62kwh Leaf Plus Efficiency Posting

[Marktm]

My latest battery data is attached.



Did a small "experiment" last night - purely anecdotal;
- Put a fan under the Leaf battery area all night:
- Starting data after returning from 100 mile trip at about 65 mph with ambient temps in the mid 90's:
- 7:00 PM - Ambient temp 85 oF, Garage floor temp 85 oF, Average battery temps about 97 oF (LS pro)
- Ending data at 7:00 AM - Ambient temp 77 oF, Garage floor temp 80 oF, Average battery temps about 86 oF

 

[DougWantsALeaf]

My S+ has the efficiency ev01 rims and I do drive... modestly. The wife vetoed the coil overs. So did my 18 year old daughter.

I am doing another Kansas run in a month, so curious to see how the thermals work when it's in the 80s vs 40s&50s when we did the run in Nov.

 

[DaveinOlyWA]

My S+ has the efficiency ev01 rims and I do drive... modestly. The wife vetoed the coil overs. So did my 18 year old daughter.

I am doing another Kansas run in a month, so curious to see how the thermals work when it's in the 80s vs 40s&50s when we did the run in Nov.

Considering the weather trends, you might be looking at 100º

 

[DougWantsALeaf]

It hit 103 in Chicago (per my dash thermomoeter) today. Hoping it breaks back to the 90s or 80s for the trip. Not much thermal space at 100F.

After 6 hours in the 100ish weather, car was still at 6 temp bars.

 

[DaveinOlyWA]

It hit 103 in Chicago (per my dash thermomoeter) today. Hoping it breaks back to the 90s or 80s for the trip. Not much thermal space at 100F.

After 6 hours in the 100ish weather, car was still at 6 temp bars.

Yep, slow to heat up, slow to cool off. The real issue is getting it hot on long fast drives with a charge on the road. That will be long time of sustained heat. I don't go over 80% SOC if possible when that is possible.

 

[GerryAZ]

I had 10 temperature bars on 6/6 after parking in shade at my office during the day followed by freeway driving, DCQC, and more freeway driving before arriving home. It was much hotter on 6/10 so here is a photo as I was leaving my office after the car was parked all day in the shade. The location of my office is generally a little warmer than the official temperature at PHX airport.

 

[Marktm]

I had 10 temperature bars on 6/6 after parking in shade at my office during the day followed by freeway driving, DCQC, and more freeway driving before arriving home. It was much hotter on 6/10 so here is a photo as I was leaving my office after the car was parked all day in the shade. The location of my office is generally a little warmer than the official temperature at PHX airport.

Wow - thought it was hot here in Houston! Do you have a shady spot on your driveway? Again, anecdotally, it seems that continually watering my shaded driveway under the Leaf, with a low energy fan blowing air under it does cool fairly rapidly. We've been having hot weather also (near 100 oF), but the dew point has been much lower that normal ~70 oF. Might be worth a try to cool more effectively if % humidity is quite low.

 

[DougWantsALeaf]

I have taken my car through the carwash before between DC stops to try to shed a couple extra degrees. It does seem to help a little as there is a fair amount of surface.

I would be curious if a a water spritzer and fan lowered from the center panel in the car (point away from high power connection) could help accelerate the heat dissipation.

 

[Marktm]

The heat transfer calculations would be challenging for any water evaporation type set up. However, the possible energy that could theoretically removed is quite promising:
- For each gallon of water that is evaporated, more than 8000 btu's is required (8.33 x ~1000)
- The specific heat of lithium packs is around .25 btu/lb-oF, so a 8000 lb pack would cool about 4 oF if all heat involved was released by the pack (neglecting any btu s required to cool the air)
- No way 100% heat is removed for each gallon, but what % is depends on many heat transfer considerations (radiation, natural and forced convection - film coefficients of fairly good air velocity, inner pack core heat transfer, etc, etc.)
- However, it does seem logical that if the pack is at 100 oF and the dew point of the atmosphere is around 70 oF (the usual here), there would seem to be a pretty good driving force to do some significant cooling - especially of the (concrete) surface below the pack when parked overnight (this is what I did). "Spritzing" would likely be even more efficient.

Is it worth to use valuable water to do this? Maybe some heat transfer expert can do a reasonable calculation.

 

[LeftieBiker]

Maybe use humidified air, to increase the amount of heat moved per unit volume over dry air?

 

[Marktm]

Maybe use humidified air, to increase the amount of heat moved per unit volume over dry air?

A wet surface with dry air blown over it will quickly take the water film to the dew point and also that "film" will transfer heat quite well (especially with good air velocity). That's why a concrete driveway will cool quite quickly if kept wet and forced air with a fan - if the dew point is relatively low and done long enough to take out the energy required. You then end up with a cool surface (and cool air) to help with both radiant and forced convection heat transfer - especially if done say overnight when the air typically goes close to dew point anyway (here in Houston).

Using humidified air (assuming at dew point) would cool OK if the battery pack was actually exposed - but would lose the effectiveness of a good film coefficient (water film) to help with overall energy removal. Which is best? Depends on the actual configuration.

One further finding was during this continued heat wave of near 100 oF daily and about 70-75 oF dew point, after 3 days of the Leaf sitting in the garage unused, the battery temps were approx 89 oF. After one night of watering the garage floor and blowing a fan during the night, the battery temp went down to around 83 oF - during which time the Leaf was never used. Don't think I'm going to "save my battery", but it's fun :mrgreen:

 

[SageBrush]

One further finding was during this continued heat wave of near 100 oF daily and about 70-75 oF dew point, after 3 days of the Leaf sitting in the garage unused, the battery temps were approx 89 oF. After one night of watering the garage floor and blowing a fan during the night, the battery temp went down to around 83 oF - during which time the Leaf was never used.

You have to tease out the effect of not using the car from the watering.
I did a variant of watering last summer that seemed to work well but I had the same confounder of not using the car so I was unsure of the effectiveness.

In my case, I was not trying to cool the pack, I wanted to avoid heating up the pack from the hot ground that had been cooking in the sun. My solution was to cool it down with water as a one time watering event, somewhat equivalent to parking in the shade.

 

[SageBrush]

Amazing weather today. Yesterday was up to 100F, and after a warm night my home was 80F in the AM. Lucky for me rain arrived in the afternoon and the ambient dropped to 73F, and then we had 5 - 10 minutes of hail. Since 5PM or so ambient has been in low 60sF and that will continue through the night.

It will get hot again by Monday but the respite sure is welcome and the home will have a chance to discharge retained heat.

 

[Marktm]

In my case, I was not trying to cool the pack, I wanted to avoid heating up the pack from the hot ground that had been cooking in the sun. My solution was to cool it down with water as a one time watering event, somewhat equivalent to parking in the shade.

My configuration lends itself to this approach as there is a "carport" that shades both the inside and outside concrete from the hot sun. Any "water" cooling can escape the reheat of the hot sun. Again, don't think it'll "save the battery" as it seems only a few degrees cooling at best.

I'd actually like some hail here - but ain't going to happen.

 

[DaveinOlyWA]

problem with an exterior cooling is the lack of contact to the cells themselves. They reside in a case that is covered by panels designed to reduce air friction which means two air barriers to overcome. The clearance inside the battery case is VERY small and gen two packs did add spacing (the equivalent of one extra standard washer which is actually what they did...) between modules but even in winter, the amount of cooling is rather minimal.

For whatever reason I am unsure of, in observations, I was seeing more cooling from the low 90's than I was when temps were over 105 (the highest I was able to observe while testing) in basically the same conditions. There were only 3 trips recorded.

The only differences was the 105º session was higher SOC and more DC charging than the low 90's session which was a full charge leaving home, then two 15 minute DC's during the day. All were round trips to the same place where speeds were primarily 65 mph for most of the trip.

I had planned to collect more data but the situation never really arose and simply didn't find the time to spend a day without a reason to be out and about.

 

[Marktm]

problem with an exterior cooling is the lack of contact to the cells themselves. They reside in a case that is covered by panels designed to reduce air friction which means two air barriers to overcome. The clearance inside the battery case is VERY small and gen two packs did add spacing (the equivalent of one extra standard washer which is actually what they did...) between modules but even in winter, the amount of cooling is rather minimal.

Plus, the thermal conductivity of the Li modules are quite low, so inner pack cooling via convection is going to be low. It could be that the radiant transfer dominates, and if so, cooling would seem to be very limited - but maybe a 5-10 degrees drop is helpful at 100 plus temps.

EDIT:
Just thought I'd add that my shiny galvanized roof on my cabin will essentially air condition itself overnight on super clear nights. The inside gets much cooler than the outside ambient temps. I'm thinking it's the radiant heat into what is a "black body" of very low temperatures - almost zero absolute on super clear nights.
HOWEVER, turning my leaf upside down every night is probably not going to happen :mrgreen:

 

[DougWantsALeaf]

It seems you could build a single piece top battery cover with a molded heat exchanging set of small tubes and then put a small fan in the pack to push the air across those tubes. Even a modest amount of additional cooling would make long distances less frustrating.

 

[SageBrush]

It seems you could build a single piece top battery cover with a molded heat exchanging set of small tubes and then put a small fan in the pack to push the air across those tubes. Even a modest amount of additional cooling would make long distances less frustrating.

The only practical way I can think of to mitigate rapid-gating from serial DC fast charging is to drive slowly. 55 mph Vs 70 mph would be close to 40% less pack heat generation. And somewhat paradoxically but for similar reasons, you may want to to avoid charging in the low SoC range so that the car keeps to lower charging amperage.

From from great, but I think travel times better than what you and others have posted are possible. When it comes to the LEAF, patience is a virtue :lol:

 

[DougWantsALeaf]

Sage

Yes, the pack (even in cool weather) reverses temp loss and starts going back up around 20% on dash/27% SoC.

It's not just about speed, it is also about well timing stops to meals to minimize the feel that you are waiting for the car.

My hot weather run (temps predicted in mid 90s) is coming soon.

 

[Marktm]

My next cabin trip of 100 miles (each way) will be in this 95+ degree weather. I can charge at the cabin, but I'm thinking to fully charge in Houston, wet the gravel under the Leaf (in the shade) overnight and make it on one charge. I'll monitor the temps. I really don't have to quick charge as we take my wifes ICE on any longer trips.