Battery Temperature, isn't 20c the sweet spot?

[RodHam]

I decided to check the battery temperature after preconditioning for my usual departure time of 6:10AM. The car is connected to a Juicebox Pro 40, the car is fully charged thru the night and at precisely 3hrs to departure time the EVSE indicates a draw of 0.7 kW as the car starts testing or whatever it does towards preconditioning. The outside temperatures was a balmy 4c and at 6:10AM I disconnect the EVSE, start the car and unlock the service menu to see the battery temp, which was only 10 Celsius! I thought that the battery performs best at 20c.

The Juicebox Pro 40 shows a temp of 15 to 20c during charging but I failed to notice the temperature on the Juicebox application during preconditioning, will check it tomorrow morning.

Is there a reason why my battery is only 10c and all online specs say 20c is the best operating temperature?

 

[janner]

Rodham - Very interesting post. How did the 0.7kW vary throughout the three hours of Precon and what happened when the cabin heating started up?

Our local BMW i3 R&D guy said that the battery pre-con heater was 1kW but there is a larger spike of power than this when my car precons albeit over the three hours I typically use from 1 to 1.5 kWHrs. Others seem to use more energy than this and I have seen some claim that as much as 5kWHrs can be used - bit surprising to me.

On battery temperature I suspect that the preconditioning gets the battery into the 'comfort zone' of 10 - 25 deg C and once driving the battery will reach 20 deg C before the cooling system cuts in.

 

[RodHam]

This should show power consumption during preconditioning a total of 1.669 kWh or $0.12 of Quebec Hydro electric

I did leave the battery temp showing during the first 15 minutes of the drive and the temp stayed steady at 10c.

 

[janner]

Rodham

That's really good information, Thanks.

 

[janner]

Rodham

The graph is very interesting, thanks. As you have the equipment to measure things, would it be possible to post a graph of level 2 charging, particularly the last hour before 100% and the following hour.

 

[RodHam]

Rodham

The graph is very interesting, thanks. As you have the equipment to measure things, would it be possible to post a graph of level 2 charging, particularly the last hour before 100% and the following hour.

See next post for an expanded view of the graphs.

 

[RodHam]

Well the temperature has finally dropped to -20c or -4f here in Montreal with lots of snow and ice.
It seems that preconditioning will warm the battery to a temperature range that I don't understand. At -20c it only warms the battery pack to -2c or 28.4f (verified on 3 separate preconditioning). These are set departure time preconditioning.

I'm including graph images from my EVSE for your enjoyment. This image shows the entire charge and preconditioning.

This image is an expanded view of the charge portion.

This image is an expanded view of the preconditioning portion.

Edit: Corrected my assumption about the temperature shown on the Juicebox App (Jan 06 7:32AM)
The service menu shows a battery temp of -2c or 28.4f, another effect of the colder pack is the greatly reduced recapture braking force and much higher kWh/100km numbers to maintain any kind of speed. The battery pack does reach +10c within 15 or so minutes of driving.

 

[alohart]

I'm pretty certain that a JuiceBox and its app know nothing about an EV's battery pack temperature. My JuiceBox reports its circuit board temperature which I'm guessing is what its app is showing. That would explain the low temperatures that you are seeing.

 

[Jeffj]

Hi Rodham - I have a Juicebox Pro also, and I've seen the temp meter, but my question is how do you know that the temp being reported is the battery temp? Is there something in the protocol between the car and the EVSE that indicates battery temp? I can see the display being the temp of the Juicebox itself, and make myself believe that the Juicebox might only warm up to -2C (18C above ambient) while its delivering charging current.

 

[RodHam]

Hi Rodham - I have a Juicebox Pro also, and I've seen the temp meter, but my question is how do you know that the temp being reported is the battery temp? Is there something in the protocol between the car and the EVSE that indicates battery temp? I can see the display being the temp of the Juicebox itself, and make myself believe that the Juicebox might only warm up to -2C (18C above ambient) while its delivering charging current.

When I get into the car and disconnect it, I unlock the service menu and check the battery temp and I thought it always matches what I see in the App, besides the EVSE is outside in -20c ambient. I will check again tomorrow morning!

 

[RodHam]

I was just on the OpenEVSE forum and it looks like the temp gauge on the app is showing the evse temps which coincidently match the battery's temp the few time I've compared it. So I will only use the service menu battery temp in the future.

Edit: Next Day (Jan 06, 7:29AM)
This morning outdoor temperatures were -9.5c and battery temp +11c and App showed the Evse at +4c

 

[janner]

Rodham - another very interesting post, thank you for the graphs.

It may help increase battery temperature if you timed the charge to finish just before preconditioning started - you would then have the residual warmth from the battery charge as a start point for the pre-con. Precon heater is only 1kW and the battery pack can't absorb too much heat in one go - as your graphs show it takes energy then lets it dissipate through the pack before taking more energy.

Do you know what the battery temperature was at the end of charging?

 

[janner]

Does anyone know what the three blips in Rodham;'s charging graph are? There's one at the end, one about 45 minutes before the end and one about 90 minutes before end.

 

[RodHam]

I'm going to guess that those blips are the battery thermal management systems kicking in. The curve is usually smooth but this one is from an evening of -22c.

 

[janner]

Makes sense. Thanks.

 

[janner]

Rodham. Was this precon with the latest November update software?

 

[RodHam]

Rodham. Was this precon with the latest November update software?

Thought I had the latest, took delivery Dec 6th but it has the march update I001-15-03-502.

 

[i3atl]

My November update cars seem to target 10C as well for battery preconditioning.