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Re: battery heater and days subzero parking

Posted: Fri Jan 05, 2018 11:03 pm
by LeftieBiker
arnis wrote:9 temperature bars very "temporarily" is absolutely fine. Don't worry.
Just don't do this every week for years.
We don't actually know this. It may cause smaller amounts of damage that only add up to a substantial amount over time.

Re: battery heater and days subzero parking

Posted: Sun Jan 07, 2018 3:11 pm
by arnis
Exactly. There is no need to worry about battery degrading of "few days" in "that one day it got to 9 bars for few hours".
aka battery degraded for 5 days in 1 hour, or smth like that.

Re: battery heater and days subzero parking

Posted: Tue Jan 16, 2018 6:40 pm
by Dooglas
Levenkay wrote:Hitting 9 temperature bars (about 5 bars of "rise") during a multiple-QC journey from Bellingham to Portland in mid-40 degree F weather. I haven't bothered to chase down exact numbers, but isn't that about a 50 or 60 degree difference between the pack and a highway-speed airflow? I have to believe that even a modest forced-circulation liquid heat exchange system would get the heat out with way less temperature drop, and still let the pack stay insulated in cold environments (just don't run the circulation pump in that case).
This is sure hard for me to understand. I have driven a Leaf as my primary vehicle in the Pacific NW for the past 5 years, including numerous trips on I-5. I don't recall ever seeing above 6 temperature bars. With air temperatures in the mid-40s, it is difficult to comprehend why passive cooling while underway wouldn't do any cooling job that needed to be done.

Re: battery heater and days subzero parking

Posted: Tue Jan 16, 2018 7:50 pm
by LeftieBiker
This is sure hard for me to understand. I have driven a Leaf as my primary vehicle in the Pacific NW for the past 5 years, including numerous trips on I-5. I don't recall ever seeing above 6 temperature bars. With air temperatures in the mid-40s, it is difficult to comprehend why passive cooling while underway wouldn't do any cooling job that needed to be done.
Low speeds and/or short driving times. The pack has a lot of mass compared to the passive cooling's ability to move heat.

Re: battery heater and days subzero parking

Posted: Thu Jan 18, 2018 10:06 am
by Dooglas
LeftieBiker wrote:Low speeds and/or short driving times. The pack has a lot of mass compared to the passive cooling's ability to move heat.
Yes, I understand that passive cooling will not be as efficient at low speeds or when the vehicle is parked. A drive between Bellingham and Portland would not, however, involve short driving times and typically would be conducted at speeds of 50-70 mph with the possible exception of congestion around Seattle or Tacoma. And all this at air temperatures in the mid-40s?

Re: battery heater and days subzero parking

Posted: Sat Jan 27, 2018 9:00 am
by DaveinOlyWA
Dooglas wrote:
LeftieBiker wrote:Low speeds and/or short driving times. The pack has a lot of mass compared to the passive cooling's ability to move heat.
Yes, I understand that passive cooling will not be as efficient at low speeds or when the vehicle is parked. A drive between Bellingham and Portland would not, however, involve short driving times and typically would be conducted at speeds of 50-70 mph with the possible exception of congestion around Seattle or Tacoma. And all this at air temperatures in the mid-40s?
OAT helps but not as much as we want it to.

Nissan to increase range did a lot of wind tunnel testing which resulted in most the undercarriage being covered to lower air friction and that means the battery pack is exposed to little moving air.

As far as never seeing much over 6 TBs, that is due more to a VERY conservative fast charge profile than any cooling of the pack. On the 30 kwh LEAF with a much more aggressive fast charge profile, its easy to get to 8,9 or 10 TBs.

Re: battery heater and days subzero parking

Posted: Sat Jan 27, 2018 11:58 am
by LeftieBiker
Nissan to increase range did a lot of wind tunnel testing which resulted in most the undercarriage being covered to lower air friction and that means the battery pack is exposed to little moving air.
It's my understanding that there is an air passage running the length of the car, from an intake in the nose to an exhaust opening in the tail. This allows significant cooling when the car is moving, but virtually none when it is stopped.

Re: battery heater and days subzero parking

Posted: Sat Jan 27, 2018 1:35 pm
by DaveinOlyWA
LeftieBiker wrote:
Nissan to increase range did a lot of wind tunnel testing which resulted in most the undercarriage being covered to lower air friction and that means the battery pack is exposed to little moving air.
It's my understanding that there is an air passage running the length of the car, from an intake in the nose to an exhaust opening in the tail. This allows significant cooling when the car is moving, but virtually none when it is stopped.
That has been mentioned concerning the 30 kwh LEAFs and there is evidence of faster cooling at highway speeds even on very warm days but no positive evidence or confirmation of that including examining drawings of battery compartment, etc.

If it exists, it would be shocking that no one has physically located it on their LEAF.

Re: battery heater and days subzero parking

Posted: Sat Jan 27, 2018 1:49 pm
by jjeff
LeftieBiker wrote:
Nissan to increase range did a lot of wind tunnel testing which resulted in most the undercarriage being covered to lower air friction and that means the battery pack is exposed to little moving air.
It's my understanding that there is an air passage running the length of the car, from an intake in the nose to an exhaust opening in the tail. This allows significant cooling when the car is moving, but virtually none when it is stopped.
Unfortunate as the 24Kwh Nissan eNV-200(and possibly other Kwh's) has air cooling when charging, at least QC'ing. I saw a video of a guy driving one all over Norway and he was so excited it had cooling when charging, coming from a Leaf that didn't have that feature. Odd Nissan did that for the NV but not Leaf :? I really wish we could get the eNV-200 here, passenger version with a 40'ish kwh battery would be real sweet 8-)

Re: battery heater and days subzero parking

Posted: Sat Jan 27, 2018 4:46 pm
by arnis
Air passes through motor compartment between the pack and body. To observe that, just open the
safety hatch at rear seat footwell. There is a cover. Observe airflow while driving. Or look at Leafs that are cut in half.

Just running AC fans is enough to have some air flow happening while stationary. Though if AC
is doing a lot of work (more than 1kW) the air cooling the battery might be slightly warmer than ambient when stationary.
There is no point to drive fast as battery metal case is not going to take in internal heat to the surface fast enough.

New 30kWh battery has cell pouches closer to each other - and have worse heat transfer rate into the air inside the pack.
Also, much faster charging rate allows more heat to accumulate in shorter period of time.

Battery pack cooling system makes vehicle considerable more expensive. At least 500 $€. And it doesn't solve degradation problem
that happens due to hot climate. Only one that happens due to heavy usage or DC charging. Which is not a majority of that problem.
It's the chemistry that likes lower temperatures. Leaf battery can handle cold temperatures (below +5C) way WAAAY better than Tesla's
chemistry, that can't handle ANY charge (without damage) at 0*C even when almost empty. Leaf can charge/regen at low temperatures.
Tesla can handle heat without accelerated degradation. +35*C is totally fine. Leaf on the other hand is cooking chemistry at that point.
Active cooling won't cool down pack when vehicle parked. At all. And if it is +30*C in the sun, pack will be at least 35*C after driving.

So no. Forget the idea that active cooling will prolong Leaf battery degradation in hot climate. It will only do that if it is NOT hot but
DC charging makes it hot. This is why e-NV200 has that. It is designed to be rapidly charged all the time (as a company vehicle).

If Tesla didn't have Supercharging capability (so like up to 50kW) and it wasn't powerful (like up to 150kW)
I'm pretty sure it wouldn't even have battery cooling loop, as there wouldn't be any point. It can handle 40*C easily. Actually, Tesla tries to
warm up battery to at least 30*C, sometimes to at least 40*C and even 50*C when ludicrous. It would just have heating elements like Leaf does. Tesla uses battery cooling only when supercharging or after extreme driving, like autobahn or many powerful acceleration events. It usually cools the drivetrain, not the battery.

Devil is in the details... or.. chemistry in our case.

Why 40kWh Leaf doesn't have active cooling? Because it can only charge at 50kW rate (exactly the same as 30kWh Leaf), it can only discharge at averaged 45kW rate (top speed limitation) and it's still not suitable for long distance driving. Aka battery will not heat up enough and passive cooling is absolutely fine. Why 60kWh Leaf will have battery cooling? Because it will charge at faster rate ( up to 100kW expected) and it is suitable for long distance* travelling.

*That means it can be used to drive far and charge fast enough for long distance travelling. 50kW charging, whatever the range, is not suitable for long distance travelling.

Why Volt has active cooling? Because it has an ICE (aka free heat). More battery range out of smallish pack.
Why BMW i3 has active cooling? Because it doesn't have acceptable air cooling (very crammed due to small vehicle).