My winter project is to build 5 modules of 16s 50Ah batteries – 80+ EVE LF50K cells on order.
I have several (about 50?) 4.21 modules already, and I will need to order some new 4.4 modules.
Each module will be contained in a telecom battery case (5" wide, 22" long, and about 11" high, with terminals on the front 5" edge.
These modules will be installed in my old diesel compartment, behind the motor and gearbox, on a platform over the prop shaft.
Why 50ah modules? Simple. It gets cold here, to the point that I bring my batteries in for the winter.
Until now, I have been disconnecting 4-cell blocks of my 100Ah pack and taking them out by extending one arm out over the engine and lifting – this is getting old and less fun every year.
This new method will be much easier to wrangle in and out of my boat, without requiring tools. Just unplug the 175A Andersen connectors of each module, slide and lift.
Now, as to what needs to be in each module, versus what can be common to all modules:
- do I just install the cell modules in each box, and then provide a couple of 2-pin connectors that daisy chain the batteries back to a single controller that is aware of all banks?
1a) how do I handle module disconnects?
- do I put a controller in each module and get some kind of disconnect switch (SSR, latching relay, shunt trip breaker) directly controlled by the module controller
- I love the current sensor, that is going to be built/ordered shortly.
3a) Will there be an option for a hall-effect sensor instead of a shunt?
3b) I know we should be able to assume current will be split evenly amongst all modules, is there any value in sensing current of each module as well as overall and comparing?
What are your opinions / preferences as far as module enable/disable control is concerned?
I think latching relays are the best option as far as long term power consumption goes.
But what about the power consumption of SSRs under low-current conditions, like the 5 days/week that the boat is only running a 48v-12v dc-dc converter for the bilge pump (yet to actually activate itself this year) and BMS electronics? 5 days of power consumption could add up if contractor coils need to stay energized 24/7 on each module…
My boat does not have extensive charge management. It has a charger that I enable when we dock, and it either finishes on its own or the BMS interrupts it, then it latches off and needs human intervention to reset. So the boat is on its own for at least 5 days. And if the weekend sucks, we may not go to the boat at all and then its 12 days… So I don’t like the idea of continuous holding current on a coil…