Battery thermal management - does it work when car is unplugged?

[agileone]

Canucks have similar concerns, but at the other end of the range : how much energy will be consumed if I have to leave the car outside overnight, by -30C (-22F). It is rare, but on the occasional ski trip, this might happen.
Sure it can be plugged, even on 110, just to compensate, but this is not always possible.

I will need real answers for these questions before I send my $$$$$ to Tesla...

 

[stopcrazypp]

I think this is a great question and still needs some significant expansion. The follow-up posts have been great, but fail to answer the whole picture. I really am curious about the real world effects of the extreme heat here.

The evening in the garage is certainly an issue, but let's not forget how cooling systems work. They are heat exchangers and typically transfer heat utilizing and air conditioning compressor or via some type of radiator to the surrounding environment. Both require an air exchange to occur with the outside the car environment. Thus keeping the Model S cool in my already 100 degree garage will increase the temperature of the garage, making the whole system work even harder? Also, what about when I am parked outside at work? I have covered parking, but it is still ~110 in the afternoon right now. How much energy will it take to cool/maintain the battery pack for 8-10 hours? Thanks!!

This question is asked a lot. The key point to remember is that the only source of extra heat from the car when it is unplugged, is from the cooling pump, electronics, and battery discharge losses. This will only be a fraction of the 2kWh per day that people are estimating the cooling system would use. Most of the work the cooling system is doing is maintaining the temperature differential of the battery vs outside (pump starts when enough heat soaks back in).

It shouldn't be an issue unless your garage has a heat buildup issue in the first place (from significant "unlimited" sources of heat, like the sun through a window or appliances like water heaters, washers or dryers). If that is a case, installing a ventilation fan might be a good idea with or without the EV.

Heat buildup will be more severe when charging (esp. if you have the 20kW charger), but that's more of a safety and efficiency issue (you are plugged in so you don't run the risk of draining your battery).

 

[stopcrazypp]

For those who need an answer before buying, you should contact your Tesla rep rather than waiting for someone to measure it (unofficially in conditions that may not match what you are considering).

 

[rsquared99]

For the AZ guys - I've had my Roadster in Surprise for just short of 3 years now. The S has better cooling characteristics than the Roadster, so hard to tell how this translates for your cars. I've left the Roadster at spring training ballparks for 4 to 5 hours, unplugged, and unshaded, and never had a problem with the cooling system using so much energy that I can't make the return trip. Longest of these routes is about a 130 mile round trip and I've used the A/C to and from the ball park (during the trip back, the usually A/C loses cabin cooling for a couple of 5 minute periods to help cool the batteries.)

I've plugged in the car to recharge at 1 to 2 am in my non-cooled, always hot garage nearly every night since I got the car. Never had the car not finish charging for the next day's use. I considered installing a vent fan, but thought I'd try it first and see how it handled the heat. Seems to do okay, so I never installed the fan. Even hot nights cool to what, mid-80's? The Roadster system seems to handle it. Since it's the last annual checkup under warranty, I'm driving the car to LA this month to get it checked out.

About 6 weeks after I got the Roadster, I took it out on one of the county black top highways on a 115 degree day to do some...er, tests for acceleration. After about 1/4 hour, the Roadster alarmed and told me PEM was being set to half power due to overheating. I slowly drove the car back to my garage (about a 20 minute drive) and plugged it in. I called Tesla, set the car so they could get a remote readout and left the car plugged in, where it showed an "waiting to charge" state. The car A/C ran for about 24 hours before the batteries got cool enough to charge, and then charged as normal. Tesla sent a ranger out to check the car the next day, anticipating the requirement to change out the PEM. Remote engineering analysis showed the car did what it should have done, so the original PEM was left in the car. Based on this incident, Tesla installed a software change to increase the high temperature limit in the PEM because they had not expected the car to see the surrounding ground temperature that AZ black top generates. I haven't had such an incident again.

It's just a car and I try to treat it like a car. I'm not babying it, nor running spreadsheets or doing battery pack data analysis because that's not interesting to me. I try to follow the instructions Tesla gave me, leaving the car plugged in when it's in the garage. I've done a couple of trips 3 - 5 days in length and charged the car in range mode during those times while I was on the road. My original standard ideal mileage charges were 192ish. I'm now getting 185ish after 22,500 miles and 3 years. Hope this helps someone. PM me if you have any direct questions I can try to answer.

 

[hcsharp]

Canucks have similar concerns, but at the other end of the range : how much energy will be consumed if I have to leave the car outside overnight, by -30C (-22F). It is rare, but on the occasional ski trip, this might happen.
Sure it can be plugged, even on 110, just to compensate, but this is not always possible.

I will need real answers for these questions before I send my $$$$$ to Tesla...

I had a few discussions with Tesla and Tesla owners here in VT before buying my Roadster. If you leave it outside in -30C without plugging in then the battery will get cold. It won't use up any of your battery keeping it warm. If you turn the car on (say, for example to drive it or pre-heat the cabin) then it will start using energy to heat the battery up. If you start driving right away then your car will run just fine except that you will have no regen until the battery warms up to about 3C. The reason for this is that it will shorten battery life significantly to charge it while the cells are at or below 0C.

So in short, if you park your car unplugged overnight at -30C, get in and start driving you won't have any regen until it warms up (a long time at that temp) and you will lose 10 - 20 ideal miles of energy right away heating the battery. At least that's what the Roadster does. I know from experience.

 

[Jason S]

Great info guys! Thanks so much for contributing to the thread on both the hot and cold sides.

 

[NuclearPowered]

I think NuclearPower most likely meant how long can the 'self-cooling' battery thermal system kick in, if parked without plugged in for within a 12 hour period? e.g. Leave the house in the morning with 90% SoC, then park at work for 8 hours without plugged in at 60% SoC. Here in AZ summer, even though the ambient temp is 110F, the asphalt can reach 120 to 130F. Will the BMS attempt to keep the battery temp at 85F in this case? It would probably take a huge amount of energy to cool the battery for 8 hours straight without plugged in.

Exactly what I meant.

I have measured blacktop temperatures with an infrared thermometer in the 140s which is not atypical in the summer. I'll try and get a thermometer under the car at work this week.

Sent from my DROID BIONIC using Tapatalk 2

 

[Doug_G]

Canucks have similar concerns, but at the other end of the range : how much energy will be consumed if I have to leave the car outside overnight, by -30C (-22F).

From what I've seen, none. I've cold-soaked my Roadster at -27C, and it did not draw any energy to warm the pack. The Roadster heats the pack if it is plugged in, but if not it lets the pack get cold.

When you start the car up with the battery that cold the regenerative braking is initially disabled. Also initially the batteries have higher internal resistance, so you have a little less power available and you lose range much faster than normal. But that inefficiency rapidly warms the pack above freezing, and within 10-15 minutes everything goes back to normal. When I tried it I figured I lost about 10 ideal km during the warm-up period.

Frankly it handles the cold way better than my ICE car does.

 

[surfingslovak]

Exactly what I meant.

I have measured blacktop temperatures with an infrared thermometer in the 140s which is not atypical in the summer. I'll try and get a thermometer under the car at work this week.

Sounds like a great project. You might want to peruse this thread on MNL. Luke, a Leaf owner, placed two wireless temp sensors on the outside wall of the battery enclosure, inside the underbody cover and recorded data throughout the day.

 

[kevincwelch]

My garage is poorly ventilated, so in the summer it gets up to about 100-110 degrees. In the winter, the garage would be about 10-20F, rarely down to 0. When in the garage, the Model S would be plugged in with a NEMA 14-50.

I am assuming that being parked and plugged in during these times the Model S would be OK in terms of battery management.

 

[dsm363]

My garage is poorly ventilated, so in the summer it gets up to about 100-110 degrees. In the winter, the garage would be about 10-20F, rarely down to 0. When in the garage, the Model S would be plugged in with a NEMA 14-50.

I am assuming that being parked and plugged in during these times the Model S would be OK in terms of battery management.

I think you're correct. Even if it wasn't plugged in, the Model S will use it's battery pack and manage the pack's temperature to within its safe range. Of course if it's in the garage, keep it plugged in as you said then there really isn't anything to worry about.

 

[VolkerP]

I agree, there is nothing to worry about Kevin's setup except overall energy usage and increased wear of the cars A/C system. I would add some ventilation to that garage if possible.

 

[kevincwelch]

I agree, there is nothing to worry about Kevin's setup except overall energy usage and increased wear of the cars A/C system. I would add some ventilation to that garage if possible.

Good to hear. The garage has two static vents on the roof, but adding a powered fan or two is probably a good idea.

 

[ElSupreme]

Good to hear. The garage has two static vents on the roof, but adding a powered fan or two is probably a good idea.

My garage is insulated from the outside, but the garage doors face south and are a dark brown color. So it gets quite hot in there in the summer, but only during the day. If my garage gets too warm I plan on putting a small exhaust blower, or fan on the side and set it on thermostat . But remember you will be charging mostly at night. How warm is your garage then? Mine is generally pretty cool.

 

[kevincwelch]

If my garage gets too warm I plan on putting a small exhaust blower, or fan on the side and set it on thermostat.

That's exactly what I was thinking of doing.

But remember you will be charging mostly at night. How warm is your garage then? Mine is generally pretty cool.

In the summer, I would say low 70s - upper 60s. At work, the garage is shaded and open, so I estimate it is in the low 80s.

 

[strider]

Will the BMS attempt to keep the battery temp at 85F in this case? It would probably take a huge amount of energy to cool the battery for 8 hours straight without plugged in.

Where did you hear 85F? As others stated, in the Roadster, the A/C will only kick on if the battery is at 40C (105F).

 

[dsm363]

That's exactly what I was thinking of doing.

In the summer, I would say low 70s - upper 60s. At work, the garage is shaded and open, so I estimate it is in the low 80s.

You're fine then. I really don't think you need to worry about extra ventilation for your Model S and the garage.