V2V DC charging

[DBeckwith]

I know the new NACS standard includes male to male connection capability. The intent is level 2 urban charging where cable management is too difficult to maintain. They do this with J-plugs in Europe now.

So, with this in mind, could Tesla add V2V charging with such cables, instead of the AC ports? And taking it a step further, could they eliminate the inverter at each end and directly use DC.

Such a solution should be much more efficient and possibly quicker.

 

[MP3Mike]

So, with this in mind, could Tesla add V2V charging with such cables, instead of the AC ports?

It is possible, and Tesla might make something like that available on vehicles that support Powershare. (Like the Cybertruck.) I expect them to make a NACS adapter for the Powershare Mobile Connector to do this, but they haven't announced anything.

Lucid does exactly that, they sell an adapter that plugs into their mobile charging EVSE to put a J1772 end on the side you normally plug in to an AC outlet so that you can charge a J1772 vehicle from a Lucid charge port.

RangeXchange Charging Adapter

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And taking it a step further, could they eliminate the inverter at each end and directly use DC.

This would essentially be turning the vehicle into a mobile CCS charging station. It is possible, but highly unlikely. That would require putting a high power DC-DC converter in the vehicle, which would likely only be used when charging another vehicle. (Which is a fairly rare occurrence for most people.)

 

[DBeckwith]

Forgive my ignorance, but is the circuitry that matches the source DC voltage to the receiving vehicle be the issue? And if so could that circuitry be included in a cable specifically designed for V2V DC charging?

 

[MP3Mike]

Forgive my ignorance, but is the circuitry that matches the source DC voltage to the receiving vehicle be the issue?

Yes.

And if so could that circuitry be included in a cable specifically designed for V2V DC charging?

I suppose it could, but it would be very big, heavy, and expensive. (It would require a lot of cooling.) With the expense scaling based on how many kW you wanted it to support. (Probably something like $15k for 25kW. But I could be way off on that, in either direction.)

For example, it costs like $150k for a CCS charging station. A good portion of that is AC to DC rectification, but a bunch can be DC to DC to match the voltage depending on charger design. (Tesla leads on this as they cost something like $300k for 4 stalls, or $75k/each. But that gives you ~370kW of power to share across the 4 stalls. Or ~90kW/stall if they are all in use with empty vehicles.)

edit: Maybe it wouldn't cost that much, I think Porsche charged ~$500 to upgrade their on-board boost converter from 50kW to 150kW. But maybe that is different as it was only designed to boost the voltage from ~400v to ~800v, which could make it simpler and cheaper. (Or they were selling that option at a loss.)

 

[DBeckwith]

Would it be cheaper if it were only for emergency situations charging a depleted battery. I'm thinking of a tow truck scenario.

 

[MP3Mike]

Would it be cheaper if it were only for emergency situations charging a depleted battery. I'm thinking of a tow truck scenario.

Cheaper than what? But no, I think the equipment would cost way more than a ~$200 tow to the nearest charger.

Even for the AC solution Lucid charges $125 for the J1772 adapter cable, and that has to connect to the mobile EVSE, which Tesla charges $230 for their equivalent, so you are looking at $355 for a ~7-9kW AC type solution.

It is possible that Lucid could do something "inexpensive" with their "wunderbox" to provide vehicle to vehicle DC charging, but if they could have, I would have thought they would have done that instead of offering the J1772 adapter to hook to their mobile charger to provide vehicle to vehicle charging.

 

[vcor]

...could Tesla add V2V charging with such cables, instead of the AC ports? And taking it a step further, could they eliminate the inverter at each end and directly use DC....

No way. When charging via DC high voltage, the "provider" like a Supercharger, is told by the vehicle what voltage is needed in any instant to properly and safely charge the vehicle. It's not a single voltage and the voltage varies from 0% SOC to 100% SOC. In addition, different models have different voltage ranges they use.

If the battery needs 400v at one point during the charging and you attempt to connect it to 410v, it charges the battery too quickly, heats up, and can even catch fire! If you try and charge it at 390v (when it still needs 400v), then the battery will start to drain although there is circuitry to prevent this. The chance of having one vehicle at the exact needed voltage would be exceptionally rare, and in a few seconds, it would be unbalanced anyway.

So there is no possibility of connecting one battery (DC) to another car's battery via DC directly. You have to be able to control the voltage, which means large inverters - first to convert the DC to AC, then back to a different voltage needed by the car you are attempting to charge.

From a real-world need, it doesn't make sense. Few cars run out of power. There are plenty of warnings to avoid this scenario, to begin with. That said, there is always some yahoo who ignores all warnings and gets into trouble. They can pay for a tow to solve their incompetence. I doubt many people would want to be charged $2-3K for extra electronics to deal with a scenario that should never happen. Then on top of that, who wants to wait for an hour draining your battery to deal with someone else's incompetence?

 

[MP3Mike]

You have to be able to control the voltage, which means large inverters - first to convert the DC to AC, then back to a different voltage needed by the car you are attempting to charge.

You wouldn't need to convert to AC and then back to DC, you can just use a DC-DC converter to buck/boost the voltage appropriately.

From a real-world need, it doesn't make sense. Few cars run out of power.

I 100% agree with you here.

 

[vcor]

You wouldn't need to convert to AC and then back to DC, you can just use a DC-DC converter to buck/boost the voltage appropriately.

A DC-DC converter is a DC-AC-DC conversion (although the AC is typically high frequency to reduce the size/weight/cost, not 60 Hz). Likely doesn't matter much except to us engineers! The concept of directly connecting one battery pack to another pack for charging can't be done without some significant and costly conversion electronics.

 

[pdx_m3s]

DC to DC vehicle charging is not a thing. No way to synchronize the pack voltages.