The strategy that I have used with 96V FLA, 96V AGM, 120V FLA, 144V FLA, 156V LiFePO4 and now my marine 48V LiFePO4 battery bank is a single battery charger of the appropriate voltage, current and charging profile to charge the pack(s) as a single unit. This includes packs that were built as serial only or a combination of serial/parallel batteries or cells.
Typically similar batteries purchased near the same time stay in balance for at least tens of charging cycles. With EVs, that meant checking the individual batteries/cells quarterly and top-balancing with a small 12V or 3.2V charger. With my lithium pack that has stand-alone BMS modules on each cell, the "checkup" is annual. I haven't needed to add extra balancing for more than 2 years.
I believe that the simplicity of this system lowers the risk of "honest" mistakes. After more than 1000 charging cycles on various systems, I haven't had any failures beyond just wearing the battery(s) out (FLA only).
Fair winds,
Eric
Marina del Rey, CA
---In electricboats@yahoogroups.com, <jbwrites2@...> wrote:
Damn guys, you make me feel like a rank amateur!
Sine Metu's dedicated 12 battery, 12v, 40Ah LiFePO4 battery configuration consists of 3 banks of 4 batteries in series, bringing them up to 48v; then the 3 banks are hooked up in parallel to build up to 120Ah. All of which feeds the 3.5Kw electric drive aboard a 50 year old, 24 foot, 5,500 pound displacement sailboat in San Diego.
All of this is BMS controlled.
Once the system is completely setup, I hope to charge everything from the drive feed's bus bar by an AmpAir 100 watt wind generator (guessing 90%) and by ReGen (10%) from the drive while sailing, or by a 48v, 15A charger at the dock. I'll get back to you with real performance numbers, hopefully, by Christmas, but the shore power charging system seems to work keeping everything topped off and happy. The engine's controller is being upgraded currently by Electric Yachts and not hooked up, so I have not been putting any real loads on the system yet.
Oh, and the 12v house system is charged from the 48v bank via a Morningstar 15A MPPT and/or bypassed entirely by the 48-12v Sevcon DC-DC converter (installed as a backup). 12v loads are low: Bilge pumps, VHF, navigation and cabin lights (all LED), stereo and navigation equipment.