Page 1 of 4

Using speed to control battery temperature

Posted: Tue May 29, 2018 10:38 am
by TexasLeaf
I recently bought a 2018 Leaf SL. I have already had a couple of instances where the battery got hot and would not DCFC very fast. I'm hoping in the future to take some long distances trips in my Leaf so I'm thinking of ways to mitigate the hot battery and slow charging issues.

I made some long distance trips in my 1st generation Ford Focus Electric. One thing I found out driving an EV without fast charging is that the faster you drive the longer it takes to get where you want to go. It makes sense that the same principle could be applied to battery heating and slow charging.

Battery heating is caused by amperage to and from the battery. The Leaf thermal management system controls the amperage to the battery when charging but we control the amount of amperage from the battery with the speed we travel. We know that the battery has the ability to cool itself but the cooling system gets overloaded over long distances and with multiple fast charges.

There must be some speed at which the battery cools enough to allow full amperage during fast charging. But what is that speed? There are of course other factors such as accessory use and ambient temperature that would enfluence this threshold speed but when need to establish a baseline then work on the other stuff.

We can't changed the way the Leaf was designed but we can control the way we use it. Reading through this forum there appear to be some pretty knowledgble people that frequent here. I have found a lot of threads on the battery over heating issue but very little on how to manage the over heating.

I plan to perform some tests to see at what speed does the battery not get too hot to accept full amperage on fast charging. This is going to take some time, driving around in a loop at different speeds and stoping to fast charge when needed. Texas in summer would be a good place to perform these tests.

If anyone has performed these kinds of tests or knows of any good ways to manage battery temperature on long trips I would like to hear about it. Please don't just regergitate the infromation on battery temperature in the owners manual. I'm looking forward to hearing about your experiences, thoughts and ideas on this issue.

Re: Using speed to control battery temperature

Posted: Tue May 29, 2018 11:58 am
by LeftieBiker
One issue I can see with trying that in Texas is that the ambient temp may often be too high to actually cool the pack if it's above 5 bars but below 8.

Re: Using speed to control battery temperature

Posted: Tue May 29, 2018 12:01 pm
by TexasLeaf
It looks like I'm going to ignore my own request and regurgitate some of the owners manual. Most things we do to increase power economy should also reduce battery heat. So things like using ECO mode and not using climate control will also reduce battery heating.

But some things we do for increasing power economy, like using regenerative braking and pre-conditioning the cabin, actually work against us when trying control battery heating. So basically anything we can do to reduce or eliminate amperage to and from the battery will help reduce battery heat.

One thing that is very import to this issue that's in the manual is that we should not fast charge when the battery temperature is near the red zone on the battery temperature gauge. What the heck does "near" mean? If we are able to control and even reduce the battery heating by managing the power consumption, just exactly where does the temperature on the battery temperature gauge need to be so that we know we will get full amperage during a fast charge?

But we are getting ahead of our selves. First we need to find out "if" we can control battery temperature on long trips. Once we answer the "if" question then we can answer the "how much" question we need answered for full amperage fast charge.

Re: Using speed to control battery temperature

Posted: Tue May 29, 2018 12:25 pm
by TexasLeaf
LeftieBiker wrote:One issue I can see with trying that in Texas is that the ambient temp may often be too high to actually cool the pack if it's above 5 bars but below 8.



The 2018 Leaf doesn't have temperature bars, just a gauage with blue, normal and red ranges. Right now it's 96 degrees F outside, my Leaf has been sitting in the sun all day and the battery temperature is just a little on the red side of middle normal. So there is a little room between Texas ambient temperatures and the red zone.

Yesterday was just about as hot and I did a long trip in my Leaf. I didn't have any real trouble with battery temperature until my last charge after driving about 250 miles. If I can find a way to control battery temperature in Texas then we know we can control battery temperature almost anywhere.

Re: Using speed to control battery temperature

Posted: Tue May 29, 2018 12:52 pm
by arnis
Yes. There are ways to reduce heat buildup.
1) Do not accelerate hard, be very gentle. In any given moment, keep motor power below 20kW. Including uphill
In case of "I need to go faster right now" accelerate at power UP TO 30kW. This is important. Those seconds DO matter.
2) Do NOT regen hard. Keep regen up to 20kW. So slow down slower.

3) Start your journey at 100% charge state.
4) Visit quick chargers before you drop below 20%. This is important.
Rather than discharging below 20% on the next leg, consider charging more before departure.

So it would be easy to remember as 20-20-20 rule :)

Speed itself doesn't matter a lot.
Using AC is fine. It might even help to use mild AC while QC as outside fan is blowing while vehicle is stationary. That is good.

Re: Using speed to control battery temperature

Posted: Tue May 29, 2018 2:03 pm
by SageBrush
arnis wrote:Yes. There are ways to reduce heat buildup.
1) Do not accelerate hard, be very gentle. In any given moment, keep motor power below 20kW. Including uphill
In case of "I need to go faster right now" accelerate at power UP TO 30kW. This is important. Those seconds DO matter.
2) Do NOT regen hard. Keep regen up to 20kW. So slow down slower.

Speed itself doesn't matter a lot.

I like this advice.

Re: Using speed to control battery temperature

Posted: Tue May 29, 2018 2:04 pm
by SageBrush
@TexasLeaf,
Are you able to monitor battery temps with LeafSpy ?

That would be really interesting data

Re: Using speed to control battery temperature

Posted: Tue May 29, 2018 2:25 pm
by TexasLeaf
SageBrush wrote:@TexasLeaf,
Are you able to monitor battery temps with LeafSpy ?

That would be really interesting data


I don't have LeafSpy yet but this test would be a good reason to get it.

Re: Using speed to control battery temperature

Posted: Tue May 29, 2018 2:30 pm
by DuncanCunningham
TexasLeaf wrote:
SageBrush wrote:@TexasLeaf,
Are you able to monitor battery temps with LeafSpy ?

That would be really interesting data


I don't have LeafSpy yet but this test would be a good reason to get it.
ha ha having a leaf is the best reason to have Leaf Spy Pro. you'll love it.

Re: Using speed to control battery temperature

Posted: Tue May 29, 2018 2:57 pm
by TexasLeaf
arnis wrote:So it would be easy to remember as 20-20-20 rule :)

Speed itself doesn't matter a lot.
Using AC is fine. It might even help to use mild AC while QC as outside fan is blowing while vehicle is stationary. That is good.


I very much appreciate your suggestions but I am a little skeptical. As a rule I don't like rules-of-thumb. I prefer more explicit information like, "if your battery temperature is 110 degrees F or less you can get a full charge to 80% at full amperage".

Your comment about speed goes against the grain. For a change in speed you need a cubic change in power and amperage. But these are the kinds of issues I need testing for.

I would also have to do some testing to see if the running the AC when charging helps or hurts. Sure the condenser fan will blow air across the batteries but it's hot air coming off the condenser. If you have any empirical data to share I would like to see it.

I would also like to point out that I really don't like the idea of driving slow to reduce battery temperature. I had to do a lot of slow driving in my 1st gen Focus Electric for range on long trips. With my 2018 Leaf I was hoping to never have to drive an EV slow like that again.

I will probably just start out trying to reduce energy consumption by turning off e-Pedal and turning on ECO mode. If that doesn't work I will reluctantly try slower speeds. If I still don't feel comfortable with the driving slower speeds I might just bite the bullet and just deal with the longer charging sessions when they happen.