Welcome to Tesla Motors Club
Discuss Tesla's Model S, Model 3, Model X, Model Y, Cybertruck, Roadster and More.
Register

Using dual TT-30s for charging?

doghousePVD

My grandfather’s car
Dec 3, 2018
669
616
New England, USA
Has anyone used a Y-connector with dual TT-30s, one on each phase? It should nominally deliver 30A at 240V, so charge at 24A. I could make one, and they have them for sale on Amazon.

Yes, I know the setup is not to code/"legal", and one could touch a hot plug. That's not my question.

Has anyone actually used this? How often? How hard is it to find separate TT-30 on opposing phases? Did you have a TT-30 extension cord? Were campgrounds very opposed to this when they found out?

I'm off to a camping trip to Baja California this winter with a trailer. No 14-50s, Chademos, J1772s or Superchargers south of Ensenada. I've looked at the Tesla hotel destination chargers, which may or may not be available to a non-guests. Round trip Ensenada - Cabo San Lucas is about 2000 miles. A full charge with a single TT-30 is over 24 hours.

Looks like there is just one welding shop about halfway down, so they probably have a 6-50. There are a few others in the south: Cabo San Lucas/Las Paz
 

doghousePVD

My grandfather’s car
Dec 3, 2018
669
616
New England, USA
Partial answer - the campground at Okefenokee Swamp had dual TT-30 on alternate phase at all the “30 A” sites. They also have 50 A on some sites but they were filled.

In short, I’ll get a combiner cable. Fortunately it wasn’t necessary at that stop, but could be another time.
 
I'm actually interested in this as well. I think there is a significant safety concern with the potentially unused TT-30 plug having 120V on it (as you alluded).

Did you get a combiner/Y-cable? I see them on Amazon and may try it out at a local campground with a multimeter.
 

doghousePVD

My grandfather’s car
Dec 3, 2018
669
616
New England, USA
The risk of hot prongs is very low. The TT-30s are wired to opposite sides of the 14-50, only the neutrals are connected together.

Only if the TT-30 outlets are miswired and the Tesla charger malfunctioned could there possibly be a hot uncovered prong. A 14-50 with only one hot and a neutral won’t connect, so no current flow.

A combiner won’t work if they are GFI outlets, or if they are connected on the same phase. But not dangerous.
 
  • Disagree
Reactions: Rocky_H

Rocky_H

Well-Known Member
Feb 19, 2015
7,332
9,031
Boise, ID
The risk of hot prongs is very low. The TT-30s are wired to opposite sides of the 14-50, only the neutrals are connected together.

Only if the TT-30 outlets are miswired and the Tesla charger malfunctioned could there possibly be a hot uncovered prong. A 14-50 with only one hot and a neutral won’t connect, so no current flow.
That's not correct. This is exactly the same risk/danger as trying to combine any two 120V outlets like this, regardless of whether they are 5-15, 5-20, or TT-30, etc. And yes, it does have that risk of having a live electrified exposed prong if one side gets pulled out of the outlet. The monitoring and safety cutoff protection against that is what you pay extra for if you get a professionally made device like a Quick220 (TM). It will only allow full connection if it can detect that both sides are making connection into their outlets. If either side gets pulled, it disconnects the other side as well, so it won't allow an exposed prong that is live and a shock risk.

Simple ones that are just Y joiners are always going to have that risk.
 
  • Like
Reactions: DCGOO

bradtem

Member
Dec 18, 2018
59
94
Sunnyvale, CA
That's not correct. This is exactly the same risk/danger as trying to combine any two 120V outlets like this, regardless of whether they are 5-15, 5-20, or TT-30, etc. And yes, it does have that risk of having a live electrified exposed prong if one side gets pulled out of the outlet. The monitoring and safety cutoff protection against that is what you pay extra for if you get a professionally made device like a Quick220 (TM). It will only allow full connection if it can detect that both sides are making connection into their outlets. If either side gets pulled, it disconnects the other side as well, so it won't allow an exposed prong that is live and a shock risk.

Simple ones that are just Y joiners are always going to have that risk.
The quick220 does not seem to have a TT-30 model. I see the risk you are talking about in that while RVs never use 240v and thus would not feed current between the two hots, a Tesla does. Firmly in place risk would be low but not zero. All you would need would be a relay that connects the circuit only when the other hot is live, so it need not be a very expensive device.

I have been told there is a risk to trying to combine from two plugs on different phases if you used long cords -- ie. if you had a plug on one post, and another plug on another phase 20 feet away on another post, and you then used an extension cord to draw between the two hots. That induction with the large distance between the conductors could be an issue. Anybody heard of that? Wen you see two TT-30 on the same pole, are they going to be on different phases, or might they be on the same phase? If there are some on the same phase, you wold want a different adapter which would at least let you draw max amps at 120v (32a or 40a depending on model of TMC) which is better than 24a from a single TT-30. You would have even more risk from a Y-splitter of this type. And two 5-20Rs on the same phase but different breakers could also let you draw 32a at 120v with the same issue. I have never looked to see when they have two 5-20Rs with 2 breakers for them if they put them same phase or different.
 

doghousePVD

My grandfather’s car
Dec 3, 2018
669
616
New England, USA
At the two parks I tested with a voltmeter there were two TT-30s in the pedestal, and they were wired on different phases. I didn't have a combiner at the time.

If they were same phase, just a simple TT-30 => 14-50 would be fine, and I have used it those two parks at 24A at 120V (80% rule). Not exciting, but doubt the effort to make a work at 32 A across two plugs isn't worth the effort. A bit more risky, too.
 

bradtem

Member
Dec 18, 2018
59
94
Sunnyvale, CA
At the two parks I tested with a voltmeter there were two TT-30s in the pedestal, and they were wired on different phases. I didn't have a combiner at the time.

If they were same phase, just a simple TT-30 => 14-50 would be fine, and I have used it those two parks at 24A at 120V (80% rule). Not exciting, but doubt the effort to make a work at 32 A across two plugs isn't worth the effort. A bit more risky, too.
Well, in 10 hours at 24a you are going to pick up about 100 miles overnight. At 32a it's 133 miles. So yes, modest for the work. Now, if you have a 40a internal charger it's a larger difference. 166 miles is starting to approach a "fill up" in a SR+/mid range since good practice is to go from about 20% to 90% and that's 165 miles. Except of course only the long range can charge at 40A. Now in emergency charging, ie. daytime charging while you sit waiting because you tried to travel a link that is too far between chargers, every amp counts. But you would need to build a custom connector for that situation.

If you are skilled (which I am, enough at least) one might buy one of these Y-adapters and cut it and put 45 amp anderson power poles on it, so you can rewire it on demand in different configurations, including left disconnected with right hot and neutral to the two hots, left and right to the 2 hots for opposite phase, and left and right paired to one hot and neutrals paired to the other hot. Or pre make a kit of ways to switch the wires. Frankly, I have not see dual TT-30 too many places. However, in Canada, 50a is more rare at parks, and 30a is a wussy overnight.
 

Rocky_H

Well-Known Member
Feb 19, 2015
7,332
9,031
Boise, ID
That induction with the large distance between the conductors could be an issue. Anybody heard of that?
I have never heard of induction being any issue with EV charging ever, in any circumstance.
Wen you see two TT-30 on the same pole, are they going to be on different phases, or might they be on the same phase? If there are some on the same phase, you wold want a different adapter which would at least let you draw max amps at 120v (32a or 40a depending on model of TMC) which is better than 24a from a single TT-30. You would have even more risk from a Y-splitter of this type. And two 5-20Rs on the same phase but different breakers could also let you draw 32a at 120v with the same issue. I have never looked to see when they have two 5-20Rs with 2 breakers for them if they put them same phase or different.
Huh--combining amps is a whole different deal I have not tried to do anything with. It sounds like that would be feasible, but I'm not sure I would try something like that.
 
I have never heard of induction being any issue with EV charging ever, in any circumstance.

Huh--combining amps is a whole different deal I have not tried to do anything with. It sounds like that would be feasible, but I'm not sure I would try something like that.
Well, if the voltmeter confirmed the wiring and the phases, and you could see the distinct breakers there should be no reason not to try it. I mean somebody could wire two TT-30 on the same pole without sending 30a to each but that would be pretty dumb and would mean 2 RVs would blow the master breaker almost as quickly as the car would.

However, my expectation is that finding this situation would be pretty rare unless you make a lot of visits to RV parks with only TT-30. It's not unknown to find parks that have two adjacent spaces in 69 configuration so they have two TT-30 on the same pole. But I've had my TT-30 adapter in my frunk for a long time and only used it for the first time last month, and would not have been able to double team it. However, if I were planning a visit to a specific park and checked with them, I could see wanting to do it, because gaining 166 miles or 200 miles can be a big deal vs. gaining 100 miles if you are off trekking far from the supercharger and chademo networks. Which I like to do.
 

doghousePVD

My grandfather’s car
Dec 3, 2018
669
616
New England, USA
Well, if the voltmeter confirmed the wiring and the phases, and you could see the distinct breakers there should be no reason not to try it. I mean somebody could wire two TT-30 on the same pole without sending 30a to each but that would be pretty dumb and would mean 2 RVs would blow the master breaker almost as quickly as the car would.

However, my expectation is that finding this situation would be pretty rare unless you make a lot of visits to RV parks with only TT-30. It's not unknown to find parks that have two adjacent spaces in 69 configuration so they have two TT-30 on the same pole. But I've had my TT-30 adapter in my frunk for a long time and only used it for the first time last month, and would not have been able to double team it. However, if I were planning a visit to a specific park and checked with them, I could see wanting to do it, because gaining 166 miles or 200 miles can be a big deal vs. gaining 100 miles if you are off trekking far from the supercharger and chademo networks. Which I like to do.
I would try to plan for a two+ day stop. I make a lot of two day stops anyway. Towing means I really want to head out with a full battery.
 
I would try to plan for a two+ day stop. I make a lot of two day stops anyway. Towing means I really want to head out with a full battery.
Of course you may not have a two-day stop. And if you're not towing, you very probably don't have one, and either way you probably want to use the car at some time during the day, where it will lose energy and not be charging. While such a massive shift of plans will work, it's hardly an answer.
 

Products we're discussing on TMC...

About Us

Formed in 2006, Tesla Motors Club (TMC) was the first independent online Tesla community. Today it remains the largest and most dynamic community of Tesla enthusiasts. Learn more.

Do you value your experience at TMC? Consider becoming a Supporting Member of Tesla Motors Club. As a thank you for your contribution, you'll get nearly no ads in the Community and Groups sections. Additional perks are available depending on the level of contribution. Please visit the Account Upgrades page for more details.


SUPPORT TMC
Top