Battery Temperatures During 6.6 kW Charging Indoors

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SageBrush

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I'd like to take pro-active steps to prolong range in the used LEAF I'll be buying soon. I've decided to install a 40A outlet in the garage but I'm wondering if I should buy a 3.3 kW EVSE or dial down a 6.6 kW device for less battery temperature increase.

All thoughts are welcome. I'm particularly interested in data that relay end battery temperatures for cars charged in 90F ambient closed garages since that will be my summer scenario.
 
People don't seem so much worried about faster charging L2(as apposed to L3) but I also have a 40a EVSE as well as lower charge rate EVSEs. What I do is mainly use my 19a EVSE and only use my 40a(which charges at 27.5 on a 6.6kw Leaf charger) when I really need it. I figure why charge the battery faster than I need, faster charge=more heat. Now I suppose you could take that a step forward and say to just use the OEM 120v EVSE if your really in no hurry but from everything I've read L2 charging(and the faster the better) is more efficient than slower L1, so I kind of split the difference of economy vs heat. I've found 19a works nice most all of the time, gives me ~25%/hr(with a 24Kwh Leaf) so in less than 4hrs I have a full battery, even if I started almost empty. A 16a EVSE will give your ~20%/hr or 5hrs from near empty. I rarely use my full power EVSE, I just don't generally need the speed, but it's nice to have for emergencies.
Another advantage to a 20a+ EVSE for cold climates is morning warmup, the heater can use up to ~20a(from your EVSE) so if your EVSE is less than that you'll actually lose charge while preforming morning warmup, even if plugged in.
 
The problem isn't L2 charging, the problem is the temperature at the time you charge (which you implied).
Charging only generates meaningful heat (for a Leaf) when you get to L3.
Having said that, I limit my charge events (during the day) in the heat of the summer...no matter what "level" of charge.
 
jjeff said:
People don't seem so much worried about faster charging L2(as apposed to L3) but I also have a 40a EVSE as well as lower charge rate EVSEs. What I do is mainly use my 19a EVSE and only use my 40a(which charges at 27.5 on a 6.6kw Leaf charger) when I really need it. I figure why charge the battery faster than I need, faster charge=more heat. Now I suppose you could take that a step forward and say to just use the OEM 120v EVSE if your really in no hurry but from everything I've read L2 charging(and the faster the better) is more efficient than slower L1, so I kind of split the difference of economy vs heat. I've found 19a works nice most all of the time, gives me ~25%/hr(with a 24Kwh Leaf) so in less than 4hrs I have a full battery, even if I started almost empty. A 16a EVSE will give your ~20%/hr or 5hrs from near empty. I rarely use my full power EVSE, I just don't generally need the speed, but it's nice to have for emergencies.
Another advantage to a 20a+ EVSE for cold climates is morning warmup, the heater can use up to ~20a(from your EVSE) so if your EVSE is less than that you'll actually lose charge while preforming morning warmup, even if plugged in.
Thanks for the comment and advice.

The more I think about the car baking while charging the less I like high powered charging. What is the heat capacity of the battery ?
 
SageBrush said:
...

The more I think about the car baking while charging the less I like high powered charging. What is the heat capacity of the battery ?
Not sure what you mean by "heat capacity" but as stanton said it's best to charge in cooler temps so if you could use the timer to charge during the early morning hours it's probably best to use a higher powered EVSE for a short period of time during the coolest part of the night vs a lower power EVSE that would need to charge during a warmer period of time. Of course if you need to use the car you've got to charge, just try and not use higher power charging during the hottest times if you can.
 
jjeff said:
Not sure what you mean by "heat capacity".
It has a precise scientific definition. Here's the Wikipedia page, but the general idea is that the higher some object's heat capacitance is, the more heat energy needs to be added or removed from it to change its temperature by some amount.
 
heat capacity of the battery: it takes many hours to return to ambient. I seem to remember somebody testing it and reporting 5-15 hours, with a T-1/2 time of something like 8 hours. I have personally seen that even 12amp L1 adds temperature to my battery. I mostly bicycle to work in the summer and have the choice of when to charge. On the nights that I charge, the battery temp increases 5-10F versus the nights that I don't charge. Ambient temps are 80-90F day and 50-60 F night. I park outside at night in summer for the desert cooling. If given the choice, I would use the 6.6 KW charging and drive right away. If driving at in-town speeds, the battery cools to ambient much more quickly (than stationary). However, if driving at freeway speeds right away, that generates more internal heat, so probably not much help. In the end, the batteries are degrading, so just use them as much as you can. High mileage drivers (like Uber) will see much more value than us low mileage drivers.
 
Reddy said:
heat capacity of the battery: it takes many hours to return to ambient. I seem to remember somebody testing it and reporting 5-15 hours, with a T-1/2 time of something like 8 hours. I have personally seen that even 12amp L1 adds temperature to my battery. I mostly bicycle to work in the summer and have the choice of when to charge. On the nights that I charge, the battery temp increases 5-10F versus the nights that I don't charge. Ambient temps are 80-90F day and 50-60 F night. I park outside at night in summer for the desert cooling. If given the choice, I would use the 6.6 KW charging and drive right away. If driving at in-town speeds, the battery cools to ambient much more quickly (than stationary). However, if driving at freeway speeds right away, that generates more internal heat, so probably not much help. In the end, the batteries are degrading, so just use them as much as you can. High mileage drivers (like Uber) will see much more value than us low mileage drivers.
Thanks Reddy.

I would be very interested in data, even if it is temperature bars read off the car display.
I had similar thoughts to how you handle the battery charging -- at night and before drives.
 
At those low speeds (3kW or 6kW) it doesn't make any difference over, lets say, 10 hours of night time.
Either you heat it during 3 hour charge period and then leave it to cool for 7 hours or you
heat it for 6 hour period and leave it to cool for 4 hours. In both scenarios it will most likely
be still at cooldown due to daytime use.
 
arnis said:
At those low speeds (3kW or 6kW) it doesn't make any difference over, lets say, 10 hours of night time.
Either you heat it during 3 hour charge period and then leave it to cool for 7 hours or you
heat it for 6 hour period and leave it to cool for 4 hours. In both scenarios it will most likely
be still at cooldown due to daytime use.
I'm willing to bet that the battery temporal temperature profile matters a lot in some cases, rather than just paying attention to end of night temperature.

E.g. peaking at 50c for a shorter time is going to be different for long term battery health than peaking at 40c for a longer time.

This NREL article
http://www.nrel.gov/transportation/energystorage/pdfs/long_beach_btm.pdf
is interesting in its own right, but comes up with 1000 joules per Kg*C for heat capacity for a Li-ion cell chemistry. Since the 24 kWh pack weighs 300 kg, that implies that one kWh of heat would raise the pack temperature 12C. IIRC, about 3% of power is lost to heat in the battery so a 30 kWh charge would be ~ one kWh heat. A 10 kWh daily use and charge at night at 20C ambient could then lead to a max average battery temperature of 24C, say in a QC scenario.

The actual temperature increase would be affected by ongoing heat dissipation, itself very dependent on the local charging environment.
In the end, user data would be the most interesting! At least to confirm the above estimates.

Charge rate:
kWh added:
Temperature data of the different sensors:

C'mon, data geeks!
 
My personal actual data rounds down to this:
with constant driving and charging (at 3kW rate) battery tends to level out
at +10C above ambient temperature. At least 2-3 deep cycles.
With QC cycles (at least 30-40kWh with driving in between) it appears to go up to +20C above ambient.

Charging at 3 or 6kW will result in cooldown in both scenarios (after long drive).
6kW charge rate will slow down the cooldown more than 3kW rate.
Driving is usually around 15kW discharge speed. Even with airflow it
results in more heat buildup than 3 or 6kW charging.
DC charging is on average 30kW rate. Without airflow it heats up a lot.

3% inefficiency is definitely too little.
Tesla charging at 100+kW rate has AC compressor at maximum power.
That compressor can extract heat at least at 6kW rate (I estimate it is more powerful than Leafs compressor).
 
arnis said:
3% inefficiency is definitely too little.
Tesla charging at 100+kW rate has AC compressor at maximum power.
That compressor can extract heat at least at 6kW rate (I estimate it is more powerful than Leafs compressor).
That removal rate of heat is mostly related to charging over 80% when the battery resistance increases.
 
arnis said:
Yes.

As one example, the Tesla Power wall has a reported 92% round trip efficiency. That includes:
AC to DC
Battery charge
Battery discharge
DC to AC
 
arnis said:
Driving is usually around 15kW discharge speed. Even with airflow it
results in more heat buildup than 3 or 6kW charging.
.
This is interesting. How much 6 kw charging experience have you accumulated, and in what ambient temps ?
 
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