• Feb 18th 2011 at 8:02PM
  • 24
Towing a vehicle, especially one that's powered by batteries and driven by an electric motor, can, if done incorrectly, be destructive. Recently, one of Frito-Lay's electric Smith Newton delivery trucks was towed for a parking violation and, according to Green Car Advisor, was reclaimed by Frito Lay employees who arrived with a flatbed tow truck. Well, as GCA's Robert Calem points out, it's unusual to witness an impounded vehicle towed, rather than driven, off the lot.
This oddity drove GCA to dig deeper and reach out to Bryan Hansel, chief executive officer of Smith Electric Vehicles, for an explanation. The Newton has no transmission connecting its electric motor to the rear drive wheels. Furthermore, the Newton is not equipped with a "neutral" selector to disengage the wheels from the motor. Therefore, towing the Newton with its rear wheels on the ground would force the electric motor to spin. However, since the delivery truck's liquid cooling system is inactive when the vehicle is off, excessive heat could build up and destroy the motor.

Hansel told GCA that the proper way to tow a Newton is to either drop the driveshaft, which connects the electric motor to the rear wheels, or to lift it from behind with the front wheels on the ground. Obviously, tow truck drivers are unlikely to spend half an hour pulling a driveshaft, so Hansel simply advises that Newtons either be hauled away on a flatbed or not towed at all.

Many battery-powered vehicles, including the Nissan Leaf and Ford Transit Connect, are engineered in such a way as to eliminate potential towing issues. However, the use of flatbed tow trucks nearly guarantees that hauling away a plug-in vehicle will not be a motor-destroying event.

[Source: Green Car Advisor]

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    • 1 Second Ago
      • 4 Years Ago
      What are they talking about? An underpowered electric motor doesn't generate any heat. It just spins. The only problem in towing is the gear ratio. If the drive train is in to low a gear the motor can over rev while towing and be damaged. Any EV with a single speed gear box can be towed as long as you stay below the car's maximum speed. For the Leaf it's 90 MPH
        • 4 Years Ago
        the tesla has a parking pawl.

        you can't drag it by its back wheels.

        the body work is too low to tow it by its front wheels

        • 4 Years Ago
        Smith were talking specifically about their vans, not electric cars.
        I believe they have a two speed gearbox.
        • 4 Years Ago
        Unless you have a completely frictionless environment spinning a shaft in a bearing will ALWAYS generate some heat.
        If the system is basically closed up and designed to be cooled by running a liquid through it, even this heat could get excessive over time.
        The motors in question are liquid cooled and therefore may have no way of dispersing even small amounts of heat when the cooling system is not active and moving the heated liquid to the radiators.
        An air cooled motor with open venting etc.. would probably be sufficiently cooled just by the movement of the vehicle itself.
        • 4 Years Ago
        P.S. The Volt can easily be damaged in towing because of the complex clutch arrangement in the transmission.
        • 4 Years Ago
        A spinning motor with magnets generates voltage. The faster it spins the higher the voltage, very possibly higher than the operating voltage of the system. The voltage is usually fine in the motor but quite destructive to the power electronics. The manf. has three choices
        1) design the motor to have low voltage at high speeds, i.e. smaller magnetic field, this has a negative effect on the power density of the design during operation.
        2) design the power electronics with high voltage capabilities. This has a negative effect on cost (at the moment)
        3) short one side of the IGBTs in the power electronics, all three to HV- for example. All the phases of the motor are therefore shorted together. This prevents the voltage from damaging the electronics but causes a constant flow of current through the motor and power electronics. This current flow is the same as during operation causing heat (I^2R losses + magnetic and iron losses in the motor) and if not gotten rid of damage either the power electronics and/or the motor.

        It's a problem only with PM motors. Generally cars with PM motors will have a maximum towing speed with the ignition on and towing time with the ignition off. Unfortunately that's not labeled on the car and towtruck drivers have no idea that they need to do something different.
      • 4 Years Ago
      Half an hour to drop a drive shaft? I watched some Boston tow truck drivers drop the drive shaft of a Jeep Grand Cherokee in less than 5 minutes...
      • 4 Years Ago
      Towing with the ignition on would simply charge the battery. However this will never be the case for a parking violation. Autobloggreen has got it right, and option 2 is most reasonable. I don't believe the argument about extra cost, the car has to be designed for regen capability and must deal with worst case peak voltage, so I would say most designs will not suffer from towing.
        • 4 Years Ago
        Key off, contactor to pack is open. Even with the car on regen is minimal with no brake on some EVs and all have pack protection, they must. Leaf has an electric parking brake and prawl.
      • 4 Years Ago
      must be permanent magnet motor. tesla uses induction motor which does not have that problem.
      • 4 Years Ago
      Slidebeds rule! don,t see many boom trucks down here in the south, except the big boys for semis,of course. I have fond? memories of my 2am barclosing towjobs.
      • 4 Years Ago
      If a car is towed for a parking violation - aren't they in the same situation with a FWD vehicle with the parking brake on or with AWD vehicles?

      Try to tow either one of those with the wheels on the ground and you will damage something...

        • 4 Years Ago
        I think they disconnect the parking brake cable in that case.

        Anyways I think this is an issue for any RWD car too. Many recommend disconnecting the driveshaft before towing to prevent transmission damage. So it's not isolated to EVs at all.
        • 4 Years Ago
        Nah, they hoist one end and dolly the other. That way all four wheels are off the ground and stationary. No need to mess with anything on the towed vehicle.
      Judy Karimi
      • 2 Years Ago
      can one tow an electric vehicle using Reese Hitches? http://4wheelonline.com/towing/Reese.177038
      • 4 Years Ago
      The unanswered question here is where would liability be for the damage?
        • 4 Years Ago
        That's a fair argument, stansso. I was thinking of how it would play in my town, where there is no municipal towing fleet - contractors are used.

        Generally, municipal vehicles aren't held liable for much of anything. I've seen firemen who are responding to a call use their fire engines as battering rams to move cars illegally parked in front of fire hydrants. Likewise, police vehicles are certainly allowed to be used to damage vehicles by performing PITT maneuvers and ramming when deemed necessary.

        But, also generally, most cities don't own their own towing fleet. Towing is usually contracted out.
        • 4 Years Ago
        Typically, the court will accept that the tow operator is an "expert", considering their primary occupation is towing vehicles.

        The court would then typically find that as "experts", tow operators should be able to identify the proper way to tow any vehicle, and also to have the experience to know when they *don't* know the proper way to tow any vehicle.

        The court would then likely find that a tow operator who towed a vehicle without proper knowledge of proper towing procedure for that specific vehicle acted negligently, and would therefor be held liable for any damage caused by improper towing.

        If they don't know how to tow an EV, they shouldn't try to tow an EV. If they can't tell the difference between an EV and a standard vehicle - they're morons.

        (that's how I would approach the case, anyway - every judge is different)
        • 4 Years Ago
        @letstakeawalk --

        You try that argument when the city owns the tow vehicle and see who wins. Better yet, try that argument after the police tow a vehicle from a sensitive area.

        I bet the liability would transfer to the owner because they broke the law to begin with.
      • 4 Years Ago
      "or to lift it from behind with the front wheels on the ground"

      I want to see that.
        • 4 Years Ago
        I have had my Ford Ranger EV towed 4 times in the 4 years I have owned it. Only the first time I had it towed was it with a tobar truck, all other times have been on flatbeds. When I did tow it, I towed it backwards, because it's rear wheel drive. The steering lock was good enough that we didn't have issues with sway, but then we didn't need to go highway speeds.
        I think if there is an issue, towing with a bar, dollies might be the preferred option for the drive wheels.
        • 4 Years Ago
        Cars are rarely towed that way because the steering is on the front axle and there's too much risk of vehicle sway.
      • 4 Years Ago
      Can't this be used as regen to charge the car battery? :P
      • 4 Years Ago
      This isn't anything new, cars have needed to be towed different ways for quite a while now. I haven't seen a tow truck driver that didn't have a dolly with them, so it wouldn't be hard to tow a vehicle properly, they just have to spend an extra 10 minutes doing it.

      From a liability standpoint, I'm not a lawyer, but since they have the capability to tow a vehicle safely (with the rear dolly and the front lifted), they should be found liable for any damage from mishandling the vehicle.
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