Battery preconditioning

All Jaguar I-Pace related discussions
Captain.Plummet
Posts: 502
Joined: Thu Mar 14, 2019 5:26 pm
Location: UK

Re: Battery preconditionin

Post by Captain.Plummet » Fri Feb 26, 2021 4:55 am

dernotte wrote:
Thu Feb 25, 2021 11:39 pm
You can clearly see of this graph what happen when you set the preconditioning with a full battery, and and plugged car.
I monitor the car since 9am, and the departur time was set for 2pm. At 12:30, the car decided to pre warm the battery (red, green, yellow line) for min,max,avg temperature of the battery, probably warmed by the hot coolant (line green and orange), It took one 1 hour to raise the battery temp from -10c to +20c. It seems that preconditionning always stop at 20c for the battery. And then at 1:30pm the car started to precondition the cabin for 30 min, and you can see the cabin temperature (blue line) reaching 20c.

Capture d%u2019écran, le 2021-02-13 à 17.52.02.png
You have to consider the state of charge too. Assuming that the external charger is 7.5kW, all of the charging occurred whilst the battery was at -10degC. After preconditioning starts the battery provides the power for heating. It is still being charged too, but the overall SoC will fall. Eventually the SoC will begin to increase, but it takes a couple of hours to get to that point during which time 15kW has been consumed and the available range is little more than it would have been had just the cabin been preconditioned. Better to charge to full with a warm battery, let the car cool and then precondition for 30 minutes before departure.

User avatar
MjrPayne
Posts: 355
Joined: Sat Mar 31, 2018 2:48 pm
Location: Finland

Re: Battery preconditioning

Post by MjrPayne » Fri Feb 26, 2021 5:47 am

I have noticed that battery is warming up even when charging 3,7kW charger at home to full. Staring with 20% SOC/10C temp and when full, battery temp was 19C. So you could use this info to adjust your charging so battery is full just before leaving. Also during winter I've noticed that battery is cooling down during normal steady driving. In the long drive the temp usually drops down to 7-8C (starting from 15-16C from the garage). Or if you start with cold battery, it stays cold until SOC goes below 20%, then it starts warming due lower voltage which means higher current. So I don't see much benefits to precondition battery except if it's really cold like -20C. I haven't test that cold because having a warm garage and while out, stopping times too short to let battery below freezing point.
Blue HSE since 21.1.2019
Backup -04 XJ SuperV8

I rather cry in Jaguar than in Tesla

Maxwell_400
Posts: 429
Joined: Mon Oct 14, 2019 10:09 am
Location: Norway

Re: Battery preconditioning

Post by Maxwell_400 » Fri Feb 26, 2021 8:36 am

MjrPayne wrote:
Fri Feb 26, 2021 5:47 am
I have noticed that battery is warming up even when charging 3,7kW charger at home to full. Staring with 20% SOC/10C temp and when full, battery temp was 19C. So you could use this info to adjust your charging so battery is full just before leaving. Also during winter I've noticed that battery is cooling down during normal steady driving. In the long drive the temp usually drops down to 7-8C (starting from 15-16C from the garage). Or if you start with cold battery, it stays cold until SOC goes below 20%, then it starts warming due lower voltage which means higher current. So I don't see much benefits to precondition battery except if it's really cold like -20C. I haven't test that cold because having a warm garage and while out, stopping times too short to let battery below freezing point.
That is my impression too, I only precondition if it is really cold and I need the range or if I am going to fast charge later.

Some quick, inaccurate calculations;
Full battery, battery lasts for 3 hours, average current usage is then 68Amps.
At 20 degrees the pack internal resistance is approximately 30mOhms -> power loss to heat battery = 138Watts = 414Wh
At 0 degrees the pack internal resistance is approximately 70mOhms -> power loss to heat battery = 138Watts = 966Wh
At -20 degrees the he pack internal resistance is approximately 210mOhms -> power loss to heat battery = 970Watts = 2890Wh

Full battery, battery lasts for 2 hours (driving hard), average current usage is then 100Amps.
At 20 degrees the pack internal resistance is approximately 30mOhms -> power loss to heat battery = 300Watts = 600Wh
At 0 degrees the pack internal resistance is approximately 70mOhms -> power loss to heat battery = 700Watts = 1400Wh
At -20 degrees the he pack internal resistance is approximately 210mOhms -> power loss to heat battery = 2100Watts = 4200Wh

To heat a perfectly isolated aluminum block of 600kg one degree you need 0.9 J/g K * 600kg = 150Wh
The heat loss to the environment is probably to large at zero degrees to get an effective heating of the battery, From top of my head I see that I need 3.6kWh (7kW*0.5h) during half an hour to raise the battery from -10 to 0 when preconditioning and one will use more energy from 0 to 10 than -10 to 0 when ambient is -10.
I-Pace SE++, MY20, 18" summer & winter, no panoroof, towbar, spare wheel, 20C, TCU 19.2, BECS: BP-AAE-BC-AC-BE

RobN
Posts: 157
Joined: Tue Feb 04, 2020 9:09 am
Location: UK

Re: Battery preconditioning

Post by RobN » Sun Feb 28, 2021 11:13 am

Great further insight into the complexities of preconditioning thanks.

It seems to me even if you're in the relatively mild UK winter it's better to charge when warm after coming home as Captain Plummet suggests, rather than trying to warm a cold battery pack the following day (even if you topped up with cheap-rate power overnight on the timer)?

I wonder though if this issue is less critical when the weather's warmer as the differential from cold to operating temperature would be much smaller?

Clearly, there are a lot of variables here, but it would be useful (certainly to me) to have a rough guide for optimum charging/preconditioning in a set of common situations (e.g. Spring/Summer/Autumn/Winter + overnight topping up/full charge from low + imminent short trips/long trip.
SE MY20 Corris Grey, 20” wheels, oyster leather 10 way seats, panoramic roof, black trim + privacy glass + 7kWh Podpoint & ICE XK8 Conv 1996 (Jag owner/enthusiast since 1994 :D )

Maxwell_400
Posts: 429
Joined: Mon Oct 14, 2019 10:09 am
Location: Norway

Re: Battery preconditioning

Post by Maxwell_400 » Mon Mar 01, 2021 7:43 am

RobN wrote:
Sun Feb 28, 2021 11:13 am
Great further insight into the complexities of preconditioning thanks.

It seems to me even if you're in the relatively mild UK winter it's better to charge when warm after coming home as Captain Plummet suggests, rather than trying to warm a cold battery pack the following day (even if you topped up with cheap-rate power overnight on the timer)?

I wonder though if this issue is less critical when the weather's warmer as the differential from cold to operating temperature would be much smaller?

Clearly, there are a lot of variables here, but it would be useful (certainly to me) to have a rough guide for optimum charging/preconditioning in a set of common situations (e.g. Spring/Summer/Autumn/Winter + overnight topping up/full charge from low + imminent short trips/long trip.
The maximum power for AC charging is 7.6kW (MY21:11kW). Even when battery is at -8 degrees, SOC=60% it will accept a charging power of 60kW. My take is to charge when power is "cheap", the car does not spend any power to heat the battery other than self heating. DC fast charging and charging at less than -10 is a different story.
I-Pace SE++, MY20, 18" summer & winter, no panoroof, towbar, spare wheel, 20C, TCU 19.2, BECS: BP-AAE-BC-AC-BE

User avatar
MjrPayne
Posts: 355
Joined: Sat Mar 31, 2018 2:48 pm
Location: Finland

Re: Battery preconditioning

Post by MjrPayne » Mon Mar 01, 2021 1:07 pm

Here's what I found. Started at 3C degrees SOC 30% 50kW charger. It took about half an hour before reaching max charge at 19C. That 19C was easy to see (hear) when a heat pump switched off. Outdoor temp was about -15C. Notice how warm battery kept a cabin temp warm enough without turning precondition on.

Screenshot_2021-02-18-12-20-38-859_com.powercruisecontrol.ipace.jpg

Screenshot_2021-02-18-11-51-53-209_com.powercruisecontrol.ipace.jpg

Blue HSE since 21.1.2019
Backup -04 XJ SuperV8

I rather cry in Jaguar than in Tesla

Grunt
Posts: 79
Joined: Fri Aug 07, 2020 12:39 pm
Location: Belgium

Re: Battery preconditioning

Post by Grunt » Tue Mar 02, 2021 6:12 pm

electric beagle wrote:
Thu Feb 25, 2021 4:33 pm
Interesting thanks so I have had no issues with cabin preconditioning which as you say even in the cold normally sorts things in less than 30 mins but I have only once tried to set a departure time with the aim of maximising range and that failed perhaps because I was too close to the departure time.

I am reading that there is little real point in preconditioning the battery as that is disproportionately expensive and time consuming? Shame that JLR didn't change the battery warming design for the 21 which might have made it more efficient and effective. Having heating and cooling between the cells seems to be a no brainer.
Hi Electric Beagle,

To my understanding, warming the battery has much more benefits than optimising net charge capacity.

The chemical process to discharge runs much slower in a cold battery. The result is that your effectively available capacity will be much lower.
In fact, you can charge your 20°C warm battery to for instance 84 kWh, but the actual capacity of this battery cooled down to -10°C will be far lower - typically 25% less for lithium ion batteries, so as low as 63kWh. (At -20°C, the operating limit, you would barely see half of your 84kWh charge available).

If the battery warms up, this capacity will reappear. This means that there is no point in warming up a battery for a higher nominal charge and then letting it cool down again - the "extra charge" will seemingly disappear until the battery is warm again.

Further, the internal resistance of the cold battery is much higher. -10° vs +20° will be a multiple, as the x7 increase in the estimations of Maxwell400 show. Seems legit. This leads to higher discharge losses while driving, eating another few kWh.

Because of this heat loss (and battery management), the battery will warm up during use. Leading to the same situation, battery heated up using kWh. The difference is that while driving, these kWh will come from the net battery capacity, not from the charger...
It will take much longer than a few miles to warm up the battery; in my experience, starting from a cold battery and driving through cold weather (-5°) the battery will not go beyond 6-8°, not even close to the 17-20°C of a preconditioned battery. Still, at those 6-8° temperatures internal resistance is reasonable (50% higher than at 20°, so eating a few hundred watt as opposed to several kW) and net capacity as well (around 5% lower than at 20° as opposed to 25%).

As the example of Dernotte shows, heating the battery won't eat 15kWh; in his extreme example the battery was warmed up from -10 to +20 in one hour at the charger, pointing to around 7kWh. If you go drive, the internal resistance and BMS will anyway consume at least half that, heating up the battery from -10 to about 6-8°C.

Nevertheless, the conclusion remains valid. Preconditioning the battery really makes no sense for short drives.
For medium length drives, say 100km or more, the difference won't be significant. If you precondition, you'll eat kWh from the charger; if you don't, you'll use them from battery. Given that discharging at low temperatures is detrimental to battery longevity, I would precondition.
If you want more than about 70% of normal range in cold weather, then you need to precondition the battery.

From these observations, I would charge as close to the departure moment as possible. The heat induced by charging will then be available for the drive, increasing net available capacity and reducing internal resistance.

As for having heating & cooling between the cells being better than using a sandwich with top and/or bottom cooling & heating: both Tesla's future 4680 packs and Lucid's packs use the same sandwich approach as the I-Pace, not like the old construction of the 2170-based packs. From which I conclude that the sandwich approach is better. Easier to produce, more compact, much less friction in the cooling circuit, cooling/heating concentrated where most of the heat buildup appears.

Maxwell_400
Posts: 429
Joined: Mon Oct 14, 2019 10:09 am
Location: Norway

Re: Battery preconditioning

Post by Maxwell_400 » Tue Mar 02, 2021 7:16 pm

Grunt wrote:
Tue Mar 02, 2021 6:12 pm

The chemical process to discharge runs much slower in a cold battery. The result is that your effectively available capacity will be much lower.
In fact, you can charge your 20°C warm battery to for instance 84 kWh, but the actual capacity of this battery cooled down to -10°C will be far lower - typically 25% less for lithium ion batteries, so as low as 63kWh. (At -20°C, the operating limit, you would barely see half of your 84kWh charge available).
Just want to chime in, what I have seen on my car is 74kWh at -20 and 86kWh at +25.
I-Pace SE++, MY20, 18" summer & winter, no panoroof, towbar, spare wheel, 20C, TCU 19.2, BECS: BP-AAE-BC-AC-BE

electric beagle
Posts: 617
Joined: Fri Jul 17, 2020 9:23 pm
Location: United Kingdom

Re: Battery preconditioning

Post by electric beagle » Mon Apr 05, 2021 7:09 pm

So I have had another attempt at preconditioning my car. I have a fully charged car and the car is still plugged in. It is 19:00 tonight and I am trying to set preconditioning for 14:00 tomorrow.

Each time I try to do this the preconditioning instruction fails. Is this a fault? There is plenty of time.for the precondition to complete and the charge to come to full. This is stupid.

Has anyone with a MY21 managed to successfully set a departure time?
MY21HSE, Portofino Blue, Oyster interior, Wireless Charger, Cupholder Covers, Active Air Suspension, Adaptive Dynamics, Clear Sight rear view mirror, Panoramic Roof, Privacy Glass, Upgraded Cabin Lighting, Aluminium trim, Andersen EV Charger

RS1980
Posts: 12
Joined: Thu Nov 12, 2020 4:04 pm
Location: Germany

Re: Battery preconditioning

Post by RS1980 » Tue Apr 06, 2021 4:22 pm

Did you use the App or the in-car display to set the departure time?
For me, it also failed when I used the app, but worked fine via in-car display.

I remember that I got it to work once via app, but this was before my upgrade to 2.0.8, so maybe something was messed up with the upgrade...
I-Pace S MY21

Post Reply