# Temperature sensitivity of Chevy Volt battery



## john61ct (Feb 25, 2017)

Longevity and even small increases in temperature are inversely related.

Very hot conditions can cut lifetime by 80-90%.

Just as true for storage as while in use.

This is the case for every chemistry I've heard of being used for propulsion.

There is no hard B&W line, but a curve relationship. Hotter is worse, cooler is better, until you run into charging rate issues, say below 15-20°C

Storage isolated at low SoC is ideal in even freezing conditions, but then the cells need warming in order to discharge efficiently.

Charging, the closer to freezing the slower the rate needs to be.

Fast charging (over 0.5C) is best over 25-30°C


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## Duncan (Dec 8, 2008)

As long as you avoid the extremes you should be OK
I have the cooling system hooked up to circulate the coolant - I believe that without that you may end up with localised hot spots 
But no cooling or heating except I pass the coolant through my controller to cool the controller

Saying that I'm in Southland NZ - it does not get that hot here - and when its damn cold I don't drive my car much as its lacking in creature comforts


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## BAstereo (Dec 28, 2018)

I don't think you'll see 150f inside the pack when sitting. Sure, you'll get that inside the cab. But, are you putting the batteries in the cab?

I would guess that your pack is out of the sun, like under the truck bed? As long as you don't have any sun load, you shouldn't see a huge raise over ambient temperature when parked.

You might need cooling when driving, just depends on how much current you're pulling from the battery. I'd go on the side of caution and plan for cooling and heating the pack. Maybe building so it can easily be added once the vehicle is in use if needed.

Pay attention to what John61 said above. Charging should be limited even at cool temps. 15c is 59f
The cells I have a spec sheet handy with say not to charge at all below 0c and limit discharge.
If your winters are below freezing, you should probably include battery heating.


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## zubmio (May 19, 2020)

Thanks for your insight guys!

Unfortunately, I didn't go with "under the bed" battery mounting. The battery is mounted in the bed, instead. I intend to use the original (Volt) cover/enclosure so the battery pack will be sealed. Still, being in the bed it would be exposed to direct sun and that's why I threw 150F as a possible temperature after (worst case and maybe unrealistically high) sitting in the sun for hours. To avoid direct sun exposure I could use a bed cover, but unfortunately it happens to be black so it actually may make it worse. Either way, I take it I should utilize liquid cooling even if it means to keep the batteries at ambient when parked and to help with temperatures when driving. 
Speaking of driving/discharge … for me, working on the EV and driving it is for fun. In that, there are times when I want to see the motor amps needle go over 1000A and to feel the kick in the back ... hopefully even some squeal from the tires. Having been designing lower HP motor controllers for 25-ish years it felt good to design something that gets up there in terms of power. So, my MaxForcer controller is set to limit motor amps to 1200 A and battery amps to 800 A (hopefully somewhat close to 400 A from each string). I know that challenges battery longevity, but the question in my mind is how much and what makes sense to do to avoid/reduce the damage. Normal cruising at 60mph or so will cause about 100 from the battery pack (50-ish per string).

In your answers above you guys say that at cold temperatures charging rates need to be limited/reduced. I take it that means I should make sure that my charging rate would needs to go down to 0.2C or even 0.1C if I was ever to charge the batteries in, let's say, 5-10C ambient. Assuming that charging is as bed as discharging does that mean I shouldn't even think to drive (leave the garage) in those temperatures? Or, is charging somehow worse than discharging for betteries that are cold?

By the way, I don't have a need nor do I plan to drive it when it is really cold - I am asking more so to understand the effects and to figure out what kind of a system for cooling/heating I should go for.

Thanks


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## Ladogaboy (Apr 25, 2010)

To put the effects of heat into perspective, there are only minor differences between the battery chemistry used in the Gen 1 Chevy Volt and Gen 1 Nissan LEAF. There are Volts with many hundreds of thousands of miles with only minimal battery degradation, while there are similar LEAFs that have lost 50% or more of their original capacity.

If you can keep the internal battery temperature to less than 100 F, you should still be within operational tolerances for the battery (even per GM's thermal management parameters). However, there is a reason GM uses the AC system to cool the battery. Cycling ambient air doesn't provide enough cooling, especially when driving and discharging the batteries, which can push the temperatures way past 100 F if not actively cooled. 

Cold temperatures shouldn't be as much of an issue unless you're trying to draw power from or recharge the battery when it's extremely cold.


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## Duncan (Dec 8, 2008)

To Ladogaboy's point - the Volt needs the cooling because it has to operate in places like Nevada and the American deserts
In more temperate places - simply NOT a problem 
I'm cruel to my battery - I draw up to 1200 amps and use the car on the track
The highest temperature I have seen was less than 30C - 
IMHO the reason the Volt batteries are so much better than the Leaf is the coolant flow - NOT the maximum temperatures but the temperature equalisation - when the coolant is flowing you simply won't get any localised hot spots


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## Ladogaboy (Apr 25, 2010)

Duncan said:


> To Ladogaboy's point - the Volt needs the cooling because it has to operate in places like Nevada and the American deserts
> In more temperate places - simply NOT a problem
> I'm cruel to my battery - I draw up to 1200 amps and use the car on the track
> The highest temperature I have seen was less than 30C -
> IMHO the reason the Volt batteries are so much better than the Leaf is the coolant flow - NOT the maximum temperatures but the temperature equalisation - when the coolant is flowing you simply won't get any localised hot spots


I think it really depends, though. Ambient temperature matters, but I wouldn't discount the impact of heavy loads, both charging and discharging. Bjorn Nyland, in testing Nissan LEAFs on long distance runs, regularly gets the internal battery temperature up to 50 C (over 120 F) even when the outside temperatures are 0 C (32 F) or colder.


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## zubmio (May 19, 2020)

By now I have:

wired an Arduino Due, adopted/modified open-source code to be reading cell voltages, module temperatures, and sending it via HC05 BT module to my phone.
Installed a pump, small radiator, expansion tank and a little control system that maintains desired temperature of the battery bank. When parked and ambient temperatures are cooler than desired temp range (say 20C-25C) the system can warm them up by powering the heating element with 230VAC and running fluid through the battery pack. If I am to drive when it is cold (not very likely) I can switch the heating element to be powered from the pack voltage and keep batteries from getting cold if needed. If ambient is warmer then desired temp, and/or the truck is in the sun, and/or while driving, so far I am only having a small radiator with fans that should help cooling the batteries and keeping them equal. Once summer rolls around I'll see if that may be good enough or will I need some sort of active cooling.

So far I am running water through the battery pack but I am not sure I am free of air bubbles. This is where my question comes from. I am about to switch to antifreeze and I want to try to do better in making sure I don't have bubbles in the system. My expansion tank is the highest point in the system and it is where I would/did pour the coolant. What concerns me is the geometry of the coolant path within the batteries, so:
First: ... to confirm: are coolant paths through cells in parallel (meaning, a drop of coolant that gets into pack's inlet can go past one/closest cell and get out of the outlet), or are coolant passages somehow made (in series) such that all of the coolant that gets in has to go past all the cells before it gets out. I gather it is the first/parallel option ... ?
Second: due to the fact that the the modules that are under the back seat have coolant inlet and outlet somewhat high I am wondering how to flush water out and replace it with antifreeze. I guess I should have paid more attention in classes dealing with fluid mechanics, but I am a sparkie so I should get a break on that .... any suggestions or tips you have would be appreciated

Thanks


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## morvolts (Jun 19, 2008)

The best way to purge the system(I hope that was distilled water you used for testing),is to put a vacuum on the system
and introduce the proper Dexcool/distilled water mix.There are many different vacuum /cooling system machines,many high end cars require them(Porsche for one)It wouldnt really be that hard to build one,vacuum tank,vacuum pump,a few adapters for radiator cap,a couple of valves. Do you have the system designed with a burp line or is the expansion tank your only purge for air?


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## zubmio (May 19, 2020)

It is distilled water that I used for testing. In fact, I know that I didn't purge antifreeze well at all (probably from the back part of the battery set) since my "water" now has light pink color. I have bought a couple of gallons of premixed antifreeze that GM uses for Volt batteries. Coolant capacity for Volt is 1.5 gallons so I should be good knowing that I don't have much volume outside of the actual battery. My system only has the expansion tank for air to be purged. I do also have a valve/splitter in the hose right after the outlet of the battery pack. With that I can steer the coolant to be pumped back into expansion tank and let any air that comes out of the pack be replaced with coolant. Once So, my main concerns are:
1. how to pump this "water" out of the back part of battery set .... I guess I am going to look into finding a good vacuum pump that I can possibly use just for the back modules if not for the entire system
2. Considering geometry of the cells how to make sure I don't end up with air bubbles trapped somewhere in the battery pack and have no way to "pump" them out. This is where my fluid mechanics knowledge isn't good enough. What I wonder about is whether an air pocket (let's say, for argument sake, in one of one of cell passages in the back piece of the pack) would be pushed out through coolant outlet simply by ensuring that I am pumping coolant in the inlet. Or, could that air pocket still be trapped there(?)


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## Duncan (Dec 8, 2008)

zubmio said:


> It is distilled water that I used for testing. In fact, I know that I didn't purge antifreeze well at all (probably from the back part of the battery set) since my "water" now has light pink color. I have bought a couple of gallons of premixed antifreeze that GM uses for Volt batteries. Coolant capacity for Volt is 1.5 gallons so I should be good knowing that I don't have much volume outside of the actual battery. My system only has the expansion tank for air to be purged. I do also have a valve/splitter in the hose right after the outlet of the battery pack. With that I can steer the coolant to be pumped back into expansion tank and let any air that comes out of the pack be replaced with coolant. Once So, my main concerns are:
> 1. how to pump this "water" out of the back part of battery set .... I guess I am going to look into finding a good vacuum pump that I can possibly use just for the back modules if not for the entire system
> 2. Considering geometry of the cells how to make sure I don't end up with air bubbles trapped somewhere in the battery pack and have no way to "pump" them out. This is where my fluid mechanics knowledge isn't good enough. What I wonder about is whether an air pocket (let's say, for argument sake, in one of one of cell passages in the back piece of the pack) would be pushed out through coolant outlet simply by ensuring that I am pumping coolant in the inlet. Or, could that air pocket still be trapped there(?)


Getting the air out is not easy - the cooling passages go up and then down
I got the air out of my pack by sitting it on its end and the flowing water through it


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## swoozle (Nov 13, 2011)

FYI...


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## piotrsko (Dec 9, 2007)

Buy yourself a cheap battery tester style of coolant checker, add concentrate coolant until mix is correct proportions.

You have to purge the bubbles?, CRUD, I never did that 6 years ago, OMG my battery life is going to be shorter.

Gm anticipated bubbles, it self purges after a while, or at least my 2011 did. Took a week of DD to get the level in my tank to stabilize, thought I had a small leak.


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## brian_ (Feb 7, 2017)

zubmio said:


> First: ... to confirm: are coolant paths through cells in parallel (meaning, a drop of coolant that gets into pack's inlet can go past one/closest cell and get out of the outlet), or are coolant passages somehow made (in series) such that all of the coolant that gets in has to go past all the cells before it gets out. I gather it is the first/parallel option ... ?


Yes. The part that sticks out on each side of the module is a manifold, and the cooling fins shown in the image posted by swoozle are all connected in parallel. Any drop of coolant goes between one pair of cells in it's loop through the system. As Duncan noted and as you can see in the image, the passages within the fin are loops which could potentially trap a bubble at the top.


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## Duncan (Dec 8, 2008)

Re purging the bubbles
I suspect that its actually not that important - the Bolt with the next generation battery has a much simpler cooling system

I suspect that the Volt system is actually massive overkill so a few bubbles will not cause any problems


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## brian_ (Feb 7, 2017)

Duncan said:


> I suspect that the Volt system is actually massive overkill so a few bubbles will not cause any problems


A difference between a Volt and a Bolt is that the Volt is a plug-in hybrid, while the Bolt is a pure battery-electric vehicle. That means that the Volt battery has only about a quarter of the Bolt's capacity, but is expected to deliver almost as much power (the Volt battery is rated by GM for 120 kW for 10 seconds, while the Bolt motor is only rated for 150 kW peak). The Volt battery is pushed harder in its stock installation, so it is cooled better. Yes, it could also have been a conservative design.


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