How efficient is regen?

[Spence]

I'm asking because I was wondering why a recharging station couldn't simply spin the rear tires (like a dynamometer) to use the car's built-in system to top off the battery. Could be a universal charging station for any EV with regen.

 

[arcus]

Kind of like a perpetuum mobile?
The only thing you would gain would be an extended charge time, as there would be significant energy loss to propel the wheels.

 

[Spence]

That's what I was wondering- there are likely losses in the electronics for the plug-in charging- which is more efficient?, also with a 4WD EV, would it work to just spin 2?

 

[Spence]

PS Hello, Denton! I went to NTSU in the late 70s.

 

[arcus]

PS Hello, Denton! I went to NTSU in the late 70s.

Nice! You would probably not recognize the town if you haven't visited in a while. I've been living here for the last 10 years and the expansion is quite significant since I moved in.

 

[dm33]

I'm asking because I was wondering why a recharging station couldn't simply spin the rear tires (like a dynamometer) to use the car's built-in system to top off the battery. Could be a universal charging station for any EV with regen.

J1772 is already pretty much a universal charging standard.
Spinning wheels adds lots of mechanical moving parts making it much less efficient, lots more parts to break and wear out than plugging in an electrical connection.

In general, regen is pretty efficient for what it does. But direct electrical connection is much more efficient.

 

[Ande]

Regen on Tesla is pretty efficient, but not all electric cars have that.
That said, if you wanted to charge a Tesla that way, unless it would be a slow charge, tire wear would be a problem. think about it, 60kW of power + friction loss would wear the rubber.

In Europe Type2 is the EU standard for charging connector, plug compatibility is easier to solve, than mechanical maintenance of such charging devices.

 

[Naonak]

I believe there is a video of someone charging their Model X to full by towing it for a long distance. Might find it in a search.

 

[Carl]

I remember that video, and the result was about 50% regen IIRC.

 

[aus]

I just read in one of the big car mags, a company was proposing charging through the regen pathway instead of going through a charger that all cars currently use. The article claimed that charging through the regen pathway was much faster. They did NOT propost spinning the wheels backwards, just charging the way regen charges.

 

[Shock-On-T]

It's an excellent idea.
Obviously you'd sacrifice efficiency over a direct plug, but it would certainly be universal to any EV that had regen braking.

I suspect it would be cheaper to just have a bunch of adapters attached to whatever was going to power the wheel turning machine.

 

[Shock-On-T]

To answer your original question, it's pretty inefficient (but better than wasting it).
I think around 30-50%.

That's why if you're doing serious hypermiling (Australian outback), you're actually better off with regen set to 'Low'.
Going downhill it's more efficient to just roll faster than to hold your speed while charging batteries.

 

[David99]

To answer your original question, it's pretty inefficient (but better than wasting it).
I think around 30-50%.

That's why if you're doing serious hypermiling (Australian outback), you're actually better off with regen set to 'Low'.
Going downhill it's more efficient to just roll faster than to hold your speed while charging batteries.

Tht's not quite correct. Regen is about 90% efficient. What you are referring to is probably ratio of energy spend going up a mountain and then down again. That will give you only 30% back. But of course you have also drive the car over some distance which costs energy. So you cannot get that back.

It is not more efficient to let the car roll down a hill faster with less or no regen than using normal regen. The faster you go the more you lose due to air drag. You can go down a hill fast and get nothing back or you can go down slower while regenerating back into the battery. It's very simple, actually.

Driving in a way where you never need regen would be the most efficient, of course, but that is unrealistic in city traffic. And any time you go downhill, regen is always giving you energy back while coasting gives you nothing.

 

[Shock-On-T]

Driving in a way where you never need regen would be the most efficient

That's precisely what I'm saying.

If you're in a position where you can minimize regen (eg. Australian outback) you should do so.

Your speed at the bottom of a slope without regenning (new verb?) is faster than if you'd been regenning.
That extra speed covers a certain distance before slowing down to the speed you'd have been at if you had been regenning.
That distance is 'free' range, and is worth more than the energy you'd have gained by regenning.

There is one caveat, but let's not worry about that...

 

[Brass Guy]

This argument (coasting vs regen) has been going around for years.
My take is: it depends on how steep and/or long the hill is. If you might only gain 5-10 mph, you're probably better off coasting and get the free distance after. If you'd hit (what I'd call) terminal velocity, you'd obviously be better off with regen.

Back to topic, the OP has a point: you can regen up to at least 60kw. Sure it's less than supercharging, but far more than AC charging.

Driving the wheels I think would be very inefficient overall. Using electricity to drive a motor to drive the wheels to generate current that needs to be rectified just seems wasteful. But if there was a way to tap into the regen circuit, I think we'd have something.

If I understand enough about the induction motor, when in regen, it generates 3 phase current. So the car is capable of taking 60 kw of AC current in the stator and charging the battery with it. I always wondered why this wasn't the car's charging system. Shouldn't everybody be able to charge with at least 20 kw at single phase?