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jasontav asked

Lithium Smart Charging strategies.....


I am about to deploy 2x 150Ah Lithium Smart batteries in 24V configuration to replace traditional lead-acid. I have BMS and multiple battery protects to enable disconnect of the charger and load as required. All solar chargers are Victron.

I am unlikely to cycle them below 80% SoC on a regular basis (but they will be cycled every night/day) - and it is very unusual not to have enough solar power to fully recharge everyday.

Will the longevity of the battery be increased if I use a reduced charging voltage?

If so, can I use the regular equalisation feature of the MPPTs to provide the "at least once a month" charge to 14V? (from the manual: Batteries must be regularly (at least once every month) charged to 14V (max. 14,4V) in order to fully balance the cells)

I was considering a very short Absorption time as per the manual (Absorption time: 2 hrs for a 100% charge, or a few minutes for a 98% charge.)

any input gratefully received......

Lithium Battery
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1 Answer
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ben answered ·

To first order, all the data we have show that LiFePO4 batteries’ lifetime capacity improves when run at lower states of charge most of the time, with an occasional run up to the top as you mention.

If you can find a combination of settings (voltage, absorption time) that will place the cells somewhere more in the range of {70%, 90%} or even {60%, 80%} you will probably extend their life somewhat. You definitely have that luxury since you don’t expect to draw them down very far, very often.

One downside is that current-based state estimation, like what you get from a BMV, will tend to drift if you never reach a full charge. But when you do charge to 100% once a month or whatever, it will synchronize back and be accurate once again. How fast it drifts, and whether someone cares about having that last bit of accuracy, will vary.

I do not know the answer to your question about borrowing the equalization feature to do the top-balancing charge. It sounds like a good idea, though.

The last thing I would mention is that there is no guarantee that your solar supply can take the batteries to 100% with a long absorption curve. Some setups need another charge source (marina, shore, generator) to make this happen reliably.

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