DC/Level 3 Charging to 100%: What is your comfort level?

Charging from AC or DC to the DC battery at the same ampere rate would heat identically.

 

I've done a modicum of research on this. Battery's degrade when 'charged', and the degredation is on a curve. The lower you charge to, the more cycles you can get out of the battery, but the less electricity you get in the battery that you can use. '100%' charged is a general 'sweet spot' on the curve that allows for adequate amounts of energy to take you where you want to go, without cratering the number of charge-discharge cycles. There is no standard definition for this, each manufacturer publishes specs for their battery on what they consider 100% along with the number of cycles if you go there. This is reduced again by the auto-manufacturers, generally to improve the cycle capability.

 

The advantage of the Hyundai Kona EV, is that the battery will not overheat when charging as the vehicle's computer will turn on the heat pump to cool the battery as necessary. When purchasing an EV, look for that feature. Many AZ Leaf owners are suing Nissan because the Leaf didn't have that feature and vehicles were damaged while charging in hot weather.

 

"The number one reason to Fast Charge Level 3 to 80% is cost. Above 80% charging slows down and costs" - I agree! Not only does it get very expensive, but it will take a long time to reach 100%. It may also be inconsiderate to others who may be waiting in line to charge. The next time it could be ourself who is waiting in line to charge. Makes good sense to stop at 80%.

 

I second this. Charging etiquette says charge to max of 80% on the level 3 charger then move on. Need to charge to 100%? Disconnect from the level 3 charger and hook up to a level 2 charger for that final 20%. These actions represent good manners at the level 3 charger and help everyone to keep moving down the highway.

Cheers,

BC Doc

 

I really don't concern myself with battery charging SoC levels. I trust that the boffins at Hyundai have set it up so that the battery will stay healthy over the reasonable lifetime of the car as long as I charge it normally. I charge based on my immediate need and any billing/time considerations. For example, I charge overnight at the local level 2 charger until about 6am, because that's when the overnight rate expires. I don't care whether it's at 80% or 100% or whatever. At DCFCs, I will charge to whatever SoC level I need to continue my trip according to ABRP. That's rarely above 60% or so. My AC charge limit is set to 100% and my DC charge limit is set to 90%.

 

Will have road trip charging post coming up in a week or so. However, I've noticed that 80% is not the slow down point for fast charging. Seems to be hitting 73% then charging drops to less than half. From 60ish kw to 23ish, and then even lower after 80%.

 

FWIW - We replaced a 2016 Model X P100D with a Kona EV, since we both worked from home and the MX is a pig, efficiency wise. At the time of sale, it had almost 30MWh of DCFC put in it, at all temperatures and many cases of 100% charging since we had both free supercharging and exceptionally low occupancy chargers. It had 4.5% battery degradation at 128k km (80k miles) as visible in TeslaFi when we sold it. If you are concerned with battery degradation, I suggest picking up A Better Route Planner app and a compatible OBDII Bluetooth LE reader, since you can see both the battery temperature and the car's reading for degradation inside the app and have the app update your routes in real time based on current SoC.

In another anecdote, our Spark EV gained range after we DCFC'd it since it'd charge quite a while at 10kW or so past reading 100%. We think what was happening was the battery wasn't balanced well and DCFC would fix that - not that this would ever happen to the Kona EV, but amusing, nonetheless.

 

Just charge to 100% at DCFC if you need to. It is however slow, inconsiderate for others (if at a busy charger) and potentially expensive to do.

Kona balances the battery at 90%, or at least we can observe a few minutes of pause at charging at 90%:

 

Yeah, any good BMS should do balance charging to any setpoint. I consider this more a design issue or possibly a bad part on the Spark's side. Even my home-made batteries when charging with their balance lead connected would be fully balanced by the time they hit the set voltage level - which I usually keep well under 100% rated capacity for safety.

 

What was on said "balance leads"? Active energy-shuttle circuitry? Passive or active dissipation of high
cells to top-balance? Just curious..

_H*

 

For these batteries I’m using fairly standard RC plugs (JST and XT60) - and a D6 Pro Duo that raises the pack to a specific voltage then uses the leads to slowly bring each cell to the same voltage. If they’ve been sitting a while I’ll hook up an IGST BG-8S and charge my phone off them for a week or so per pack to pull the level down to storage then balance again with the same device - which uses passive dissipation, I believe. The packs themselves do not have a BMS. I do however have a battery voltage monitor reporting back to the controller when the machine is in use and the VESCs are set to cut off the attachment motors at a low voltage and the drive motors at a critical one for extra safety.

Edit: the machine uses 4x of these packs in 2S2P for 50v@120A continuous over 1.2kWh. The packs themselves are 6S3P with 2170 cells.