Varying rate of charge vs SoC% for longevity

john61ct · Jul 13, 2019

This question has been of interest to me for some time, from another thread.

spinningmagnets said:
I am no electronics expert, but I collect information from many sources that seem to be competent. EV cars have a large battery pack, and after that large pack has been depleted, many potential customers express some concern over the amount of time needed to charge up the pack.

To address these concerns, many products make sure to emphasize that "in just 30 minutes" that perhaps 100 miles' worth of range can be added by a smart charger.

That caught my eye. Apparently, when a pack is empty (*3.0V per cell) it can absorb a higher rate of charge than when it nears a full state of charge state.

So then, it appears to me that the fastest possible charging would incorporate a sliding amount of amps, that is tied to the heat of the pack. And...if that is true, then pack cooling can increase the rate of the sliding charge.

My understanding is that yes, heat is **correlated** with the chemical over-activity that causes high charge C-rates to reduce longevity.

And keeping cells from getting too hot is in general A Good Thing.

I am skeptical that active cooling in itself would lower the longevity hit of fast charging.

Better to charge at lower C-rates whenever possible, only occasionally do we really "need" fast charging.

Also note if you're going to discharge at high C-rated, draw down high DoD anyway, as is common for EV usage, then you're not getting great longevity anyway, the added "abuse" of fast charging may well come out in the wash.

spinningmagnets · Jul 13, 2019

Tesla is now using active pack cooling. The battery packs have an 8-year warranty the last I checked...but...every time you use the fast charge feature, it is logged, and that record affects any compensation (*pro-rated) for an early battery death.

So apparently Tesla believes that the fast-charge does affect the pack-life in some way.

john61ct · Jul 13, 2019

I did not think its deleterious effect was in question.

But as I said, not a (relatively) major area of concern in a propulsion usage context.

For me I try not to exceed 0.3C charging, and discharge is very rarely that high for long, maybe a few hours per month total.

So if I wanted to "fast" charge, that might mean bumping up to .6C, and 1C would be very rare, few times a year maybe.

Varying rate of charge vs SoC% for longevity

john61ct

1 TW

spinningmagnets

Moderator

john61ct

1 TW

Similar threads