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FalconFour
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Cooler Leaf - on Heat Energy Storage & Ice Packs

Sun Aug 17, 2014 1:07 am

I've searched around a fair bit on these matters, and I think I might be onto something. I live in Fresno, where heat is a big concern for EVs like the Leaf. My 2013 Leaf S usually starts a morning at 6 temp bars, ends on the high end of 7, was even driving around on 8 not too long ago. No fast chargers (probably for good reason now that I consider it). Very few places other than home to charge. It's all environmental heat, and that poses an interesting set of conditions for experimenting.

The big problem is that the battery stores a lot of heat energy - a sort of napkin-sketch example would be to say it probably has 1 kWh of energy stored as a heat differential between the environment and the battery temp at night. So even though it's 70F outside, the battery might only get down from 100F to 90F by the morning, then back to 100 where it's driven and cycled, rinse and repeat. Not so great for lithium chemistry.

I also found that the motor/controller under the hood has a *very* bad effect on this, caused by its cooling system behavior. I went out to check on it today, after it'd been charging from 20% to 90% at 4kW, and found that under the hood was hotter than I'd ever felt it before! I'm talking ICE engine hot. But the fan wasn't running! I left the hood open and ran the A/C at 82 for about 20 minutes, which ran the cooling fans constantly with the A/C cycling on and off (slowly, with low heat output/power consumption). Only way I knew to get the fans to run. It cooled off the block to lukewarm temp, but during that time, you wouldn't believe how much heat billowed out from the hood before the air was cool again.

All that heat was typically stored in the car from night to night, which in turn transfers to the battery (which I'd think would be cooled by the chilly motor components). I would think the cooling fan would be running, at least at a low speed, while charging. Seems pretty obvious to me - laptops have done it from the start, even modern desktop PCs vary their fans as needed. With the concerns about battery heat and longevity, how could Nissan forget this important detail?

So, what I've been doing lately - before discovering the motor heat issue - I've been playing with placing ice-chest freezer blocks in the emergency disconnect switch box. There's a fairly large space in there to put them, and since cold air falls while heat rises, the cold air circulates and conducts through the metal of the battery pack, rather effectively using the ice to cool the battery overnight. That day I came home with 8 bars was when I started playing with the concept, and the next morning, I started off with 6 bars, only hitting 7 halfway through the day. It's only been a week, so I don't have much data to play with... but I figured I should get a topic and discussion going on this.

Anyone know how to kick that cooling fan on while charging? Maybe a command through the OBDII interface through the Leaf Spy app? :D
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LeftieBiker
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Re: Cooler Leaf - on Heat Energy Storage & Ice Packs

Sun Aug 17, 2014 1:16 am

You might get substantially more cooling by blowing air through the ducts that cool the pack *backwards*, from the rear to the front. That would allow you to start with air as cool as possible. You could always place some large bottles of frozen water just behind the fan(s) to drop the temp of the incoming air. I built a portable car A/C unit years ago, when my First Civic's A/C inevitably failed. A couple of large freeze blocks had a substantial cooling and dehumidifying effect (I used a cooler for the housing, and let water collect in the bottom, to be drained).
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Re: Cooler Leaf - on Heat Energy Storage & Ice Packs

Sun Aug 17, 2014 2:35 am

FalconFour wrote:My 2013 Leaf S usually starts a morning at 6 temp bars, ends on the high end of 7, was even driving around on 8 not too long ago.
...
I also found that the motor/controller under the hood has a *very* bad effect on this, caused by its cooling system behavior. I went out to check on it today, after it'd been charging from 20% to 90% at 4kW, and found that under the hood was hotter than I'd ever felt it before! I'm talking ICE engine hot. But the fan wasn't running! I left the hood open and ran the A/C at 82 for about 20 minutes, which ran the cooling fans constantly with the A/C cycling on and off (slowly, with low heat output/power consumption). Only way I knew to get the fans to run. It cooled off the block to lukewarm temp, but during that time, you wouldn't believe how much heat billowed out from the hood before the air was cool again.

All that heat was typically stored in the car from night to night, which in turn transfers to the battery (which I'd think would be cooled by the chilly motor components). I would think the cooling fan would be running, at least at a low speed, while charging.

Interesting... I'm not usually around my Leaf when it's charging (usually down in an underground garage @ work) but I've never observed any of the fans running while charging either. And yes, I know what you mean about the under hood temps although, mine charges indoors, so I'm sure it's nowhere near as bad.

Haha, that's funny about running the AC @ 82 degrees. For me, since I have a '13 SV w/hybrid heater (w/heat pump), it's quite funny to run the heater at high temps. The fans run and it's just cool air coming thru the radiator to the PDM stack. If you'd gotten an SV or SL, that'd be your solution... ;)

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EVDRIVER
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Re: Cooler Leaf - on Heat Energy Storage & Ice Packs

Sun Aug 17, 2014 8:53 am

There is enough charger waste heat transferred form the radiator to no need a fan running. The hood also acts as a conductor of the heat and this is not being transferred to your pack so it's senseless to worry about. The thermal mass of the back is great during charging and a fan on the radiator has no relation to pack heat, if you move it faster from the engine compartment it will just heat to a garage garage faster. if it is outside it is moot and inside it is moot as well since you would need to vent a garage not the car. The ice is a pointless waste of energy consumed for no practical gain. The inverter and motor you mention have no involvement here since this is waste charger heat. Effectively anything you are doing will have no impact on your pack temp other than parking on a cooler surface or location.

donald
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Re: Cooler Leaf - on Heat Energy Storage & Ice Packs

Sun Aug 17, 2014 9:10 am

But surely for the cooling fans to cool the motor you'd have to have the liquid cooling system active, and that only operates when the car is in motion?

The fans run with AC because the condenser at the front has to be cooled else the AC won't work.

The only way to cool the motor/charger is to pass cold air over it. This is actually quite easy to do - set your heating on rather than your AC on (I assume your 2013 has a heat pump?). With AC, the radiator acts as a condenser and has to eject heat, whereas with the heating on the radiator acts as an evaporator and draws heat out of the air. You'd then be fanning colder air over the motor/charger.

You could get some big mains operated fans and put them flat on some castors, you can roll it under the car and ventilate. This will prevent heat build up in the charger system and avoid heat soak.

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Re: Cooler Leaf - on Heat Energy Storage & Ice Packs

Sun Aug 17, 2014 9:54 am

FalconFour wrote:I've searched around a fair bit on these matters, and I think I might be onto something. I live in Fresno, where heat is a big concern for EVs like the Leaf. My 2013 Leaf S usually starts a morning at 6 temp bars, ends on the high end of 7, was even driving around on 8 not too long ago. No fast chargers (probably for good reason now that I consider it). Very few places other than home to charge. It's all environmental heat, and that poses an interesting set of conditions for experimenting.

The big problem is that the battery stores a lot of heat energy - a sort of napkin-sketch example would be to say it probably has 1 kWh of energy stored as a heat differential between the environment and the battery temp at night. So even though it's 70F outside, the battery might only get down from 100F to 90F by the morning, then back to 100 where it's driven and cycled, rinse and repeat. Not so great for lithium chemistry.

I also found that the motor/controller under the hood has a *very* bad effect on this, caused by its cooling system behavior. I went out to check on it today, after it'd been charging from 20% to 90% at 4kW, and found that under the hood was hotter than I'd ever felt it before! I'm talking ICE engine hot. But the fan wasn't running! I left the hood open and ran the A/C at 82 for about 20 minutes, which ran the cooling fans constantly with the A/C cycling on and off (slowly, with low heat output/power consumption). Only way I knew to get the fans to run. It cooled off the block to lukewarm temp, but during that time, you wouldn't believe how much heat billowed out from the hood before the air was cool again.

All that heat was typically stored in the car from night to night, which in turn transfers to the battery (which I'd think would be cooled by the chilly motor components). I would think the cooling fan would be running, at least at a low speed, while charging. Seems pretty obvious to me - laptops have done it from the start, even modern desktop PCs vary their fans as needed. With the concerns about battery heat and longevity, how could Nissan forget this important detail?

So, what I've been doing lately - before discovering the motor heat issue - I've been playing with placing ice-chest freezer blocks in the emergency disconnect switch box. There's a fairly large space in there to put them, and since cold air falls while heat rises, the cold air circulates and conducts through the metal of the battery pack, rather effectively using the ice to cool the battery overnight. That day I came home with 8 bars was when I started playing with the concept, and the next morning, I started off with 6 bars, only hitting 7 halfway through the day. It's only been a week, so I don't have much data to play with... but I figured I should get a topic and discussion going on this.

Anyone know how to kick that cooling fan on while charging? Maybe a command through the OBDII interface through the Leaf Spy app? :D


Please keep testing! While I do not have high ambient temps to worry about here in the Pacific Northwest, I do experience HIGH pack temps on occasion while DC quick charging repeatedly on road trips. A solution to cool the pack through the HV access would be great.
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Re: Cooler Leaf - on Heat Energy Storage & Ice Packs

Sun Aug 17, 2014 11:48 am

donald wrote:But surely for the cooling fans to cool the motor you'd have to have the liquid cooling system active, and that only operates when the car is in motion?

The fans run with AC because the condenser at the front has to be cooled else the AC won't work.

The only way to cool the motor/charger is to pass cold air over it. This is actually quite easy to do - set your heating on rather than your AC on (I assume your 2013 has a heat pump?). With AC, the radiator acts as a condenser and has to eject heat, whereas with the heating on the radiator acts as an evaporator and draws heat out of the air. You'd then be fanning colder air over the motor/charger.

You could get some big mains operated fans and put them flat on some castors, you can roll it under the car and ventilate. This will prevent heat build up in the charger system and avoid heat soak.



The topic here is charging heat not motor or inverter heat and they have nothing to do with the pack. In addition the car does not need to be moving to cool the charger which is cooled by a pump that circulates water during charging and is not contingent on fan use nor does it have any relevance on pack cooling. Adding additional cooling for the charging or the inverter/motor is pointless. Non of this adds any benefit to the pack temp or has any value. This thread is based on a fundamental misunderstanding of the LEAF systems and a proposed solution that has no relevance on pack cooling. Heat is not soaking from the engine compartment to the pack in any meaningful manner.

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Re: Cooler Leaf - on Heat Energy Storage & Ice Packs

Sun Aug 17, 2014 11:53 am

FalconFour wrote:
All that heat was typically stored in the car from night to night, which in turn transfers to the battery (which I'd think would be cooled by the chilly motor components).


Not sure I follow. The motor compartment and battery case seem fairly well separate. Not much potential for heat transfer.

I would think the cooling fan would be running, at least at a low speed, while charging. Seems pretty obvious to me - laptops have done it from the start, even modern desktop PCs vary their fans as needed. With the concerns about battery heat and longevity, how could Nissan forget this important detail?


I'd be surprised if they "forgot". Part of "varying fans as needed" is to not use them at all when not needed. No doubt the charger has some thermal sensor that would either invoke the fan, or terminate charging at some predetermined temperature(s) to keep the charger's electronics within a safe range. That your charger continues to operate and we don't hear increased OBC failures with age, suggests it's probably being adequately cooled.
I noticed you're still working with polymers.

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Re: Cooler Leaf - on Heat Energy Storage & Ice Packs

Sun Aug 17, 2014 12:09 pm

Nubo wrote:
FalconFour wrote:
All that heat was typically stored in the car from night to night, which in turn transfers to the battery (which I'd think would be cooled by the chilly motor components).


Not sure I follow. The motor compartment and battery case seem fairly well separate. Not much potential for heat transfer.

I would think the cooling fan would be running, at least at a low speed, while charging. Seems pretty obvious to me - laptops have done it from the start, even modern desktop PCs vary their fans as needed. With the concerns about battery heat and longevity, how could Nissan forget this important detail?


I'd be surprised if they "forgot". Part of "varying fans as needed" is to not use them at all when not needed. No doubt the charger has some thermal sensor that would either invoke the fan, or terminate charging at some predetermined temperature(s) to keep the charger's electronics within a safe range. That your charger continues to operate and we don't hear increased OBC failures with age, suggests it's probably being adequately cooled.




You have this correct. There is no issue with the system design nor does there need to be any additional cooling to the charger/inverter/motor. This is pointless and adds no benefit. There is a fundamental misunderstanding of the entire cooling system and how heat is distributed in the vehicle, this thread is going in circles and will likely continue to do so. I suggest some download the service manual and study the cooling design.

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Re: Cooler Leaf - on Heat Energy Storage & Ice Packs

Sun Aug 17, 2014 12:32 pm

EVDRIVER wrote:The topic here is charging heat not motor or inverter heat and they have nothing to do with the pack.
Is it?

Either you or I haven't read/understood the OP thoroughly.

I understand the OP to mean that he was running the AC to cool down the charger. The charger has no water cooling in it, so what's the point in wanting the cooling fans running unless to cool the motor/inverter assembly. The heat transfer between the two is assured. And then the thermal soak caused by that hot unit is a hindrance to the battery pack cooling down.

If I have misunderstood the OP, then I don't see what the relevance of the discussion about running the AC was.

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