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EVs immobilised by flat batteries or breakdowns

A few weeks ago while driving back from a weekend away we came across several long queues on the Autobahn apparently due to stuck vehicles. One, on our carriageway, was caused by a car half on the hard shoulder and half in the slow lane. The police were there and I couldn’t see why two police officers and the driver couldn’t move the car a few meters on the level. A little further on there was a car stopped in the middle lane of the other carriageway. Again the police were in attendance but seemed unable to move the vehicle to the hard shoulder. As there was a good 5km of queue behind this one there should have been enough people to pick it up and carry it off the road.

After some internet searching I came across this article:

https://www.motoringresearch.com/car-news/transport-minister-astonished-hazard-electric-car-motorway-breakdowns/

“When an electric vehicle ceases to function, it stops; it does not coast in the way that other vehicles do,” said Barnoness Randerson, Lib Dem transport spokesman, during the debate.

“Smart motorways are supposed to be the future, but the future is electric. Those vehicles stop very suddenly. They also cannot be towed; they have to be put on a low-loader, which is a much more complex and longer process that will put rescue teams in greater danger.

Indeed, during a test of real-world electric car range, Carwow found that some EVs were “difficult to move” when the batteries were run truly flat. Most cars in the test ‘locked up’ once they were out of juice. The tested included everything from the Tesla Model 3 and Audi E-tron, to the Kia e-Niro and Nissan Leaf.

 

Is this true/realistic or has the problem been somewhat exaggerated? I am used to manual cars with conventional handbrake that can easily be pushed. Are EVs such a problem to move when something goes wrong? What about conventional cars with electric handbrakes, can they get stuck as well?

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  • Hopefully I can add some clarity, but unfortunately it isn't a straightforward or simple answer!

    Firstly, yes I think the problem has been exaggerated but also that it is a real issue. The trouble is not all EVs use the same batteries, motors etc and then the manufacturers also have their own ways of control, protection and safety.

    The majority of EVs on the road today use a Permanent Magnet (PM) motor, and the motors are usually directly connected to the wheels, via some gearing but no clutch, this means that the motors can't be disconnected from the wheels. Being a PM motor, if it is being mechanically driven, the magnets will enduce a voltage in the windings of the motor (back emf) and if the motor control electronics (inverter) isn't operational (vehicle has broken down) then this voltage is uncontrolled and increases with speed, hence the vehicle manufacturers not wanting the vehicles to be towed or at least towed while the driven wheels are on the ground. But the vehicle should be able to move a very slow speeds, so pushing off the carriageway onto the hard shoulder shouldn't be an issue.

    However, if there is an electrical load connected to the inverter, the electricity generated by the motor when the vehicle is moved will drive current into the load and the result is that there will be a resistance in the motor making it more difficult to move the vehicle. This would be down to how the vehicle manufacturer has designed and implemented the EV powertrain.

    Regarding the vehicle being immobilised, all EVs are fitted with a similar 'park' function to that on a regular automatic transmission. This consists of a small pin which engages in a hole in the powertrain and 'locks' the powertrain. It has the same safety features and control as the one on an automatic transmisson, so it should be able to be released if the vehicle needs to be moved. For example the Jaguar I-Pace has a parking release handle under the bonnet which if the vehicle is completely dead, the gearbox lock can be manually released by pulling on this handle. But I'm not sure if this is in the user manual or widely known by rescue services. Electric handbrakes can usually be released in the same way.

    I hope that makes sense and you can see how what you experienced can occur. In real terms it shouldn't be any more of a risk than an ICE vehicle breaking down.

    Regards
    Pete

Reply
  • Hopefully I can add some clarity, but unfortunately it isn't a straightforward or simple answer!

    Firstly, yes I think the problem has been exaggerated but also that it is a real issue. The trouble is not all EVs use the same batteries, motors etc and then the manufacturers also have their own ways of control, protection and safety.

    The majority of EVs on the road today use a Permanent Magnet (PM) motor, and the motors are usually directly connected to the wheels, via some gearing but no clutch, this means that the motors can't be disconnected from the wheels. Being a PM motor, if it is being mechanically driven, the magnets will enduce a voltage in the windings of the motor (back emf) and if the motor control electronics (inverter) isn't operational (vehicle has broken down) then this voltage is uncontrolled and increases with speed, hence the vehicle manufacturers not wanting the vehicles to be towed or at least towed while the driven wheels are on the ground. But the vehicle should be able to move a very slow speeds, so pushing off the carriageway onto the hard shoulder shouldn't be an issue.

    However, if there is an electrical load connected to the inverter, the electricity generated by the motor when the vehicle is moved will drive current into the load and the result is that there will be a resistance in the motor making it more difficult to move the vehicle. This would be down to how the vehicle manufacturer has designed and implemented the EV powertrain.

    Regarding the vehicle being immobilised, all EVs are fitted with a similar 'park' function to that on a regular automatic transmission. This consists of a small pin which engages in a hole in the powertrain and 'locks' the powertrain. It has the same safety features and control as the one on an automatic transmisson, so it should be able to be released if the vehicle needs to be moved. For example the Jaguar I-Pace has a parking release handle under the bonnet which if the vehicle is completely dead, the gearbox lock can be manually released by pulling on this handle. But I'm not sure if this is in the user manual or widely known by rescue services. Electric handbrakes can usually be released in the same way.

    I hope that makes sense and you can see how what you experienced can occur. In real terms it shouldn't be any more of a risk than an ICE vehicle breaking down.

    Regards
    Pete

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