Battery temperature gauge in red after fast charging (or a long day of driving)?

[SageBrush]

Annoyingly difficult to avoid highways with 70mph limits with some of this, at least typical navigation isnt much help.

Yep

For the last part of my mini-series in how to live with a LEAF outside or local commuting, here is a bit of LEAF physics (love it or hate it!)

Power is proportional to the cubic increase in speed
Example: doubling the speed will require an 8x increase in power
Heat generation in the pack is proportional to Power

Let's look at 70 mph Vs 65 mph
Driving at 70 mph will generate (70/65)^3 = 125% more heat generation than 65 mph and you will go 70/65 further.
So while not exact for reasons I will not go into, it is approximately true that driving at 65 mph will let you drive (70/65)^2 = 1.16 = 116% further than at 70 mph within the same temperature budget

A 200 mile drive at 70 mph can be an ~ 230 mile drive at 65 mph (as limited by pack heating), with the trade-off being more traveling time of (70/65)x

There is quite a bit more that can be mentioned, but hopefully this is enough to get you back on the road. We'll talk again when wind foils your best laid plans.

 

[Chad E. Mo]

I follow the slow trucks at a polite distance, at least 70', usually 100'.

I don't get any aerodynamic benefit, but the psycho/social payoff is striking. It is mind-boggling how much hate you can get for driving slower than the crowd... we're still talking 60 - 65 mph, when everyone else is going 70 -80 mph.

But everyone can see the big truck in front of me going slow, so they get in the passing lane and don't give me a second thought.

 

[duncan-s]

I don't get any aerodynamic benefit,

I've thought there was still some aerodynamic benefit when doing that, even if it's not dramatic. Say I'm following a ~60-65mph rig for a while at what seems to me a respectful distance, then back off a few mph to let the truck get farther ahead. I've noticed a couple of times the "power meter" in the console showing higher consumption rather than decreasing the way I'd expect. I'll have to pay attention and see if it's consistently that way or just a fluke from where the hills were or whatever.

 

[Bombastinator2]

At 25 MPH and over 400hp working to drag it, I'd be more worried about rolling backwards before I could get off the throttle and on the brake.

lol. Fair enough. Perhaps that’s why convoys aren’t so much of a thing anymore.

 

[Bombastinator2]

I follow the slow trucks at a polite distance, at least 70', usually 100'.

I don't get any aerodynamic benefit, but the psycho/social payoff is striking. It is mind-boggling how much hate you can get for driving slower than the crowd... we're still talking 60 - 65 mph, when everyone else is going 70 -80 mph.

But everyone can see the big truck in front of me going slow, so they get in the passing lane and don't give me a second thought.

Needs to be more like 30’ for it to really work. Or it did. Cars are a lot more aerodynamic now. When it really works you can actually hear it. The wind noise mostly goes away. My dad had a CB in his car. We were always in back. Dad had a diesel vannagon. Weighed nothing relative to everything else, and it had brakes from a heavier faster vehicle. To call the thing a dog was massively inadequate. Thing wouldn’t hit 50 in a good headwind. Merging onto the freeway was downright dangerous. It was designed to be a night bus in German towns and never go over 50kph. Stopped fine though.

 

[Chad E. Mo]

I'm quite familiar with the aero behavior when I'm in the pocket. That just pisses people off.

I want to drive the speed limit without getting killed.

One time, I was doing 65 and the teen in a Compass behind me was doing 75 without paying attention. I was so happy we both didn't die.

Another time, I was towing and a kid in a Grand Prix went right up onto my trailer. I even had my hazard lights on. Again, distracted.

 

[Bombastinator2]

I'm quite familiar with the aero behavior when I'm in the pocket. That just pisses people off.

I want to drive the speed limit without getting killed.

One time, I was doing 65 and the teen in a Compass behind me was doing 75 without paying attention. I was so happy we both didn't die.

Another time, I was towing and a kid in a Grand Prix went right up onto my trailer. I even had my hazard lights on. Again, distracted.

One I saw recently was pretty stunning. Dude stopped at a stop sign and then rammed a car passing through. I was told it’s called a roll thru. What was amazing is it apparently happened because the guy was watching videos on his phone. He was still doing it when he got out of the car, and only paused it to talk to the other driver (who was of course royally pissed) he actually said it wasn’t his fault. I stopped and offered to corroborate testimony to the guy he rammed.

 

[Jerther]

I've thought there was still some aerodynamic benefit when doing that, even if it's not dramatic.

Mythbusters did an episode on that. Apparently there's much benefit when following closely but that's obviously dangerous (and annoying), but the benefits gradually diminish for a surprisingly long distance.

 

[Bombastinator2]

Interesting. I’ll have to look that up

 

[mbrub442]

Did a 650km trip (each way) with our 40kWh 2018 Leaf, this summer and needed to charge about 4 times along the way. We noticed that the battery temp was getting higher with each successive charge, and really slowed down the charging rate after the second high voltage charge...like sometimes down to 12-16kW power. Car kept going until we got close to the end, and got hit with turtle mode (and a warning to not go any faster, and preferably go slower) - we were on the highway, so I kept to about 100kph or just under, until we decided that maybe we should pull over and let it rest. Rested for 15 minutes and the temp came down below the red on the gauge. We eventually got where we needed to be, but it took a while - like we were charging almost as long as we were driving. We also figured that the battery wasn't getting any rest most of the time, it was either charging or driving. We expected this might happen and planned accordingly, but I'm not sure I would do it again. On the return trip we were more cognizant of keeping to around 80% while charging, while still trying to maximize our travel between chargers....no turtle mode on the way home, and the temp did stay high, but not in the red. We added another charging stop on the way home to compensate and it did seem to help.

 

[Steve52]

Did a 650km trip (each way) with our 40kWh 2018 Leaf, this summer and needed to charge about 4 times along the way. We noticed that the battery temp was getting higher with each successive charge, ...

Yes, the well known "Rapid Gate" issue with the Leaf. Since the Leaf has an air cooled battery, it's rather bad for the battery to run it in the Red temp zone as it can lead to early degradation of the HV battery.

 

[mbrub442]

Yes, the well known "Rapid Gate" issue with the Leaf. Since the Leaf has an air cooled battery, it's rather bad for the battery to run it in the Red temp zone as it can lead to early degradation of the HV battery.

Yeah, we don't plan on doing it again - after 6 years the battery still tests perfectly. We mostly charge on L2 at home and let it run down to about 20% first.

 

[Jeffrey Stumpf]

Thought I would pose the question here. Recently had my 2016 battery warranty work completed and ended up with a whopping 150 miles of range (160 under Eco mode)! Compared to 115 when new. So, was inspired to try a longer trip and see how it went. Traveled to Asheville, about 120 miles away, including a short trip on the Blue Ridge Parkway which involved a lot of climbing. Also found at least 3 broken chargers on the way...

Did some shopping around town, then hit a fast charger on the way home. Left it on up to 97%, started driving and realized the temperature gauge was fully in the red. So I looked for a place to pull over and give it a few minutes to cool off. I was by then impatient to get home, so a few minutes would get the gauge out of the red but wouldn't take long to climb back into it. Stopped a couple more times on the way home, even consulted the manual which only advised to "slow down". I was at that point in the Nantahala gorge where it was cool and moving only 35-40 mph but still staying in the red. Eventually just said the hell with it (the manual didn't indicate any extreme danger) and drove home.

Any experience or advice with this? Should I plan to let the car sit for a while after using a fast charger (seems to negate the point)? Was I in danger of blowing up the batteries? Or is it not a big deal?

Also, maybe not really the fast charger but just that I was driving most of the day, just stopping for an hour once, a half hour later, on a slightly warm day? Didn't notice the gauge until after the second charge of the day.

Thanks for any feedback!

This is normal. The system is designed to accommodate high temperatures. If needed the computer will reduce acceleration ( Turtle Mode ) to prevent battery damage or any safety issues. Only once since 2018 was I put in the turtle mode on a very hot summer day on a road trip. It had reduced acceleration but got up to freeway speeds on the on ramp without issues. I just did not pass cars at the same speed. ( less acceleration). Other than that, I had no no issues. Once I finished the trip everything went back to normal. The road trip was 460 miles with 3 or 4 DCQC stops. The worst case charge rate was 2 hours to go from 1% to 100%. Which I did not mind and had a nice long dinner and did some shopping while charging. I also learned that I no longer need to charge to 100% between charging stops and now only charge enough to get to my next charging stop. Sometimes that is 100% but most times it is 80% of less.

 

[Bombastinator2]

Yep

For the last part of my mini-series in how to live with a LEAF outside or local commuting, here is a bit of LEAF physics (love it or hate it!)

Power is proportional to the cubic increase in speed
Example: doubling the speed will require an 8x increase in power
Heat generation in the pack is proportional to Power

Let's look at 70 mph Vs 65 mph
Driving at 70 mph will generate (70/65)^3 = 125% more heat generation than 65 mph and you will go 70/65 further.
So while not exact for reasons I will not go into, it is approximately true that driving at 65 mph will let you drive (70/65)^2 = 1.16 = 116% further than at 70 mph within the same temperature budget

A 200 mile drive at 70 mph can be an ~ 230 mile drive at 65 mph (as limited by pack heating), with the trade-off being more traveling time of (70/65)x

There is quite a bit more that can be mentioned, but hopefully this is enough to get you back on the road. We'll talk again when wind foils your best laid plans.

My understanding is that wind resistance builds up quickly though. So much that at multiple Mach the heat resistance of the wings of an aircraft are a major consideration. It may eat into that savings. Evs are built for low drag, so less so than it might. It’s not going to be zero though. Back during the gas crunch of the 1970s the speed limit was lowered from 60 to 55 because of that. My understanding was that the sweet spot was 45 mph, which is why model Ts weren’t meant to go faster than that. Should vary by aerodynamics though and the model T wasn’t exactly aerodynamic

 

[Chad E. Mo]

...A 200 mile drive at 70 mph can be an ~ 230 mile drive at 65 mph (as limited by pack heating), with the trade-off being more traveling time of (70/65)x

<snip>... We'll talk again when wind foils your best laid plans.

This cannot be overstated... the gentle 5mph headwind will consume the "extra" 30 mile buffer you wisely added in case the charger was broken, or construction detours, or whatever. Best to be pessimistic when planning the trips, and heed the weather forecast for each leg of the trip.