[Iyke]

I just had an RAC call out for a family member. We both have EVs.
The 12v battery on my father in laws EV had an issue. Long story short the RAC staff member couldn’t wait to let us know how much he doesn’t like EVs.
started saying the batteries cost a fortune and that they can’t be recycled etc.
I pointed out that the batteries have second lives and can be used for things like energy storage in homes.
I just found it strange and quite ill-informed.

Has anyone else had an experience like it?

[Rolebama]

All the mechanic/technicians I know hate EVs for the simple reason they are not allowed to work on them. From their point of view they are nothing but trouble. Irate customers because of the lost time taking them backwards and forwards to the only people allowed to work on them. Waiting for the phone call to say they can collect it, and then having to present hefty bills to the owners.
One of my sons-in-law is a BMW Master Technician, and cannot work on EVs because the dealership he works in has not got the right equipment. They can't get the right equipment, because as I understand it, they employ non-technicians, ie apprentices, who may get their hands on it. So all their EVs have to go to dealers in London who charge twice as much, sometimes more, than them.

[olduser]

The big worry is the high voltages, around 440V, and high currents, though there are many safety devices built into the control system.
But it doe's mean before starting to work the safety steps MUST be gone through.
After that, it's just normal diagnostics.

The cost comes in due to the major replaceable modules are performing several functions, at high voltages, and currents.
The dealers are forced, by the manufacturers warranty, to replace these rather than have them repaired by a specialist.
I do wonder, what happens to the units taken out of service?

The 12V battery is supplying most of the axillaries found on any car, and is involved in some of the safety systems.
It is kept charged by the traction battery's (via the charging module) unfortunately the charging system is too smart, and stops charging when the battery is fully charged.

In an IC engine car, the battery is charged by the alternator via the controller, this system never really stops charging the battery there was always a 'trickle' charge.
This very small over charge helps to keeps the cells balanced.
(Since the advent of the sealed battery, this is now more tightly controlled, so even on IC engine vehicles out of balance cells is causing more batteries to be replaced early)

When I ran an EV, and came across another EV owner with 12V problems arranging the battery to charge overnight, into overcharge (to rebalance the cells) cured their troubles.
Note: Some cars will need an error code cancelling if the 12V battery is disconnected.

EV batteries can, and are recycled.

[NMNeil]

@olduser And yet there's no problem letting someone work on a system that uses petrol pressurized at around 40psi, or has an exhaust temperature of around 200 C ?
Back in the day I made good money when they first introduced electronic ignition and we would get plenty of owners who wanted to get rid of that new fangled unreliable system and replace them with points. Same for the first fuel injection where the owners wanted them replaced with carbs.
As for the proper equipment, the same complaint was made when the first OBD1 was introduced and the garage owners wouldn't invest in the code readers.
So nothing new really😎

[Drivingforfun]

@NMNeil

My granddad, bless him he died before 2000, was the same when ECUs came out. He would not want to touch anything with an ECU because it's not something he could take apart with spanners and physically see what was wrong!!

[NMNeil]

But thing change. When I first started working in garages the carburetors were either SU, Stromberg, Motorcraft or Weber (I may have missed a couple). So if you could fix those you could work on 99% of British cars.

[Drivingforfun]

I read a post by someone talking about his first decent job after uni, which would involve having mechanics looking to him for guidance... looking round he saw most were blokes in their 40s and 50s and he must have seemed anxious as the director told him "indeed some have 30 years' experience, others have one year, repeated 30 times"

[Rolebama]

I have no idea if this is relevant, but with standard CRT TV or monitor, there is a condenser capable of throwing an adult across a room. Even the standard 'leave it for 24hrs', was no guarantee of it being discharged. I speak from experience on that.*
I am taking a guess that there are condensers in EVs which possibly store far more current for longer periods than 24hrs.
*I used to repair computers and I soon discovered that a lot of monitors suffered from poor soldering, and I never took anybody's word that any monitor had stood for the 24hrs, so I did.

[olduser]

Originally Posted by Rolebama

I have no idea if this is relevant, but with standard CRT TV or monitor, there is a condenser capable of throwing an adult across a room. Even the standard 'leave it for 24hrs', was no guarantee of it being discharged. I speak from experience on that.*
I am taking a guess that there are condensers in EVs which possibly store far more current for longer periods than 24hrs.
*I used to repair computers and I soon discovered that a lot of monitors suffered from poor soldering, and I never took anybody's word that any monitor had stood for the 24hrs, so I did.

Not that I have experience of them for EV's but in converting from DC to AC, there are largish capacitors involved to smooth the created AC wave form.

The AC wave is created by making use of a Fourier series.(An infinite number of square waves added together will make a sine wave - as a matter of interest the converse is true, an infinite number of sine waves will when summed make a square wave)

The square waves being made by switching the DC on, and off but we can only produce a finite number of square waves, the resultant sine wave would not be smooth but would have many corners on it, these cause heating, and loss of efficiency in the motor, so capacitors are used to smooth the AC.
It is possible for these capacitors to be left fully charged.

[olduser]

Originally Posted by NMNeil

But thing change. When I first started working in garages the carburetors were either SU, Stromberg, Motorcraft or Weber (I may have missed a couple). So if you could fix those you could work on 99% of British cars.

Brings to mind the saying, "it ain't the devil you know but the devil you don't know that'll get you".

[NMNeil]

Originally Posted by olduser

Not that I have experience of them for EV's but in converting from DC to AC, there are largish capacitors involved to smooth the created AC wave form.

EV's use BLDC motors which run on DC and are controlled by a PWM signal.
They are, I believe the most efficient electric motors available. No AC involved except maybe for converting the mains AC to DC for charging.

[olduser]

I think you will find that the PWM (Pulse Width Modulation) is fed into the motor controller to convert into AC with a frequency proportional to the PWM.

If we apply PWM DC directly to a motor it makes a lot of noise as it runs in tiny jerks, and it will heat up.
The windings, which are inductors, cannot respond to the near vertical steps in the waveform, as inductors they resist the changes, the magnetic domains in the magnetic material being driven by the windings have a property called reluctance which has to be overcome to change the polarity of the induced magnetism, this takes a finite amount of energy, and time, all of which adds up to heat.
AC makes these changes relatively gently.

I could be out of date but I looked into variable speed drives in industry before, and after electronic control systems became available.
Variable frequency AC eventually came out as the way to go for the reasons above.