I have a 5th wheel... We use a 50 amp to 30 amp reducer in times when we can't get a 50 amp outlet. Fairly common. Do those reducers work on our Mobile chargers as well? I know they sell the different adapters for the mobile chargers, but don't have time to get and might need to use a 30 amp wall plug at our destination next week.
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50 amp to 30 amp reducer
- Thread starter jtrevill
- Start date
The problem is that the mobile charger adapter is what sets the max amperage draw on your charger. If you are using the 50 amp adapter on a service that is only 30 amps, you are going to trip the breaker. You can manually set the max charge rate to 24 amps and get away with it, but it would be best just to invest in the 30 amp adapter.
Ugh... I seriously didn't even see that post. Thanks for searching for me lol.... That's the info I'm looking for.
It's kind of implicitly built in. Just get a 30Amp Plug for your UMC. It's the safest and close to as cheap as just buying an adapter.
If you have 50 Amp plug you run the risk of overloading it. That's easy to manage in an RV, but the Tesla will pull the max the plug is allowed to. You can throttle it back. But it's risky that you might forget.
If you have 50 Amp plug you run the risk of overloading it. That's easy to manage in an RV, but the Tesla will pull the max the plug is allowed to. You can throttle it back. But it's risky that you might forget.
He's not looking at a 30 amp 240 plug but an RV 30 amp 120 plug... it's a no go all around. I was initially thinking he was looking at at 30 amp 240 plug also.
Oh, I see.
I'm not sure, but if you feed 120V across the 30Amp UMC Plug it might run ok (that's all the 120V UMC adapters are doing). It will pull 30 Amp 120V.
It might see that one hot "leg" is grounded though and barf. I don't think it cares about Voltage, it does care about voltage drops over time but I don't think it cares about absolute voltage across its "load".
He can certainly do is a 20Amp 120V UMC adapter.
The RV 30 amp should be grounded fine and perfectly safe. Won't be a huge difference between 20Amp 120V and 30Amp 120V anyway, both pretty slow. But better than nothing.
See, I just checked it will work. But they really should make it a 30 Amp Socket not 14-50, risky you pull to much load on the 30 Amp outlet. Tesla will try to pull 50Amp.
Wait, a "normal" 14-50 (50Amp) at half voltage might actually be ok. I think it will pull a full 20 Amp at 120V (I think). 50Amp 240V will pull 40 Amps at 240V. And pull 20 Amps at 120V. So it might just work and be fairly safe.
TT-30P to NEMA 14-50R Adapter for EV Charging at Campgrounds – EVSE Adapters
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Use a 50 amp load on a 30 amp RV circuit? 30 amp RV circuits are only 120V, where the 50 is 240V. How do you select which half of your RV is powered? I made up an adapter to use a RV30 outlet to 14-50. It requires moving the neutral wire to the opposite HOT in the 14-50. It is very non standard and I marked the hell out of it, NOT for RV use, EV only. I've never used it though. If the adapter you have, doubles up and feeds 120 in to both halves of your 5th wheel, that adapter will never work on your car (sounds dangerous to use if that is what it does).
We had to do workarounds and such years ago, but this is 2020 now, and you can just buy the perfect almost official looking TT-30 adapter from EVSEAdapters, and you're good to go. It will automatically announce the appropriate 24A limit to the car too.
Any of these kinds of 14-50 to TT-30 adapter plugs you find in RV supply or camping supply places just will not work for electric car charging because they are wired the wrong way for what an EV needs.
@DCGOO points out the problem. RVs are not actually trying to use 240V, which was a surprise to me when I learned it. They just have a lot of 120V loads that they need to spread out across two different circuits, so they don't overload something. So those pigtail adapters take the 120V hot line from a TT-30 outlet in the pedestal and put it on BOTH "hot1" and "hot2" of the 14-50 receptacle end. An RV is only looking for 120V connections from either side to ground anyway, so that's fine--just less total amps to work with.
But an EV charging unit is trying to read a voltage difference across hot1 to hot2, and when they are hooked up to the same wire, there is 0V, so it just sits there doing nothing.
So you can find some of these kinds of adapters that are specifically marked for EV charging that wire it differently inside in an "improper" way to put the 120V and ground across those two hot1 and hot2 pins to make it work. But those don't tell the car to proper current limit, so you would have to remember to manually dial it down, so I don't really recommend those. It's kind of unnecessary risks since there is a better version of adapter available now.
Any of these kinds of 14-50 to TT-30 adapter plugs you find in RV supply or camping supply places just will not work for electric car charging because they are wired the wrong way for what an EV needs.
@DCGOO points out the problem. RVs are not actually trying to use 240V, which was a surprise to me when I learned it. They just have a lot of 120V loads that they need to spread out across two different circuits, so they don't overload something. So those pigtail adapters take the 120V hot line from a TT-30 outlet in the pedestal and put it on BOTH "hot1" and "hot2" of the 14-50 receptacle end. An RV is only looking for 120V connections from either side to ground anyway, so that's fine--just less total amps to work with.
But an EV charging unit is trying to read a voltage difference across hot1 to hot2, and when they are hooked up to the same wire, there is 0V, so it just sits there doing nothing.
So you can find some of these kinds of adapters that are specifically marked for EV charging that wire it differently inside in an "improper" way to put the 120V and ground across those two hot1 and hot2 pins to make it work. But those don't tell the car to proper current limit, so you would have to remember to manually dial it down, so I don't really recommend those. It's kind of unnecessary risks since there is a better version of adapter available now.
I don't think an "Adapter" (after the "smart" UMC plug adapter) can communicate any current limits. I think, by luck, (as I posted earlier) the math just so happens to work out. When you run a 14-50 (smart adapter on the UMC) it will run at a 40A load at 240V (80% of 50A). When you only supply 120V it is forced to only pull 50% which is 20A. Which is 66% of what a 30A (120V) could supply. So this EVSE Adapter will only bring you from 16A (80% of 20A) adapter to 20A. I suspect it won't know how to pull 24A even. It's running in on a 14-50 (50A 240V) mode with a really bad voltage drop of 50%.
BTW a Wall Connector with a TT-30 plug on it and set to 60Amp Circuit (240V) (48A actual load) would get the full 24 Amp 120V.
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RVs do not have any 240v appliances - nothing is connected across both phases. So it ends up not making any difference, just need to make sure the load stays below the 30a limit. I’m sure there are exceptions, but that’s how it generally works.
You're usually very on top of this, so maybe this is a brain fart, but not much of this is making sense. Maybe it's being communicated strangely?
You're right, that most of those simple ones from other places that are just wire remapping don't do that. The EVSE one does, because it includes the little chip from the original official Tesla part that they cannibalize to build theirs. It looks and acts like a real adapter to the UMC.
That's not how any of that works. Using half the voltage or double the voltage will not change the amps at all. It would still try to pull 40A. Bad Thing (TM), obviously.
None of this is true either. With the EVSEAdapters parts that they build now, they buy official Tesla adapter plugs that match the amps of what they are going to build for. So for a TT-30 they are going to build, they are starting from a 30A plug type, probably the 14-30. They take it apart and take the plug off of it, but they preserve the temperature sensor, and the chip that sends the car the official signal to tell it that 24A is the proper limit.
That would try to pull 48A and trip the breaker. You're still going on that mistaken idea that half the voltage means it pulls half the current.
First the link I provided from EVSE was a TT-30 to 14-50 "adapter". I didn't realize they also had a TT-30 UMC adapter (which I'm sure we both agree would be ideal).
The car does not regulate current to a theoretical spec. If the voltage drops (from its theoretical setting) you will see the current drop. If the 240V voltage drops 50% it will pull 50% of the current.
My guess is the EVSE TT-30 adapter might be able to trick the UMC (which tells the Vehicle) to pull 24 Amps at 120V. But I think it would have to fake a 60Amp 240V adapter (maybe, read further). Which doesn't exist. There are true 120V adapters that are manufactured for 15A and 20A outlets. My understanding is there is no "communication" from the plug. It's just resistors. Different resistor values tell it what kind of adapter is plugged in. It may have resistors for Voltage and Current. Or there are single resistors that combine Voltage and Current (which has been my hunch). But what ever, there might be a combination that the UMC supports (even if not sold by Tesla) that can be configured for 120V 30A (with appropriate resistors). The over temp could be just a Hi/Lo signal or an analog value. Either way the plug adapters are dumb. I would not call it a "chip". I think the Wall Connector works the same way with the current dial (just sets a resistor level). I think 15A and 20A assume 120V. And the rest assume 240V. I'm not 100% sure on that.
Now I have not tested any of this and don't know for sure. But if it worked the way you said, this adapter from EVSE would not work and it would try to pull 40A at 120V (because the UMC would have a 14-50 UMC Plug on it). It is listed as specifically compatible with Teslas and no mention of manually turning down the Amps in the vehicle. Unfortunately there are no reviews on either this TT-30 to 14-50 Adapter nor the TT-30 UMC Adapter. I definitely recommend the TT-30 UMC Adapter. It would definitely be safer and very possibly get the optimum Amps out of the TT-30.
TT-30P to NEMA 14-50R Adapter for EV Charging at Campgrounds – EVSE Adapters
@mswlogo the car very carefully regulates current. If you set it at 40a and plug it into a wall connector at home (240v) it will pull 40a. If you plug into a WC at a commercial location with three phase it will also pull 40a (208v). Of course assuming both are on 40a capable circuits.
24a at 240v will carry 2x the power over 24a at 120v, but it’s still the same amperage.
There is no tricking the converter in the car. At 240v it will handle 48a. At 120v the Max it handles is 24a. But it will handle it fine.
The Tesla adapters are specifically coded for Max current. If someone wants to play Frankenstein and force fit the standard wall plug adapter (5-15 - regular house plug) from Tesla into a 240v outlet it will still limit it to 12a.
Just the design decision they made, but, the heating within a specific wire is directly related to current and not related to voltage so it makes sense. P = I^2 * R
24a at 240v will carry 2x the power over 24a at 120v, but it’s still the same amperage.
There is no tricking the converter in the car. At 240v it will handle 48a. At 120v the Max it handles is 24a. But it will handle it fine.
The Tesla adapters are specifically coded for Max current. If someone wants to play Frankenstein and force fit the standard wall plug adapter (5-15 - regular house plug) from Tesla into a 240v outlet it will still limit it to 12a.
Just the design decision they made, but, the heating within a specific wire is directly related to current and not related to voltage so it makes sense. P = I^2 * R
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It will only pull 40A at 240V with a 14-50 UMC plug. I’m not sure where you are getting 48A from. It should pull 20A at 120V.
The current models will pull up to 48a with a wall connector. That’s the built in limit of the car.
You're misunderstanding the "voltage drop" condition. It measures the voltage at the beginning, and then after it ramps up the current to start charging. If it starts out at 240V and continues at 240V, there is no voltage drop. If it starts at 120V and continues at 120V, there is no voltage drop.
You are treating this as if the UMC expects 240V, and if it sees 120V instead, that it sees that as a huge "voltage drop". But it has no expectation of a voltage level. It will treat 240V or 120V the same if that's what you are plugging it into.
The adapters have never (and still don't) try to communicate an expected voltage level--only current level. So this has always been available to pin-swap between 240V and 120V outlet types at the same voltage level, and the UMC always handles it seamlessly without a hiccup.
They are not made for any particular voltage other than just having the physical prongs on it that enforce what you can physically plug it into.
The gen1 UMC used to use resistors in the plug adapters. The gen2 switched it, and it really is a computer chip that handles that amp limit signaling.
They don't assume any voltage.
It does work--with the expected problems of not announcing the current properly. The UMC will try to pull 40A (old Gen1 UMC) or 32A (new Gen2 UMC), and that will overdraw the current for the thickness of wire, and heat it up a lot, which will cause resistance, and probably sag the voltage down. And now it's a race to see which safety systems will detect the problem first. Maybe the circuit's 30A breaker will trip. Maybe the car's voltage drop safety systems will kick in, and it will lower the charging to 3/4 of what it was trying to use and see if that helps. So yeah, that's why I appreciate that EVSEAdapters starting making the real type ones that announce the current, so people will not be expected to know about these issues and have to remember to take those actions to compensate for them.
That is a good point, that the item description really needs to include that notice that people will need to do that with these types of non-signaling pigtails.
Well, you can get whatever amps the circuit can supply with this type--possibly even more than it's supposed to handle if you let the current go higher than 24, but you are right that the official-looking ones are safer.
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