Recycled waste heat of Tesla Model S is used for warming up the battery

Tesla Model S recycles waste heat coming from the driver motor and power electronics and then uses this ‘energy ’ to warm up the battery.

2/20/16 4:00 am chumakdenis 1

Have you ever been curious why Tesla Model S doesn’t have a heat pump?

The economy might be a good answer, but not for a car that costs as much as 100 thousand dollars – even Nissan Leaf has a heat pump.

It would be unacceptable greediness from Tesla Motors and would destroy the reputation of Tesla as a luxurious automaker completely.

Besides, there are so many other things that could be not used in case economy was needed – for instance, space welding techniques.

Anyway, here is the answer.

The heat pump improves range loss but adds expense…a lot of expense.

That’s why Tesla Motors decided to use recycled waste heat from the driver motor and power electronics for warming.

Cool, isn’t it?

I mean, resistive heating in the cabin and/or battery is a good thing too, but the recycled energy of the car is so much better.

Let’s learn more.

Tesla Motors has a patent app outlining a practical approach to cabin heating where waste heat from the drive motor and power electronics is used to warm the cabin.

 As it turns out, the production Model S uses a similar but subtly different approach.

Waste heat from the drive motor and power electronics is still used to warm the vehicle.

Nevertheless, Tesla chose to heat the battery instead of the cabin with the waste heat.

Here’s a detailed sketch that explains how all this stuff works.

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Detailed Tesla patent sketch shows waste heat being used to heat the cabin.

In the patent, the cabin liquid glycol heating loop can be connected to the drive motor and power electronics glycol cooling loop with some valves.

Note that the patent shows 4 loops: 3 glycol loops and one refrigerant loop.

Now let’s take a look at a simplified sketch of the production version of Tesla Model S.

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Production Model S uses waste heat to heat the battery instead of the cabin and has eliminated 1 Glycol loop.

There are two big changes between the patent and the production vehicle: the waste heat is used in the battery instead of the cabin and one loop has been eliminated. The production vehicle now has only three loops, not four. Tesla eliminated the Glycol cabin loop.

Do we know this for sure? Is it 100% true that this is the case in the production vehicle?

We have no direct information from Tesla Motors itself, but we have a quote from an article in the MIT technology review:

 

“Tesla takes a different approach. Once you start driving, heat generated by the motor is used to heat up the battery. This approach is more efficient since it uses waste heat rather than electricity. But it takes a while to work because the motor doesn’t produce much heat. As a result, it might take several minutes before the battery is warm enough to provide full acceleration.”

 

Additionally, we have some screen shots of the Model S in “diagnostic mode”.

Here is the diagnostic mode system schematic -- battery loop in parallel -not connected- with the drive motor and power electronics loop.

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This diagnostic mode schematic was posted on the Tesla Model Club forum in regards to the article where Tesla outlines practical approach to cabin heating with the following comment by member “Ingineer” (an electrical engineer).

 

On another sketch we see the drive motor and power electronics loop hooked in series –connected-with the battery cooling loop.

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Battery loop in series–connected-with drive motor and power electronics loop. Front radiator is bypassed.

So, while we have no direct confirmation from Tesla that this cooling scheme is used in production, all evidence indicates that Tesla Model S warms the battery with waste heat from the drive unit and power electronics.

Kind of a cool thing of them, isn’t it?

Verdict

The ‘heating’ scheme is easily implemented, low cost, improves cold weather range and is in tune with the “keep it simple” approach.

We do like it and hope that other automakers will be using recycled waste heat too – we’ve heard at 2016 NAIAS that Chevy Bolt will be using kind of the same technology, but it’s too early to talk about it since we even don’t have a production version of the car.

Let’s simply wish Tesla Motors good luck and wait more cool technologies from them.

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