After our first cruise with the new LFP battery we are thrilled. It was 6 days and 2-hours and during that time we did not give any thought to power conservation. We had the fridge, freezer, and all electronics running the whole time.
We used a total of 626 amps for an average of 102A/day. This is significantly less than we have used on any previous cruise in spite of adding the freezer. I have modified the AB icebox conversion from a mechanical thermostat to a digital that runs the compressor on low speed and eliminates the short-cycle that happens with the mechanical. I also added a much more efficient PWM controlled fan that both cools better and is completely silent. We also get a huge boost from the Peukert's ratio being 1.0 rather than the normal LA 1.25. We also get gains from the discharge voltage being 13.2v rather than 12.6 or lower for LA.
All-in-all, it comes to +30% gain in total efficiency.
Thanks.I put 280 ah of lithium on my boat and have the some observations as you. No longer worried about charging the batteries back up to 100% and even some light motoring seems to keep up with my power needs (similar to you - fridge, freezer, instruments, some inverter use).
I like your meticulous mounting of your battery. Very tidy instal.
I'm sure you aware but one item to consider is a load dump from your alternator if /when your BMS cuts out. You need to have a lead acid battery in parallel or some other solution to absorb that energy or things are liable to get fried.
Also, seems like you are relying on the BMS to stop charging the batteries when they are full. For me, I would prefer to have some redundancy to avoid overcharging. Even a mechanical thermo fuse on the cells which in turn powers a rely which in turn powers the field wire to the alternator would be a last line of defence protection from dangerous (i.e. fire) levels of overcharge.
Better alternator solution would be a Balmar or other external regulator but there is a cost of course....
Sounds like you have all the details in hand.Thanks.
First off, the alternator is an Ample Power 105A hot rated externally regulated alternator. The Regualtor is a Xantrex InCharge with added controls for limiting the max field current and electronic thermostatic control based on the alternator case temperature.
For alternator protection, I have an AGM start battery and they are both connected to the alternator through a diode-based combiner but that will be changing to an ArgoFET combiner. The LFP can shut off, but the AGM cannot so no diode "boom"
I am not relying on the BMS for charge cutoff. The alternator is externally regulated, and I have the charge voltage set to 14.2V (3.55v/cell) with the sense wire on the AGM side of the combiner. Absorption time is set for 30-minutes to allow the BMS to top balance the cells up to 3.55V then it drops to 13.3V for float. The active balancing comes on at 3.45V.
I have a 1.0ohm resistor on the field wire which limits the output on my 105A Ample power alternator to 60A max and keeps the temperature below 90ºC. I will also be adding a thermostatic switch to the field wire that will cut the alternator off if the output lug hits 95ºC as a safety backout. So far, the BMS has only shut down for HVC once and that was for testing purposes on the first charge. I had the charge current at 25A with the cells out of the box and no conditioning or top balance. I set the HVC at 3.55V and it tripped with 250Millivolts of delta. I then reduced the current to 2A with a 14.0v cutoff and the active balancer in the JK proceeded to top balance the cells to 3.499v with delta = 0.003V. (see screen shot.)