Re: [electricboats] Parallel LiFePO4 Packs

Great advice.

My 30kwh pack batteries (lithium ion, 20P(1.5kwh, 42vnom)) are only connected to a charging system after reaching somewhere between 33 and 36v, and then only charging overnight to 48v (max. batt spec is 49.1v).  I manually disconnect the next day.  Going further, I do not totally trust BMS cards (and for good reason) and so I only power them up maybe once every 6-18months to check cell balance across the 240 cell pairs.  Even with that, I have heard from at least one European owner of THINK cars with these batteries/BMS indicate to me that he has seen even unpowered BMS cards drain a cell pair.  So there's that risk also.  Further on the non-trusting side, the software I wrote to communicate with 20 BMS cards and manage all the balancing only enables balancing on one of the 20 module strings at a time---only the worst one.  This has the advantages of minimizing the number of bypass circuits that are enabled and lowering the risk that they will degrade quicker or worse, that one of them might get stuck ON.  Since all the modules are in parallel, as a string is bypass balancing, the other parallel strings will supply that string with current, maintaining the string voltage and only slowly dropping the pack voltage---far better than bypassing ALL the high cells in the pack to bring them all down to the low voltage.  Works like a charm.

 

Anyway, stay safe.

 

-MT

 

From: electricboats@groups.io [mailto:electricboats@groups.io] On Behalf Of Harley Clark
Sent: Wednesday, November 22, 2023 5:22 PM
To: electricboats@groups.io
Subject: Re: [electricboats] Parallel LiFePO4 Packs

 

I don't know if it is general knowledge that fully charged LFPO batteries must be disconnected from a charging source.  Lately I have heard of some unexplained fires in boats that are docked while their owners are absent and have wondered if the batteries were being over charged by solar panels or wind. The BMS should be set up to physically disconnect the batteries. 

This can be complicated by solar and wind if these sources must be redirected to another load path to consume this unwanted charging current.

Hopefully, Everyone is hearing old news

 

On Tue, Nov 21, 2023 at 10:07 AM THOMAS VANDERMEULEN <tvinypsi@gmail.com> wrote:

wow, Reuben ... !  A full MegaWatt hours of capacity?!?!   According to one source, that's enough to power the average household of 5-weeks!!
What is your cruising range on motor alone?  Must be close somewhere around 70 Nautical Miles.
[-tv]