Winter charge failure: don't use scheduled charge when very cold.

[SSedan]

Mine charges below 5F, even below zero on a 30amp outlet.
Yes if cold I have to schedule a little earlier so it has time to warm the pack before charging. I did have this sort of bite me once when I needed a range charge in the morning and when I got up told it to do the last 10% and it didn't because it took too long to warm the pack before I left but chalk that up to owner error, I learned from it.

Here near Green Bay we have had a bunch of -10f or a little colder morning already this winter and I haven't had any trouble parked outside and I leave early, and have a short commute and being middleaged with kids I am home right after work so it is often parked for 6-7 hours before the scheduled charging starts, and then only charges for a 2-3 hours, only that long because the battery warmup at lunch or when I leave work has consumed a handful of miles.

 

[AWDtsla]

Something is wrong here. The 6kW battery heater should easily be able to overcome a temperature down to 0F or below.

I wouldn't be so confident. There is absolutely no insulation under the pack. The only thing holding the heat in is the air-gap between the cells to the bottom aluminum skin.

It takes me 45-60+ minutes to heat the battery in my garage to 50C. That ends up being something like 0.75C per hour at 12C ambient with no wind. -18C outdoors sounds like a real problem, even though you only need to be slightly over 0C to accept charge.

Tesla should have had 50kW of pack heating available, not 5kW.

 

[AWDtsla]

I wish disagreeing would make my battery heat faster. Maybe we can concentrate the hate directly into my pack.

 

[thomasmb]

I had a similar issue last year. During the winter (in Norway) I experienced that the car would only charge if I started charging immediately after I drove it (so, when the battery was warm). Also had issues of limited regen that wouldn't completely go away even after an hour of driving and starting the trip with a battery that had just finished charging. Initial attempts to talk to Tesla support were brushed of more or less telling me I didn't know how it was supposed to work because it was complicated and that it probably worked as designed.

This became a real issue one day when I went to visit family for a weekend. Instead of using my 11kW charger at home, I only had 3kW available here and the car didn't charge at all. I visited a Service Center the next day or so because I was scheduled to test drive a Model X for the rest of the weekend. I just barely made it with the range I had.

The issue turned out to be one of the cooling pumps, which had leaked fluid and corroded, which had stopped the pump. Also some of the fluid had leaked onto wiring elsewhere corroding that. They had to replace the pump and the wiring harness under the hood. About a week later Tesla had fixed it, and I never had the issue again.

 

[AWDtsla]

I had a similar issue last year. During the winter (in Norway) I experienced that the car would only charge if I started charging immediately after I drove it (so, when the battery was warm). Also had issues of limited regen that wouldn't completely go away even after an hour of driving and starting the trip with a battery that had just finished charging. Initial attempts to talk to Tesla support were brushed of more or less telling me I didn't know how it was supposed to work because it was complicated and that it probably worked as designed.

LOL .That's what happens when everyone drinks the koolaid. Infinite circular loop between the cult and the company.

"Everything is fine, nothing to see here"
"You're holding it wrong"
"Nobody will ever need more than 5kW of heat"

 

[scottm]

The guy who invents a diesel fueled auxiliary heater that fits into the deleted frunk bin space, that splices into coolant system may do very well selling to EVs in cold climate areas.. Fire that little furnace up and keep battery snuggly warm and spill some heat into the interior heat exchanger to finally warm my toesies.

 

[jeffro01]

The guy who invents a diesel fueled auxiliary heater that fits into the deleted frunk bin space, that splices into coolant system may do very well selling to EVs in cold climate areas.. Fire that little furnace up and keep battery snuggly warm and spill some heat into the interior heat exchanger to finally warm my toesies.

To me that completely defeats the purpose of having an EV... The moment I have to burn a fossil fuel, might as well go buy a BMW...

Jeff

 

[scottm]

I'd only use on very cold days (<20C) or if very much needed the range for long trips. Not a city use, every time kind of thing. You don't have these conditions in SF. This would be a cold-climate thing only.

It would sip so little as compared to having to propel a car on hydrocarbons...

..view this solution as a hybrid of sorts.

 

[mongo]

I wouldn't be so confident. There is absolutely no insulation under the pack. The only thing holding the heat in is the air-gap between the cells to the bottom aluminum skin.

It takes me 45-60+ minutes to heat the battery in my garage to 50C. That ends up being something like 0.75C per hour at 12C ambient with no wind. -18C outdoors sounds like a real problem, even though you only need to be slightly over 0C to accept charge.

Tesla should have had 50kW of pack heating available, not 5kW.

There is also the plastic of the battery modules. Not much, but it helps, there are also air gaps between the cells and the bus bar plates. Assuming a quarter inch of acrylic and no air gaps/ boundary conditions, the bottom of a 5'x8' pack would lose 11.5 kBTU/ hr with a 50 degree F differential (environment of 5F(-15C) and battery at 55F (12C)) that equates to ~3.4 kW energy loss from that side. So a 6 kW heater would counter many weather situations, esp if the cabin heater is aiding the top side of the pack (10-12kW total).

You may be getting disagrees due the 50kW heater comment. That would require a 200+ amp circuit at 240 V and put out 170kBTU. That's enough energy to transform 7.5 pounds(3.4kg) of ice (0C) to steam every minute.

 

[AWDtsla]

There is also the plastic of the battery modules. Not much, but it helps, there are also air gaps between the cells and the bus bar plates. Assuming a quarter inch of acrylic and no air gaps/ boundary conditions, the bottom of a 5'x8' pack would lose 11.5 kBTU/ hr with a 50 degree F differential (environment of 5F(-15C) and battery at 55F (12C)) that equates to ~3.4 kW energy loss from that side. So a 6 kW heater would counter many weather situations, esp if the cabin heater is aiding the top side of the pack (10-12kW total).

Not taking into account wind. Still, at 11.5kBTU/hr you're closing in on 100% duty cycle on the heater, depending on SoC. Also the heater is 5.5kW @ 450V. Your pack is not sending it 450V!

Look, the bottom of the pack was designed as a tertiary cooling mechanism. Nice if it's summer. I'm frankly surprised there has been no OEM or third party insulation system. Some thinsulate like material to cover the bottom of the pack. I'd buy it.

You may be getting disagrees due the 50kW heater comment. That would require a 200+ amp circuit at 240 V and put out 170kBTU. That's enough energy to transform 7.5 pounds(3.4kg) of ice (0C) to steam every minute.

Fine, I'll up it 70kW. Under full throttle the whole system is dumping more than that anyway. There's 100kW+ I^2R losses just in the pack at 1500A, forget about motor and inverter.

Also, that much power is not a problem when either on a supercharger, or in regen, or when sufficient battery energy is available. Lower total energy expended for pack heating before start of charge or start of drive.

 

[mongo]

Not taking into account wind. Still, at 11.5kBTU/hr you're closing in on 100% duty cycle on the heater, depending on SoC. Also the heater is 5.5kW @ 450V. Your pack is not sending it 450V!

Actually, the lack of an air boundary condition is equivilent to a high wind (constant exterior temperature). I assume heater is PTC, so it could hit near peak power at a lower voltage without burning up at the high end. Versus a constant resistance load.

Look, the bottom of the pack was designed as a tertiary cooling mechanism. Nice if it's summer. I'm frankly surprised there has been no OEM or third party insulation system. Some thinsulate like material to cover the bottom of the pack. I'd buy it.

Agreed, but it would be a logistical nightmare to have all northern dwellers going to the SvC twice a year to have the heat shield added/ removed. A double layer bottom that can be filled or drained of coolant might work instead.

Fine, I'll up it 70kW. Under full throttle the whole system is dumping more than that anyway. There's 100kW+ I^2R losses just in the pack at 1500A, forget about motor and inverter.

??? Up it? Am I missing something?
That is an interesting idea, but to balance the 100kW dissipation of the 44 mOhm battery resistance you would need a 222 mOhm external load dissipating 500kW (assuming 400V pack at start).
The 3 forgoes a discrete battery heater, I wonder if part of that strategy is use of the DU to cause cell self heating. Sort of strange to have SOC drop while connected to a charger, but if it speeds the process up it's good overal.

Also, that much power is not a problem when either on a supercharger, or in regen, or when sufficient battery energy is available. Lower total energy expended for pack heating before start of charge or start of drive.

Sure, the supercharger can pump out 120kW or so. But there is a systems level problem I was alluding to with the ice to steam comment: you can only move so much heat at once.

Say we run a 20 degree F temp delta on the coolant (40% gycol), and assume the loop is 1 inch with a length of 48 feet. 1 GPM is 10kBTU or about 3 kW. So at 20kW we'd be at 60kBTU or 6 GPM. That's 3.3 ft/s and a head pressure of 5.5ft. Fairly reasonable.
Now bump that to 40kW, 13.6 GPM is 7.4 ft/s (faster than recommended) and head pressure goes up by 4× or so to 22ft. Go to 80kW and you are 4x again 88ft of head pressure.

And all this assumes you can transfer the heat out of the fluid into the cells that quickly. Running a refrigerant with the phase change point adjusted to the desired cell temp might work, puts the heat where needed without cooking the warm cells. But at the power levels you are talking, that is basically a house size heat pump.

 

[AWDtsla]

??? Up it? Am I missing something?

Doubling down.

That is an interesting idea, but to balance the 100kW dissipation of the 44 mOhm battery resistance you would need a 222 mOhm external load dissipating 500kW (assuming 400V pack at start).

The 3 forgoes a discrete battery heater, I wonder if part of that strategy is use of the DU to cause cell self heating. Sort of strange to have SOC drop while connected to a charger, but if it speeds the process up it's good overal.

Sure, the supercharger can pump out 120kW or so. But there is a systems level problem I was alluding to with the ice to steam comment: you can only move so much heat at once.

Say we run a 20 degree F temp delta on the coolant (40% gycol), and assume the loop is 1 inch with a length of 48 feet. 1 GPM is 10kBTU or about 3 kW. So at 20kW we'd be at 60kBTU or 6 GPM. That's 3.3 ft/s and a head pressure of 5.5ft. Fairly reasonable.
Now bump that to 40kW, 13.6 GPM is 7.4 ft/s (faster than recommended) and head pressure goes up by 4× or so to 22ft. Go to 80kW and you are 4x again 88ft of head pressure.

And all this assumes you can transfer the heat out of the fluid into the cells that quickly. Running a refrigerant with the phase change point adjusted to the desired cell temp might work, puts the heat where needed without cooking the warm cells. But at the power levels you are talking, that is basically a house size heat pump.

My point about I^2R losses, is that the car dumps out this much heat into the coolant loop now. Imagine putting out 500kW of power to the motor, if efficiency of the system falls to 70%, that's 125W of heat alone. You can calculate some of this at the pack level. If you drop 100V under 1500A, that's 150kW of head being lost inside the pack itself under acceleration. So this is a sanity check on your math. I don't buy that 5kW is near any thermodynamic limit.

Furthermore let's use a real world example, a standard electric tankless heater you might pick up at home depot. 36kW of draw, max flow of 3.8 GPM with 40F input and 105F output. Of course, we wouldn't mind going from -20F to 122F (max power temp). Frankly, the coolant heater should work on the same principle. Not constant power draw, but constant output temperature.

Scroll down for handy lookup table for flow rates: Stiebel Eltron Tempra 36 Plus

 

[AWDtsla]

@mongo BTW, no reason to think the pack heater is PTC. Always seems to behave like a resistive heater, current draw only depends on pack voltage.

 

[mongo]

Doubling down.



My point about I^2R losses, is that the car dumps out this much heat into the coolant loop now. Imagine putting out 500kW of power to the motor, if efficiency of the system falls to 70%, that's 125W of heat alone. You can calculate some of this at the pack level. If you drop 100V under 1500A, that's 150kW of head being lost inside the pack itself under acceleration. So this is a sanity check on your math. I don't buy that 5kW is near any thermodynamic limit.

Furthermore let's use a real world example, a standard electric tankless heater you might pick up at home depot. 36kW of draw, max flow of 3.8 GPM with 40F input and 105F output. Of course, we wouldn't mind going from -20F to 122F (max power temp). Frankly, the coolant heater should work on the same principle. Not constant power draw, but constant output temperature.

Scroll down for handy lookup table for flow rates: Stiebel Eltron Tempra 36 Plus

I was looking at the on demand water heaters for reference power consumption/ flow when I wrote my first post on the topic (checking if any of them were 50kW).

The WH comparison only works if you can drop the coolant back down to 40F before it gets back to the heater. Otherwise, you quickly hit the boiling point. Similarly, the peak acceleration power dissipation comparison is flawed due to that heat being fairly uniformly distributed through the mass of all the cells. The pack then has to reject the excess heat into the cooling loop. Watch Bjorn's Autobon speed run to see how quickly the cooling system is overloaded. Heating the pack works in reverse, all the heat is applied to the outside of the cell and needs to work its way into each cell core before it is safe to charge. While also not violating any delta T rates for the pack/module/cell.

I could be off on the pack PTC assumption, seems wasteful to only have it hit rated output at max battery voltage given its thermal time constant and ability to PWM/ cycle it.

 

[Snowstorm]

I park mine in an unheated, uninsulated garage in Toronto and never had an issue charging it. 240v 30amp, 6kw circuit. Even for days colder as cold as -20C. If it is sitting in the cold for the entire night, it would charge very slowly or not at all for like 10-15 minute in the morning before speeding back up to normal 6kw charging as the pack warms up a bit. Range mode is off.

 

[NeverFollow]

The guy who invents a diesel fueled auxiliary heater that fits into the deleted frunk bin space,
that splices into coolant system may do very well selling to EVs in cold climate areas..
Fire that little furnace up and keep battery snuggly warm and spill some heat into the interior heat exchanger
to finally warm my toesies.

To me that completely defeats the purpose of having an EV...
The moment I have to burn a fossil fuel, might as well go buy a BMW...

I doubt that the electricity you are getting in winter is produced from solar panels,
and might in fact been produced by coal or gas. So in this case the result would be very similar.

Do you heat your home using electricity or instead do you use fuel or natural gas?
I think this could be also a similar debate.

 

[mknox]

The guy who invents a diesel fueled auxiliary heater that fits into the deleted frunk bin space, that splices into coolant system may do very well selling to EVs in cold climate areas.. Fire that little furnace up and keep battery snuggly warm and spill some heat into the interior heat exchanger to finally warm my toesies.

The Model S / X cabin heat is not on a coolant loop. It is an electric resistance heater to air device. The coolant loop runs through the battery, motor, inverter, on-board charger(s) and front radiator with various pumps and valves to direct flow.

 

[scottm]

The Model S / X cabin heat is not on a coolant loop. It is an electric resistance heater to air device. The coolant loop runs through the battery, motor, inverter, on-board charger(s) and front radiator with various pumps and valves to direct flow.

Thanks, I had forgotten that coolant loop is drivetrain only. Interior electric only.

Any aux heater in Tesla S that is meant to heat batteries and warm toes would have to splice into the coolant loop, and also have its own heat exchanger core in-cabin - or maybe simpler, offer heated air piped into the fresh-air intake ductwork at the cowl...

The more important use case would be coolant loop for battery heating. Hot air into cabin is only a bonus byproduct.

This is too funny, just last winter my brother spliced in an electric powered coolant heater into his diesel VW Beetle to pre-warm the block (for easier starting and more rapid heat up for cabin comfort)... and here I am talking about splicing in a diesel powered coolant heater to warm up the battery of an electric car!

 

[scottm]

I'm frankly surprised there has been no OEM or third party insulation system. Some thinsulate like material to cover the bottom of the pack. I'd buy it.

I have seriously been thinking of doing some kind of spray-on application of insulation ... that could be scraped off in the spring, and re-applied next fall. This is the underside of a car, covering no serviceable area.. and I don't care if it looks ugly while on, or when scraped off. It's the underside of car with the road staring back at it. I don't care if road debris kicks up and knocks a chunk off... hoist the car and spray in a little more to fill that area. I don't care what the aerodynamic effect (drag) reduction this causes in the winter... I don't do road tripping in the winter very much and speeds under 90km have very little drag no matter what.

It just has to be reasonably good adhesive... water proof / closed cell so as not to absorb water.. reasonably dense / sturdy so it would not be scraped off too easily (driving over a snow / slush ruts on road).. non-flammable and have some meaningful amount of insulative R-value per inch - I'd go up to an inch thick coating.

Anybody got a line on hardening spray-on aerogel?

 

[jsmay311]

The Model S / X cabin heat is not on a coolant loop. It is an electric resistance heater to air device.

Really? So do you get hot air basically instantaneously when turning on the heat in an S/X like you do with a space heater? That's awesome if true.

I had thought that pretty much every EV resistive cabin heater was in a coolant loop for safety reasons (and/or maybe other reasons too, like smell, or noise, or packaging difficulties of having a high-powered direct-to-air heater in a car, etc.).