EVSEs (car chargers) should be designed to do pass-through on dryer plugs
As an update to my proposal for a special circuit breaker to assist in managing home power I thought I would propose a much simpler alternative for those who have a dryer plug in their garage.
The proposal is a small modification of existing portable EVSE designs (the proper name for what is often called an electric car "charger") many of which come with the ability to plug into a dryer plug -- by unplugging the existing dryer.
The idea is simply to have a special dryer plug which has a pass-through dryer socket on it, so the dryer can be plugged into it. The EVSE would include current monitoring lines on the dryer socket, to know how much current is going to the dryer.
Any time the current to the dyer is more than tiny, the EVSE would alter its "pilot wave" -- the signal that tells the car how much power is available -- to reduce the amps it reports. Normally on a dryer plug it will report 24 amps, which is 80% of the 30 amp rating of the plug. If the dryer starts to draw 2 amps, it would reduce the available power to 22 amps.
If the dryer starts to draw more, it could either continue this, or simply shut down the power to the car entirely to be on the safe side. Truth is, few dry their clothes in the middle of the night, and even if they do, missing out on an hour at 24 amps is not likely to be a problem, since 7 hours still provides far more than most people drive in a day.
It would be nice if Tesla made a version of their mobile charger that did this, and it's a good feature for any plug-in EVSE, including the ones people take on the road to plug in at vacation homes or friend's houses. If those houses have an available dryer plug, it means they can set up the EVSE and not interfere with dryer operations.
There are two kinds of dryer plugs, so a version for either type would be needed.
This could apply to other plugs, such as 14-50 found in RV parks, but the main value would be with dryers, since dryer plugs are sometimes found in garages.
Note that a second alternative is simply to swap the dryer for a gas dryer. Gas dryers are more efficient and cheaper to run, and can be picked up for not much more than electric dryers, if you have a gas line in your laundry area. In theory the gas dryer will pay for itself in a few years (especially if you can sell your electric dryer.) You then have an empty 30 amp plug to run to your car.
Dryer circuits have enough power to charge typical cars at a rate of around 5.5kw, or about 25-30 miles/hour. That's 200 to 250 miles of range during the 8 hour off-peak night power cycle, which should be enough for anybody, though it's not the full rate many cars can take.
It should be noted there is a product called the Dryer buddy which does a variation of this -- it has a relay to shut off the car if the dryer is running. It costs $340. Doing it in the EVSE is much cheaper as it's mostly software and inductive current measurement which are cheap.