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Charging 2 Tesla’s at home with standard included wall connector and 2 50amp circuits

Charging 2 Tesla’s at home with standard included wall connector and 2 50amp circuits

We currently own a model 3 performance (built July 2019) and a brand new model S performance to be delivered early December 2019.

I am on a time of use rate plan with my cheapest rates only from 12am to 6am daily.

That leaves us with only 6 hours to charge 2 Teslas overnight.

We have installed 2 separate dedicated 50amp circuits (one for each car) both with a NEMA 14-50 plug.

When I look at the model 3 charging screen, it shows a max of 32amps when plugged into a 50 amp circuit.
Does the model S also max out at 32 amps when using the included mobile charging connector?

So if both Tesla’s were charging simultaneously, it would be 32a + 32a = 64a total coming off my main circuit, correct?
Am I missing anything here?

I’ve run some rough numbers based on our individual commutes, and 32 Amp charging. Our new model S will need approx 4 hours to recharge each night and my model 3 will only need 2 hours because my commute is only 1/2 as long.

Should I schedule charging so the model S charges from 12am to 4am and the model 3 charges from 4am to 6am?

Or should I just set the model 3 charge speed down to 16amps and let both cars start charging simultaneously at 12am?

Which choice would generate the lowest peak load on my electrical panel?

My goal is to put the lightest load (wear & tear) possible on my electrical panel, while still getting our charging done within the 6 hour “super off peak” window for my electric bill.

32amps charge speed is more than enough to cover the daily use of both our cars. I don’t need to charge them any faster.

I don’t want to have to go out and purchase the Tesla wall connector(s) at $500+ each. I would much rather just use the included connectors that come with each car.

NKYTA | 6 December 2019

If you are worried specifically about “peak” load, pick option 2.

But bear in mind that charging will be slightly less efficient, costing you slightly more $ in electricity.

My old 2012 UMC goes to 40A, my wife’s newer 3 UMC to just 32A as yours does.
We have short commutes, and I can charge at work, so my wife’s 3 charges overnight once a week on our lone 14-50 outlet.

greg | 6 December 2019

While you can do this with Mobile chargers (I do something similar at home with two Model 3s). You do need to do a bit of manual configuring/settings adjustments for start time and such.

The S' on board charger will at least do 32 amp, it may do more, but you can't get more than 40amp off a 50amp circuit anyway (80% of the 50amp circuit = 40 amps) for a long term load like this. So you'd get at most 8amps more than the existing 32amp and no more.

And the Mobile connector is I think limited by design to 32 amps anyway.

If you start the S at midnight, then the 3 a little later, the S will likely have started its charge taper already. Or you could start both at midnight, with max current = 16amp for each to spread the load - it means the S will take longer to charge though than it should, and should you do a longer than usual trip your S may not be fully topped up by the 6am cut off..

Despite the cost, a really big benefit of the Wall Chargers/connectors is that they will support higher amperage and you can link the two wall chargers by a data link cable and set one the master charger and the other the slave.

The two chargers then talk to each other over the data cable and simultaneous charging is possible, it will not exceed the set amperage for the circuit(s) as it iwill ensure the combined load is managed.

I know its expensive to buy two of these. But it would be the best solution to this issue as it would be set and forget.
And you could have avoided that second 50amp charging circuit install.

NKYTA | 6 December 2019

@greg

“And the Mobile connector is I think limited by design to 32 amps anyway.”

My 2012 S UMC does 40A. I’m not sure about the newer Ss UMCs, they could be 32A, dunno, unfortunately it didn’t make sense to upgrade mine. Wife needed a 3, who am I to disagree!

“If you start the S at midnight, then the 3 a little later, the S will likely have started its charge taper already.”

Taper is what you see at a SuperCharger, fast DC - DC charging. AC charging has no taper.

I grant that your other statements are correct, and having dueling HPWCs with extra ability is very cool!

It doesn’t sound like the OP needs them though.

greg | 7 December 2019

@NKYTA
Gen2 UMC is 32 Amp design. OP clearly stated these are recent vehicles not old model S' like you have. Which support higher rates.

AC charging still has taper. Watch A model 3 car charging on AC next time and see the amps drop below the maximum allowed as the car charges and battery fills.

It happens less dramatically than at a SC but it does happen.

I see it on my 3 all the time as it charges at night. Starts at 32 Amp but closer to charge end as SOC rises amps drops to 16 or fewer.

NKYTA | 7 December 2019

@greg, I'll take your word for it that the new UMCs are 32A.

I charge my car on AC (J1772) at my office daily, sometimes to 70, 80 or 90%. I've never seen a taper...

Over 90% I can imagine it, but not in my experience. Unless newer Ss are different.

Passion2Fly | 7 December 2019

Both portable chargers for M3 and MS will be limited to 32A. If you decide to buy a wall charger, you could go up to 40A on a 50A circuit. Regarding you max load of 64A on your electrical panel, it depends... with a 200A service, I wouldn’t worry too much... that’s what the circuit breakers are for... Now, if your service is only 100A, that’s pushing it. I don’t think that you can have two 50A circuits anyway as per code regulations...

milesbb | 8 December 2019

If your two 14-50 outlets were installed to code you will have no problems running both at the max 32 amps. Do not over think this. Start both at midnight and always be charged in the morning.

bp | 8 December 2019

For the S, 32A may be too low if you've run the charge down. Recommend either getting Tesla's 14-50 connector or even better would be a wall connector (HPWC) - which can run at 40A (or higher for the HPWC).

32A is probably fine for Model 3 charging overnight.

Tesla2018 | 8 December 2019

I already had two 50 amp outlets in my house before I installed one for the car. One for an electric range and another for an electric dryer. My 5 ton ac unit is also wired into my electric panel. Have had everything on at the same time without any problem. Going to have to check the reading on my smartmeter thats on the outside of the house to see how many kwh I am using with everything running. I can check my hourly use on the FPL website and I dont think it was over $1 for any one hour period since my cost is about 10 cents per KW.

tes-s | 8 December 2019

It may be too late - but I think a better configuration would be a single 100a circuit with two wall connectors.

Rocky_H | 10 December 2019

Your copy of this post on this forum left out the most MASSIVELY important piece of information:

"The main circuit to the house is only 100 amps."

https://teslamotorsclub.com/tmc/threads/charging-2-tesla%E2%80%99s-on-10...