The Electric Propeller Company
625C East Haley Street,
Santa Barbara, CA
93103
805 455 8444
james@electroprop.com
www.electroprop.com
Chris,
So the genset puts out 35A?
What is the draw of your motor?
What is the AH of each string?
In my case I have a 16KW genset putting out about 80A while my motors draw 50A total leaving my around 30A to charge the batteries. So running under power and charging occurs. In your case you can't do both I assume. I don't know if running 2 strings would confuse 1 BMS. I also assume you need both strings to get your required AH and not one string as a backup.
Honestly Chris I'm not a fan of splitting a pack. I can kind of see it with smaller voltage systems but then you can buy 400AH batteries as well. Expensive as hell!
So again I think James at the Electric Propeller Company may have more info but here is my thought on BMS and Charging.
A BMS must have the ability to read each batteries SOC. It would then do a balancing of the individual batteries based on the SOC by decreasing the Voltage on the higher ones and then charging the pack up until the batteries are balanced. I would think that the charger doesn't care what it's charging as long as it's setup is for the pack your doing. Again I have little experience on split packs but small vehicles like E-bikes and such would probably run into this a lot more often. I've seen some discussions on split packs to get higher AH on the DIY sites as well but honestly I had enough on my plate I didn't get into it.
Steve in Solomons MD
Lagoon 410 S2E
Steve,
Thanks for all the information about your system.
With my current FLA bank (2 X 8 Trojan T-145 6 volt batteries) I always run the 2 strings in parallel. I only switch a string off for maintenance. For my boat I really need both strings for capacity, and will likely need 2 X 48V strings if I go the LiFePo4 route. If I know that when I start my trip that I will need to motor for quite some time to reach an anchorage, I'll run my generator, regardless of my bank SOC so that I don't have to listen to the generator for hours on end once I'm on the hook. My generator is a 4.2 kW 120 VAC unit that feeds into a Victron Quatro charger/inverter. It has an internal automatic transfer switch that selects between shore power, or generator. It gives preference to the generator. It does support BMS interface as I described earlier. So, I wouldn't want the charger to wait until the bank was already depleted to start charging if I had a day of significant motoring and wanted some peace and quite once anchored. Also, with the size of my boat, I sometimes need both the charger and the batteries working together to keep SOC from getting too low before getting back to the dock.Because of my 2 banks is why I posed the question about needing 2 BMS. Either that, or I should just permanently parallel the 2 banks, 2 X 16 cells in parallel. Not sure how this would work from a BMS perspective. Maybe 1 X 32 cell BMS?
Chris
Posted by: James Lambden <james@electroprop.com>
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