Anyone know the charge rate for a standard 120V/30A RV outlet?

Anyone know the charge rate for a standard 120V/30A RV outlet?

I test drove a Model S today and love it, but I have a question they could not answer. I plan to park my Tesla in the same garage where I store my RV. RV's use either 240V/50A or 120V/30A. My RV uses 120V/30A which I already have wired in my garage. The web site shows the charge time for a 240V/24A, but not my 120V/30A. Would the 120V/30A circuit provide a faster charge time than a wall outlet or do I need to call in an electrician?

iholtzman | 8 september 2013

Upgrade to a 240V/50A and use it for both your Tesla and RV. My guess is you will only get about 10 miles of range per hour of charge on the high side. You are only charging at 3.6KW (120V X 30A) vs 9.6kW (240V X 40A max amperage without HPWC) so you will get about 3 times more range per hour than what you currently have.

shop | 8 september 2013

On any plug, you normally should charge at 80% of the breaker rating, so a 30a connection should be limited to 24a charging. And that is what Tesla plug adapters do, limit charge rate to 80% of breaker rating. However, Tesla does not provide a TT-30 adapter (which is what a 30A RV plug is), so you would have to make your own adapter. Also the Tesla UMC for some unknown reason restricts any charging at 120v to a maximum of 20 amps. So, with a home made adapter, you would end up with a charge rate of about 6 rated miles per hour of charging.

I would strongly recommend getting an electrician to install a Nema 14-50 240v plug instead.

jbunn | 8 september 2013

120V 30A does not sound correct. Are you sure it's not 220V 30A? The formula though is straightforward.

Standard wall outlet 120V 15 amp. About 4 miles per hour
120V 30A = 8 (Double the amps, double the power)
240V 15A = 8 (Double the voltage, double the power)
240V 30A = 16 (Double both, and it's times 4)

The formula is approximately; Charging Time = Volts x Amps

When Volts = 120 and Amps = 15, charging time in hours = 4

Brian H | 9 september 2013

"When Volts = 120 and Amps = 15, charging time in hours = 4"

I don't think so. That's about 60mi/hr.

Carefree | 9 september 2013

jbunn, he is correct. It is 120V/30amp. It is aTT30 plug for smaller RVs like travel trailers and small motorhomes.

jat | 9 september 2013

@jbunn - you can only draw 80% of the circuit's current on a continuous load. The formula you want is:

V * A * .86 / 308Wh/mi = rated miles per hour charge rate

Ie, 120V * 20A * .86 / 308Wh/mi = 6.7 rated mi/hr

(as shop points out, the UMC limits 120V charging to 20A)

Having to share an outlet seems pretty painful to me - the convenience of just keeping things plugged in would be worth the small cost of adding an outlet.

elguapo | 9 september 2013

Short answer - call in an electrician.

DouglasR | 9 september 2013

@shop "Also the Tesla UMC for some unknown reason restricts any charging at 120v to a maximum of 20 amps. So, with a home made adapter, you would end up with a charge rate of about 6 rated miles per hour of charging."

If the OP used a NEMA 14-50 adapter, and then a NEMA TT-30P RV Plug to 14-50R Adapter like that found on (, would the UMC still limit the current to 20 amps, or could he dial it to 24 amps?

I agree with you that it is still better to add a 240V outlet.

Peter7 | 9 september 2013


Just a note, the Model S itself, not the UMC, restricts 120V charging to 20A. Perhaps if they release a TT-30 adapter they will also update the S's software to accept 24A from the TT-30 but for now we are stuck at a max of 20A at 120V regardless what you can provide the car.


shop | 9 september 2013

@DouglasR, Yes, even in your scenario, you would be restricted to 20A. It kinda sucks, but then again, Tesla isn't supposed to support home made adapters. It would be really nice if Tesla came out with a TT-30 adapter, but considering they never made one for the Roadster (which still has a much large adapter selection), I would guess the importance of a TT-30 adapter is somewhere below that of the styling of the bolt heads holding the battery to the car.

crazybrit | 24 december 2013

Does anyone have real world experience charging at a 30A RV outlets? I am planning a trip next week, and they only have these available. What can I expect for a charging rate?

tes-s | 24 december 2013

No real world experience, but I think the UMC would limit you to 16 amps. AFAIK there are only two 120v adapters for the UMC - one for 15 amp circuits (NEMA 5-15) that comes with the UMC, and one for 20amp circuits (NEMA 5-20) that is available for purchase. The UMC limits to 80% of circuit capacity, os you would be limited to 12 or 16 amps depending on which adapter you have. You would still need an adapter to connect the 5-15 or 5-20 plug on the UMC to the 30amp plug.

lammersc | 24 december 2013

I actually bought a TT-30 to NEMA 14-50 adapter from an RV Parts store. The NEMA 14-50 adapter is on the end of your UMC plug, and would plug into the 14-50 to TT-30 adapter. I checked the wiring of this adapter, and they split the single 120 VAC line on the TT-30 plug end of the adapter to both hot wires on the 14-50 "recepticle" end of the adapter. While I have not actually needed to charge with this adapter, I assume that since the Tesla would see 120 VAC on both hot wires of the 14-50 UMC adapter, it would assume it was operating with a full 50-Amp circuit. The TT-30 adapter, however, is only rated for 30-Amps, so you would most likely need to dial down the current manually to 24-Amps (i.e. 12 amps per line, and most likely a setting of 12-Amps on the "Tesla Charging Panel"). This should give you around 6-mi/Hr of charging. Probably well worth a call to the Tesla Customer service guys to have them check with engineering and make sure.

shop | 24 december 2013

tes-s, lammersc, please, you have both posted incorrect info - read on. And crazybrit, if you truly only have access to a 30A RV connection (hopefully only for overnight charging? You'll get about 5 or 6 hours of rated charge/hour), then I hope you realize you need to buy or build a special TT-30 adapter since Tesla does not make one?

The TT-30 to NEMA 14-50 adapters you find in RV and camping stores WILL NOT work for Tesla charging without modification. As you correctly pointed out, lammersc, they wire the single 120V hot from the TT-30 to both NEMA 14-50 hots. This results in the Tesla seeing 0V across the hots and thus won't charge.

To use a TT-30 adapter, you must rewire it so that it connects the 120V TT-30 hot to only one of the NEMA 14-50 hots, and then neutral to the other hot. It matters which hot gets the 120V (the UMC cares about that). This is documented in this document:

Or you can buy a ready made, properly rewired TT-30 adapter from here:

When using such an adapter, you start with the Tesla supplied NEMA 14-50 UMC adapter. So the Tesla thinks it can charge at 40A, and thus you must dial down your amperage to 24A. Tesla has a built in limitation, however, that it only allows charging at a maximum of 20A when you have a 120V connection.

And yes, I've used a TT-30 in the past. As I said, a slow but steady 5-6 miles per hour of charge...

crazybrit | 24 december 2013

I am making my own adapter from these instructions I understand the off-the-shelf adapters don't work. However I am looking for folks who have real world experience with the charging rate. There is a lot of speculation on this thread, and I have searched the forum and can't find anything.

Roamer@AZ USA | 24 december 2013

Put in a 50 amp RV. You will be much happier.

crazybrit | 24 december 2013

Roamer, I think you are responding to the OP. I need to know the answer for a road trip

Pricee2 | 24 december 2013

+1 @ Shop. I tried the adapter from an RV store and it did not work.

I have the adapter from evseadapters and it does work. If you only have the single charger it can only charge at half the 40A because you are only supplying power to one side of the charger.

Pungoteague_Dave | 24 december 2013

@shop I sthe expert here and I defer to him. However, I have experience plugging in to several standard 120V wall outlet and to a 30ARV outlet at a marina. Charging rates in our experience for 120 range from 4-6 mph, none higher. A 240V 1450 is cheap and quick. Even an HPWC is fairly cheap given what we pay for these cars, and gives the advantage of always being at the ready (no coiling and uncoiling the UMC).

crazybrit | 24 december 2013

Thanks Shop. You answered my question. Our postings crossed in the ether.

tes-s | 24 december 2013

Thanks for the info shop - you can buy a third party adapter to plug the 240v 14-50 Tesla plug into a 30amp 120v outlet.

_thierrY | 14 april 2014

I've bought the TT-30 adapter from and it works fine.

I did not experienced any limitation to 20 amps as sometime reported. Maybe it was the case with previous software versions (I am using 5.9). Set to 24 amps, I get a solid 14 km/h charge (8,75 miles/hour).

shop | 14 april 2014

Hmmm. _thierrY, what version of 5.9 are you on? I'm on 5.9 (1.51.94) and I just tried it and I only got 20A, even though I had set my max amps to 24A. Maybe there are different car charger versions as well. Where are you located, what country?

Pricee2 | 14 april 2014

thierr & shop.. If you don't have dual chargers the max you can get is 20A on 120V. Half the capacity of a single charger.

_thierrY | 14 april 2014

I have dual charger and I'm in Canada. I own my car since 3 weeks... so I guess I have the most recent software and hardware.

I've been using my RV TT-30 plug many time since and it always worked fine at 24 Amps. Yesterday, I plugged at 16h45 and it charged fine until this morning at 7h30. I got 200 rated-km charged.

shop | 14 april 2014

OMG, maybe the difference is dual chargers versus single chargers. I honestly never thought that would be the case. I do only have a single charger.

Now why would a car charger only charge at 20A with 120V? Each charger has got to handle 40A since that's what I push through it with my single charger - 40A at 240V.

Can anyone else with dual chargers charge at 24A on 120V? This is the first time I've seen it confirmed anywhere on these forums.

Pricee2 | 14 april 2014

The way I look at it is half as much in = half as much out of each charger.

Rocky_H | 14 april 2014

Wow, this would be one of the oldest solved mysteries I've seen on this forum if this turns out to be the answer.

shop | 14 april 2014

I've emailed ownership about this, we'll see if we get back anything interesting.

Here's my theory. There is a software limit per charger of 20A at 120V (simply due to an over protective programmer, ie. the limit isn't needed). In dual charger cars, the current gets split between the two chargers - which actually makes sense, it would be hard to do otherwise. So in dual charger cars, the software sees each charger getting 12A at 120V and all is fine.

Anyways, it seems that we've found yet another use case for dual chargers - it give you an extra 4A of charging at 120V. And if you are charging at 120V, every little bit extra helps!

AndreyATC | 14 april 2014

I think MS limits charge current to 20A on TT-30, even though it supports 30A
It's still faster than 15-20A from some 120V TM adapters, but still, veeeery slow
You'd be lucky to get anything above 7mph

shop | 14 april 2014

AndreyATC, please read a few posts up - with dual car chargers, it seems you can get 8-9 miles/hour charge at 24A.

shop | 14 april 2014

@_thierrY, what version of 5.9 do you have? Press the Tesla logo and there should be subversion in parenthesis (like 1.51.94).

shop | 14 april 2014

@_thierrY - also, can you take a picture of your car's charging screen at 120V, 24A? No one else has been able to replicate this, even folks with dual chargers on the latest software version (.94).

Brian H | 15 april 2014

How does that theory handle HPWCs? 2 x 40 = 80. On good days.

Rocky_H | 15 april 2014

Brian, this artificially programmed limit only comes up with 120V. For HPWC, they're using 240V, so it doesn't seem to come up.

_thierrY | 16 april 2014

@shop : I'll come back with pictures of my screen tomorrow. How can I post picture on this forum?

_thierrY | 16 april 2014

120 V @ 24 A : IT’S POSSIBLE

Here is my setup.

A) I have a VR TT-30 plug with ground slot up (as per NEMA standars).

B) I used the adapter and it fits well with ground pin up.

C) I have V5.9 (1.51.94) software installed (However, I believe it was working before the upgrade.)

D) I have a dual charger

Now here are the results. For you guys, I used theses awkward units you have down there (you know, like the one were waters freezes at 32 and boils at 212…)

1) At 24A, I got a steady 8 mi/hr charge rate.
It was a cool day thought : 32F as you can see. On a warmer day, I got 14 km/hr (that is almost 9 mi/hr).

2) I went over the 20% safety margin in the name of science. The MS let me go up to 30A (I did not tried to go higher and I came back at lower rates after a couple of seconds.)

Et voilà!

shop | 17 april 2014

Great post _thierrY, nice pics. Well, we have a puzzle on our hands. I personally don't have dual chargers, and it doesn't work for me. A person over a TMC does have dual chargers but he couldn't get it past 20A.

I've always known Canadians were special :-)

shop | 17 april 2014

Actually, _thierrY, I think you guessed right in your first post on this thread - the dual charger person who wasn't able to charge at 24A has an early model S, and yours, of course, is the latest hardware only being 3 weeks old. My car is fairly old too. So it is possible that they made a hardware change somewhere along the way.

If anyone reading this thread has a relatively high VIN (recent) Model S and wants to try it out, please do so and let us know if you can charge at 24A on a 120V circuit (like a TT-30). I suspect it would work whether you had a single or dual charger.

MN_Bob | 28 maj 2014

My 85KWH MS was built in March 2014. Now running 5.9 (1.51.106) software. Single charger. I can charge continuously at 24A at 120V. I wired an adapter to go from the Tesla 6-50 plug to a 120 volt source. It only works with the neutral connected to one side of the 6-50. If it is connected to the other side, it gives an error message & will not charge. For test purposes, I briefly increased the current to 30 amps. It looked as though the car's software would allow up to 40 amps at 120 volts. I didn't try over 30 amps. Don't try this unless you know what you are doing.

AndreyATC | 28 maj 2014

My MS was pulling only 20A from TT-30
I was hoping for 24A, but oh well...

_thierrY | 29 maj 2014

@AndreyATC : was was the software version of your MS when you tried to get to 24A. We are trying to find out if its a software or hardware issue.

Pricee2 | 30 maj 2014

@ MN_Bob If you have a single charger I question that you got more than 20 amps of actual charge.

I have a TT-30 outlet at my house and the evse adapter. I can set the charge rate to 40amps but the actual charging amps never goes above 20amps. I have a single charger and am at release V5.9 (1.51.106) had the same charge rate results at two previous release levels. I also have an NEMA 14-50 in my garage and a NEMA 6-50 in my shop.

In theory you can get 2.4KW of charge on 120v 20amp charge or about 7.75 rated miles per hr. The most I have seen has been 6 rated miles per hr. but my voltage drops to 117v on my TT-30 outlet when charging.

shop | 30 maj 2014

It seems that relatively recent model cars ( say 2014 onwards), can in fact charge 120v at greater than 20A. Doesn't have anything to do with single or dual chargers. This is based on info from these forums.

Pricee2 | 30 maj 2014

shop, that may be true but I would like to see photographic evidence of it.

shop | 30 maj 2014

There is photographic evidence - just search here or TMC. I remember seeing the picture.

MN_Bob | 31 maj 2014

I discovered that I can charge at 40 amps at 112 volts. After letting it charge for an hour or so, it showed 13 MPH. Details on car & software above a few postings.


Link to the thread where I posted the jpg:

Look for post #427, dated 5-31-2014

MN_Bob | 31 maj 2014

I am sorry I goofed up the second link. Here is another attempt to make the 2nd link work:

Link to the thread where I posted the jpg:

Look for post #427, dated 5-31-2014

shop | 31 maj 2014

Thanks MN_Bob - when did you buy your Model S - ie. how new is it?

MN_Bob | 1 juni 2014

Shop, my 85KWH MS was built in March 2014. Single charger.