Electric Vehicle Battery Thermal Issues and Thermal Manageme

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MLucas

Well-known member
Joined
Jun 7, 2012
Messages
833
Location
Niagara on the Lake, Ontario, Canada
Came across this excellent presentation today about battery thermal management from the SAE and the National Renewable Energy Laboratory. I've been keenly interested in the wilting Leafs saga and have been doing a lot of research on this topic. This presentation clearly mentions that high temp EV applications require larger batteries to last fifteen years. The Leafs passive TMS is just not up to the job to protect those southwestern Leafs. This has really been bothering me lately, because this affects all of us in the EV community and the way Nissan is handling the issue is going to effect the publics opinion of these vehicles. Having to take this issue so far as requiring mediation and the Lemon Law is very extreme - I think with a $5 billion dollar investment that Nissan would handle these customers in a very different way. Its clear the batteries are not handling the intenst temperature very well, this should encourage Nissan to develop a better thermal management system for these cars and they should be fixing the cars that have the problem. With this story on the news, they won't be selling many more Leafs in that region any time soon.

Here's the link, I'll get off my soap box now: http://www.sae.org/events/aars/pres...ermal Mgmt Tech to Improve Life and Range.pdf
 
Thanks for the report. It is very interesting.

If I summarize it in layman's terms I would say if the battery gets too hot it will wear out quicker. If it gets too cold it won't work as well while it's cold but it will bounce back when the temps go back to the normal operating range.

I think that actually makes EVs better suited to colder climates in terms of longevity but in colder climates range would also suffer when it's cold. It's like one of those choose your poison things.

I guess in the long term EVs will do better in places with the least temp swing. In Canada the east and west coast are probably the best places for them.

As for myself I have a garage and bring in the little iMiev every night. I think it's the only way to go year round with an EV in Montreal. I also find that the 120V charger is great for an overnight 30-80 %SOC charge and that works out to be 75 (ideal) KM which is perfect for me.

It does sound like the presentation is written by a battery thermal management solution company and the message is (spend money on a thermal solution and offset the costs of the thermal solution by putting smaller batteries in the car)

I'm not so sure that that would work for me. I would rather see a bigger battery and adapt to the shorter range in the winter. In the north we already have to accept less sunlight and shorter days in the winter and tons of sunlight and super long days in the summer. So it would be nice to have the extra range to go with those long days.

But I guess the best EV solution is the one Tesla is taking: Big battery, Big Thermal management, Big car, unfortunately the last one is big money...

When thermal management systems mature,come down in price and get more mainstream EVs will really catch on.

But for now I guess the lesson is to baby the battery keep it warm or cool depending on where you live and try to use only what you need in terms of charge. This winter 2013 will be an eye opener for a lot of Canadian EV purchasers. Onlookers up here are waiting to see how these cars do in the snow and cold.

Don.....
 
OK. I will show my ignorance. Is the Leaf's battery thermal management system the same as our MiEVs? I am hoping that Mitsubishi saw this problem that Nissan did not see, and has done something to protect us from the high heat situation. San Antonio is hot, but not like AZ.
 
Let me see if I can summarize some of your questions from my research. I'm no expert, but I keep seeing recurring themes while I'm reading and searching for data.

The magic number that lithium-ion cells like to be kept at is 71 degrees - +/- is okay but keeping them close to that is best. Much like keeping the cells charged to around 60% is best but not practical. Like Don, said extreme heat WILL damage the cells, extreme cold won't damage the cells but will reduce the effectiveness of those cells. The number at which this damge will begin is at 104 degrees. This is the absolute number I have read in many different sources including this presentation and our very own i MiEV owners manual.

Nissan had been telling its customers 140-150 degrees was the number, this is not correct as made evident by the southwest wilted Leafs. From the presentation, you can see the i-MiEV is mentioned directly in the portion about the Air method of thermal management, three types are mentioned from what looks like Good, Better and Best. The i MiEV probably has the best Air method of thermal mangement as so far no one on this forum from the southwest has mentioned battery capacity loss like the Leafs.

The Leafs simply have a fan to pull air across the cells to try and cool them, this apparantly is not adequate. From other articles I have read, Nissan rushed the Leaf to market to be the first - Carlos Ghosn the CEO of Nissan has been quoted as saying that engineers will always tell you no its not ready, so somebody has to make the decision.

Every other manufacturer has put a lot of engineering and expense into their thermal management systems. The Volt, Tesla Model S, Focus all have liquid thermal management systems which are the best but have higher cost and could potentially leak. The i MiEV does have an Active Thermal Management system using air that is managed by the climate control system. For those in colder climates, a battery warming system is available. Apparently, Mitsubishi felt this was needed enough for Canadians by making it standard equipment on those cars.

As long as the car has adequate thermal management, the battery should last ten years with 70% capacity approximately. Which isn't bad for a lithium-ion battery, try making the lithium-ion batteries in your well used tools or laptops last that long. This shows the chemistry in our EV batteries is far superior to a common laptop battery and will last if kept within its operating parameters.

For southwest EVs, definitely read the owners manual on operating your vehicle above 104F/40C. The car is designed to protect itself from damage so if driven agressively like highway operation or uphills - the power down light might come on and the car may shut down (owners manual pg. 1-10). In the future, EVs may all have liquid Thermal Management Systems or at least be offered as an option in high temperature locations like a Cold Weather package is.


http://green.autoblog.com/2010/01/25/is-the-nissan-leaf-battery-pack-under-engineered/

http://gigaom.com/cleantech/tesla-ceo-nissans-leaf-battery-is-primitive/
 
NeilBlanchard said:
I am fairly certain that the Leaf battery pack is passively cooled -- no fans at all.

You could be right, but I've read both ways - fan/no fan. But, it is a passive system under equipped for high temp locations. With high temp being the killer, it doesn't make sense to not have an Active Thermal Management system in place. Nissan really messed this up.
 
I have the cold weather package on my car in Michigan. From what i read it really does not do anything until the temps get will below freezing. So what i am going to do is just keep the car plugged in if the temps are below 40F out. In the summer it does not get that warm here most of the time below 90F so i don't worry about it in the summer.

Last night it got down to 26F the car was in the garage not plugged in but in the garage it only got down to 45F so no big deal.

It is going to be extra work to plug it in every day at work but i would rather be putting a L1 charge in there which is going to add some heat then letting the battery go flat.
 
JrCRXHF said:
I have the cold weather package on my car in Michigan. From what i read it really does not do anything until the temps get will below freezing. So what i am going to do is just keep the car plugged in if the temps are below 40F out. In the summer it does not get that warm here most of the time below 90F so i don't worry about it in the summer.

If you look at the presentation I linked to in my original post in this thread on slide 11, you'll see the power stays fairly constistent only dropping slightly until the temp reaches -15C. That is why the battery warmer doesn't engage until its that cold, it wouldn't really do any good until that point. You'll still have between 80-90% capacity in the colder temps.

I'm in about the same latitude as you are and going into my first EV winter. This is all new to me too and I have some anxieties over this. So far at 9C this morning - I only used an extra bar with the heater on the first step (just above the green dot). I'm still doing okay and I've been L1 charging at work. I should do okay.

How far is your commute? You may want to check out some of the threads on preparing your car for cold weather. Some of us are insulating the doors and the heater unit. I've done both. That will keep the energy use down and don't forget the seat heater.
 
Hey everyone - I have a question about the MiEV's battery TMS. Can anyone here confirm if the battery is cooled only during L3 Quick Charging? Or is it also cooled during normal operation of the vehicle?

In the presentation from the OP, on page 19 it shows the i-MiEV system and says "i-MiEV (fast charge)". Furthermore, if you look at this press release from Mitsubishi where they give more details on the battery cooling system, they say:
http://media.mitsubishicars.com/releases/dc8be352-eeff-4d6b-a6e0-e62dec3a22fb

Battery Temperature Conditioning System
This system performs two critical functions: to cool the battery pack during Level 3 quick charging so that it does not get excessively hot...
and

Battery Cooling System
When the vehicle’s ECU detects that a Level 3 DC quick charging connector has been plugged into the vehicle, it then determines whether the battery pack requires cooling based on battery temperature information from the BMU (Battery Management Unit). If it deems that cooling is necessary, the ECU then signals the compressor heater control unit that controls the compressor, A/C control unit and the HVAC system while communicating simultaneously with the battery management unit (BMU) to engage the battery ventilation fan.

The cooling system only becomes operational when it detects that the battery temperature is above 68 °Fahrenheit (20° Celsius); in this initial phase the HVAC blower fan and the battery ventilation fan are engaged. If the ECU determines that the battery temperature exceeds 86° Fahrenheit (30° Celsius), then the HVAC blower fan and the battery ventilation fan are supplemented by the air conditioner.

Based on everything I've read, the cooling system only activates during fast charging. I live in Phoenix and am very interested in the upcoming Outlander PHEV which I assume will use a similar TMS - hence my interest. It seems the MiEV is certainly capable of conditioning and chilling the air medium used to cool the battery, but it's not clear when exactly it does this. I would hope that air conditioned cooling would happen during normal operation if the battery gets hot, and not just when fast charging. Has anyone in the southwest confirmed if the TMS activates during the high summer temps?

BTW, CarandDriver also said in this article that the MiEV will fully charge and discharge it's battery - is that accurate? I know the Leaf uses about 93% of it's capacity and the Volt uses 65%.
http://www.caranddriver.com/reviews/2012-mitsubishi-i-electric-vehicle-test-review

Thanks!

PS, I'm a Volt owner and fairly active over on GM-Volt (and occasionally over on MNL as well). I'm quite excited about the Outlander PHEV and have started a fan site at http://www.insideoutlander.com for those interested please check it out.
 
JouleThief said:
BTW, I'm a Volt owner and fairly active over on GM-Volt (and occasionally over on MNL as well). I'm quite excited about the Outlander PHEV and have started a fan site at http://www.insideoutlander.com for those interested please check it out.

I'll have to follow this one. If Mitsubishi properly markets this vehicle unlike it did the i MiEV, then it could be a winner. No other vehicle on the market today operates in either a series or a parallel mode - its one or the other, or Volt or Prius. I'm liking this PHEV from Mitsubishi more and more. As much as I like my i, I think I'll like this one too. That would be awesome if I could convince the spouse to unload his 2009 Nissan Versa. Wishful thinking. :p
 
NeilBlanchard said:
The i MiEV battery pack fan operates with L1 and L2 charging, when it is needed.

Thanks. So is it correct then that the air-conditioner is only activated during quick-charging? That is to say the air is never conditioned during normal L1/L2 charging? The fan is just blowing ambient air?

Also, is the battery cooled when not charging if ambient temperature is high? For example, is the battery cooled when driving or parked in high temps if not charging? The Volt, for example, will operate it's liquid TMS during high ambient temperatures if the battery SOC is above 75% even if not plugged in.
 
If I got it correctly the Leaf has got Lithium Manganese, Tesla gets Lithium Cobalt and the i-MiEV has Lithium Iron Phospate. Lithium Iron Phospate can take about 10 times as many full charge cycles if not more. That is why we get 7 years for our batteries.

Of coarse batteries dont like overcharge but only Lithium Cobalt explode immediately when overcharged. Lithium Manganese might melt and you had to really torture Lithium Iron Phosphate for them to fight you.

Reverse polarity is the death for all of them. That happens with of the shelf BMS when they balance fully charged batteries and you discharge them. You wont notice the weakest cell reversing and that is it. Those BMS have been designed for Lead Acid. Their inventors did not know about Lithium and Lithium is a perfectly different animal living at least 10 times as long as Lead.

The i-MiEV does bottom balancing (the final two bars blinking). So when you really discharge them they run down simultaneously with little chance of reverse charging one of them.

The i-MiEV does have thermal management. So both Leaf and Tesla do compare badly when it comes to survive bad weather and ignorant drivers.
 
peterdambier said:
The i-MiEV does bottom balancing (the final two bars blinking). So when you really discharge them they run down simultaneously with little chance of reverse charging one of them....The i-MiEV does have thermal management.
Hi Peter, thank you for your post. We have two separate topics: Bottom Balancing and Thermal Management.

BOTTOM BALANCING
I did not realize that the iMiEV does bottom balancing in addition to the conventional top-balancing of the cells. I'm curious as to to where you found this information? As you pointed out, this would be further protection to avoid cell reversal but I had not thought it was used for this purpose as I didn't think that the balancing currents would be high enough to counteract the huge discharge currents. I've read some pretty compelling arguments against bottom balancing when compared to top balancing when charging, but I hadn't heard of the two being used together in the same system nor bottom balancing during discharge. Interesting, and shows one technically has to keep doing one's homework to stay up with this stuff.

THERMAL MANAGEMENT - BATTERY FAN
I do not have CHAdeMO, so do I still have a battery fan? I've never heard a battery fan turn on, even on the hottest days we've driven the iMiEV or when we were L2 charging in 100degF (38degC) weather. The only noise I hear is the water pump. Has anyone heard their battery fan?

THERMAL MANAGEMENT - AIR CONDITIONING
If we were to manually turn on the air conditioning, does that mean that cool air would be channeled through the battery pack ... or is it simply activated automatically when charging using CHAdeMO?
 
Hi JoeS,

I remember in the newer manual they mentioned with 2 bars and blinking bottom balancing is done. That is why once a month or at least once per season you should go down to 2 bars and let them blink for a short time but charge to full immediately after that.

Bottom balancing is the only balancing that should be done. Top balancing inevitably will result in the cell with the least capacity reversing when discharging - sooner or later. With 88 cells our batteries still show enough capacity when one cell is down.

There used to be a procedure for the elder i-MiEVs, ours, that says once a year a controlled discharge should be done and a controlled charge immediately after that.

Just tried with my wife:

A big glass and a small glass of champagne. Bottom balancing, same contents got empty at the same time. Top balancing both filled to the rim would get one of us tipsy.

Happy new Year!
 
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