Is it ok to tow the vectrix behind a pickup with the front wheel lifted off the ground and the rear wheel rolling? also key on or off when towing? thanks COOPER.
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Support V is for Voltage
I have not tried it, but I recall reading here that some folks have done it without any issues. Key off (not in the ignition), would be my guess (with the fork NOT locked, so the rear of the bike can swing side to side during turns). I've been thinking of buying one of these hitch tow adapters for my car to have in case of emergency, but my insurance includes roadside assistance and towing, so I've been postponing this purchase...
Hope someone that has actually done it will chime-in, as I'm not positive what happens and if/how much current is generated during a tow, and whether it would cause heating-up of the motor more than in normal operation. I'd think towing would be equivalent to coasting down a hill, so nothing bad should happen, provided the bike is secured properly in the front. Again, I have not tried it, so I can't guarantee it will be totally safe...
With ignition turned off there is no limitation of the regen voltage from the rolling backwheel. Possibly that it can hurt the motorcontroller.
Hello Bluesstreak,
I think that you can do it with no risk, when you switch off the ignition key you are on free wheel.
motor voltage exceeds battery voltage above 70kmh
if you exceed this speed with the ignition off, the body diodes in the IGBT module will rectify the motor voltage, and you will have significant regen current
key on might be ok, as the motor controller can still use field weakening to keep the motor voltage down, just as it does while riding normally
Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah in July 2010. Done 194'000km
In the spirit of "getting to the bottom of it", I looked at this article:
https://itp.nyu.edu/physcomp/lessons/dc-motors/dc-motors-the-basics
In there they show a basic H-bridge switching circuit to drive the motor. The schematic shown there has diodes protecting the transistors from back currents generated if the motor is spinning as a generator. Wouldn't the Vectrix have something similar? And wouldn't is effectively disconnect the electronic control from the motor and therefore no current will flow at all when the wheel is forcefully spun with the bike off? Yes, there will be voltage created, but without a closed circuit to allow current to flow, nothing should happen to the electronics, correct? Provided the diodes are rated to withstand high enough voltages, higher than what the motor would generate, that is.
And the motor itself should not overheat due to current, because ... there is no current flowing when there is no load connected. The only heat will be from friction and eddy currents and hysteresis losses. Friction heat should be minimal and nowhere near as much as the heat generated from when the motor is running under load or when acting as a generator. Heat from eddy and hysteresis should also be well-controlled and low, no?
Thoughts?
EDIT: I guess my logic above may be flawed, since it only takes into account the circuitry to drive the motor, and not the regen circuitry, which I think antiscab is referring to... I'm not clear how regen works if the bike is off...
The freewheel diodes are actually a part of the transistors
Think of a diode as a one way path
They stop the voltage from the battery going to the motor when the transistors are not conducting, and also provide an alternate path for the motor current when the transistors are in the off state.
their blocking voltage in the case of the vectrix motor controller is 600V
Their reverse voltage is only ~1.4V
If the motor voltage is more than 1.4V above battery voltage, a current will flow, with net power going to the battery
If you need to tow with the rear wheel on the ground, it would be best to disconnect the motor from the motor controller.
you could probably get away with just disconnecting the battery from the motor controller (as it's easier)
All the parts on the MC I can see can go to 200V (the motor voltage at 110kmh)
Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah in July 2010. Done 194'000km
Thanks for all the replies fellas. I do have a battery cut-off switch located under the seat, since I removed fans there is plenty of room for other items under there. I would like to use one of those towing hitches that is made just to lift the front wheel of the ground and it does swivel but I am not sure still if it would be ok to tow like this, please continue to help with this idea of towing like this as it may be helpful to others besides me. THANKS COOPER.
hello all,
I have try something very easy, take a slope at 100km/h and switch off the ignition key, if you don't touch the throttle, you are on freewheel, if you try to speed up then you obtain a very little regen and if you try to regen then you obtain a very little power up, very strange the comportment of the IGBT without power . I think that there no risk for a few kilometer on moderate speed behind your pickup.
I think what confused me was the direction of the diodes in the H diagram in my first link above: it doesn't make sense as the top pair of diodes is facing "down" while the bottom pair is facing "up". And, on top of that, they are marked as Zenner diodes, meaning they'd breakdown in both directions, if I understand how they work...
This second diagram makes more sense with the diodes all facing "down" and not being marked as Zenner. And your explanation makes sense with it (i.e., the diodes will "open" and with just a little overvoltage beyond the battery voltage): http://electronics.stackexchange.com/questions/80137/how-diodes-protect-h-bridge-dc-motor-driver
Anyway, my electronics circuit knowledge is very limited and 20+ year dated and unused since, so I'm taking opportunities like this to re-educate myself and hopefully clarify for others :)