I’ve had the snowflake blue battery on cold mornings that went away during cabin heat while plugged in, so my battery has been heating on extremely cold days. I’m not sure how to translate, still had a lot of dots into kW since the model 3 gauge isn’t demarcated. More regen then when hoping into a cold car with no preheating where I get 0 regen.
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Model 3 Battery Heating?
- Thread starter ratsbew
- Start date
I’ve had the snowflake blue battery on cold mornings that went away during cabin heat while plugged in, so my battery has been heating on extremely cold days. I’m not sure how to translate, still had a lot of dots into kW since the model 3 gauge isn’t demarcated. More regen then when hoping into a cold car with no preheating where I get 0 regen.
eprosenx
Active Member
I tell my car (parked outside in Portland Oregon) to heat up most days while I shower before leaving the house.
While I have not gotten an icon that I think indicates a battery heater is running, it does seem like the car draws way too much energy from shore power (60a Wall Connector) to just be heating the cabin. I have posted charts from my Sense unit in a thread I created in Battery and Charging for the M3 that show this draw. If I have left the car warming up for quite a while I have full regen when I start driving.
Or it could be some days are just not as cold, so I am reading into it too much...
While I have not gotten an icon that I think indicates a battery heater is running, it does seem like the car draws way too much energy from shore power (60a Wall Connector) to just be heating the cabin. I have posted charts from my Sense unit in a thread I created in Battery and Charging for the M3 that show this draw. If I have left the car warming up for quite a while I have full regen when I start driving.
Or it could be some days are just not as cold, so I am reading into it too much...
I was not implying that the heating element used to warm the cabin also warms the battery, I just meant that the user activates battery heating by turning on cabin heating when the car is plugged in. You can find this information in the user manual under the heading "car status". What was on page 44 I think is now on page 52.
"Note: In cold weather, some of the stored energy in the Battery may not be available until the Battery warms up. When this happens, a portion of the Battery meter is blue and the driving distance value has asnow ake image next to it. If Model 3 is plugged in, you can heat your Battery using wall power by turning on climate control using the mobile app. When the Battery warms up, the blue portion on the meter and the snow ake image are no longer displayed."
I'm in Canada. I think the Model 3 does have a battery heater.
I plugged in my cold soaked model 3 (120v outlet) with scheduled charging set at 7pm. Battery had snowflake symbol. Plugged in cold soaked at 4pm - I could see the flashing tesla logo on the mobile connector. Checked the app and it was not charging, but range was going up and snowflake symbol went away after about 10 minutes.
Looked like the battery heating up to me. Snowflake symbol never showed up the few more times I checked the app. At 7pm car started charging on schedule as normal.
As said several times earlier, there is no dedicated heater, but when required the engine generates heat and acts as a batteryheater
... then it has a battery heater. Thanks tips.
We can go back and forth here about semantics but semantics is important to the technical aspect of heating the Model 3. To someone who doesn't care then yes the Model 3 has battery heater, but then if you don't care why ask the question? to be more technically accurate, the Model 3 has a system for heating the battery, but it is not a dedicated heater. It is a coolant loop, that when needed pumps waste heat from the motor to warm the battery.
Are you sure on the motor being the heat source?
The motor is designed for efficiency so the copper winding are sized to reduce resistance. That runs counter to the heating mode where you need resistance to generate heat (unless you go high frequency like an induction cook top). But say for a moment they could pump enough current though the windings to generate X kW of heat, how do they capture the heat? The stator is part of the drive unit casing so you are heating up the entire drive unit (and loosing heat via surface area, normally the drive unit wants to be cooled). The only connection to the glycol loop on that side is the oil/glycol heat exchanger. So once you have warmed up the entire mass of the drive unit, then you start warming the coolant, however you are still losing heat to the ambient environment. Very inefficient.
The inverter is designed for efficiency in the normal operating mode. However, you can also bias the switching devices to a partially conductive state. Instead of the windings with a fixed resistance, you can set the resistance to whatever you need for heating. A single off the shelf MOSFET can handle >1kW if you need the case cool. The amount of circuitry needed is minimal, the parts are already rated to handle fully current switching, and they are direct mounted on the glycol cooling plate so the heating efficiency and responsiveness is much improved.
Anyone know what the the stator resistance is?
At 4kW, if the coils are .01 Ohm, then it needs to loop 600 amps continuously on the motor side.
At 0.1 Ohm it would only be 200 Amps, but if they were that high of resistance then the motor would drop 100V at 1000A = 100kW waste heat (25% of a 400V pack).
Any idea what the stator resistance is? I gave couple number in the post above this one.
Back-EMF is a non factor for this, I agree.
Interesting appnote! With distributed sensing, it seems like they can still accomplish the goal. If that is even needed. With the proper heat sinking, the die will not get to the max temperature point, even with imbalance. Basically, all that needs to happen is to derate the max current by the max temperature delta on the part and the transfer function.
4 kW with 3 phases = 1.33kW each = 350V * 4 Amps. Using the NTD12N10 curve for reference, 4 Amps at 25C is 5 VGS, at 100 C that is 6 Amps, so even with a 75 K temp gradient, there is only a 50% power difference. That would not happen since the junction to case/ heat sink thermal impedance works both ways.
Otherwise, you are tying to the get heat from this to the pack somehow, and it is build to shed heat to the environment. Unless that passage is for flow though rotor cooling and they are using it with inductive heating?
From
hacer
Active Member
I don't have numbers, but I can guess at some bounds: The model 3's rear motor has a peak mechanical power output of 211 kW. Eyeballing https://i.imgur.com/YzwChjM.jpg I'd say there is about 14mV of back EMF per RPM (extrapolation of the zero torque RPM matching the max battery voltage). Peak power happens at ~ 5,800 RPM, so back-EMF is ~81V. So the motor current would be 211kW/81V = 2,605A. If we assume 75% efficiency at peak power that would mean 70.3 kW of resistive loss giving 0.01 Ohms. If the efficiency is 60% then it would be 140 kW of resistive loss giving 0.02 Ohms. So probably somewhere between those two. Personally my guess is closer to 0.02 Ohms since peak-power is not very efficient.
0.02 might be a bit much. If the motor was running 2,605 amps with 0.02 ohms of winding resistance, that would mean 135 kW of winding loss and a voltage (due to resistance) of 52.1V and the voltage to the motor would be 133V * 2,605 = 346 kW.
Isn't it the is case that peak power at high RPMS is not any less efficient since the current is low?
hacer
Active Member
Why do you think the battery heater is a puny 4kW? Even if it is since each phase is a sinusoid, you need to account for the peak power since this is what the transistors will have to carry, and it will be worse than that because of the PWM that is happening to drive the motor at the same time (one of the transistors in the bridge still need to switch hard on for the motors needs).
Heat from the motor is absorbed by the oil within drive unit, which is pumped and filtered and remains in the drive unit. That oil flows through an oil-coolant heat exchanger that transfers the heat from the oil to the battery coolant loop. From there, the heat is transferred to the battery pack.
hacer
Active Member
Yep, the inverter would be supplying 346 kW to the motor of which 60% would be mechanical power (211 kW) and 40% resistive losses. The inverter will have no trouble driving 133V to the motor from the > 350V battery.
If you look at the dyno curve, the peak power is near 5,800 RPM which is a fairly low vehicle speed. Tesla just announced a higher top-speed of 162? MPH because they think it's OK for the motor to spin at 19,000 RPM. So that would mean peak power happens at 49 MPH. That is the RPM where you can get peak power, and it is happening near peak current (just as the peak current limit is removed on the dyno curve). So it is NOT happening when "current is low", instead it is at max current and about 1/3 of the voltage available.