Lack of battery heater may cause very slow SuC charging speed

[mongo]

I don’t think so because the battery’s coolant loop can only absorb so much energy at once and too fast of a rate of temperature rise will create uneven heating within the pack.

Agree that pack has a max absorption rate/ temp delta limit.

However, the motor and pack are on two different loops so motor heat does not necessarily get transferred to the pack. The 3 motors should have less loss due to the use of PM motors (no rotor losses). No reason the heating load couldn't be shared between the two drive units.

 

[int32_t]

That's only a partial quote, full text is:

Depends on where you look in the manual. In the specs section of the current Model S manual, where I got that quote from, it says exactly what I wrote there. Time for a screenshot!

And regardless, I do want "better long-term performance" from my battery, since I plan on keeping this car as long as it'll drive.

 

[scaesare]

Model S/X dump huge quantities of heat from their motor and inverter into the coolant loop. This is not a problem.

Also managing this much heat with the coolant is not a unsolved problem either. Just imagine an ICE car that has ~300kW of output. If it's thermal efficiency is 15%, it's dumping 2MW of heat into the coolant loop at full output. Granted they can aim for 90C, but still a whopping 2MW!!!

On average, the amount of heat that the driveline transfers in to the battery is likely significantly less than the coolant loop heater on the S/X is capable of.

Tesla has stated that the S uses about 15KW of power at a steady state 55MPH on flat ground. I see about 20KW at 70MPH. (different models have differing draws, but the difference is slight).

The driveline is in the neighborhood of 90% efficient. That translates in to 1.5-2KW of heat to xfer to the pack. The coolant loop heater is capable of 6KW.

 

[Big Earl]

Model S/X dump huge quantities of heat from their motor and inverter into the coolant loop. This is not a problem.

Also managing this much heat with the coolant is not a unsolved problem either. Just imagine an ICE car that has ~300kW of output. If it's thermal efficiency is 15%, it's dumping 2MW of heat into the coolant loop at full output. Granted they can aim for 90C, but still a whopping 2MW!!!

Sure an ICE car can dump a ton of heat into the coolant loop. The difference is that it isn’t dumping it into a battery pack with a relatively small cooling circuit and battery cells that require pretty precise thermal control. The battery needs to heat evenly from the outside to the inside, so dumping 300 kW of energy into it at once is pretty much out of the question. The stock 6 kW battery heater on the Model S and X varies its power to maintain a specific temperature differential in the battery’s cooling circuit.

 

[Big Earl]

Agree that pack has a max absorption rate/ temp delta limit.

However, the motor and pack are on two different loops so motor heat does not necessarily get transferred to the pack. The 3 motors should have less loss due to the use of PM motors (no rotor losses). No reason the heating load couldn't be shared between the two drive units.

The electronics loop and the battery loop can be combined or separated depending on what the system wants to do with the excess heat. When separated, the heat from the motor goes into the radiator at the front of the car. When combined, the heat from the motor goes into the battery pack.

 

[mongo]

The electronics loop and the battery loop can be combined or separated depending on what the system wants to do with the excess heat. When separated, the heat from the motor goes into the radiator at the front of the car. When combined, the heat from the motor goes into the battery pack.

Right, so the electronic can moderate the amount of motor heat transferred to the pack by switching between series and parallel modes. In heating mode, the AWD 3 could use either or both motors to heat the pack up (to the max heat input the pack allows). Reducing the heat a single motor produces is also a benefit .

 

[AWDtsla]

The stock 6 kW battery heater on the Model S and X varies its power to maintain a specific temperature differential in the battery’s cooling circuit.

Absolutely incorrect. It is either on or off. Nor does it need variable power, given it's hugely undersized. 1+ hour heating times are common from 50F to max power temp.

 

[Big Earl]

Right, so the electronic can moderate the amount of motor heat transferred to the pack by switching between series and parallel modes. In heating mode, the AWD 3 could use either or both motors to heat the pack up (to the max heat input the pack allows). Reducing the heat a single motor produces is also a benefit .

I guess my point is that the battery can absorb less heat than a single motor can produce, so adding the heat of a second motor would just be wasted. You could dump the extra heat into the radiator, but that wouldn’t help accomplish the goal of heating the battery pack up more quickly.

 

[Big Earl]

Absolutely incorrect. It is either on or off. Nor does it need variable power, given it's hugely undersized. 1+ hour heating times are common from 50F to max power temp.

It might show the status as on or off on CANBUS, but it definitely modulates the power in certain conditions. @David99 has noted that the power use ramps up and down when heating and commented on it in another thread.

 

[AWDtsla]

On average, the amount of heat that the driveline transfers in to the battery is likely significantly less than the coolant loop heater on the S/X is capable of.

Tesla has stated that the S uses about 15KW of power at a steady state 55MPH on flat ground. I see about 20KW at 70MPH. (different models have differing draws, but the difference is slight).

The driveline is in the neighborhood of 90% efficient. That translates in to 1.5-2KW of heat to xfer to the pack. The coolant loop heater is capable of 6KW.

Ok let's take your 90% value, with ludicrous acceleration it's ~50kW heat. Of course, no way it's maintaining 90% at max power.

 

[AWDtsla]

It might show the status as on or off on CANBUS, but it definitely modulates the power in certain conditions. @David99 has noted that the power use ramps up and down when heating and commented on it in another thread.

No it doesn't, and it can't. The only thing that changes how much power it's putting out is current pack voltage.

 

[AWDtsla]

I guess my point is that the battery can absorb less heat than a single motor can produce, so adding the heat of a second motor would just be wasted. You could dump the extra heat into the radiator, but that wouldn’t help accomplish the goal of heating the battery pack up more quickly.

You're confusing energy and power.

 

[Big Earl]

No it doesn't, and it can't. The only thing that changes how much power it's putting out is current pack voltage.

Why can’t it modulate power? The cabin heater modulates its power. The 6 kW battery heater in my Fiat modulates its power. What’s different here that requires it to operate at either full power or nothing?

 

[AWDtsla]

And that sounds deadly serious.

At one point it said your warranty was void if you did that.

 

[AWDtsla]

Why can’t it modulate power? The cabin heater modulates its power. The 6 kW battery heater in my Fiat modulates its power. What’s different here that requires it to operate at either full power or nothing?

Cabin heater is a PTC element. It modules power automatically by decreasing resistance as it warms up, lowering power. I believe it also has 2 circuits. Coolant heater is a single resistive element on a relay. It consumes pack voltage at it's coil resistance, or it consumes nothing.

Not only can't it, but it doesn't even make a sense from an engineering perspective. It has such a slow temperature rise that cycling it just isn't a problem. It takes a massive amount of energy to heat 1200lbs of matter, which is also by the way completely uninsulated.

 

[scaesare]

Ok let's take your 90% value, with ludicrous acceleration it's ~50kW heat. Of course, no way it's maintaining 90% at max power.

Hence, my description starting with "on average".

The few-second bursts of that type of acceleration aren't going to budge the temp of a pack with 1200lbs of thermal mass much at all.

 

[scaesare]

I guess my point is that the battery can absorb less heat than a single motor can produce, so adding the heat of a second motor would just be wasted. You could dump the extra heat into the radiator, but that wouldn’t help accomplish the goal of heating the battery pack up more quickly.

On average I don't believe this to be true. The S/X packs happily absorb 6KW of resistance heating for long periods of time. On average, the drivetrain is likely providing 1-2KW of heating.

 

[AWDtsla]

Hence, my description starting with "on average".

The few-second bursts of that type of acceleration aren't going to budge the temp of a pack with 1200lbs of thermal mass much at all.

Actually by my calculation, it would take ~12 minutes at 50kW heat to get the pack let's say -20C to 50C. Or about half the average american commute.

 

[Big Earl]

Cabin heater is a PTC element. It modules power automatically by decreasing resistance as it warms up, lowering power. I believe it also has 2 circuits. Coolant heater is a single resistive element on a relay. It consumes pack voltage at it's coil resistance, or it consumes nothing.

Not only can't it, but it doesn't even make a sense from an engineering perspective. It has such a slow temperature rise that cycling it just isn't a problem. It takes a massive amount of energy to heat 1200lbs of matter, which is also by the way completely uninsulated.

The cabin heater is controlled by pulse width modulation. Its output is essentially infinitely variable.

 

[scaesare]

Actually by my calculation, it would take ~12 minutes at 50kW heat to get the pack let's say -20C to 50C. Or about half the average american commute.

However in order to get 50KW of waste drivetrain heat in to the pack, that means you'd have to be operating the drivetrain at 500KW. Or in other words, a Performance-model dual-motor car floored for 12 minutes.

If that were even possible, you'd be going MACH 6 by that point.