Battery Design and Engineering Issues

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DaveinOlyWA said:
all this makes me wonder?? when is heat an issue the most?

when charging or discharging?

i thought it was when discharging. when the car is moving, air will be moving as well. if the pack is passive heat control, that would mean, heat exchangers, cooling fins, etc. seems to me that ventilation would be ample at all but parking lot speeds.

My guess is it's just as you say when discharging and think the real problem is charging, but, of course, when charging the thermometer can detect overheating and slow down the flow of the charge so you don't end up with another, massive Dell Laptop!
 
TimeHorse said:
Bugger, can't we just set up a sales location in Washington, D.C. so I can drive my LEAF by the Capitol building and remind Congress that we need more EV subsidies?

You may have missed it - but they have extended the EV project to LA & DC i.e. now they are in the early rollout areas. You can get your Leaf early next year ...
 
Quick Charging can self-regulate (slow down) as needed to avoid cell over-heating.

The 240v 3.3kW (15-amp) charging is but a "trickle", and even the "future" 30-amp (6.6 kW, 4-hour) is unlikely to have a heating problem, but they could also self-regulate. The 120v charging (12 or 15 amp) is even less of a problem.

Regen is probably limited below what it could really do, just to be conservative on regen control and battery life, but it is likely that it would also self-control if heat is a problem.

Driving at parking lot speeds does not cause much heating. Faster speeds only heat a little, but very fast speeds, heat a bit more. Even heavy acceleration, which will generate substantial heat due to the high discharge currents, is usually of limited, short duration, so (unless frequent) is rarely a big heat-quantity producer.

The BIG producer is going up hills. Then, the car should self protect, and warn you of the approaching situation via the left-hand-side Battery Temperature gauge.

Self-protection might force you to slow down, or even stop.
 
evnow said:
TimeHorse said:
Bugger, can't we just set up a sales location in Washington, D.C. so I can drive my LEAF by the Capitol building and remind Congress that we need more EV subsidies?

You may have missed it - but they have extended the EV project to LA & DC i.e. now they are in the early rollout areas. You can get your Leaf early next year ...

Wow, that's sweet, EVNow! That's why I follow you on Twitter! :)
 
missed my point. charging usually does not generate as much heat as discharging. u will most likely charge in garage, out of sun, etc. batteries will be relatively cool especially if doing timer charge for better TOU rates.

one question that i am not sure of; for quick charging must generate some sort of heating issue. since mostly likely batteries would have been recently discharged so would be warmer than normal. wondering if time to 80% might be significantly longer in summer than winter especially in AZ?
 
In CA, we don't have much real weather, humidity, or bugs. We tend to have mostly over-crowding, smog, "crazy", and lack of water.

If it seems good when you visit, it was probably a hollywood set backdrop hung up for tourists.

"You don't want to move to CA", says Obie-Wan. :)
 
DaveinOlyWA said:
missed my point. charging usually does not generate as much heat as discharging. u will most likely charge in garage, out of sun, etc. batteries will be relatively cool especially if doing timer charge for better TOU rates.

one question that i am not sure of; for quick charging must generate some sort of heating issue. since mostly likely batteries would have been recently discharged so would be warmer than normal. wondering if time to 80% might be significantly longer in summer than winter especially in AZ?

Hi Dave,

I would expect the pack would be warmer during the later stages of a quick charge, but since the quick charge is only to 80%, we stay away from the last 20% when most of the charging heat is generated.

I'd expect the motor and controller to generate more heat than the battery at high speeds and/or hill climbing. (But with water cooling this will be a non-issue.)

I'm still working on my battery guessing, but it's looking more like the pack of 48 four-cell modules is two strings of 24 for about 345V nominal. If the Leaf cells are the 33Ah capacity listed on AESC's site, and if they're capable of a 10C discharge rate,** then each string should be good for 330A continuous and two parallel strings should be good for 660A. I'm thinking the pack is going to be absolutely loafing during all phases of operation - and I really don't expect heat during charge or discharge to be a problem (or a factor). I'd be surprised if the Leaf draws more than 250A max.

** A 10C discharge rate is pretty low to average for current cells. These old 20Ah LiMn cells from EiG are 5C continuous, 10C peak. Even if the Leaf pack was made from 5C capable cells, that's 330A continuous for two parallel strings, and 660A for <10 second pulses.

Andy
 
curious since L3 charging is DC and a direct connection to the high voltage bus, wondering if the heat build up would be relatively small. in my Zenn, the batteries dont really heat up at all charging or discharging but the charger gets very warm. so warm that i usually pop the hood when home. it has only passive cooling with radiator fins and whatnot but it puts out a pretty good amount of heat.

if the charging system was more efficient, maybe heat buildup is not as much of an issue as we are making it out to be
 
The Nissan Leaf Info Screen at: http://green.autoblog.com/photos/nissan-leaf-info-screens/full/#3195511
may give us a clue about the A/C energy use. First the climate control shows a Kw scale of 0 to 6. Second, the screen has the following message "Turn on Climate Control for -22 miles".

When I compare the 6 Kw A/C use to the -22 mile range penalty, it seems nearly consistent. Since I live in a hot climate, this is an important clue as to the mileage penalty, I can expect from using the A/C continuously. It will be approximately 25%.
 
LeafHopper said:
Since I live in a hot climate, this is an important clue as to the mileage penalty, I can expect from using the A/C continuously. It will be approximately 25%.

I can live with that, assuming the 60-70mph "sweet spot" that would still allow for 100 miles without AC. Besides, I'm training myself to toggle the AC in my Focus between "on" and "recirculate" in preparation.
 
I would like to know whether the Leaf's A/C will have a variable speed compressor or will it be all-or-nothing with the temperature adjusted by mixing in hot air like many of them are. A variable A/C will cost a bit more but will save considerable energy. My other question is, if it is a single-speed A/C, can it be turned on and off frequently? Many A/C's require a wait of about 3 minutes between on and off cycles to allow for pressure release. And many of the new more efficient A/C's in cars have a big problem with bacteria lodging in the coils which can cause an unpleasant smell for a few minutes after the A/C is shut off.
 
Since I have driven the Mini-E for the past 15 months I thought I'd contribute my 2 cents to this discussion regarding battery temperature and its effect on range, performance, etc. Of course, the Mini-E is quite different from the Leaf in many respects, but a few things I thought might be useful to consider:

1) If the Mini-E battery temperature goes above 115F, regen is shut off and therefore affects range. In addition, max power is limited to avoid further overheating.
- Although I live in Southern California, getting to 115F happens pretty easily when you park in the San Gabriel Valley sun all day and then accelerate quickly home at 5pm.
- Shutting off regen never made complete sense to me, but I will say that when that 115F threshold is crossed, it makes one rather wary of what the car will do next.
2) I found that not only would I be concerned about range while driving the MiniE, I became obsessed with the battery temperature. I still am to this day. On warm summer nights, I park at home with the windows down. During the day, I park about a 5min walk away from work under a cluster of massive Chinese elm trees which haven't been trimmed in decades.
3) There is no question that low temperatures affect range more than anything else. Even here in Southern California, I found that a battery temp around 60F would reduce my typical range of 100 miles down to 80 miles (and lower if I really punched it). Reportedly, subzero temps in the East Coast actually made the cars dead and unusable at times.

To be honest, I began to feel that the battery temp issue along with the range issue was a deal-breaker for making EVs truly a possibility for the mass-market. I am VERY curious to see how the Leaf handles these issues in the real world. My basic impression is that the Leaf's battery chemistry is inherently superior to what the MiniE used and much less temperature-labile. But hey, I'm not battery engineer and I assume someone on the forum might have an idea about this? I haven't seen any long-term real-world test drives of the Leaf yet, but one would assume that this is exactly what Nissan has been doing for awhile. That being said -- Tesla's Model S is supposed to have a 'water-cooled' system for their batteries. The Leaf battery system doesn't sound very robust. Thoughts?
 
I am a big ev and Leaf fan but.......

I am concerned about about battery temps hot and cold

a "cold weather package" is coming I think on the fall 2011 leaf

think it will allow charger to warm batteries

I would much like that option , and ,may delay my purchase til I see how the Leaf deals with high temps too
we get both here in this part of Virginia

Kevin
 
I wonder if EV batteries would benefit from having the juice from braking pushed into a capacitor instead of back into the battery. Does the constant alternation between charging and discharging the battery shorten its life?
 
wq2345 said:
To be honest, I began to feel that the battery temp issue along with the range issue was a deal-breaker for making EVs truly a possibility for the mass-market. I am VERY curious to see how the Leaf handles these issues in the real world. My basic impression is that the Leaf's battery chemistry is inherently superior to what the MiniE used and much less temperature-labile. But hey, I'm not battery engineer and I assume someone on the forum might have an idea about this? I haven't seen any long-term real-world test drives of the Leaf yet, but one would assume that this is exactly what Nissan has been doing for awhile. That being said -- Tesla's Model S is supposed to have a 'water-cooled' system for their batteries. The Leaf battery system doesn't sound very robust. Thoughts?

We have discussed this a lot before.

http://www.mynissanleaf.com/viewtopic.php?f=9&t=914

Just remember
- Tesla, mini-E use cylindrical consumer grade cobalt oxide cells with bad thermal characteristics
- Manganese spinal takes abuse much better & has low internal resistence
- Though Volt (and Ford) use cooling now, Gen 2 Volt with will not use liquid cooling

So, having no thermal management in mini-E and letting those lose to customers purely for Carb play was very bad form by BMW. They obviously cared only about carb credits rather than effect on EV market.
 
wq2345 said:
Since I have driven the Mini-E for the past 15 months I thought I'd contribute my 2 cents to this discussion regarding battery temperature and its effect on range, performance, etc. Of course, the Mini-E is quite different from the Leaf in many respects, but a few things I thought might be useful to consider:

1) If the Mini-E battery temperature goes above 115F, regen is shut off and therefore affects range. In addition, max power is limited to avoid further overheating.
- Although I live in Southern California, getting to 115F happens pretty easily when you park in the San Gabriel Valley sun all day and then accelerate quickly home at 5pm.
- Shutting off regen never made complete sense to me, but I will say that when that 115F threshold is crossed, it makes one rather wary of what the car will do next.
2) I found that not only would I be concerned about range while driving the MiniE, I became obsessed with the battery temperature. I still am to this day. On warm summer nights, I park at home with the windows down. During the day, I park about a 5min walk away from work under a cluster of massive Chinese elm trees which haven't been trimmed in decades.
3) There is no question that low temperatures affect range more than anything else. Even here in Southern California, I found that a battery temp around 60F would reduce my typical range of 100 miles down to 80 miles (and lower if I really punched it). Reportedly, subzero temps in the East Coast actually made the cars dead and unusable at times.

To be honest, I began to feel that the battery temp issue along with the range issue was a deal-breaker for making EVs truly a possibility for the mass-market. I am VERY curious to see how the Leaf handles these issues in the real world. My basic impression is that the Leaf's battery chemistry is inherently superior to what the MiniE used and much less temperature-labile. But hey, I'm not battery engineer and I assume someone on the forum might have an idea about this? I haven't seen any long-term real-world test drives of the Leaf yet, but one would assume that this is exactly what Nissan has been doing for awhile. That being said -- Tesla's Model S is supposed to have a 'water-cooled' system for their batteries. The Leaf battery system doesn't sound very robust. Thoughts?

Nissan tested the LEAF near the North Pole...probably with the 'winterized package'. There was a photo of it on one of these threads, but I can't remember where it is.
 
leaffan said:
Nissan tested the LEAF near the North Pole...probably with the 'winterized package'. There was a photo of it on one of these threads, but I can't remember where it is.

In this one:

http://www.mynissanleaf.com/viewtopic.php?f=9&t=1030
 
Norway said:
leaffan said:
Nissan tested the LEAF near the North Pole...probably with the 'winterized package'. There was a photo of it on one of these threads, but I can't remember where it is.

In this one:

http://www.mynissanleaf.com/viewtopic.php?f=9&t=1030

Yeah! That's it! Thanks Norway! I wonder if they've printed their results after 6 years of testing there? Wouldn't that be great to hear that the batteries didn't lose any electrons by being heated? :)
 
The problem with cold is not permanent damage (unlike extreme heat) - but lowered maximum capacity of the cells. IIRC, the BMS will think the cells are maxed out much before they actually are - leading to low charge and low range.

I wonder whether Nissan will have some kind of battery heating with their "Cold weather package".
 
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