Quixotix
Posts: 20
Joined: Mon Jul 12, 2010 1:24 pm

Tow to recharge

Wed Jul 28, 2010 5:35 pm

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.

Dav
Posts: 275
Joined: Tue Apr 20, 2010 5:19 pm
Delivery Date: 26 Jun 2015
Location: San Diego, CA
Contact: Website

Re: Tow to recharge

Wed Jul 28, 2010 5:44 pm

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.

User avatar
gasmiser1
Posts: 431
Joined: Fri Jun 18, 2010 3:27 pm
Location: Cambria, CA Central Coast of Calif.
Contact: Yahoo Messenger

Re: Tow to recharge

Wed Jul 28, 2010 5:48 pm

Quixotix wrote: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.
-----------------------------------------------------------------------------------------------------------------
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.
2nd leased 2014 Nissan LEAF, 2500 miles, leased 5/4/14
(1st Leaf, 3/29/11, leased until 5/4/14, 45,000 miles)
2014 Chevy Volt, 11,200 miles, leased 11/2013
Future Tesla Model S owner :-)
Central Coast EV Member
SF BayLEAF Member
Model S Member

User avatar
LTLFTcomposite
Posts: 4674
Joined: Fri Apr 23, 2010 6:06 pm
Delivery Date: 10 Dec 2011
Leaf Number: 5926
Location: Central FL

Re: Tow to recharge

Wed Jul 28, 2010 6:43 pm

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
LTL
White 2012 SV delivered 10 Dec 2011 returned 25 Nov 2014 replaced with stopgap ICE Sentra
[35 months] [35K miles] [9 Bars]
2013 Volt replaced after 36 months/30k miles with ICE Rogue
2016 SV-adjacent May 2016 lost 4th bar March 2018

Quixotix
Posts: 20
Joined: Mon Jul 12, 2010 1:24 pm

Re: Tow to recharge

Wed Jul 28, 2010 7:46 pm

gasmiser1 wrote: 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.
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.

Image
Last edited by Quixotix on Thu Jul 29, 2010 10:10 am, edited 2 times in total.

User avatar
TimeHorse
Gold Member
Posts: 999
Joined: Thu May 13, 2010 4:40 am
Delivery Date: 02 Nov 2011

Re: Tow to recharge

Thu Jul 29, 2010 5:53 am

Quixotix wrote:To reduce "range anxiety" Nissan could add a special function to recharge the batteries by towing the car.
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?
RIP CO2 Fre, 27 months, 42,282 mi & 11 bars.
unAmerican Job & Nissan's Rapid Depreciation cost $20,000!
5 hours on the road daily w/o Charge at Work on 100%.

Long Live CO2 Fre, Maxed 2013 SL, 20,000 mi/yr lease.
http://aecn.timehorse.com/" onclick="window.open(this.href);return false;

User avatar
garygid
Gold Member
Posts: 12464
Joined: Wed Apr 21, 2010 8:10 am
Delivery Date: 29 Mar 2011
Leaf Number: 000855
Location: Laguna Hills, Orange Co, CA

Re: Tow to recharge

Thu Jul 29, 2010 6:56 am

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).
See SOC/GID-Meter and CAN-Do Info
2010 Prius, now for sale
2011 LEAF, sold in 2015
2018 Tesla Model 3
2014 Tesla S, Model 3 in 2019
PU: SDG&E
Solar PV: 33 x 225W -> 7 kW max AC
To Sell: X-treme 5000Li EV motorcycle

Quixotix
Posts: 20
Joined: Mon Jul 12, 2010 1:24 pm

Re: Tow to recharge

Thu Jul 29, 2010 10:04 am

TimeHorse wrote: ... 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 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.

DaveinOlyWA
Posts: 14100
Joined: Sat Apr 24, 2010 7:43 pm
Delivery Date: 16 Feb 2018
Leaf Number: 314199
Location: Olympia, WA
Contact: Website

Re: Tow to recharge

Thu Jul 29, 2010 10:42 am

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.
2011 SL; 44,598 miles. 2013 S; 44,840 miles.2016 S30 deceased. 29,413 miles. 2018 S40; 15,000 miles, 478 GIDs, 37.0 kwh 109.81 Ahr , SOH 94.61, Hx 120.15
My Blog; http://daveinolywa.blogspot.com" onclick="window.open(this.href);return false;

Quixotix
Posts: 20
Joined: Mon Jul 12, 2010 1:24 pm

Re: Tow to recharge

Thu Jul 29, 2010 1:59 pm

DaveinOlyWA wrote: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.
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).

Return to “Engineering”