Tesla: Help Us Charge Two Cars on a Single Circuit

[[email protected]]

Tesla: We have a single 50 amp circuit to the Teslas. Last night, the Model S was finishing up, and the Model X charge time rolled around. The resulting 80 amp spike caused the breaker to trip. All good. But, Tesla, please help!

Option one: make the cars communicate to each other to avoid charging at the same time.

Option two: instead of setting start times for charge, make it so the end time can be scheduled. That way, we can start a car charging, and know it will end before the other car starts. This may result in some decrement in the number of miles charged if the charge ends before the desired mileage is reached, but that is better than overloading the system even if it is circuit protected.

 

[Derek Kessler]

Can't the new HPWC handle load balancing with multiple chargers on a single circuit?

 

[thimel]

Can't the new HPWC handle load balancing with multiple chargers on a single circuit?

Yes it can. So they just need two of the new HPWCs

 

[[email protected]]

Our circuit is a 14-50, so looking for a software scheduler which would be a very inexpensive fix. The "2 Tesla" problem is going to grow with Model 3....and I doubt there a lots of HPWCs out there...so, a simple software solution would be very helpful. As it is today, the software turns the charge on...just looking for a solution to turn it off.

 

[Obsoletion]

I would just set them both to 25 amps.

 

[GasKilla]

I have 2 EVs on a single circuit, wife's car is scheduled to start charging at 8PM and my tesla starts at 1AM. Baised on our "normal" commutes this works out fine. The software already allows you to schedule the start of charging and reduce the amp draw. You could also buy 2 HPWC and let them manage the amps. But it's really not that hard to determine a delay between the start of charging two cars, unless you both are driving 100+ miles a day getting a full charge shouldn't be an issue ...

 

[brkaus]

Our circuit is a 14-50, so looking for a software scheduler which would be a very inexpensive fix. The "2 Tesla" problem is going to grow with Model 3....and I doubt there a lots of HPWCs out there...so, a simple software solution would be very helpful. As it is today, the software turns the charge on...just looking for a solution to turn it off.

How are you plugging in two devices to a 14-50? Or do you have two 14-50 sockets on a single circuit? This would probably be against code in many areas.

I would just set them both to 25 amps.

Great idea!

Personally, my long term plan will be installing two HPWC devices to share a 50A breaker.

Programming the cars to coordinate with each other is a good idea, but it sounds rather complex in implementation. How do the cars know they are part of the "shared circuit"? I think I even pitched for this a while back. I'm sure there is a solution, but having two 50A outlets on a single circuit is generally a bad idea, so I don't see them supporting something like this.

 

[guipingfang]

Great idea!

Personally, my long term plan will be installing two HPWC devices to share a 50A breaker.

Programming the cars to coordinate with each other is a good idea, but it sounds rather complex in implementation. How do the cars know they are part of the "shared circuit"? I think I even pitched for this a while back. I'm sure there is a solution, but having two 50A outlets on a single circuit is generally a bad idea, so I don't see them supporting something like this.

I think it will be better to charge the car when it needs and with two HPWC devices to share a 50A breake,
maybe not two I think about it.

 

[andrewket]

Tesla: We have a single 50 amp circuit to the Teslas. Last night, the Model S was finishing up, and the Model X charge time rolled around. The resulting 80 amp spike caused the breaker to trip. All good. But, Tesla, please help!

Option one: make the cars communicate to each other to avoid charging at the same time.

Option two: instead of setting start times for charge, make it so the end time can be scheduled. That way, we can start a car charging, and know it will end before the other car starts. This may result in some decrement in the number of miles charged if the charge ends before the desired mileage is reached, but that is better than overloading the system even if it is circuit protected.

Tesla has already solved this problem. The new wall chargers can automatically load balance.

 

[AZ Desert Driver]

I would just set them both to 25 amps.

Such a simple, elegant and zero cost solution.
On a parallel track - I met a guy who has a 50 amp circuit, but chooses to charge at 25 amps because he thinks that the lower current flow will extend the life of all the electrical gear. He has all night, so why not charge slowly?
My question - is this really true? will lower current flow cause a measurable impact on hardware life?

 

[CmdrThor]

I would just set them both to 25 amps.

Actually you would want to do both at 20 so the total is 80% of the 50 amp breaker.

Installing two Wall Connectors that communicate with each other to share the circuit would be the safer option and wouldn't be a code violation.

 

[McRat]

Cutting back individual power to 20a is good, but depending how you drive, it could be simpler still.

Car A charges 40a while car B charges off any 120v outlet.
Then switch as necessary. This works because few people empty their battery each day.

But yes, Completion Time as an option is very good for folk with short night time power plans. Ours ends at 8am so I program cars to complete at 6:30am when we leave.

 

[brkaus]

Actually you would want to do both at 20 so the total is 80% of the 50 amp breaker.

So true. I can't believe I missed it. One of the reasons it is a bad idea to have two 14-50 on the same circuit out in the wild and why I doubt Tesla would support it.

 

[Yinn]

Tesla: We have a single 50 amp circuit to the Teslas. Last night, the Model S was finishing up, and the Model X charge time rolled around. The resulting 80 amp spike caused the breaker to trip. All good. But, Tesla, please help!

Option one: make the cars communicate to each other to avoid charging at the same time.

Option two: instead of setting start times for charge, make it so the end time can be scheduled. That way, we can start a car charging, and know it will end before the other car starts. This may result in some decrement in the number of miles charged if the charge ends before the desired mileage is reached, but that is better than overloading the system even if it is circuit protected.

Option 1: HPWC communicates with each other.

Option 2: I would like this for other reasons - so that battery can be warmed in the morning.

Option 3: Upsize your wiring and breaker. If you went up to a 100amp circuit, you can charge either car whenever you want. If you're running 2x 14-50 outlets and expecting them to run at the same time, you really shouldn't be on a 50amp circuit anyway. Imagine if you had an electric stove top on the same circuit, wouldn't it be unreasonable to expect your Tesla and stove to talk so that your charge can shut off when you cook?

 

[UberEV1]

Superchargers come in A/B pairs, why not have a single HPWC with two (A/B) outputs. Safely meets requirements if only a single circuit is available, allows batteries to charge at highest possible rate when charged serially (better for each battery) or allows HPWC to "allocate" current according charge status of each car to minimize total charging time for both, and reinforces company's mission to make EV ubiquitous (i.e. multiple EVs supported within a single household).

 

[TexasEV]

To the OP, you don't need a software solution, you need to follow the electrical code and either install each 14-50 outlet on a separate circuit, or use the new HPWCs that allows two cars to share a circuit. No way Tesla is going to come up with a software solution that lets people avoid following the electrical code in their garage.

 

[brkaus]

Superchargers come in A/B pairs, why not have a single HPWC with two (A/B) outputs. Safely meets requirements if only a single circuit is available, allows batteries to charge at highest possible rate when charged serially (better for each battery) or allows HPWC to "allocate" current according charge status of each car to minimize total charging time for both, and reinforces company's mission to make EV ubiquitous (i.e. multiple EVs supported within a single household).

The current HPWC does allow master/slave of up to 4 devices and will safely share the available power specified by the master.

Many people wouldn't want both HPWC in the same location, else they would be driving over the cords or have to unplug.

Of course, some would like both together, but the majority of the cost is in the cord set and the high power electronic parts that would have to be duplicated anyway. So an HPWC with two cords would likely not be much less than an HPWC with one cord.

Could always install two HPWC next to each other. One could also get an HPWC and a J-Wall (converted HPWC with a J1772 plug) if they had a Tesla and something else.

 

[andrewket]

Btw, a recent study concluded that the amount of TIME that a battery is charged has a significant impact on degradation, and therefore charging a pack faster (more watts) is better. If true, it would be better to charge the cars serially vs in parallel.

I'm currently on a plane and can't find a good URL for the source. I'll try to remember to update this post. It was a surprising conclusion.

 

[vandacca]

Btw, a recent study concluded that the amount of TIME that a battery is charged has a significant impact on degradation, and therefore charging a pack faster (more watts) is better. If true, it would be better to charge the cars serially vs in parallel.

I'm currently on a plane and can't find a good URL for the source. I'll try to remember to update this post. It was a surprising conclusion.

I think that's the conclusion that Jeff Dahn came to as well in his University of Waterloo lecture a few years ago.

 

[CSFTN]

They built your requested feature into the wall chargers rather than the car (as far as communication is concerned). I'd suppose there is a security problem if the cars talk directly to each other. Meanwhile, the concept that you can dial in, on the charging screen, a "must terminate charging no later than" really should be there. That would be easy.