Dual bank Auxiliary Battery management/monitoring

[Piddy]

Morning all,

After replacing the engine last year I am now starting to address things like Solar and battery management systems.
The boat is 30+ years old so there are quite a few legacy issues such as two separate auxiliary battery banks (all FLA) separated by a 1-2-1-off switch and a pretty power hungry fridge. I know these aren’t great but that is what we’ve got! The budget isn’t huge but I know there is money to be spent.

Up ‘till now we have coped with this arrangement mainly weekend sailing but with regular 2-3 week holidays. Our plans for the next few years are to spend 3-5 months aboard hence requiring better battery management. I don’t want to be marina dependent for all of this time so solar will be added (I’m currently looking at 2 x 200W panels on a gantry) but I’m getting stuck on how to monitor the batteries. All of the bms systems seem to be designed for 1 battery but with an option to monitor just the voltage of another. Ideally I want to monitor volts and amps on both banks. Currently I run with both banks joined together at the 1-2-1 switch using the theory that partially discharging one big bank is better than really hammering 1 smaller bank and then switching over but that's not to say it couldn't be done better. I do like the idea of being able to separate them for isolating duff batteries.

What would the best way to monitor the batteries?

The picture below is how it is arranged at present:

 

[pvb]

All of the bms systems seem to be designed for 1 battery but with an option to monitor just the voltage of another. Ideally I want to monitor volts and amps on both banks.

Take a look at the Simarine Pico monitor. It's hugely versatile, and is capable of monitoring up to 6 batteries/banks, and 20 current measuring devices. Plus temperatures, tank levels, whatever. It also has just about the best-looking display on the market. I fitted one about a year ago.

Currently I run with both banks joined together at the 1-2-1 switch using the theory that partially discharging one big bank is better than really hammering 1 smaller bank and then switching over but that's not to say it couldn't be done better.

Your theory is correct. A bigger bank also recharges more easily.

 

[Poey50]

Morning all,

After replacing the engine last year I am now starting to address things like Solar and battery management systems.
The boat is 30+ years old so there are quite a few legacy issues such as two separate auxiliary battery banks (all FLA) separated by a 1-2-1-off switch and a pretty power hungry fridge. I know these aren’t great but that is what we’ve got! The budget isn’t huge but I know there is money to be spent.

Up ‘till now we have coped with this arrangement mainly weekend sailing but with regular 2-3 week holidays. Our plans for the next few years are to spend 3-5 months aboard hence requiring better battery management. I don’t want to be marina dependent for all of this time so solar will be added (I’m currently looking at 2 x 200W panels on a gantry) but I’m getting stuck on how to monitor the batteries. All of the bms systems seem to be designed for 1 battery but with an option to monitor just the voltage of another. Ideally I want to monitor volts and amps on both banks. Currently I run with both banks joined together at the 1-2-1 switch using the theory that partially discharging one big bank is better than really hammering 1 smaller bank and then switching over but that's not to say it couldn't be done better. I do like the idea of being able to separate them for isolating duff batteries.

What would the best way to monitor the batteries?

The picture below is how it is arranged at present:
View attachment 97477

If you run with both banks combined, which makes sense, then effectively you have one bank. I'd monitor that alone and use the voltage monitoring on the engine battery.

 

[rogerthebodger]

I have a very similar battery setup with 2 domestic battery banks

When we are onboard we have the 1 2 B switch in Both as the bigger bank will discharge less so will have a longer like.

I have my solar also in seperate banks connected to each bank so I can separate the banks is one bank goes faulty so I can run on either bank without running the other bank down due to the faulty battery bank.

I also have a 1 2 B switch that allows me to switch between the engine start or domestic batteries to start the engine.

I have a seperate engine battery solar panel that can we switched to charge the domestic bank via the 1 2 B switch.

I have 2 alternators a small one charging the engine battery and a bigger charging whichever domestic is selected (normally both)

When the domestic switch is off a reduced solar charging is connected directly to the 2 separate domestic bank with their own regulators.

I have ammeters for each battery bank and solar panel outputs.

Volt meters for each battery bank give me an indication of the voltage thus an indication of the charge.

I have not felt the need for a battery capacity meter although it may be useful fo some people.

Living just south of the tropic of capricorn we get plenty of sun particular in the summer.

 

[Jokani]

Take a look at the Simarine Pico monitor. It's hugely versatile, and is capable of monitoring up to 6 batteries/banks, and 20 current measuring devices. Plus temperatures, tank levels, whatever. It also has just about the best-looking display on the market. I fitted one about a year ago.

+1 for Simarine Pico, mine monitors 7 batteries in 3 banks, I'm pleased with it

 

[Piddy]

Thanks. The Pico unit looks good - pricey but very capable.

 

[Buck Turgidson]

another + for the pico. Mine is just the Pico one but it serves my needs. 2 years in service and zero issues. looks mint too!