EV Voltage

Are there actually any contactors at all in a BEV? I would assume its 100% solid state.

Yes, for safety. The contactors are typically inside the battery such that the high voltage is completely isolated (both sides) when the vehicle is turned off. The 12V system's job is to boot the computers and then engage the contactors so that traction power can flow - if the computers say no then the battery remains isolated. If the plastic 'service plug' is pulled then the battery is isolated so it's safe for mechanics to work on the car.

If the vehicle detects an anomaly (eg airbags triggered) the first thing that happens is that the contactors open to isolate the battery. They can also blow a pyro fuse so that the battery is permanently isolated until taken to a workshop which is able to check for crash damage. There also can be a first responder loop which doesn't carry any power, but is just a signal that when cut to isolate everything in case of cutting occupants out of a crash.

Theo

Typically within the battery pack.

Knowing more and more about less and less, ultimately knowing everything about nothing.

If the current is at its maximum, i.e. not varying, then di/dt = 0.

Before WW2 manufacturers use to brag about 10 or 12 horsepower, but they used a formula based on cylinder size and so on which became out of date, so they were much more than that.

My 175cc Honda m/c was rated at "20PS" which is about 20HP.

I like Rolls Royce saying that their power was "adequate".

If I is at its maximum, and the circuit is suddenly switched off, I goes to zero very fast, and dI/dT is thus very high.

Well there is that, yes.

The energy associated with an arc depends on storage in inductors and whether the arc can be sustained at the voltage across the contact gap and the speed at which the contacts separate. The medium also makes a difference where sulphur hexafluoride is used in some HV switches to quench the arc.

EVs generally have a last ditch physical contact, and Ed China has a tear down of such a failed switch on YouTube for those interested.

The Bentley version would provide a spec and used essentially the same engine as the RR. So it was known to an approximation.

Except it doesn't work like that. There is inductance and capacitance all over the place.

The motors are all AC, and lord knows there have to be massive clamp diodes to take care of breaking any inductive circuits

They're three phase variable-voltage variable-frequency drives. There will no doubt be snubber networks to control transients as the MOSFETs/IGBTs turn on and off. The aim being to commutate the current through the windings so there aren't any sharp edges (which would cause EMI, amongst other undesirable effects).

Theo

The latest "pioneering" thinking is to use metastable chemicals in batteries. Obviously it needs more research (so there's the excuse to milk the taxpayer once more). And already - despite my sole A level in chemistry - I have decoded this as meaning they want to use explosives in batteries to store energy. What could possibly go wrong ?

If the greenies were serious about climate change etc etc, then the very first rule of EVs would have been exchangeable batteries. Eliminating the embarrassing charge times and making them pretty much drop in replacement for ICE cars.

But no, we had to allow a free for all with manufacturers being allowed to fight for their corner of the market. Guaranteeing the pisspoor

And so it come to pass.

It really is this simple. If the "alternative" to the current <whatever> is so s*it you need to pass laws to force it into the market, then the public will react accordingly.

See also: paper straws and CFL lightbulbs.

The very first cars ever made - in the 1800s - were electric. If only someone had bothered to do some frankly primary school research into why they did not take off. It would have saved trillions - and more importantly a fucktonne of public goodwill.

It literally "off the top of my head". You get the idea etc etc ...

Certainly I've never heard any noises on the radio attribuable to the drive.

Dunno about arcing precautions but the first plug in Kuga I had was subject to a recall due to some issue with charging the batteries. When it went in to have the batteries changed it had to be parked in one corner of the garage with barriers erected to stop anyone touching it and a guy had to come all the way from Germany to disconnect everything and make it safe. It did make me wonder why it was safe for me to drive it about for several months beforehand yet it needed such elaborate precautions once in the garage?

Richard

The barriers and signage setup is a H&S requirement for anyone working on an EV high voltage system - to prevent anyone touching anything when any of the safety protections are disabled, eg a random mechanic or customer wandering in.

Perhaps the garage has have a safety protocol that they have to do it any time anyone has an EV with a high voltage issue in the workshop? Even if they haven't actually undone anything yet.

Theo

All the instruments, lights, door locks, entertainment systems, security systems, etc. run off a good old-fashioned 12V lead-acid battery. All EVs charge this from the traction battery when running and many will charge it, while turned off, if the 12V battery gets low, as long as the traction battery is not too low.

Indeed EVs can need a "jump start", if the 12V battery is too low (either failing or left parked up for months) and they can't power up the control systems.