conductors OCP (fuses or breakers) need to be sized to carry any current that can flow through this path.

oh, well that presents an interesting question. if I am charging at 10 amps and discharging at 20 amps through the same circuit breaker then no I use the net of 10 amps or the sum of 30 amps to calculate wire guage.

scott harris · Apr 7, 2024

timselectric said:
Also, if this parallel connection is going to be switched on and off.
The batteries on the two sides need to be very close to each others voltage, when switching on.

they most likely always will be since I need both motors to steer the boat (using differential thrust for steering), but out of curiosity what happens if there is a large voltage mismatch and I connect them both via the switch?

OM617YOTA · Apr 7, 2024

Is there a reason to not run everything to bus bars? Both motors, both batteries, and the SCC.

scott harris · Apr 7, 2024

The two batteries (yellow boxes) are mounted midship with one on each side to keep the boat balanced. So before the solar panels I just kept everything separate. now thatvi have mounted 3 solar panels maybe you are right I should just make it a parallel system.

timselectric · Apr 7, 2024

scott harris said:
oh, well that presents an interesting question. if I am charging at 10 amps and discharging at 20 amps through the same circuit breaker then no I use the net of 10 amps or the sum of 30 amps to calculate wire guage.

10a but,
That's just one scenario. You have to size for the largest scenario.
Probably the maximum output for one battery would be enough.
The Best option is to just turn it into a single system. And size everything accordingly. With bus bars and proper OCP.

timselectric · Apr 7, 2024

scott harris said:
they most likely always will be since I need both motors to steer the boat (using differential thrust for steering), but out of curiosity what happens if there is a large voltage mismatch and I connect them both via the switch?

Large surge of current as the fuller battery dumps power into the other.

Two batteries one SCC

scott harris

New Member

timselectric

If I can do it, you can do it.

timselectric

If I can do it, you can do it.

scott harris

New Member

scott harris

New Member

OM617YOTA

Solar Enthusiast

scott harris

New Member

timselectric

If I can do it, you can do it.

timselectric

If I can do it, you can do it.

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