What’s your daily SOC range?

[robby]

Mine are calibrated daily. And drift daily. Two will report 100% while still drawing 20a charge for a few more hours. Three of them only reset to 100% if they see an over voltage alarm. Don't get me wrong, they are usually within 10% of the true SOC. But I don't call that accurate.

I suspect your problem has to do with your very small daily DOD. In these kind of usage cases I suspect it decreases the accuracy of the BMS.

 

[toms]

The accuracy of the coulomb counter is more to do with the current draw. The efficiency of LiFePO4 is significantly different at different C rates, so if you discharge slowly and recharge quickly your SOC will be out.

 

[TimE]

Simply stating that water is by far the best heat carrying fluid, tho it has drawbacks which is why there’s transformer oil. To compensate the different fluid through the heat exchanger must move more volume or redesigned for the medium to achieve the efficiency rating of the chiller IF that’s even necessary.
W/m K;
Ammonia .507 nasty
Ethylene glycol.258 toxic
Transformer oil .136 low reactive
Water .609 mild reactive subject to freeze.

Winstons are excellent cells, very expensive(4X?) and unlike the vast majority of the cells used on this forum they use a plastic case.
I very much believe that your project works ,however consider costs to be marketable. If the system, cells+bms+chiller+housing is four times the cost, well I’ll just buy four batteries as needed.

The intended market is military, telecoms, super-yachts where batteries are in engine rooms. We don't need to use Winston cells. Any aluminium cased cell will do.
The cost of a tank with a lid to drop the cells into plus an aquarium cooler and the oil is not significant but the benefits are of the order of at least 25% additional life in higher ambient environments. On installations using high charge and discharge C ratings such as some super yachts, the ability to cool the batteries so you can charge them up faster is very desirable.
The largest superyacht lithium bank we are aware of cost €500k. 25% increase in life of that bank would be significant.
We know of a few super yachts with lithium banks in engine rooms where generator are running at least 8 hours per day. Those banks don't last. 5 years tops. Heat kills them

 

[timselectric]

I suspect your problem has to do with your very small daily DOD. In these kind of usage cases I suspect it decreases the accuracy of the BMS.

It's only been a month since my DOD decreased.
Accuracy was no better, before. Actually I think that it was worse at a 70% DOD.