MG4 just got towed, will it still work?

Although this would suggest that cars could have a towing mode in principle, where the brake is off, motor freewheels and cooling is on. Though I suppose if anything went wrong there'd be no way to warn the tow truck driver to stop - flash hazards maybe?

And maybe there would be insufficient air flow for cooling on the back of a tow truck shielded by the cab?
 
But you'd think if it were dumping that energy as heat there would be a lot of it at speed. And to generate heat it would have to put a resistance across the motor - and that would slow it down, just like regen?

I'll have to research this one I think!
 
But you'd think if it were dumping that energy as heat there would be a lot of it at speed. And to generate heat it would have to put a resistance across the motor - and that would slow it down, just like regen?
There's always some resistance and heat losses, it is inevitable, but it will be much less than a regen load, so you probably don't feel it when in N on a motorway.

Anyway, good luck with the research, that's the best theory I have.
 
This sort of fits in this topic heading, so here goes.
If I was to flat tow my MG4 behind the motorhome, turned on, park brake off and a (theoretical at the moment) throttle match to the motorhome, so accelerating enough to keep up when driving and regen when stopping or on long down hill runs ..... what would happen once the battery was fully charged from the regen?

T1 Terry
 
I think we're going to have to wait for @Coulomb come back on this one for any kind of answer I'd trust.

My guess would be that when in neutral the motor controller produces a field to match that produced by the motor being driven by the wheels at the current speed. Perhaps in ICE car terms it would be to apply just enough fuel to rotate the engine but no more ?.

Edit: This was a reply to 'I'm just interested in what is happening to all this harmful back EMF when I've done that.' and not the more recent posts.
 
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What happens if you throw the car into neutral whilst in motion?
I would say that if you're below the constant power speed, the motor controller will do nothing, apart from allowing the motor to coast, and as always, monitoring the speed of the motor.

If the car is above that speed, then the motor controller is already bucking the permanent magnet. In neutral, it will continue to do that, as otherwise the motor would uncontrollably regenerate, this time into the battery. It would reduce the torque producing current to zero, so the motor and car are coasting. The torque producing and magnetising currents are at 90° to each other, so they can and must be controlled independently.

So nothing bad happens. Some drivers like to coast in neutral, as they find it's good for economy. The motor controller can find zero torque more accurately than the driver with the pedal.

But you'd think if it were dumping that energy as heat there would be a lot of it at speed.
The back EMF is a voltage, a potential. Just like the permanent magnet; it seems like something for free, but it performs no work (no energy is transferred) unless it's moving inside a coil of conducting wire. Even then, no work is done, unless the circumstances are right.

In the case of an electric motor being towed with the driven wheels on the ground, there is potential energy from the tow truck spinning the motor. But it causes little heat if the car is in neutral, just mechanical losses (friction and windage), and a small electrical loss from current flowing in the windings to weaken the field of the permanent magnet.

I'll agree it sounds crazy, but that's how permanent magnet motors work. Some cars try to avoid this sort of problem with induction motors, which have no permanent magnets. But it turns out that a tiny residual magnetism in the motor can "bootstrap" an induction motor into an induction generator. So you still need precautions with an induction motor.
 
If I was to flat tow my MG4 behind the motorhome, turned on, park brake off and a (theoretical at the moment) throttle match to the motorhome, so accelerating enough to keep up when driving and regen when stopping or on long down hill runs ..... what would happen once the battery was fully charged from the regen?
I don't fully understand the idea. If the car is accelerating to keep up, then why is it being towed? Also, the battery would not be charging, as drive energy will exceed regen energy.

I also don't see how this can be done safely and lawfully. I can just imagine gettting pulled over and getting the Australian version of "Ullo ullo, what's all this then?" ???
 
I think the bit about being towed is a bit of a red herring - he is just trying to create a situation where energy would normally be put in to the battery, but little taken out and over a long time.

A simpler scenario would be to put the car on an infinitely long hill so regen was used the whole time or (I think) equivalently tow the car with your foot off the accelerator for a long time.

Whatever the answer, this must happen often for people who live in the alps and charge their car when at the top, then "drive" to the bottom.

I assume the motor controller knows or senses the battery is full and effectively goes in to neutral. If towing, the power required by the motorhome will reduce. If on a long down hill it will force you to use the brake or reach terminal velocity.
 
The reason I'm asking is trying to determine if I can flat tow my MG4 behind the motorhome, or will I have to put it on a trailer with the rear wheels off the ground.
The ello, ello, ello wouldn't have a clue that the "towed" was actually running when they pulled me over .... no engine noise and nothing running.
The (yet to be designed and implemented) drive/regen would be controlled by the strain on the A frame towing the car, throttle added if the strain gauge read negative until the strain measuring device is in the neutral, regen applied if the strain gauge read positive until a neutral reading was indicated.

If I towed it in neutral with the ignition on so the pumps worked for cooling, I must have an active braking system in the "towed" that is controlled by the towing vehicle's driver. An application of the brakes would trigger regen, once the battery was full, what then, the Prius uses MG1 to drive the ICE to waste electrical energy once the battery is full, but there is no mechanical load the MG 4 can apply ...... a big resistor bank on the roof with big fans like a rail loco might raise a few eyebrows :eek: ;)

I thought about an option of dog clutch couplings on each rear axle, probably machine the 3 roller CV joint piece off and add it there with a multiball CV joint after it, the brake pedal application would not trigger regen, but it would probably throw fault codes and regen basically being the electric motor thrown into reverse would cause all sorts of fault codes because the wheel sensors would say the vehicle is travelling forward and the sensor in the motor would say it was travelling in reverse ..... so I don't think that would work at all.

The last option is developing a steering lock and reversing the MG4 onto the Gypsy trailer, so the rear wheels were off the ground and the front wheels down and turning backwards ..... with nothing turned on, would the wheel sensors see the front wheels turning but not the back wheels and throw a fault code?

T1 Terry
 
I see. My response was in written in the context of the previous posts - sorry about that ?.

However a bit of my answer may be relevant (if true):
and regen when stopping or on long down hill runs ..... what would happen once the battery was fully charged from the regen?
I suspect it would act like it was in neutral and you would lose all your active braking in the "towed" ?.

Could the regen produce enough braking force to satisfy the requirements of the active braking law anyway? If not, then your system would have to be able to apply the towed mechanical braking regardless and the regen dropping to 0 at full charge wouldn't be a problem.

I must say, you do like an interesting project ?.
 
Yeah, I got a bit lazy when I realised I didn't know how high a hill you'd need to charge a battery entirely from regen.
 
Sorry to be negative, but I can't see any automatic system being practical and safe. If this is to deliver the MG, just pay for the proper tow. If this is for using the EV as a runabout on a grey nomad trip, I can't see it working safely and legally. Sorry it's not what you want to hear ?.
 
It's for using the MG as a drive car when parked up in the motorhome. The regen braking would be to stop it pushing against the A frame and starting to self-steer, nothing like seeing the "Towed" in the mirror pulling out to overtake .....
We no longer have a house, so I'm trying to determine which vehicle to take with us and which to leave at the workshop yard.
Naturally, my first choice would be an EV, The MG 4 fits this well, second probably the Suzuki Jimny, then maybe the Blade, but it needs a battery pack as that was lost in the workshop fire .... next is the ever-reliable Prius on the Gypsy trailer ..... the Kombi is a project too far away at the moment, the Jaguar XF V6 is going to hopefully be a money spinner, if I can sort the electrics which was why it was sold cheap at a salvage auction, the 2001 C240 Merc will now probably be the vehicle the Lexus 450h V6 and L110 transmission goes into, a rather nasty knocking noise on start up is either a bearing, or a piston tapping against the head :eek: so that will have a similar problem being towed behind the motorhome ...... as well as looking a tad outrageous :ROFLMAO:

I'll wait till the MG4 arrives on the car transporter in Murray Bridge and see how it looks bum up on the Gipsy trailer and decide from there .....

T1 Terry
 
Naturally, my first choice would be an EV, The MG 4 fits this well,
Sorry, out of my depth here…. But.
Would the V2L capabilities of the MG4 sway your decision? Running various appliances while you're off grid or as a backup ?
 
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Sorry, out of my depth here…. But.
Would the V2L capabilities of the MG4 sway your decision? Running various appliances while you're off grid or as a backup ?
And it would be a secondary storage battery for the solar, then plug it in to the inverter as a limited supply over night so it can switch between full supply, partial supply and the house battery via the inverter to make up the short fall, and use any excess via the inverter/charger to top up the house battery ...... if I flat towed it and only used it for regen braking, that would be free energy .... just need to know if it would do any damage once the battery was full?

T1 Terry
 

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