Tow to recharge

First, this is not a serious suggestion. I can just imaging what the lawyers might say.

I saw a brief mention of this idea in another thread, but I thought I'd put some numbers to it just for fun.

To reduce "range anxiety" Nissan could add a special function to recharge the batteries by towing the car. This could work behind any tow truck (towing backwards with the front wheels on the ground) or by towing the Leaf on a rope behind most other vehicles. Thus, the liability problem - "What?? :shock: You put in a special function that encourages Buba to tow the Leaf using the 5 foot piece of old rope he had?"

Anyway, I"ll make the rash assumption that if towed at 35 MPH, the motor could be made to charge the batteries at a rate equal to 1/2 the motors power rating. This is 40 KW (107 HP divided by 2 and multiplied by 745 w/HP gives 40,000 watts).

This would give you a 10% charge (enough to get home?) in about 3.5 minutes, or just over 2 miles.

Interesting idea. Toyota "strongly discouraged" towing of the RAV4-EV, implying damage within a few miles. They said "flat bed if possible, or front wheels off the ground. Do not tow with front tires on the ground."

I no longer have my owners manual, so this is paraphrased, not exactly their words.

Quixotix said:

First, this is not a serious suggestion. I can just imaging what the lawyers might say.

I saw a brief mention of this idea in another thread, but I thought I'd put some numbers to it just for fun.

To reduce "range anxiety" Nissan could add a special function to recharge the batteries by towing the car. This could work behind any tow truck (towing backwards with the front wheels on the ground) or by towing the Leaf on a rope behind most other vehicles. Thus, the liability problem - "What?? :shock: You put in a special function that encourages Buba to tow the Leaf using the 5 foot piece of old rope he had?"

Anyway, I"ll make the rash assumption that if towed at 35 MPH, the motor could be made to charge the batteries at a rate equal to 1/2 the motors power rating. This is 40 KW (107 HP divided by 2 and multiplied by 745 w/HP gives 40,000 watts).

This would give you a 10% charge (enough to get home?) in about 3.5 minutes, or just over 2 miles.

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Pulling the car in reverse probably will damage the electric traction motor.

Based on my ownership of a 2001 Honda Insight and a 2006 Prius(both require a truck flat bed tow system), I'll bet the Leaf would have to be put on a flat bed(all wheels off the ground) rather than a cradle type system. Most low modern cars can't be towed the traditional way. There are too many plastic body panels that are fragile, and the cars are too low.

As previously posted on other threads, my favorite "emergency limp home" ideas:

Mobile truck-mounted L3 chargers powered by generators that are driven via PTO off the truck engine

Bungee cord a Honda EU-2000 to the back bumper

gasmiser1 said:

Pulling the car in reverse probably will damage the electric traction motor.

Based on my ownership of a 2001 Honda Insight and a 2006 Prius(both require a truck flat bed tow system), I'll bet the Leaf would have to be put on a flat bed(all wheels off the ground) rather than a cradle type system. Most low modern cars can't be towed the traditional way. There are too many plastic body panels that are fragile, and the cars are too low.

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Admittedly I'm not very knowledgeable about high-tech electric motors, but it seems that most motors/generators could care less which way they turn (assuming the wiring is correct for the direction of rotation). Obviously the Leaf motor can run in reverse, so what would be different about generating in reverse that would cause damage?

If by the "traditional way" you are referring to the slings used on old tow trucks, then I agree completely that most modern cars can't be towed this way. But, almost all non-flatbed tow trucks (and many flatbed trucks too) now have the system that holds and lifts one set of the car's wheels - not touching anything but the tires. Most modern cars can be towed with this system if the drive wheels are the ones that are attached too. Some really low sports cars couldn't be, but I think this system will work fine with the Leaf.

Quixotix said:

To reduce "range anxiety" Nissan could add a special function to recharge the batteries by towing the car.

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Hmmm. I have to agree with the other comments here. I do agree that any electric motor is also a generator when torque is applied to a motor that is not otherwise being driven by a current. And yes, the LEAF can do reverse -- beep beep beep beep beep... -- but this is probably done through some physical gears rather than reversing the A/C. But even if it isn't, the thing to remember here is regenerative breaking is turning some motor (maybe not the main motor) into an A/C generator no doubt with some additional break force as the momentum of a car alone would only be able to charge a battery at a trickle and for a very long time compared to the desire to break. This is the effect of the LEAF's eco mode: when you're foot's off the gas, all your momentum (not already being eaten by wind and rolling resistance) is slowly being trickled back into the battery to charge it. The thing clearly to remember here is you can't regenerate and drive at the same time, natch.

So, and here I have to feign ignorance, my understanding of the regenerative breaking system of most cars is that you apply breaks as normal and while the tires slow to a stop you turn an electric motor into a generator and turn that motion into A/C. You then run it through the inverter to charge the battery. If this be the case, the problem with charging a battery via this method is that regenerative breaking is only engaged when the breaks are also. This would be a safety measure as people don't typically engage the acceleration at the same time as the break (unless they're a bit touched in the head) so it's safe to reverse the inverter to start charging -- disabling all all power to the wheels -- and instead use the dedicate circuitry to run the the motor, generate a current, run it through the inverter to generate D/C and then use that to charge the battery. So therefore, on previous Hybrid and Electric vehicles, you couldn't engage the regenerative breaking when idle or neutral or in any other car mode, only when breaking. Doing so would fail to engage the regenerative breaking and thus cause damage to the car by running current through circuits that weren't ready to accept it.

But, as I said before, the LEAF has this sluggish eco-mode feature, where you add momentum and coast, add momentum and coast, etc., always decelerating slightly while coasting as the drag, rolling resistance and battery charging eat up your speed. But this mode is exactly what our Quixotix friend is talking about! So, in principle, the LEAF may be an exception to the Thou Shalt Not rule. If you could just put the car in ECO mode, engaging the ECO circuitry while someone pulled your car while dragging the wheels you might just get some benefit. Of course, that's a lot of ifs, and as I said, I don't really know how all this stuff works.

It's an interesting idea though and I think the real question we need answered is: can the car be charged in ECO mode when there's no-one behind the wheel and the car is just free-moving?

I believe:

There is No gear change for reverse.

Towing is just like going down hill (except for the stresses on the car's towing point(s) and frame.

So, as long as the car is fully ON and in D (or ECO), the Regen should charge the car fine, up to the limits of the Regen circuitry and battery: current, heat, and SOC.

The Regen is what the EV is designed to do ... up to a point. The Regen "current" (really power, kW) can even be monitored by the user.

However, 2- or 4-wheel towing with the car OFF is NOT good, since it will have its automatic parking brakes engaged, probably on all 4 wheels.

Just pulling an unattended, parked LEAF to put it onto a flat-bed truck is likely to be a full 4-wheel skid ... not great.

For flat-bed loading when attended, manual pushing or towing, or going through a Car Wash, I do not know what Nissan will recommend ... perhaps EV ON and in Neutral so that the wheels will turn freely.

There is no manually-activated Emergency or Parking Brake on the LEAF, right? (The 2010 Prius DOES have one.)

The LEAF parking brake might be an auto-"locking" hydraulic brake pressure system.
If so, for long-term parking on a slope, Nissan might have special precautions for the LEAF (in case the "locked" hydraulic brake pressure is lost).

TimeHorse said:

... I think the real question we need answered is: can the car be charged in ECO mode when there's no-one behind the wheel and the car is just free-moving?

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I can't imagine the Leaf wouldn't charge this way (if you leave the car turned on). To NOT charge in this way, Nissan would need to program the car to shut off the regeneration feature (or the whole car) when it detected there was no driver. I don't think any cars today insist on a driver in the drivers seat before it will operate, so I don't see why Nissan would add this to the Leaf.

But, I'm sure that even in ECO mode, the Leaf will generate much less power than what I was suggesting. Generating 40 KW from a Leaf not being towed would cause it to slow very abruptly. It wouldn't make for a pleasant driving experience. While towing a Leaf (with the car on, in a forward direction [regen may not operate in reverse], and above some minimum speed) will undoubtedly charge the batteries, but I'm sure it will be a VERY slow way to charge. To charge quickly, as I suggested, would require Nissan to program in a special feature that would allow this to be done.

towing an EV that has regen enabled can be done, but without the vehicle's ability to control regen, it could damage the system which is the reason why any "reasonable" car company would recommend against it.

DaveinOlyWA said:

towing an EV that has regen enabled can be done, but without the vehicle's ability to control regen, it could damage the system which is the reason why any "reasonable" car company would recommend against it.

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But the car does have the ability to control the regen! As garygid pointed out, there is no difference between towing the car at 35 for 3 miles or coasting down a hill at 35 for 3 miles. Since you live here in Washington (as I do), you know it isn't hard to find a 3 mile long hill that you can coast down at speed. The Leaf must protect its self when coasting, so by default it will protect its self when being towed (assuming the car is on). Again, the car can't even tell if it is coasting down a hill or being flat-towed -- thus there can't possibly be a difference.

Now, if you tow it a longer distance (like maybe over 10 miles), then maybe there could be a problem. Since this is probably longer than the longest hill you can find, the car might not be designed to handle periods of regen that last this long. But, I'll go out-on-a-limb here and suggest that the Leaf can probably regen continuously for hours as long as the batteries are not fully charged. The small amount of power produced by the regen process isn't likely to tax the motor, inverter, or batteries (up to full charge). Driving 70 mph for 1 1/2 hours is going to demand a lot more of all these systems than doing regen for a couple of hours.

If the car is off, then things might be different. Possibly this is why it has an electronic parking brake. Does the parking brake self-apply when the car is off? If so, this might be to protect it from being towed when it is off (just a wild guess).

The parking brake is to keep the car from rolling away when it is parked on an incline.

It tends to hinder towing also, because the "locked" wheels cause the tires to slide ... and wear a flat spot on the bottom side!

But, that will not bother a towing company, if you are illegally parked, for example.

Even if you could get t to work it the reason it is dangerous is with any drive engaged, if one wheel is the drive wheel the car will putt to one side and veer out. In neutral there is no strong torque steer.

If one actually tried this tow-charging, it would be a lot safer to have a driver in the LEAF.

Totally unsafe without the driver, I think.

Why is no one is asking what mileage the tow truck will be getting during this process? Let's face it, "free-moving" is not going to apply if the Leaf is being dragged in Eco mode. It will be more like pulling a mule against its will.

No, wait! I've got a great idea for how two Leafs can make a long trip: Hook one Leaf in front of another one, and let Leaf#1 pull Leaf#2, which is in Eco mode, for a while. Then stop and reverse the two: Let Leaf#2 pull Leaf#1 for a while. Keep switching until you get there. :lol:

planet4ever said:

Why is no one is asking what mileage the tow truck will be getting during this process? Let's face it, "free-moving" is not going to apply if the Leaf is being dragged in Eco mode. It will be more like pulling a mule against its will.

No, wait! I've got a great idea for how two Leafs can make a long trip: Hook one Leaf in front of another one, and let Leaf#1 pull Leaf#2, which is in Eco mode, for a while. Then stop and reverse the two: Let Leaf#2 pull Leaf#1 for a while. Keep switching until you get there. :lol:

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Exactly why a truck-mounted L3 charger would be pretty cool. If you can get 80% charge in 26 minutes, that suggests you're picking up 2-3 miles of driving for every minute of L3 charging. So if you had a Leaf dead on the side of the road, five minutes of charging off the truck should be plenty to get you home or to a public charging site assuming you aren't out in the sticks somewhere. Less time, hassle, and risk to the vehicle than loading it on a flatbed.

I wonder what the highway range of Leafs would be if they were drafting, say 2 or 3 cars.

Quixotix said:

DaveinOlyWA said:

towing an EV that has regen enabled can be done, but without the vehicle's ability to control regen, it could damage the system which is the reason why any "reasonable" car company would recommend against it.

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But the car does have the ability to control the regen! As garygid pointed out, there is no difference between towing the car at 35 for 3 miles or coasting down a hill at 35 for 3 miles. Since you live here in Washington (as I do), you know it isn't hard to find a 3 mile long hill that you can coast down at speed. The Leaf must protect its self when coasting, so by default it will protect its self when being towed (assuming the car is on). Again, the car can't even tell if it is coasting down a hill or being flat-towed -- thus there can't possibly be a difference.

Now, if you tow it a longer distance (like maybe over 10 miles), then maybe there could be a problem. Since this is probably longer than the longest hill you can find, the car might not be designed to handle periods of regen that last this long. But, I'll go out-on-a-limb here and suggest that the Leaf can probably regen continuously for hours as long as the batteries are not fully charged. The small amount of power produced by the regen process isn't likely to tax the motor, inverter, or batteries (up to full charge). Driving 70 mph for 1 1/2 hours is going to demand a lot more of all these systems than doing regen for a couple of hours.

If the car is off, then things might be different. Possibly this is why it has an electronic parking brake. Does the parking brake self-apply when the car is off? If so, this might be to protect it from being towed when it is off (just a wild guess).

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There is a lot of difference Between coasting downhill Using only gravity tower As opposed to being towed. The difference is more than enough To get the lawyers all in a bunch N receive the recommendation to not do it

A more reasonable approach

Just as a note to this thread, I drove my leaf 9 miles up a mountain from elevation 2600 to 4500 feet with just a couple of power bars left at the start. I wanted to see what happened when I ran out of range. I ran out of power bars and the range went to hash marks. At that time I turned the car around to coast down hill and regenerate. Under normal conditions my range increases and I gain a power bar on the way down. The leaf did in fact regenerated but refused to display any range or power bars. I know that I gained power on the way down, but it looks like the program will not allow range or power bars to show until hooked to a charger.

When I come home I usually pick up my mail from the top of my pipestem then release the break and put it in neutral; I coast down hill and get about the first third of the car into my garage before I have to switch to drive (if my HomeLink is able to open it that day!)

kmcmahan said:

Just as a note to this thread, I drove my leaf 9 miles up a mountain from elevation 2600 to 4500 feet with just a couple of power bars left at the start. I wanted to see what happened when I ran out of range. I ran out of power bars and the range went to hash marks. At that time I turned the car around to coast down hill and regenerate. Under normal conditions my range increases and I gain a power bar on the way down. The leaf did in fact regenerated but refused to display any range or power bars. I know that I gained power on the way down, but it looks like the program will not allow range or power bars to show until hooked to a charger.

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By "coast", I assume you mean in gear but with your foot off the accelerator. The normal meaning of coast is moving with the car in neutral, and you wouldn't be regenerating at all in that mode. Your experience is interesting, but not conclusive. Now, if you normally gained two or more bars down that mountain, then I think you might have some strong evidence, but one is - as they say - within the margin of error.

Incidentally, your terminology is a bit off. Power is really the rate at which you are expending energy. The dots across the top of the dash are showing you power. The long bars on the right side of the dash are giving you an indication of how much energy is stored in your battery, or as the manual puts it, an "available charge gauge".

Ray