Lack of battery heater may cause very slow SuC charging speed

[mongo]

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.

Ah!
Yah. If one motor can produce as much heat as the pack can absorb, there is no advantage to also generating heat from the second unit. Some system level reasons exist to share the heat load between the two 50-50.

If one motor doesn't max out the pack heating, then two motor heaters can increase pack warm up rate.

6kW heat would normally correspond to 60-120kW motor input power (90-95% efficency). That's 80.5 to 161 HP. If the motor is not rated for continuous output at those powers, it likely can't handle the heat production. From EPA docs, the RWD motor is listed as 192 kW (guessing that is peak)

 

[mongo]

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.

Assuming an efficient inverter waveform. Detuning the drive can produce addition heat without additional mechanical work. That is how the 3 eliminated the battery heater.

 

[AWDtsla]

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

PWM controlling a PTC element is stupid. You can see my rant about that in another thread.

 

[AWDtsla]

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.

No, less than 250mph likely.

 

[scaesare]

Assuming an efficient inverter waveform. Detuning the drive can produce addition heat without additional mechanical work. That is how the 3 eliminated the battery heater.

Agreed, but my responses to @AWDtsla were predicated on his post several rounds up where he was speaking in the context of what the S/X can do:

Model S/X dump huge quantities of heat from their motor and inverter into the coolant loop.

 

[scaesare]

No, less than 250mph likely.

I guess I should have added the "Hyperbole for illustrative purposes only" footnote....

 

[mongo]

PWM controlling a PTC element is stupid. You can see my rant about that in another thread.

Having a PTC element provide a layer of safety in the event of a SW or HW failure. PWM allows the power output to be varied.
Other advantages

 

[scaesare]

It certainly is possible to PWM modulate a PTC heater. Here's the service manual description of the cabin heater:

The PTC heater is a high voltage heating device using ceramic heating stones as resistors. The electrical resistance of the stones increases as their temperature rises. This provides a safety mechanism to prevent overheating. The heater consists of a heating matrix including the heating stones, a conductive plate, and aluminum fins. The controller is mounted in a housing connected to the matrix and supplies the high voltage power to the heating stones. The controller uses six sets of Insulated Gate Bipolar Transistor (IGBT) circuits to switch the DC power, and a pulse width modulation circuit that provides variable power to regulate the amount of heat generated.

While the same could be done for the pack heater, it appears the goal is to simply get it up to a minimum temp as quickly as possible. The description doesn't mention PWM operation but rather on/off, thus I suspect it's simply on for the duration necessary to meet the minimum pack temp target:

The coolant heater is located under the hood, on the right-hand side near the bulkhead. The purpose of the coolant heater is to heat the battery coolant to a minimum temperature for Battery charging. The coolant heater is controlled by the DCDC converter controller, which switches the heater on or off as necessary.

The coolant heater has a sensor that monitors its internal temperature and reports this information to the THC to prevent overheating.

High voltage is supplied directly from the DCDC converter. The coolant heater HV fuse is also located internally to the DCDC converter.

 

[AWDtsla]

Having a PTC element provide a layer of safety in the event of a SW or HW failure. PWM allows the power output to be varied.
Other advantages

Overengineered. Picking a elbow temperature for the element that is appropriate for cabin heating would have been much better than the PWM control algorithm Tesla never got right.

 

[scaesare]

Overengineered. Picking a elbow temperature for the element that is appropriate for cabin heating would have been much better than the PWM control algorithm Tesla never got right.

I disagree. PWM control of the cabin heater allows a more comfortable steady-state operation.

 

[mongo]

I disagree. PWM control of the cabin heater allows a more comfortable steady-state operation.

I agree with your disagree. That is akin to sizing an ICE heater core to the max BTU output needed and then taking away the temperature knob and replacing it with an on off switch.

 

[AWDtsla]

I disagree. PWM control of the cabin heater allows a more comfortable steady-state operation.

I agree with your disagree. That is akin to sizing an ICE heater core to the max BTU output needed and then taking away the temperature knob and replacing it with an on off switch.

Cabin heaters in ICE cars works perfectly well. Heater core stays at regulated coolant temperature, and air temperature is controlled through air mix control via a simple damper.

In the case of a PTC element, a combination of total airflow and airflow mix would easily regulate cabin temperature, and it would actually turn on instantly, versus what it does now, which is just dumb.

 

[scaesare]

To add to the confusion discussion... I found this block diagram in the service manual Theory of Operation... note the "1.5-4KW" description for the coolant heater:

Interesting... 6KW is the accepted value around here it seems...

 

[scaesare]

Cabin heaters in ICE cars works perfectly well. Heater core stays at regulated coolant temperature, and air temperature is controlled through air mix control via a simple damper.

In the case of a PTC element, a combination of total airflow and airflow mix would easily regulate cabin temperature, and it would actually turn on instantly, versus what it does now, which is just dumb.

What makes you think it can't do PWM=100% when you turn it on initially?

Also, you'd then have an either/or situation that leads either to poor performance or wasted energy:

Either you pick the PTC set point thus that the total heating available is what one expects on average (rather than in MAX situations), or, you have a set point higher than the average expected, and dilute that heat output with cool air... thus wasting energy on the heating element.

 

[AWDtsla]

What makes you think it can't do PWM=100% when you turn it on initially?

It doesn't. It should be able to.

Also, you'd then have an either/or situation that leads either to poor performance or wasted energy:

Either you pick the PTC set point thus that the total heating available is what one expects on average (rather than in MAX situations), or, you have a set point higher than the average expected, and dilute that heat output with cool air... thus wasting energy on the heating element.

No, the heater core is firmly inside the cabin. It's 100% efficient in that regard. Air mix would be with recirculated air.

 

[AWDtsla]

Interesting... 6KW is the accepted value around here it seems...

5.5kW @ 450VDC. It's stamped directly on the part.

 

[mongo]

What makes you think it can't do PWM=100% when you turn it on initially?

Also, you'd then have an either/or situation that leads either to poor performance or wasted energy:

Either you pick the PTC set point thus that the total heating available is what one expects on average (rather than in MAX situations), or, you have a set point higher than the average expected, and dilute that heat output with cool air... thus wasting energy on the heating element.

AWDtsla does have a bit of a point that the PTC will only draw the power needed to maintain its design temperature. So diverting airflow would result in reduced power.
However, it would also result in taking the ambient air and packaging up to the PTC design temperature during low flows....
And it requires a hot/cold air door (which may be needed anyway to adjust air conditioning) vs electronic control of a heater in the air path .

 

[AWDtsla]

To add to the confusion discussion... I found this block diagram in the service manual Theory of Operation... note the "1.5-4KW" description for the coolant heater

BTW, try watching power draw while letting the car maintain max battery power temp. The perfect opportunity for PWM control. Nope. Cycles on and off, with quite a high period.

 

[mongo]

View attachment 276340
5.5kW @ 450VDC. It's stamped directly on the part.

Assuming not PTC, it's 4,373 kW at 400V. 3,347kW @ 350V.
Edit: is that a cabin or pack heater?

 

[AWDtsla]

Assuming not PTC, it's 4,373 kW at 400V. 3,347kW @ 350V.
Edit: is that a cabin or pack heater?

Coolant heater.