charging infrastructure supporting NACS

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the isolation transformer just makes sure there is no reference to ground on the high voltage side so someone does not get killed
It depends on context. It can also isolate from the inverter in the vehicle, so the output can be fed back into the battery and still be isolated from AC portion of the inverter.
An isolation transformer passes the current from one side to the other while keeping them electrically isolated from each other.
I read an article yesterday that crowed about the Nirvana of 277v charging. The notion that 277v charging will bring faster EV AC charging to the masses, while technically possible, is almost certainly not going to happen at any scale. The promise and potential lies elsewhere ...

My view is .... maybe. Hopefully !
Not for single home residential obviously, but perhaps for street side charging and workplace charging. There is a huge infrastructure of 277v lighting out there that might be tapped for EV charging and future V2G applications. As an (interesting to me) aside, the underlying reason that 277v infrastructure has unused capacity is due to the transition away from power hungry lights to LED.

Wondering why 277v exists at all ? US grid infrastructure is 3 phase power, and one of the integral step down stages is 480v, 3phase. A single phase is 277v
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277 is a single phase connection between one phase of 480 wye and neutral, it is common in commercial buildings with 3 phase and used for lighting circuits. May be that is what you were saying in your last paragraph?
I don't see it playing a big roll, being able to 3 phase charge like in Europe would be a bigger boon. Not a whole lot of difference between 277 and 240, just a little greater than 208 and 240.
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So I've been reading up on the NACS standard and is this just for QC? I mean I sure hope they don't do away with the J1772 standard I have on all my EVSEs! If they do ditch J1772 what's going to happen to all the J1772 EVSEs in both residential and commercial locations? I personally could care less about the QC connector as I never use it and for that I'm glad they are planning on standardizing and not having 3 QC standards but please don't tell me this will mean an end to J1772......
HI - J1772 EVs can use NACS charging with an adapter - Level 2 is easy, Level 3 ok for everything but CHAdeMO - don't kno what if anything will be available for Leaf drivers who want/need L evel 3 fast charging.
277V does seem to be useful for street lights and I suppose commercial establishments. But I wonder how big of a change it will be.

I can't imagine an apartment building that doesn't supply 240V or 208V for electric ranges, etc. So there must be 240V/208V power available in nearly all apartment buildings, offices, etc.

Is it really that big a deal to tap directly into the 480V supply in a building vs using the derived 240V/208V power that is probably already there?
Is it really that big a deal to tap directly into the 480V supply in a building vs using the derived 240V/208V power that is probably already there?
I've been visiting some commercial and industrial sites lately. Small retail is usually 240v split phase, the same as private home residential. Power supply up to ~ 1 MW have been 3 phase 208/120 or 240/120. Higher power is 3 phase 480V, and then lighting is often single phase 277V, big machines are 3 phase 480V, and the smaller 240/208/120 loads are fed from transformers in the bldg. These step-down transformers are generally sized for anticipated loads.

But as you point out and what I wrote earlier, the above is mostly irrelevant except for the fact that outside 277V lighting (both public and private) is an under-utilized infrastructure that is already in place.

As for LEAFs on the road, I'm not even sure their OBC can take 277V. Let me rephrase that: I'll be surprised if they can take 277V. Owners should realize that the LEAF is an exercise in cost-cutting to the max, and future charging changes may be (or *are*) likely to leave them out in the cold.
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I agree, the 277 at light poles assumes there is excess capacity in the circuit, and/or chargers will only be utilized when the lights aren't. Service manual I have doesn't mention 277 but I haven't look closely at it. I was more talking about newer production cars with the newer plug, not the older Leaf's
It's a pretty common flow for any higher-power (>100W) power supply. Your PC has one just like that.
The frontend (PFC) produces slightly pulsing DC, say in the range of 350-400V, so it's the first AC->DC stage. It's pulsing because a 1F grid input doesn't deliver the power continuously but rather at 120Hz pulses. There is some filtering after the PFC stage, which makes the output, say, 375Vdc with superimposed 120Hz 25Vac. The next stage is the isolation transformer, where you need high frequency (10s of kHz) for reasonable isolation transformer size. So the inverter produces 20kHz mostly square wave (which is still AC) to pass through the transformer, just to be rectified and filtered again to the final DC output. This second stage is where the regulation happens.

None of that has anything to do with regen. Regen happens directly through the motor 3F inverter, which is pretty much naturally bidirectional.
I like what tesla has done with their cars and his starlink endeavors. What keeps me from buying his products is musk just seems a bit to impulsive/on the edge for me to invest real money in his products as I just have no idea when he might slip, over the edge, and destroy it all. The twitter crap seemed like an chuckle-heads move. Even I closed my 17 year old twitter account and moved to Mastadon. Bill

But I do like his cars and SL.
I received some "bacn" (Gmail eats your Bacn) email from ChargePoint, most of which I've ignored. But, I noticed one from 12/18/23 that says in part:

"ChargePoint Home Flex, CPF50, Express 250 and Express Plus Power Link 1000 stations are now available with NACS connector options. Other stations, including CP6000 and Express Plus Power Link 2000, will be available with NACS options in early 2024."

Express 250 and Express Plus Power Link 1000 are DC FCs.