Bag of Spare Adapters?

TM now has several adapters for sale. Is there much benefit to buying some or all of them to have on hand when out on the road?

@Hills - Musterion answer is correct, and I would strongly recommend testing to make sure neutral on the 10-30 goes to ground on the 14-50 before plugging anything in. Once that is done, you can test it by plugging in the Mobile Connector without hooking up the car -- it should show green if it is happy with the wiring.

I know I wired correctly assuming the center wire of the Petra dryer cord is the neutral. I don't have a meter so I will have to wait to test. Thanks again.

@jat, @nickjhowe, and others:

After reading back through this thread, I wanted to correct another common misconception. @jat says "Leaving neutral disconnected means that any 120V equipment downstream of the 14-50 plug (if it were ever used for anything besides the Tesla Mobile Connector) would simply not work..."

Unfortunately, this is only true if one connects a single 120V circuit (using one leg and leaving the other 120V leg open). The problem is that almost all appliances that would connect to this type of plug (washing machines, dryers---mine included, etc.) use both 120V legs to run separate circuits for electromechanical relays, lights, timers, LED's, etc. These two legs are never balanced and have different currents flowing through them in normal operation, and these loads change as lights come on and so forth. Because of this if anyone plugs in a typical appliance into the adapter cord where you have not connected the neutral, you will most likely fry the control circuitry of the appliance. To see this consider one 120V leg powering a 10W circuit and the other leg a 30W circuit. With neutral connected, the currents through the two legs differ by a factor of 3 and the difference gets returned as a neutral current. Everyone agrees that if you connect this neutral to ground, you now get an unwanted and potentially dangerous ground current. But the alternative, floating (disconnecting) the neutral can cause damage. In my example, floating the neutral now causes 60V to be dropped across the first circuit. This is equivalent to brownout conditions which may or may not damage circuitry. Even worse, the other leg experiences 180V! This is equivalent to a large power surge which most likely will fry stuff---at least blowing out bulbs rated for 120V, and in worst case starting a fire. The surge gets worse as the impedances of the two legs differ more, approaching worst case 240V surge. And you know what happens when you plug in 120V electronics into 240V power...

In summary, both are not ideal options but wanted to point out how and why the floating neutral is not as risk-free as advertised above. Take care.

The two adapters that I am making, 14-50 female to 10-30 male, and 14-50 female to 14-30 male, would be used in emergency to charge the Model S only. If I am charging the Model S, then it means any dryer would be unplugged (isn't washer usually 110V?). The Model S would also be dialed down to 24 Amp. In a normal house, what else can be damaged?

@Musterion - good point, so I guess neither is a particularly good option and shouldn't be used anyplace where you might have 120V loads downstream of the adapter. In any case, mine is marked "Tesla use only - neutral unconnected".

We had squirrels chew through the neutral line to our house and the house ground was good enough (plus our always-on load was split reasonably well between the two phases to help mitigate the differences that other loads added) that we didn't have swings larger than 30V or so between the two phases. We were very lucky that things weren't fried, though most sensitive 120V loads were plugged into UPSes which corrected the voltage.

@Hills - only things downstream of the 10-30 to 14-50 adapter are at risk, so just don't plug anything but the car into it.

I ended up making an adapter since I currently only have a 14-30 outlet for my dryer in the garage and it is located too far away from my model S. I just used a 14-30/14-50 plug (it comes with support for both), 20 feet of 10 gauge 4 wire cable and a 14-50 outlet. I just limit charging to no more than 24A. I would love to get a 14-30 adapter for my model S so I could replace the 14-50 with a 14-30 outlet.

By the way, if a 30Amp breaker is placed in line between the 15-50 and 10-30, then liability is no longer a problem. Mine was cheap. Anybody want to buy one, I can ask my electrician for costing?

Please point me to the correct thread if this isn't the right one. I am completely naive to electrical adapters and plugs, and have been trying to make sense of the various, very comprehensive and very well written recommendations on this thread. I want to ensure I have the capability of plugging into the most common outlets, as we expect to travel in our Model S (old dryer outlet, new dryer outlet, RV 50 amp). I also know there is at least one location that has only a 110v outlet available, and it is a farther distance than the mobile connector will reach (by about 12 feet). My questions to all of the electrical experts...given my needs I've listed, can you describe what you recommend to purchase and/or build? Is there an extension cord suitable for the 110v outlet that would have the recommended gauge wire to avoid overheating? For custom adapters, I would use one of the websites listed on this thread to purchase adapters/pigtails, but I don't even know how to frame my needs to the supplier accurately. Help? Sorry if I sound too ignorant..I can give you all sorts of expert consultation in nursing care but electricity is a different language for me.

Almost everything you need to know is in this thread (really!). In addition, use the link below to search for 10-30 or 14-30 for additional posts in other threads.
If you still don't know what to do, one of the experts may repeat what they have already written(you will have a hard time buying extension cords of 14-50 to 10-30, and 14-50 to 14-30). If 20 ft length of mobile connector is good enough, you can buy adapters from Tesla. I know what to do now but I was the receipient of other people's knowledge. Pay particular attention to the following:
also Musterion

In addition to @Hills recommendations, I personally give my top recommendation to this charging FAQ by FlasherZ on TMC, who is obviously a master electrician among other things:

@Musterion, that is a great post, wish I read it first. With your caution, I did not plug in my homemade 14-50 to 10-30 extension adapter. Brought it to work today, and building maintenance verified that I indeed connected correctly. ground to neutral, hot to hot, etc.

@alfafoxtrot1, everything you need to buy has also been posted in this thread already., sorry, I meant everything you need to buy.

@Hills, awesome -- happy charges!
Do you still need help?

Hey guys, made a PDF document explaining how to make these various adapters with pictures, etc. Use at your own risk. Oh, would appreciate it if someone who has done this could proof read it for me. I tested out a few of the adapters myself, but of course, don't have access to all power sources.

@shop - A few corrections/questions:

  • For continuous load you need to derate by 20%, so a "50A" circuit can only support 40A continuous. In fact the car won't let you go above 40A with a single inverter.
  • J1772 can go up to at least 70A (if you have twin inverters), not just the 36A in your doc. Some stations don't support this higher current, but some do.
  • Have you tried using the TT-30 adapter? Connecting a neutral to a hot doesn't sound right to me. Maybe @Jat can comment. I'm surprised the 14-50 adapter can cope with that.
  • for the 5-20 adapter, why not use the Tesla-supplier 5-15 connector and just dial up the current to 16A?

COSMAC Elf! I know I am dating myself by writing this, but I remember working with those in college!

Great PDF!

@Hills @Musterion

I really appreciate the help in directing me to the right places. I'm a bit disadvantaged because I don't have the car yet and so the diagrams definitely help, as well as the charging FAQs. It brings the discussions down to levels even I can understand.

I think I've got what I need and once again this forum has proved itself to be a community of givers. I'm amazed at the support someone gets when they have issues...I've not seen that on other forums.

Thanks again!

I haven't been able to try the TT-30 yet but I did try the nema 5-20 which also connects the neutral to the nema 14-50 "hot" and it worked fine. The tesla nema 14-50 seems to ignore the nema 14-50 neutral connection.

@shop, awesome,
@nick, helpful as usual.
@blc1017, for me, I am just carrying the following, but I hope I don't actually need to use any of them
- the 30 ft 50 AMP NEMA 14-50 extension cord, it is in shop's pdf.
- a 50 ft. 15 Amp regular 110V extension cord. (NEMA 5-15). I know Jat advised using even higher gauge.
- homemade 14-50 female to 10-30 male extension/adapter, just like shop's.
- homemade 14-50 female to 14-30 male extension/adapter, just like shop's. I made them using Nick's wiring diagram from this thread, after reading Musterion and Jat's instructions. I brought them to work's building maintenance and had them user their meter (I don't own one) to verify that all the connections are properly made. I've plugged in the dryer outlet and sure enough the Tesla's mobile connecter lit up.
Once again I am also greatful for the patient experts on this forum.

Thanks for the comments nick. You can't dial up the current on the tesla supplied nema 5-15 adapter as it restricts you to 12a. When/if tesla provides a nema 5-20 it'll be restricted to 16a. The tesla adapters communicate with the car somehow to set max amps.

I think I did rerate all amps to 80%...

Yes cosmacelf! I was barely in high school when I built my kit.

@shop - nice work. I would quibble about the 5-15/5-20 adapter though -- how are you going to know the wire is rated for 20A without dissembling the outlet or the breaker panels? Seems like a bad idea.

Also, Musterion made the point that leaving neutral unconnected could be very dangerous if you have 120V loads on both phases downstream of the 10-30 / 14-50 adapter. So, I would more strongly label your adapter that it should never be used for anything besides the Tesla Mobile Connector.

@nickjhowe - the Tesla 5-15 adapter won't let you go above 12A.

The TT-30 works because the Tesla Mobile connector just wants either 120V or 240V across its two power connectors. It is also picky in that if it is a 120V source, it wants a particular one of them to be tied to ground. I am sure it autoranges to whatever voltage it gets in the 110V-250V range (3-phase systems will have 208V rather than 240V).

@Hills - none of the extension cords with 5-15 plugs on them will be rated at higher than 15A. However, they might just be #12 wire, and for continuous use @12a I would prefer #10 -- my heavy-duty 15A extension cord gets pretty warm when running the leaf blower for an hour, so I wouldn't want to use it to charge the car.

@shop - Thanks.

I should have said that prior to posting I DID dial up the current on my 5-15 to check - I got it up to 16A without a problem. Can you not dial yours up?

At the top of the document you make a comment about the car drawing a max of 50A; it draws 40A max with one inverter - that was the derate comment I was referring to.

Oh wow. I never did try to dial up the 5-15 adapter. Will have to try it out.

@shop - nice work - love the document - it was very helpful

I found this little goodie on Amazon:

Camco 55025 RV Power Grip Maximizer 45 Amp Adapter

any reason it wouldn't work with the Tesla charger?

it would seem to me not to be a too bad pre-fabricated "adapter" - nothing say you have to use the NMEA 5-15 plug...seems dual purpose - can either be used with one connector or both connectors plugged in and converts to the 14-50 connector we need for the Tesla charger…

I doubt it would work. The way an RV uses the nema 14-50 and the way the tesla charger uses it are different. The RV wants to see 120v on each hot relative to neutral. It can work with each hot being in phase or out of phase (you just wouldn't be able to run 240v appliances if they were in phase). The tesla adapter by contrast wants to see either 120v between the two hots or 240v between the hots. It ignores neutral.

These RV adapters typically will connect the hot from those 120v plugs to BOTH nema 14-50 hots, effectively showing 0 volts between the hots.

@shop: great doc. Like @jat said and as I elaborated above, my only worry is the floating neutral whenever you make a 3-wire (10-30) to 4-wire (14-50) adapter. I realize that if you and everyone else, to the end of time, 100% of the time plug in only a Tesla to charge, and 100% of the time set the amperage down to safe levels, you will not have a problem. If the latter doesn't happen, the breaker should save you. But if the former happens, it will blow out 120V apparatus downstream and the breaker won't protect that. There are many scenarios you might not envision where this could happen. For example, someone builds your adapter and accidentally leaves it behind plugged in at a campsite, and the next RV owner plugs into the end since the plug and receptacle match and blows up his rig.

Since I'm cautious, that got me thinking if there is a safer way to do this using low-cost equipment and I came up with an idea. @jat, riddle me this:

You can buy 240Vac high-current GFCI circuits that are pretty compact and affordable since made for pool/spa applications. Here is what one looks like (toroidal transformer loop on back) and a circuit diagram for hooking it up.

I hook this up a different way and run just the hot lines L1 and L2 through the donut (but leave out the neutral). Everything else hooked up as in the diagram, except I run the neutral wire of the 10-30, bypassing the donut, directly to the neutral and ground of the 14-50. So when you plug in the Tesla, currents in L1 and L2 cancel and nothing is tripped--Tesla charges fine. In fact if there is ground fault at the Tesla, currents will mismatch and the relay will open and protect you. However the UMC already should do this, so this doesn't give you extra capability. The difference is when you hook up any 120V circuitry, you will get neutral current. Since neutral is still connected it stays at zero potential and no apparatus can get fried. But additionally the GFCI will trip the relay open since L1 and L2 currents don't balance any more, thus disconnecting any 120V apparatus downstream automatically, and eliminating any neutral current flowing on ground in the process. So this accomplishes:

1) Only 240Vac loads not requiring neutral, like Tesla charging, will work.
2) Any 120Vac loads plugged in still have a ground/neutral reference for the instant before the device trips, preventing any damage from floating neutral.
3) Same 120Vac loads will be disconnected by relay automatically so no ground current flows back via the neutral connection.

The only thing this doesn't fix is that it still requires manually turning down the charge current. Does anyone know how the Tesla 10-30 adapter communicates that it is a 30A-limited charge adapter to the UMC? Active or passive (resistor) circuit? If I knew I could also build this into the box and then it solves all the problems at once.

Since this is a "bag of adapters" thread I would consider this an in-line adapter box you can add to the bag that can be used whenever you want safe 30A charging that is still compatible with a 14-50 extension cord.

@nickjhowe - so I tested using the Tesla supplied NEMA 5-15 adapter and, no, I couldn't dial it up past the 12A amount. The way I tested was to use the Tesla 5-15 adapter (not a home made one) and plugged into a 20A circuit and into the car. I then went to the Tesla's charging display in the car, waited for the current to ramp to 12A, and then tried to swipe up the current to more than 12A. No go.

How did you get it past 12A?

I had the 14-50 plugged in and used the in-car UI to stop charging. I then swapped the 14-50 adapter for the 5-15 adapter and plugged it in. The in car display changed to 12A. I dialed it up to 16A then started charging.

Nick - you might have found a user interface bug. I followed your procedure (which is kinda cheating since if you have a 14-50, you wouldn't be using a 5-15!), and also found that I could adjust the amps higher than 12A. However, while the spinner showed more than 12A, the car still only drew 12A. See this pic:

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