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Location: Fort Collins, Colorado

Battery Balancing L1 vs L2

Wed Apr 18, 2018 11:49 am

Does battery balancing, both the low-end and high-end, occur with level 2 charging, or just with level 1?

2016 iMiev ES, Blue

Posts: 86
Joined: Mon Mar 20, 2017 4:57 am
Location: Scotland

Re: Battery Balancing L1 vs L2

Wed Apr 18, 2018 12:13 pm

Here in the UK there is no such thing as Level 1 charging since all our supplies are 240v, (Level 2) and yes, balancing is performed.

The car always top balances to 4.1 volts if left to charge on Level 1/2 until the charge light goes out, but also sometimes seems to bottom balance if you start charging from about 2 bars or less - but that may depend on whether there is a significant imbalance present or not, and whether recent charges went all the way to 100% or not.

With bottom balancing if you are monitoring the power consumption at the wall you'll see it charge for about 10-30 minutes then "pause" for about 20-30 minutes where the power drawn drops from 3.3kW (Level 2) to only about 20 watts, and then resume. I can't think of what else productive it could be doing during this 30 minute "pause" than balancing.

Top balancing is not performed when DC rapid charging using Chademo, both because the balance resistor bleed rates are far too slow in relation to the very high charge speed, but also because DC rapid charging doesn't charge past 82% by default and even if you restart it I don't think it will go to 100%. Balancing can take up to an hour past the 98% mark so it would be unreasonable for it to try to do this on a DC rapid charger.

So if you only ever DC rapid charge the cells will eventually get out of balance, so it's important to do a full Level 1/2 charge now and then.
- Simon

EV: 2011 Peugeot Ion
ICE: 1997 Citroen Xantia V6

Posts: 39
Joined: Thu Jan 18, 2018 3:53 pm
Location: Fort Collins, Colorado

Re: Battery Balancing L1 vs L2

Wed Apr 18, 2018 12:17 pm

Thanks so much, DBMandrake!
2016 iMiev ES, Blue

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Re: Battery Balancing L1 vs L2

Wed Apr 18, 2018 2:11 pm

The "time-out" which occurs after the start of charging I've seen last anywhere from 6 to 20 minutes. Especially infuriating when it occurs at a public charger and one wants to get on with it. IIRC, we even had a report of a public charger shutting off, thinking the i-MiEV had stopped charging.

DBMandrake, interesting that you think it may be part of a balancing routine, as I was under the impression that it was merely to measure the amount of voltage "sag", if any, before continuing with the charging. I had that feature on one of my marine lead-acid chargers and it shut down the charging if the voltage dropped excessively when charging was suspended. Your contention that it may be a balancing dance makes sense, and would explain why this is a seemingly-random occurrence with varying time intervals, both in duration and the point at which the "time-out" starts. Perhaps we might pay more attention to this and even see what CaniOn is saying during this interval.

True bottom-balancing I don't believe is employed in the i-MiEV as our cells never get into that dangerous zone nor (hopefully) spend any time down there; nevertheless, the concept of intermediate-level balancing is intriguing and has not been discussed before on this forum. DBMandrake, thank you for raising this possibility.
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV

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