EV charging

A DC charging plug has two additional pins for + and -, I presume it does fancier communications over the existing (control pilot and proximity pilot) handshake pins to say "shall we do DC?" and "ok, how many volts do you want?" before anything happens on those +/- pins.

So not 'directly connected; at all.

Just a smart SMPSU running off the local AC grid, just like the cars internal charger, only bigger.

I can assure you there is nothing 'simply' about it. If you want efficiency you might not be using a crude rectifier.

Furthermore there might be little capacitance on the output, there are other ways to ensure a constant current, assuming that is what EV's are supplied with.

They could be, though I agree there is likely to be some management system that can disconnect the charger.

Otherwise there is no reason why, subject to an electronic switch, that the battery isn't otherwise directly connected to the external charger.

Where the charger is in communication with the battery control unit to set current and voltage and any other safety handshakes etc.

The external charger + pin is directly connected to the battery + The external charger - pin is directly connected to the battery -

Some negotiation happens before any voltages get applied to those pins. What's so difficult?

The negotiation is to adjust the electronics *between* the DC and the battery.

So there is not a 'direct connection'

There's no electronics between them, only a contactor and (commonly) a pyro fuse.

When you're shifting up to 1kA any components are very large and require cooling, which is why there is only switching and circuit protection.

Theo

OK, but those electronics are *in* the external charger, not in the car, so "the charger" is directly connected to the car's battery, that's all I was saying.

But you just said ; "Some negotiation happens before any voltages get applied to those pins."

And I am afraid a contactor cannot change the applied voltage or sense the current

Where does this mythical DC come from if not a switched mode power supply?

Which by definition handles kA at least on its output.

Of course kA is is switchable by semiconductors, or at leats the primary side of the transformer will be.

The diodes that rectify it will have to be at the minimum rated for the peak output. In practice you would probably use half a dozen in parallel.

In short yuou will jave AC to DC rectifier => smoothing capacitor => smart SMPS => ferrite output transformer =>smoothing caps => RF filter => car

The 'DC' part is immediately after mains rectification and there is lots more before it gets to the car

Indeed, but its not a 'direct connection to DC'

It is in fact a highly complex and expensive smart SMPS one. If Marketing calls that a 'direct DC connection' I wouldn't be surprised, but it doesn't make it true.

PS I wouldn't want to be anywhere near that when it goes bang. Which it inevitably will at some point

The DC coming across the cord, might be at 400V or 800V. This allows ordinary gauges of wire, plus some liquid cooling, to deliver a lot of power.

On the supply side of a fast charger, you would want a supply voltage of much higher value. Not because you want to rectify it and make the voltage the hobby-way. But because you want a finite amperage from the grid transformer. Like maybe a Tesla charge pad would use 11kV AC to the pedestal, and convert that to 400V or 800V DC as appropriate.

We have a Tesla charging station here, but there is very little signs of exotic infrastructure (no additional wires seeming to come to site, ordinary sized boxes at the site, no "private transformer", but there is a substation maybe a half mile away). The site originally had some other brand of charging (not particularly fast charging), which nobody used. The owner removed the first attempt and arranged for a Tesla instead (which promptly did see three cars show up for charging). A fish and chips truck sits next to the site, as our example of a "lux service" :-) At least you won't starve, while waiting.

Not enough detail here.

"What is a Tesla supercharger and how does it work?"

These would evolve over time, the design, but at least you can get some idea how they are dividing and conquering in the design. The incoming AC to the SMPS is a lower voltage at a higher current, so readily available semiconductors can be used. And then you'd need some pretty good cooling, as the SMPS has limitations as to how "efficient" it can be. Maybe it uses synchronous rectifiers on the output, instead of "diodes" like in your ATX PSU.

Paul

A transformer running at 50Hz will always bigger than one running at low RF in an SMPSU. For the same power.

Let alone feeding the bloody meter with two bob bits!..

Not when we had 15A round-pin plugs. They were far superior to 13A in terms of contact area between plug and socket. OK, they didn't have fuses or shutters but I'm sure that they could have been designed into something resembling a 15A plug rather than these rectangular pin monstrosities. The pins would have needed to be of a different size and/or spacing to prevent a mis-match but that would have been completely feasible. Aren't people still raving about some "brilliant" woman who invented the 13A plug?!

The 15A plug is alive and well and used with most theatre lamps, at least in amateur environments.

Shuttered 15A socket : MK K2893WHI

Fused 15A plug : MK 643WHI

And is standard in S Africa, and, I think other colonial places

I rest my case!

So why are we lumbered with 13A plugs? These 15A ones have silly price tags - but they wouldn't if everyone used them.

Because you can't use ring mains without local fusing, at least at the socket, and a fuse in the plug is more versatile. We used to have three sizes of mains plug, each connected to appropriate fuses in the fusebox. You still had to be careful not to overload any group of sockets connected to only one supply cable, and in general houses contained very few power sockets of any kind. The vacuum cleaner normally had a bayonet plug, to be used in the nearest light socket.