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Power sharing recommendations for Tesla & J1772 cars

quincy1414

New Member
Nov 10, 2021
1
0
Bay Area
Hello,

I am trying to figure out the best option for adding a non-Tesla EV to our current setup. We have currently have a Model 3 Standard Range Plus that charges via the Mobile Connector connected to a 14-30 outlet in our garage. We used a dedicated 30A breaker here as we were worried about the overall load on the subpanel. We don't drive a ton, don't frequently need to charge from 0-100%, and always have a nice eight hour window overnight to charge at low rates (and could occasionally charge at higher rates when necessary). This works fine for us, but we just added a MINI Cooper SE (BEV). We need to park the MINI outside so we can't rely on the 14-30 outlet. We aren't ready to spend a lot on a service upgrade or complex electrical work at this point, but want to make a smart investment that will work if we do make upgrades down the line.

I was thinking of having an electrician run a split line (?) from the 14-30 circuit across the garage and to the outside, where I can install an EVSE for the MINI. To minimize short-term cost, I was thinking of purchasing two power/load sharing EVSEs - one for the Tesla in the garage and the other outside for the MINI. I know that the Tesla Wall Connectors can power share, but only if they are the same type, i.e., I can't get a Tesla WC for the Tesla and the new Tesla J1772 WC for the MINI. I could, however, get two Tesla WCs or two Tesla J1772 WCs that would communicate and then use an adapter on one of the cars. Or I could look at two JuiceBox or WallBox EVSEs. The JuiceBox solution seems very attractive as it can plug into a 14-50 outlet (increasing portability and reducing the need for an electrician) and the boxes communicate via wifi (and thus not needing a communication wire to run across the garage between the two EVSEs). We'd then use a J1772 to Tesla adapter to charge the M3.

I realize that sharing the 30 amp circuit is not optimal, especially in cases where the cars are both charging. If we can usually add at least 100 miles overnight to each car, I would be happy. In the long-term we could provide more power while still keeping the cars while leveraging the same circuit (saving $).

- Has anyone done anything like this? If so, what is your experience?

- If both cars are charging and the juice is split, 50/50, how many mph would I get on the M3? (~11? That is good enough)

- Any issues with using an adapter to charge regularly like this?

- Any reason to go with the Tesla EVSEs vs. JuiceBox???

Thanks so much for your assistance here. Much appreciated!
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Moderator
Nov 28, 2018
12,428
14,804
Riverside Co. CA
Regarding charging speed on the tesla, a 15amp circuit (12amp charging speed) looks like 11 mph charge rate, according to teslas chart:

Screen Shot 2021-11-10 at 12.29.43 PM.png


As far as what you are asking, I think If it were me, I would look at the tesla J1772 EVSEs and I would also have an electrician do a load calc to see if that line you have can be upgraded further than 14-30, without a lot of additional cost.. especially since you are in CA and trying to ensure charging during off peak TOU times.
 

RTPEV

Active Member
Mar 21, 2016
1,195
1,468
Durham, NC
I built a J1772 Hydra EVSE which is a dual-headed J1772 EVSE that can run in either shared (split the output current) or sequential (charge one, then the other):

20160129_123710.jpg


I use an adapter for my Tesla as both connectors are J1772. The unit pictured above had a J1772 inlet that was fed by a host EVSE, but I rebuilt it later with a NEMA 14-50 plug that does not require a host EVSE (as we had moved and left our old charging station behind). It's obviously a very custom solution (not for everyone) and wouldn't necessarily save much cost over a commercial dual-headed unit or two load-sharing capable units, but I'll put it out there anyway.

But I did want to throw out my experience now that my wife and I both have long range EVs. Basically it's that we don't really need a dual headed unit any more! This was almost a necessity when I had a 2012 LEAF and she had a Volt, both with only 3.3kW chargers. Both cars needed daily charging and would take hours to charge at 3.3kW. Even when we had two LEAFs, hers had the 6.6kW charger and hers would finish charging in about 90 minutes so I could easily just manually unplug hers and plug mine in. It's when she got the Volt that I decided to build this.

Now I have a Model 3 and she has an ID.4. I charge once every 4-5 days, and she usually goes a week between charges. I can pretty much count on one hand the number of times that we have charged on the same day. It's usually very easy to just wait an extra day before plugging in. I will say that we both now have very modest commutes (me not at all thanks to the pandemic), and we are not on a TOU tariff, so it's not a huge deal for her to plug in in the afternoon and I can set my timer for charging in the late evening.

My point being, before you invest in a second EVSE, or a dual-headed EVSE, validate that you even need to plug both vehicles in at the same time. Does your situation allow you to manage your charging such that you just alternate days in which you plug each car in? If I didn't have my homebuilt EVSE at this point, knowing what I do now, I'd just get a single EVSE and timeshare it with my wife. If there was a real critical need for us to both be plugged in at the same time, I'd plug one into the NEMA 14-50 and then the other into a regular 120V outlet overnight. Yeah, I'd only get 4 mph on the 120V, but that's still about 40 miles overnight.
 

Hot Cha

Member
Aug 25, 2019
35
27
Wisconsin
I’m reading the Tesla description regarding the J1772 version of the wall connector. Is it possible to connect a Gen2 Tesla connector to this J1772 and load share? I assume so, but the wording would imply only J1772 to J1772.

The reason I ask is that I have a Gen2 wall connector powering my Model 3 and I’m looking at getting a hybrid that would charge from a J1772 connector. I’d like to load share off my 100a circuit that’s already run to my garage.
 

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miimura

Well-Known Member
Aug 21, 2013
6,844
6,739
Los Altos, CA
If you want to continue to use plug-in EVSE like the Mobile Connector, you can buy a Splitvolt or Neocharge device to share the 14-30 outlet between two cars. You would need a plug-in J1772 EVSE to use with the Mini. Alternatively, you could buy another Mobile Connector and use a Tesla adapter like Tesla Tap Mini to plug into the Mini.
 

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