Charging Best Practices

There are 7 battery modules with in a 1-2-4 arrangement (T pack). The middle 2 are single stacked 8 cell and the others are double stacked 16 cells to get 96 cells in total. Probably some cells reach optimal voltage sooner than others.

I'm pretty sure the MINI has both active and passive balancing (long term storage) like the i3 does.

 

You could start with a level 2 'lite'. Have suitable wiring and EVSE installed for 7.2+kW, but only use a breaker your current panel can handle, then set EVSE accordingly. If/when you get your panel done, you have everything there at the panel ready for an upgrade.
16A at 230V is 100% of charge in around 9 1/2 hours. 12A at 110 is 31 hours. Trust me, 110v is downright painful. 230v at any current is just so much better. I believe the charger that comes with a new SE has a 6-20 adaptor available. I have two bags of Tesla UMC2 stuff under the boot floor.
I was not fully prepared for my SE as it turned up early. My first charging upgrade from 110 on an extension cord was a 6-20 outlet in my carport. That was quite livable and just fine for overnight charging, however much I'd driven the day before. With 110v, and a 40 mile commute, I was charging if not at work. I would only hit 100% at weekends...
Having a 7.2kW EVSE means unexpected trips don't need much charging time. I'm never under 50% going into days off with my charging regime.
If your house is old enough to have ungrounded outlets, you won't be able to charge from those. No EVSE will allow charge without a ground.

 

You've convinced me on the necessity of charging to 100%. I may go less than that with every charge. But i definitely want to do 100% charges to maintain even battery wear.

Question - how long do you leave the car plugged in after it's done charging? My situation is different than yours since i have 240 in my garage where i plug in. I'm thinking about leaving the car plugged in something like 2 hours or so after charge is finished, if i don't go to 100% all the time.

 

I leave my car plugged in all the time when it's at home. It does not draw power after it reaches 100%. I've done this with my SE the entire two years I've owned it, and with over 45,000 miles on it there's no discernible drop in range.

 

Yeah I’m unclear what “float charge” means here. The charge controller stops accepting a charge once it deems the battery is full. I own several battery-maintainers/trickle chargers (C-Tek, Solar, NOCO) for ICE cars, but they purposely keep drawing a tiny current after top-up; EV charge controllers don’t do that.

 

I'm still regaining capacity and SOH now I am doing weekly 'floats' instead of weekly charges to 100%, then drive. My last float was a couple of hours and added back another 0.2Ah.

I do not know the exact mechanism, however, I am seeing my lost capacity being regained with weekly 'float' charging. The proof of the pudding is in the eating! There are quite a few different ways to balance batteries, many of them don't involve actual charging. My bet is the pack is balanced while at 100% charge and the car is plugged up.
LiIon chargers will let batteries lose a bit of charge before topping them back up.

Float is probably not the exact word, but most people understand it as having a charger hooked up to a fully charged battery.

 

Float charging is something for lead acid batteries and temperature compensation.
1. Bulk (<80% constant current and adjust voltage)
2. Absorption (~80%-98% constant voltage and adjust current)
3. Float (98%-100% slightly lower voltage than absorption)

Trickle charging could be dangerous when a constant current is applied without voltage monitoring...otherwise overcharged battery goes KABOOM!

Lithium ion is much better in that regard but there's a lot of battery management required.

 

12 volt batteries ok with cheap trickle chargers but on EV is different on HV s batteries with all charging Menagment

 

The precise reason I got the C-Tek. The Solar and NOCO chargers are just fine for most long term uses, but the C-Tek is at another level altogether, with different maps for different battery types, as well as active desulfation modes for each type.

 

Actually, they do. If they didn't, you would charge at full current all the way to 100%. By backing off it allows the cells to float. It is a term borrowed from the old lead acid days when you physically had liquid and "float" levels you had to maintain for proper battery health. All it means in Li batteries is that the charging slows down to allow all cells to reach the same voltage. A cell drawing more power heats up more than the other cells and can be damaged if it is the "only one left charging". By decreasing the charging current (by lowering the charging voltage), you allow these "slower cells" to catch up. This means all cells reach the same voltage rather than the pack reaching a total voltage. That is also why charge controllers have connections to each cell as well as the main terminals, so they can monitor the cells.

As a thought exercise, imagine two batteries, one a 1Ah, the other a 10Ah. If they are in series, then the same current flows through both batteries. The 1Ah flattens much faster and drops the voltage for the entire pack. It may well get damaged trying to keep the current flowing through. When charging, it will be at capacity before the 10Ah, and instead of dropping the voltage, it will still be at max, again damaging the battery. It is the reason electronic suppliers say never mix old and new batteries. I realise this is an over simplification, and Li is quite different to Pb, however the principle is the same.

Always going to 80% means leaving the charge cycle when the current is at a maximum, well for the SE at least. The cells won't be at the same voltage - they will be close - but not the same, so these lower voltage cells end up wearing more. It actually mentions it in the manual (somewhere) - I remember reading it, but don't have it to hand.

EDIT: in your post just below, yep the charge is disconnected once the pack reaches the final voltage - with hopefully all cells equal. Pb batteries used to trickle current in to keep them at 100%, Li doesn't need this as they self discharge much, much slower. The extra heat would also damage them.

 

Thank you for the detailed info. Yes, that was all in my understanding, but unlike SLA batteries, there isn’t a point to leaving an EV battery plugged in once 100% is reached and the car decides to notify that “charging is complete.” A smart charger for SLA batteries ramps all the way down to maintenance current and voltage and monitors while continuing to supply electricity until unplugged.