EV Voltage

They're usually 400V or 800V or something in those ballparks, with about 30% difference between full and empty (so an battery being 800V when full could be 615V when empty). Hybrids can have a bit more variation (more like

But you'd not be poking around the traction voltages with a multimeter without being fully rubber gloved up, and it makes no sense to say it's '10V down from 600V', unless your traction battery is so badly damaged that it's scrap.

Theo

My Auris hybrid's battery supplies around 700V. And if an EV's motor is 49kW, that's still gonna be 70A so it'll need fairly chunky wiring. You're hardly going to want it to be several time chunkier by having much of a lower voltage.

I think that is probably about right. They are certainly lethal.

Lets say you want 180 bhp. That comes to around 240kW

At 12V that would be 20,000 A. Compared with a starter motors say 400A. That is serious cable sizes you need, but up at 600V you are now into

Many thanks for the replies Theo/Tim Streater/TNP :-)

I am astonished, I had no idea that sort of voltage was involved. I have a Suzuki mild hybrid which uses 48 volt battery under the passenger seat and had imagined that was the norm.

Thanks for the info!

Another little detail ?

nib

and an internal combustion engine to provide most of the bhp :)

My car has a 240kW engine. In old money that's 309BHP or 313PS in new-fangled Euro-horses.

I'd known about the high voltage involved, but one thing I'd never thought about (because high-voltage DC was rare before EVs) is the issue of any arc forming. These are more difficult to extinguish than AC arcs, so I wondered if anybody knew if any special precautions are taken with EV circuitry to deal with DC arcs if they form. If so, what might they be?

It could be deduced from some basic knowledge:

you are going to need a few horsepower for a car to move. Each horsepower being *roughly* 750W but for speed 1kW will do.

A modest 50horsepower car is therefore 50kW.

If you want to keep the cables manageable (and "cheap") you need more volts than amps. So your 50,000 becomes something like (say) 500x100

All very much done without stopping and just a brief sanity check at the end, but you are still looking at voltage in excess of 500.

And given the weight and performance of the EVs I have ridden/driven,

I see other posters have put some actual numbers together, but I did that all without reference to anything (to show it can be done and keep the grey cells moving). It is being able to think like this that makes me weep when I hear the absolute bollocks spouted by people who have paid more for their hairstyle than their education on popular television. And it's why I have zero respect for the real scientists who sagely nod as it is trotted out. The rather egregious plugging of EVs by people like Prof. Hannah Fry being a case in hand. There is no way she can't not know how s**te they are.

How about "hydrogen power" which is the new eco bollocks.

Hallelujah for the IC engine. I am considering a new car, small enough to fit my 1980's garage. Any suggestions, IC only and about Kia Picanto size, welcome!

-- "The idea that Bill Gates has appeared like a knight in shining armour to lead all customers out of a mire of technological chaos neatly ignores the fact that it was he who, by peddling second-rate technology, led them into it in the first place." - Douglas Adams

My simple understanding of these things is that with AC voltages, you have a bit of cunning circuitry that detects when the voltage passes through zero (and hence the current also) and switches off at that point. Back EMF, caused by the dying current (V = DI/DT) and which is in turn responsible for the spark, is thus zero at that moment, and because V is zero, hence no spark. But with DC, current is always at the maximum, so DI/DT is at its maximum, and hence a big spark to try and maintain that current (Le Chatelier's principle).

But I'm sure it's more complicated than that! Someone will be along in a few seconds to correct me.

I bought a Picanto a couple of years ago with just that requirement, that it should fit into my 1960's garage and still allow me to get out of it. FWIW I'm delighted with it.

This site is pretty good for quick comparisons of dimensions:

Oh s*it. Had it upside down...My bad

The secret is to have no mechanical switches at all. Except maybe a last-ditch fusible link Motors are brushless. Controllers are solid state. I would imagine that there is a separate low voltage circuit for all the instruments and other stuff like windows and lights

Solid state.

The motors are three phase brushless AC motors anyway. But the solid state stuff is capable of breaking many thousands of amps and any flyback voltages are clamped with diodes etc. Usually high frequency pulse width modulations is used to control power and the inductance of the motor windings limits the start up current. Superb engineering. Shame about the batteries.

There's precharge circuitry. You get an arc because there's a potential difference between two points (let's say 400V dc and 0V), enough to ionise the air between them and cause a low resistance path. Current flows, more ionisation happens, and it becomes self-sustaining.

What the circuits do when switching is to establish a low current path first. So you have one terminal at 400V and another at 0V. You apply a high resistance path to bring up the second terminal to 400V at a low current. Because it's low current it's not enough to sustain an arc.

Now there's 400V on both terminals and so minimal potential difference between them. Next you close the main contactor and the high current connection is made. Because both sides are at 400V there's no potential difference across the contactor and so no arc is formed as it closes.

Since the motor/inverters are software controlled, you also arrange that there's no current being drawn when opening/closing contactors, both to avoid pulling arc currents and welding contactor terminals.

Theo