MG4 just got towed, will it still work?

[SilverLightningFR]

Hi,
Sorry for the rookie question, but if our MG4 electric got towed by the council is it going to damage the car/battery/motor?

Thanks for your advice!

 

[Ian Key]

I'd have thought if it was a suspended tow with the rear of the car off the ground it might be OK. If the front was up in the air so the rear tyres were on the ground then damage will be caused.

Why do you ask?

 

[Coulomb]

is it going to damage the car/battery/motor?

It depends on how they towed it. If on a tilt tray, no problem. If on a hook, it depends on whether it was towed with the powered wheels (back wheels for the MG4 models) on the ground, without a dolly.

They also would not be able to undo the parking brake, and there is probably a parking pawl in the motor. So my guess is that they would not leave the rear wheels on the ground.

The problem is that without your key fob, they can't get it into neutral, so spinning the back wheels turns the motors into generators. Above a certain speed, the generated voltage becomes higher than the battery voltage, so the motor attempts to charge the battery in an uncontrolled manner. This will cause significant drag on the tow vehicle, so perhaps they'd notice and realise that something is wrong. The uncontrolled current could cause the motor controller to burn up, probably blowing the main battery fuse. This will not be wonderful for the battery, but it should survive OK.

The bottom line is, if you can drive the car away, then it has likely suffered no damage at all.

The bad news is, in the unlikely case that the car doesn't go to ready for you, it's going to be an expensive repair; at a wild guess, thousands of pounds. And of course, it will need another tow to the repair shop. And of course, you get to argue with the council about who pays.

 

[SilverLightningFR]

Thanks for the responses, it’s what I thought. I have no idea how it was towed as they came in the night! Usually they use a dolly round here so I am expecting bad things, but remain optimistic. Hopefully if there is a problem it is covered by insurance

They seem to have towed it right, no errors or problems… the battery is on 55%, which it was in the night… how else do you know if there was damage?? I guess we dodged a bullet ?

 

[mg4mc]

Without a key the rear wheels are mechanically locked in the gearbox. They would have to either lift the rear or put the rear on a dolly.

 

[Coulomb]

how else do you know if there was damage?? I guess we dodged a bullet ?

Most of the systems will either have completely broken, or would be completely unaffected. The thing that could potentially have been "wounded" (had its expected lifetime reduced) is the main battery.

As others have said, the rear axle can't have turned, so there is almost certainly no problem. But if you wanted to be really safe, you could check the state of health (SoH) of the main battery with an OBD2 dongle and suitable software, and compare that with the SoH of other MG4s of similar age.

And now, @SilverLightningFR, would you care to confess your sin that caused the council to move your vehicle? Or was it some innocent misunderstanding, or...? ???

 

[WonkoTheSaneUK]

Just spotted the "if" in OP's question.

If you're lucky, the towing firm your council uses has one of these:-

 

[haloweenhamster]

My uncles MG ZS was robbed using one of them after they shut in the UK, police found one small part at a breakers yard
This shape & in yellow

 

[Fluffykins]

What, precisely was your alleged contravention?
There may be weaknesses in the stated case, plus there may well be procedural errors in the way the tow was called for and implemented.
I would suggest a quick foray into the forums at Free Traffic Legal Advice - Index
Go to the page for Civil penalty charge notices (Councils, TFL and so on).
Start at the second 'sticky' topic then have a read of a few live threads.
The folk there have a lot of experience fighting tickets. Some of them are legal professionals. If your case is winnable, they'll tell you. They'll also tell you if they think it's not.
Good luck

 

[Deleted member 17430]

It depends on how they towed it. If on a tilt tray, no problem. If on a hook, it depends on whether it was towed with the powered wheels (back wheels for the MG4 models) on the ground, without a dolly.

They also would not be able to undo the parking brake, and there is probably a parking pawl in the motor. So my guess is that they would not leave the rear wheels on the ground.

The problem is that without your key fob, they can't get it into neutral, so spinning the back wheels turns the motors into generators. Above a certain speed, the generated voltage becomes higher than the battery voltage, so the motor attempts to charge the battery in an uncontrolled manner. This will cause significant drag on the tow vehicle, so perhaps they'd notice and realise that something is wrong. The uncontrolled current could cause the motor controller to burn up, probably blowing the main battery fuse. This will not be wonderful for the battery, but it should survive OK.

The bottom line is, if you can drive the car away, then it has likely suffered no damage at all.

The bad news is, in the unlikely case that the car doesn't go to ready for you, it's going to be an expensive repair; at a wild guess, thousands of pounds. And of course, it will need another tow to the repair shop. And of course, you get to argue with the council about who pays.

Don't be ridiculous. The motor isn't connected to the battery you fool. If it were, the car would have driven off instead of getting towed.

 

[siteguru]

What, precisely was your alleged contravention?
There may be weaknesses in the stated case, plus there may well be procedural errors in the way the tow was called for and implemented.
I would suggest a quick foray into the forums at Free Traffic Legal Advice - Index
Go to the page for Civil penalty charge notices (Councils, TFL and so on).
Start at the second 'sticky' topic then have a read of a few live threads.
The folk there have a lot of experience fighting tickets. Some of them are legal professionals. If your case is winnable, they'll tell you. They'll also tell you if they think it's not.
Good luck

Agreed. That's what used to be known as Pepipoo Forums but they relocated when the people running/owning Pepipoo had issues.

 

[Bam Bam]

Well I may be out of order, but it really gets on my nerves when someone comes here for advice, and someone else, who clearly don't know the answer, decides just to make some stuff up and spout it as though it's from the bible.

We are inevitably speculating because we don't know what the towing method was.

Considering what the possible methods might have been seems a sensible way to proceed, and then to guess what possible damage to be caused by each of those.

If you know of further forms of towing or damage that could have been missed out then you can add to the conversation and we all benefit.

 

[Rolfe]

People, if you believe a post contravenes the forum rules, just report it. Then butt out. A bunch of posts that simply continued the bickering have been deleted.

 

[Ian Key]

What, precisely was your alleged contravention?
There may be weaknesses in the stated case, plus there may well be procedural errors in the way the tow was called for and implemented.

The OP is in Paris so the laws and regulations will be different. The authorities will either require enough paperwork to be filled in in triplicate to multiple governmental and local authorities to fill a large filing cabinet or be treated with a Gallic shrug.

 

[Coulomb]

Don't be ridiculous. The motor isn't connected to the battery

Sigh. You are of course correct, the contactors will not be on, so the battery won't be connected while towing, unless the car is in neutral. My apologies for the woolly thinking.

I'm continuing the very unlikely scenario where the car is being towed with the driven wheels on the ground, with all brakes and parking pawls somehow not interfering with vehicle movement.

Unless there is a honking great contactor to disconnect the motor from the motor controller, the motor will still be connected to the motor controller. The back EMF is still rectified by the free-wheel diodes of the Insulated Gate Bipolar Transistors (IGBTs) in the motor controller, charging the bus capacitor. The bus capacitor and various parts connected to the DC bus, which would connect to the battery when the car is in ready mode, are rated at a modest safety margin over the highest voltage of the battery. Let's say that the battery is at 420 V when fully charged; the bus capacitors might be rated for 450 V. Without the motor controller actively opposing the field of the permanent magnets in the motor, at a certain speed (roughly 45 mph, if the start of the constant speed region for the motor corresponds to wheel speed of 40 mph), the back EMF from the motor is higher than the rated voltage of the bus capacitors. If they are electrolytic, they can probably sustain say a 10% overvoltage for some minutes, but more than that (in voltage or time or both) and they will degrade quickly and likely explode. Other components could also be damaged. The IGBTs themselves will likely be rated for some 600 V, but even that will be exceeded at any speed over roughly 60 mph. Granted, a tow vehicle might not exceed that voltage, but if it did and the IGBTs failed short circuit (a common failure mode), the motor could effectively become short circuit, placing a sudden violently large load on the tow vehicle.

As I said, this scenario is quite unlikely, but my theory is that neutral gear is designed to prevent this scenario. I'd be interested in hearing from those with more experience in this area, whether this theory is correct, or wrong, or perhaps unlikely because of something I've overlooked.

For those not interested in the electronic theory, my apologies for the technobabble.

 

[tsedge]

To be fair, this is a really common misconception - so much advice out there that towing "damages the battery".

But yes, it isn't a good idea for the motor/gearbox as there's no true neutral gear and these are being exercised with nowhere for the generated current to go.

 

[mg4mc]

What happens if you throw the car into neutral whilst in motion? Isn't that a similar situation? No energy goes back into the battery, what happens to the back EMF then? And if it is harmful, why do the control systems let you do it?

 

[tsedge]

What happens if you throw the car into neutral whilst in motion? Isn't that a similar situation? No energy goes back into the battery, what happens to the back EMF then? And if it is harmful, why do the control systems let you do it?

When the car is in motion, the HV battery is still connected, it can still regenerate if it chooses to, it is just that there's no power going to the motor, it is being allowed to freewheel.

I don't know the precise details but I assume this is what makes the difference. Maybe it will regen a bit if it needs to on extended use of N?

There is no clutch or other mechanism to disengage the wheels from the motor/gearbox drive unit, so it is very different to ICE. The only mechanical disengagement is the HV battery contactors.

But it is a good question and I don't feel I have properly answered it.

Actually, just thought of another reason. The drive unit has its own cooling loop and presumably that is not operating when the car is not ON.

This may be why people warn against towing overheating systems and may be the difference in N.

The other concern would be the parking brake.

 

[mg4mc]

I've coasted in neutral for miles at a time, and it appears to totally freewheel, no regeneration and no resistance I can can notice. The car speeds up as the slope increases. This is at motorway speeds.

I'm just interested in what is happening to all this harmful back EMF when I've done that.

 

[tsedge]

Yes, presumably the cooling system is running so that is fine?