Todd Burch
14-Year Member
Yeah that "Power" graphic shows kW going in to the battery from regen, kW going out of the battery to power the HVAC, and kW used by the motor...nothing referring to heat flow.
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JRP3
Hyperactive Member
I don't think it would be all that complex to implement, if there was enough heat to make it worthwhile. You've already got coolant going from the motor to the battery pack, a simple temperature controlled diverter valve could send coolant to the heater core when the pack is warm enough, or to the radiator if it's too warm and heat isn't needed.
A lot of times things are designed with independent subsystems. Trying to unify/coordinate maximum efficiency of cabin heating & cooling with battery heating & cooling is an extra layer of engineering.
Seems like a good idea in principle, but I could imagine they have limits on how much time they can spend making everything "perfect".
Maybe they did it? I don't know. Hopefully if they didn't do it, they did a cost/benefits and decided it wasn't worth it rather than just not having time.
You have to think they really have tried hard to find every possible angle that could help with range though.
Seems like a good idea in principle, but I could imagine they have limits on how much time they can spend making everything "perfect".
Maybe they did it? I don't know. Hopefully if they didn't do it, they did a cost/benefits and decided it wasn't worth it rather than just not having time.
You have to think they really have tried hard to find every possible angle that could help with range though.
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JRP3
Hyperactive Member
I'm looking at something similar in my conversion. My batteries, motor and inverter are all in the engine compartment and I'm thinking of sealing off the compartment and using blowers to vent it in the summer, turn them off when it's cooler to warm the pack, and possibly blow some heat into the cabin.
I had a fairly detailed discussion with an engineer about this topic. As I hinted before, there are a few coolant loops, and they are allowed to mix with some automated valves. A computer decides what's most efficient. While they did consider the option to dump motor heat into the cabin, for whatever reason they ultimately decided against it.
My guess is that if it's cold enough outside that you want cabin heat, that motor heat is better used keeping the batteries at temperature.
My guess is that if it's cold enough outside that you want cabin heat, that motor heat is better used keeping the batteries at temperature.
That sound totally plausible to me. If it is that cold that you want to heat the cabin, the motor+PEM heat goes to the pack. There's just not enough heat left to dump into the cabin. Avoiding to couple two independent coolant systems might be a good decision in regard to engineering complexity, reliability, bugs in controller logic, maintenance, troubleshooting leaks, and so on.
Obviously, engine heat to heat the cabin is very tried and true with ICE's. It's a good idea and all the designers at Tesla undoubtably have long backgrounds with ICE's so I'm sure they've looked into it. I'd guess if Tesla isn't doing it then the payoff just doesn't make it worth it. Maybe not enough heat generated to make it work or not enough in all cases such that they'd have to augment it with normal heating anyway. I could easily see for reasons of cost or complication that it wasn't worth pursuing.
I'd suspect that there isn't enough heat generated. The battery pack produces a lot of heat, but from what I've seen the Roadster tries to keep its pack between 20C and 40C. The coolant is tepid, not hot. You run that through a heat exchanger and you're not exactly going to get hot air. Especially when you consider that the pack will naturally be cooler in cold weather.
Yes, they can use the cabin AC compressor to help actively cool the battery and motor loops. But there's no heat exchanger (heater core) to blow drivetrain heat into the cabin, at least how I understood it.
ToddRLockwood
Active Member
Since this thread is a year old, and the Model S is now being delivered, perhaps there is more information available. My question is: If a Model S is parked outside in sub-freezing temps without being plugged in, will the car attempt to keep the battery warm by activating the motor/battery coolant loop? Does that loop (apparently separate from the interior heating/cooling system) have its own heating element to warm the battery if necessary?
Imagine that the car is parked at a ski area for the day, and it's 15deg F outside. Wouldn't the car consume a fair amount of power just sitting there?
Imagine that the car is parked at a ski area for the day, and it's 15deg F outside. Wouldn't the car consume a fair amount of power just sitting there?
Todd Burch
14-Year Member
Disclaimer: I haven't heard Tesla's goal temperature range for the Model S battery pack.
As I recall the cold limit isn't very high. Warm temperatures are worse than cold. As a result, not too much heating is required to keep the temp in the desired range. I believe the battery temperature management loop uses uses a heat pump, with resistive heating if the heat pump cannot satisfy the desired temperatures--but I may be wrong about that. Resistive heating is less efficient than a heat pump, so it's only used as a backup.
I would estimate that, parked in 15 deg F temperatures, you still get several weeks of parking before the battery gets too low, as the heating required to maintain the desired range is relatively low. (Maybe there isn't active heating until even lower temperatures are reached?) If Tesla's bottom limit is 32 deg F for the pack, for instance, the loop only needs to heat the pack to 32 degF.
Take this all with a grain of salt though--it's just a guesstimate.
As I recall the cold limit isn't very high. Warm temperatures are worse than cold. As a result, not too much heating is required to keep the temp in the desired range. I believe the battery temperature management loop uses uses a heat pump, with resistive heating if the heat pump cannot satisfy the desired temperatures--but I may be wrong about that. Resistive heating is less efficient than a heat pump, so it's only used as a backup.
I would estimate that, parked in 15 deg F temperatures, you still get several weeks of parking before the battery gets too low, as the heating required to maintain the desired range is relatively low. (Maybe there isn't active heating until even lower temperatures are reached?) If Tesla's bottom limit is 32 deg F for the pack, for instance, the loop only needs to heat the pack to 32 degF.
Take this all with a grain of salt though--it's just a guesstimate.
Nevermind 15deg F, I would like to know how it would handle being left in -20deg F for 4-5 days at a time. Would I have to start the generator to charge it every other day...?
In my experience, the Roadster makes no attempt to heat the battery while parked, unless it is plugged in (and not in Storage Mode). Maybe there's a point where it does, but I've not seen it happen.
The thing about using resistive heaters to warm up the battery is the battery's own internal losses actually help. At low temperatures the pack's internal resistance is higher than normal, and that inefficiency generates heat. So simply driving will heat up the pack - you might not need an actual heater at all. The Roadster's resistive heater might only be used when plugged in, for all I know.
When I started up my Roadster after a cold soak at -27C it had a little less power than normal, regen was disabled, and it consumed range a lot faster than normal - but for a brief period of time. After 10-15 minutes the pack warmed itself up to normal operating range and everything went back to normal. My ICE car does not handle the cold nearly as well!
What I'm hoping is that the Model S cooling system is smart enough to use the battery pack as a heat sink in cold weather. The pack will be warmer than the air temperature, so you connect the cabin heat pump to it instead of to the radiator. As long as the pack is generating waste heat you might as well pump it into the cabin instead of outside.
The thing about using resistive heaters to warm up the battery is the battery's own internal losses actually help. At low temperatures the pack's internal resistance is higher than normal, and that inefficiency generates heat. So simply driving will heat up the pack - you might not need an actual heater at all. The Roadster's resistive heater might only be used when plugged in, for all I know.
When I started up my Roadster after a cold soak at -27C it had a little less power than normal, regen was disabled, and it consumed range a lot faster than normal - but for a brief period of time. After 10-15 minutes the pack warmed itself up to normal operating range and everything went back to normal. My ICE car does not handle the cold nearly as well!
What I'm hoping is that the Model S cooling system is smart enough to use the battery pack as a heat sink in cold weather. The pack will be warmer than the air temperature, so you connect the cabin heat pump to it instead of to the radiator. As long as the pack is generating waste heat you might as well pump it into the cabin instead of outside.
JRP3
Hyperactive Member
Cold is only a real problem when trying to charge, or regen, a lithium battery, so I would not expect any pack heating happening when parked. It also explains the lack of regen for a cold pack. When plugged in to charge I would expect the car to delay actual charging until the pack heats up enough, probably around 20F or so, maybe lower with the newer cells.
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