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Tesla Model 3/Y Thermal Limits on the Racetrack

So, you’re considering taking your Model 3 or Model Y to the racetrack. A common concern is how long the vehicle can drive without limiting, derating, or power loss. Of course, this answer is not black and white as it depends on a number of factors, such as the amount of modifications that have been done to the vehicle, experience level of the driver, the design of the track, and more.

However, after years of testing, we've found a modified Tesla Model 3 or Model Y Performance on wide, grippy tires, can hit the built in limits in as little as 7 or 8 minutes. This can be observed on the touchscreen’s UI in Track Mode, as the image of the high voltage battery will change from Green, to Yellow, to Orange, and finally to Red. You will notice considerable power loss in the orange and red phases, as the vehicle is eventually limited to very low power levels.

At first, it was assumed that either the motors or the battery were hitting a temperature limit of some sort. However, after numerous testing, we believe that the aforementioned limit was not based on temperatures, but rather the vehicle limiting the total discharge over a certain period of time. Further testing has found that it seems to be calculated using a trailing average. Basically, the BMS (Battery Management System) only allows a certain amount of energy discharged over a certain period of time. While the full recovery period seems relatively quick, somewhere in the 20 to 30 minute range, this has made driving the vehicle at pace for an extended session (20 minutes or so) very difficult, and impossible to do without power loss. Of course, you can drive a few cool-down laps to reduce your trailing average, but the benefit is limited and the limit is reached again fairly quickly. This is what I have come to refer to as “Battery Current Limiting”, and it is the most common issue facing drivers.

That all being said, there are also thermal limits in place that are unrelated to discharge rates. However, these appear to be a secondary issue, at least on the Dual Motor/Performance variants. If you have a RWD version of the Model 3, the Long Range, Mid Range, or Standard Range/Plus, the previously described Battery Current Limiting is not a concern. The single motor is unable to draw enough current from the battery pack at a fast enough rate on a road course.

The motor limits appear to be met in several different ways. First, let’s talk about “Motor Current Limiting”. The motor current limits seems to act in a similar way to the battery. The BMS looks to calculate the total amount of current traveling through the motor, and will only allow a certain amount of current to pass through over a certain period of time. On an 800A inverter, I found these limits can be hit around the 8-minute mark. While this is rather detrimental to the RWD, it’s less of an issue on the Dual Motor variants. This is because the vehicle appears to shift more power to the front motor to compensate without negatively impacting total discharge. It’s also able to split power between the motors nearly constantly, as opposed to only being able to rely on the rear motor for the purposes of discharging.

In addition, the inverter temperature and motor oil temperatures appear to hit limits that will result in power limiting, or as I call it “Motor Thermal Limiting”. This can be a prominent issue if you are in a situation where the vehicle is being DC fast charged shortly before the next on-track session. The vehicle uses the motor to pre-heat the battery pack for DC fast charging, and in the process, heats the oil and coolant temperatures up considerably. Simply driving the vehicle for a few minutes or letting it sit idle for a short period of time does not allow the motor and inverter to cool down enough.

Finally, let’s discuss “Battery Thermal Limiting”. There are maximum battery cell temperatures that the vehicle will allow before limiting power. These appear to reside around 60C. Similar to the Motor Thermal Limiting, this is most prominently an issue if the vehicle is being DC fast charged shortly before the next on-track session, as the battery pack is heated close to this limit during that process. This seems to be especially an issue on the vehicles with the higher density cells (2021+ Model Year Performance, phased into Dual Motor vehicles mid 2021). Tesla/Panasonic was able to increase the energy density in these newer cells, giving the vehicle roughly 6% more energy capacity in the same physical structure. However, this also appears to have increased the cell’s internal resistance, which causes them to heat more rapidly under heavy discharge/charge.

Now that we have a better understanding of the limits that are present, let’s explore Tesla’s method of combatting them – Track Mode. With Track Mode enabled, the vehicle will attempt to cool the battery and motors as quickly as possible until they are down to around ambient temperature. Unfortunately, there’s a problem with this strategy. First, you cannot enable this cooling while the vehicle is charging, and second you cannot enable this cooling unless the drive rail of the vehicle is on. What that means, is that in a lot of situations, you don’t have nearly enough time to cool the drivetrain of the vehicle prior to hitting the track.

Alright, now that we understand the problem – what can we do to resolve it? For that, we turn to Mountain Pass Performance.

First and foremost, let’s explore MPP’s Cooling Party Controller (CPC). This allows us to combat these limits in several different ways. Using the CPC, you can activate full cooling mode both while charging, and with the vehicle drive rail turned off. Now, those Supercharging sessions don’t have to result in a hot powertrain!

Next, the CPC allows you to run steady power (outside of normal and expected voltage drop) until hitting the hard limits of the BMS. This differs from the factory behavior, which is to throttle back the power over a few minute period prior to getting to these hard limits. This makes the vehicle more predictable and consistent to drive, and allows you to complete another lap or two without considerable power deterioration.

And, perhaps most importantly, the CPC allows you to limit the power to a preset value. This is important for a few reasons, but the net benefit is that the vehicle can run longer without power loss, while only giving up a second or two on your lap times – the perfect solution for HPDE or racing (albeit not time attack). Let’s dive deeper – if you’re reading this I am sure you’ve seen a Model 3 dyno graph -  the motors are very peaky. Full power comes between about 40 to 60 miles per hour, and then drops off steadily from there. On a road-course, most of your time is spent above 60 miles an hour. As a result, we’re primarily levelling the power curve, as opposed to neutering the car to a shell of its former self. It’s also important to understand that for every unit of power, you are netting two units of thermal load. Therefore, even a small reduction in power results in a notable decrease in thermal load.

In an effort to combat the motor limiting, let’s explore MPP’s Rear Drive Unit Oil Cooler. This is an efficient external cooler with a fan that nearly doubles the total amount of oil – resulting in significant drops in motor oil temperature and inverter coolant temperature. While this will not entirely resolve the Motor Current Limiting, it will help with avoiding Motor Thermal Limiting, especially in situations where the vehicle was recently DC Fast Charged and the motor is very hot right before your next session.

Finally, let’s see what we can do to avoid Battery Thermal Limiting by checking out MPP’s HV Battery Radiator. This large and efficient radiator captures hot coolant returning from the High Voltage Battery and exchanges it with ambient air for a rapid and significant drop in temperatures, just before the coolant flows through the refrigerant chiller for further temperature drops. I would like to mention that on my 2021 with the newer cells, I was hitting the HV Thermal Limit around 60C pretty consistently before adding this cooler, and have seen an average drop of 11C since, and have avoided the limit entirely.

Let’s spell out the strategy more clearly depending on your vehicle model.

Dual Motor and Performance variants will need to implement all three products for the best Thermal and Current limiting mitigation. I would recommend setting the total discharge limit to around 250kW, which should allow for about double the on-track time compared to what you are used to. A lower limit around 220kW should result in nearly triple the on-track time.

For Rear Wheel Drive variants, the HV Battery Radiator is not required. On my Long Range RWD, I’ve found a good limit to be about 190kW, which should allow for nearly a full twenty minute session.

I think that this solution, while not perfect, is much better than what we were given from the factory and results in a car this is more consistent, predictable, easy, and fun to drive for longer periods of time. On Dual Motor variants, it also helps to reduce the rate of energy loss, which means you can spend less time charging and more time out on the track. I’ve personally found the car to be much more enjoyable, and it allows me to really focus on driving my line, figuring out the best braking points, practicing different corner entry and exit techniques, trail-braking, etc – no longer do I feel the pressure to set a single fast-lap and then head back to a charger.

These products make the Model 3 Challenge possible. It wouldn’t be particularly fun to be racing for only 7 minutes, nor would it be fun to have the cars hitting Miata power levels after 9 minutes! Now, you can run 15 minute races without having to worry about significant power loss. So, if you haven’t already, sign up for the Model 3 Challenge! There will be several events on the East Coast and West Coast. If you’re looking for a fun and competitive series to run your Model 3 in, this is it!

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