TexasLeaf
Posts: 33
Joined: Wed Mar 21, 2018 5:37 am
Delivery Date: 21 Mar 2018
Leaf Number: 303111

Re: Using speed to control battery temperature

Tue Jul 03, 2018 6:28 am

LeftieBiker wrote:
Driving doesn't appear to contribute to the battery overheating and actually helps cool the battery when the battery reaches higher temperatures.


This has been clear for quite a while, beginning with the 24kwh pack. In fact, I posited a while back that the accelerated degradation that users of Leaf to Home were experiencing was specifically because the cars weren't being air cooled by driving them while the packs were being drained. Driving can warm the pack, but that requires either a cold pack and hot ambient air, or extremely hard driving combined with warm or hot air temps. The rest of your test is very useful.


I performed another little test last weekend. I wanted to test the theory that short 5 minute waits before and after charging on long trips would improve charging speeds. I drove about 350 miles and I CHAdeMO charged 3 times, waiting before and after each charge.

At the beginning of the test the outdoor air temperature was a little above 80 degrees F but at the end of the test the temperature was a little over 100 degrees F. I drove back and forth between to charging stations that were about 90 miles apart. I drove the speed limit which was 70 mph most of the way.

My first charge started out at 30 kW, my second charge started out at about 20 kW but my third charge started out at 11 kW. On my previous test I drove a constant 60 mph and my charging speed never dropped below 14 kW. The test regarding the wait times was inconclusive but the battery temperature gauge did indicate that driving at 70 mph increases battery temperature, unlike the previous test where 60 mph maintain constant battery temperature.

So this test is validation of the hypothesis that you can use speed to control battery temperature. Driving slower improves charging speeds in two ways, the lower speed keeps the battery cooler allowing faster charging speeds and the lower speeds consume less power requiring less time to replenish the charge. For best speed you should always try to match travel energy consumption with charging speed (i.e. 14 kW at 60 mph with 14 kW charging) unless you can maintain very good charging speed, in which case you should drive at the fastest, safest legal speed.

GetOffYourGas
Posts: 1828
Joined: Tue Dec 20, 2011 6:56 pm
Delivery Date: 09 Mar 2012
Location: Syracuse, NY

Re: Using speed to control battery temperature

Tue Jul 03, 2018 6:56 am

TexasLeaf wrote:For best speed you should always try to match travel energy consumption with charging speed (i.e. 14 kW at 60 mph with 14 kW charging) unless you can maintain very good charging speed, in which case you should drive at the fastest, safest legal speed.


This is an interesting theory. Do you have any math to back it up or is it just a gut feel?
~Brian

EV Fleet:
2011 Torqeedo Travel 1003 electric outboard on a 22' sailboat
2012 Leaf SV (traded for Bolt)
2015 C-Max Energi (302A package)
2017 Bolt Premier

TexasLeaf
Posts: 33
Joined: Wed Mar 21, 2018 5:37 am
Delivery Date: 21 Mar 2018
Leaf Number: 303111

Re: Using speed to control battery temperature

Tue Jul 03, 2018 8:16 am

GetOffYourGas wrote:
TexasLeaf wrote:For best speed you should always try to match travel energy consumption with charging speed (i.e. 14 kW at 60 mph with 14 kW charging) unless you can maintain very good charging speed, in which case you should drive at the fastest, safest legal speed.


This is an interesting theory. Do you have any math to back it up or is it just a gut feel?


The calculations are pretty simple as long as the charging speed is held constant, all you have to do is calculate the average speed including charging time. At 14 kW charging, the average speed of the Leaf traveling at 60 mph consuming 13.9 kW is 30 mph, traveling at 70 mph consuming 19.4 kW is 29.3 mph and traveling at 50 mph consuming 9.8 kW is 29.4 mph. Of course with the higher speeds creating higher battery temperatures and slower charging speeds, these calculations get skewed in favor of the lower speeds.

There are actually two reasons that slower speeds provide cooler battery temperatures, one the less current through the battery produces less heat and two, as long as the heat caused by the current is negative not positive, there is more time for the battery to dissipate excess heat.

Another thing I've been thinking of doing to reduce battery temperature on long trips is to DCFC until the charging speed tapers down to L2 speeds or until the battery is fully charged. I know that a lot of people are saying that you should only charge to 80% but I don't think they are not thinking through charging a Leaf on long trips. The few extra minutes the Leaf spends on a DCFC charger tapering down to L2 speeds or even to 100% charged allows more time for the battery to cool which may allow the next charging speed to be much faster and gives you more security that you can make it to your next charging station.

GetOffYourGas
Posts: 1828
Joined: Tue Dec 20, 2011 6:56 pm
Delivery Date: 09 Mar 2012
Location: Syracuse, NY

Re: Using speed to control battery temperature

Tue Jul 03, 2018 1:31 pm

TexasLeaf wrote:The calculations are pretty simple as long as the charging speed is held constant, all you have to do is calculate the average speed including charging time. At 14 kW charging, the average speed of the Leaf traveling at 60 mph consuming 13.9 kW is 30 mph, traveling at 70 mph consuming 19.4 kW is 29.3 mph and traveling at 50 mph consuming 9.8 kW is 29.4 mph. Of course with the higher speeds creating higher battery temperatures and slower charging speeds, these calculations get skewed in favor of the lower speeds.


Interesting. And this holds for any charging speed? Say from 14kW to 44kW?
~Brian

EV Fleet:
2011 Torqeedo Travel 1003 electric outboard on a 22' sailboat
2012 Leaf SV (traded for Bolt)
2015 C-Max Energi (302A package)
2017 Bolt Premier

TexasLeaf
Posts: 33
Joined: Wed Mar 21, 2018 5:37 am
Delivery Date: 21 Mar 2018
Leaf Number: 303111

Re: Using speed to control battery temperature

Tue Jul 03, 2018 2:32 pm

GetOffYourGas wrote:
Interesting. And this holds for any charging speed? Say from 14kW to 44kW?


Whenever I've done the analysis the results have always been the same, the best average speed is obtained when the output power is the same as the input power.

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