Hi, I have been watching this forum from time to time and I'm ready to jump in. I want to construct a 24v 8 cell lifepo4 100 Ah pack to power my trolling motor as auxiliary propulsion for my 20' Elver. I plan to use a BMS to monitor the cells and detect high and low voltage on the cells and the pack. This pack will be recharged by 200 watts worth of solar panels continuously while underway. I'm leaning toward a Victron 75/15 MPPT controller configured for this battery charging profile. The BMS may be the MiniBms used in some electric vehicles but I'm considering others.
In order to learn about this type of battery I constructed a 20Ah 12v prototype system and use it for charging a cell phone, tablet and other small devices. I instrumented this prototype with various ammeters and voltmeters to check all the charging and discharging parameters. I used top balancing for this and it seems to work well.
Question: Would bottom balancing the batteries be better than top balancing for this application? The pack will be discharged at varying rates up to 55 amps but mostly in the 20 to 30 amp range. The pack will be directly connected to the trolling motor. It will be charged at up to 6 amps by the solar panels all day. I'm thinking this operating profile is more like that of an electric vehicle and bottom balancing would reduce the risk of excessively discharging a cell. OTOH Top balancing is easier to achieve and works better with the solar charging controller.
Question: Can cutting off the electricity to the motor by a contactor relay such as when the battery pack must shut down be harmful to the motor or speed controller? Its a MinnKota Riptide 80 trolling motor. I'm thinking of why one doesn't disconnect an alternator from the battery while the engine is running.
Question: Do you use an amp hour counter to keep tabs on the state of charge? The voltage decreases very little from about 90% to 10% SOC so that would not be a great indicator. What brands seem to work best?
Thanks for any constructive thoughts about this configuration.
Best regards,
Will
Posted by: willmarsh3@gmail.com
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