Re: What to do with LiFePO4 batteries when the boat is layed up?

Scott SV Tengah

We left the boat for 4 months earlier this year and while I have a Victron based system, I think you can achieve the same on MV:

I left one fridge on (brushless pump, so pump life is less of a concern) to circulate freshwater in the tanks and had my battery monitor (BMV-712) open the bi-stable programmable relay when the battery went above 70% and close again when it went below 60%. This signal fed into the remote on/off input on my Quattro inverter and acted to turn on the inverter above 70% and turn off the inverter below 60%.

I had a 220v dehumidifier (around 200w) plugged in. 

Per my boat watcher, it worked perfectly. Our boat was drier than any other he had seen and the battery stayed in a range to maximize longevity.With my 960w solar, this keeps the battery cycling between roughly 55% and 100%. At that depth of discharge, the batteries would outlive me! Bonus is that the boat is completely dry inside, too. 

I am almost certain you can do something similar with MV. Sv Garulfo has a full MV lithium setup and borrowed my dehumidifier when they left for a brief period so they can probably explain how they did it.

Also, MV's solution doesn't seem terrible as long as the charger goes into float at a low enough SOC. If bulk/absorption ends at say 27.4v and that is the equivalent of around 65% SOC and then it holds at 27v float, then you aren't holding your battery at high SOC, so it should be ok. The flat voltage discharge curve that makes lithium so great also makes it hard to estimate SOC from voltage.  But I'm sure MV's battery monitor can talk to the chargers to tell them to shutoff charging at a user-specified SOC level?

2007 A54 #69
SV Tengah

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