Can you Tow Charge a Taycan?

[Jhenson29]

I thought you were dealing with more than just a simple circuit

It’s not about it being simple or not. It’s about whether or not the current has a path.

AC generator does generate current.

Put an amp clamp on that wire with an open lead and let’s see that current then…

I’m just saying that flat towing the car doesn’t have to generate current.

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[JimBob]

Yes, an open circuit is not going to have current in it. Unless you touch the hot side and complete a path to a point with lower electromotive potential.

And yes flat towing a car doesn't have to generate current, but it probably does. The Tesla tests showed that in that case it does.

 

[Jhenson29]

but it probably does.

Disagree. Not enough information to make that inference.

 

[whitex]

But I also don’t understand the no flat-towing rule in general. The motors (within their rated speed) can’t generate more back emf than their rated voltage and there’s no current if the circuit is open, so….what’s the issue? Anyone know?

I think there may be multiple potential issues. For example:

1. Whether or not the car can stay in Neural (actual coasting) with dead electronics (including 12V battery) - remember that towing implies car may not be not fully functional (or else it would not need a tow)
2. Can the car be towed with 2 wheels on the ground - this is why AWD vehicles (ICE too) usually say no towing with wheels on the ground

 

[Jhenson29]

I think there may be multiple potential issues. For example:

1. Whether or not the car can stay in Neural (actual coasting) with dead electronics (including 12V battery) - remember that towing implies car may not be not fully functional (or else it would not need a tow)
2. Can the car be towed with 2 wheels on the ground - this is why AWD vehicles (ICE too) usually say no towing with wheels on the ground

@Tooney pointed out the issues with something like the parking brake, and I agree. I don’t know what controls or overrides there are for that.

It may not be getting towed due to an issue though. It could be getting towed behind an RV or something.

The AWD thing, my understanding is the front and rear motors are not mechanically coupled. And, unlike and ICE vehicle, I don’t think there should be an issue back driving the drive system at speed.

 

[Tooney]

Author in this link mentions factors such as maintaining battery coolant systems when towing.

 

[JimBob]

Author in this link mentions factors such as maintaining battery coolant systems when towing.

This article lays it out. You can't flat tow as the electric motor stays engaged so will generate current into the battery + heat.

But you can tow charge an EV as you want to put current into the battery. It's a matter of degree.

 

[whitex]

@Tooney pointed out the issues with something like the parking brake, and I agree. I don’t know what controls or overrides there are for that.

It may not be getting towed due to an issue though. It could be getting towed behind an RV or something.

The AWD thing, my understanding is the front and rear motors are not mechanically coupled. And, unlike and ICE vehicle, I don’t think there should be an issue back driving the drive system at speed.

Towing on the ground would be a whole new usecase they would have to design for. Without a driver in a car, you cannot tell the towing driver to "pull over" for example when there is an issue. Another example would be if the car fails (say battery issues) and engages the parking brake as a fail-safe mechanism (once it comes to a stop), that works just fine with a driver in the car, not so much when the car is towed (would just drag locked wheel and perhaps damage the parking brake). Another issue is how to explain to customers they can tow when the car is functional, but not if there are any issues (or the car may get damaged) - someone would have to go look at some "ok to tow" light and check it periodically during towing? These are just examples, not an exhaustive list of things which would need to be solved, tested, implemented, and maintained in both hardware and software of the car. I'm sure it can be done, but my guess is that it's not a common enough usecase for there to be a decent ROI on the effort.

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