Re: Switch to LiFePO4


Brent Cameron
 

All of those leads are tied together at a common post so it’s putting each pair in parallel and unless the offending battery completely disconnects (i.e. breaks the circuit), the second battery can get back fed 24V from the rest of the bank. This is why it’s so important that your batteries are well balanced and the leads are the same length as any difference in resistance can result in a battery getting a significant portion of the full capability of the load (which on Amel’s can be very considerable with things like the bow thruster, anchor windless, A/C, appliances, etc). 

In a “drop in replacement “ battery like the Battle Born, if the internal BMS (battery management system) is sealed and the battery can’t tell an external charge source when to stop charging or a load to stop discharging (which is the definition of a drop in replacement) it CAN lead to problems. 

The current rating on many of these internal BMS systems is nothing like the full current that can be run through the loads generated on an Amel. Many drop in replacement batteries use tiny little MOFSET switches as the BMS on/off switching and these things can’t handle even the TYPICAL loads of an Amel. Remember that for a battery rated at a continuous load of say 100A, you are asking for potentially ALL of that load to pass through a printed circuit board, a few short light gauge wires (nothing like your battery cables), and some solid state FET switches. That’s a big ask. 

Remember that if your parallel wiring isn’t perfect (i.e. the leads aren't all the same length and the crimp connections don’t all have the same resistance, some of those batteries are going to be seeing a LOT more than 1C charge/discharge rate so relying on a tiny switch that can theoretically handle only a fraction of 1C is problematic to say the least. 

This can also be problematic to your charging sources like alternators that might not like seeing 100A suddenly disappear with no communication. Those diodes will go poof and at a minimum the voltages will go to about 80V just before that happens so your fancy electronics may go poof too. At a minimum, I’d install an external alternator protection device to prevent issues. 

I’d be happier if BB allowed their internal BMS to communicate with the entire system like what happens with Mastervolt on a CANbus system but I guess that’s one way they are selling for a fraction of the price. 

Brent

On Aug 16, 2020, 4:40 AM -0400, Elja Röllinghoff Balu SM 222 <Bijorka@...>, wrote:
He all

On the SM and I assume on the 54/55 each pair of batteries 2x12 V / 24 V is supplied by a seperate plus and minus . ?
so every package has one
extra line to load .
therefore, for solution 24v 50 AH, each battery itself should decide when the load is terminated ? The battery is not used to be used in the battery.

Elja
SM Balu
222

Von meinem iPhone gesendet




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Brent Cameron

Future Amel Owner & Amel Owner Registry Moderator

Oro-Medonte, Ontario, Canada

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