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

Charging at home at 16 amps instead of 32

This site may earn commission on affiliate links.
Not arguing too hard. two possibilities:
  1. Honest to golly high temperatures in the handle. This could be caused by:
    1. Bad wired connection in the handle, resulting in high temps.
    2. Bad connector contact between the connector in the handle and the connector in the car, resulting in high resistance and lots of hot temps.
  2. Bad temperature sensor.
If I'm not mistaken, the Tesla itself has a temperature sensor in the car's connector. Which might help figure out exactly what is wrong.

In any case: If I were you, when you've got a spare minute or three, unplug the handle and, with a flashlight, take a good gander inside the car's and the handle's connectors. Any grunge in there? No problem if there's not, but an eyeball check wouldn't hurt.

If there is grunge, a little denatured alcohol on a Q-tip might do wonders to clean it out.

All bets are off if there's loose/broken bits of metal.
Was happening on both my Teslas so knew quickly the charger was the cause. I had cleaned both ports and the handle with alcohol and no improvement. I was ready to buy a new one but Tesla stepped up with a replacement.
 
Infrared temperature reading. Left bottom is the NEMA14-50 with the plug inserted, while charging, NEMA14-50 is NOT removed yet from the wall

20240607T224552.jpg
 
@fholbert thanks for the idea to use IR measurements

I actually was impatient and it was flashing 4 times and not 2!
From here 4 flashes reads "Charging current is reduced due to high temperature detected in the wall plug."

@Tronguy thanks for the detailed and focused post about the contacts.
I actually found out that all four screws in the NEMA14-50 outlet were not tight!
Not sure how this happened, perhaps over time it loosens on its own?
Very odd. I deal with electric work for a long time I am sure I wouldn't do such bad job.

Tightened the 4 screws on the NEMA14-50 outlet and assembled back everything. Plugged back in.
Will see if this Mobile Charger will stop falling back to 16amps.

Also did measurements of the temperature on the plug that goes into the vehicle and it was warm but not as the outlet plug and the mobile charger itself, so not posting those images here.
 
As I’ve already said multiple times and you seem to not believe me, the outlet is the problem. There is clearly some overheating happening as the plastic appears melted and discolored. The outlet needs to be replaced.

Would recommend the Hubbell 9450A or Bryant 9450FR. Leviton does make an EV one now but it’s not readily available and more expensive than the Hubbell/Bryant one.
 

Attachments

  • IMG_6449.jpeg
    IMG_6449.jpeg
    1.2 MB · Views: 6
  • Like
Reactions: APotatoGod
Thank you all for the suggestions. There were many comments, and I couldn't address them all earlier.

Regarding the outlet issue, I appreciate the recommendation to check for overheating and consider replacing the outlet. However, I can confirm the plastic is not melted. I did not notice the black marking on the metal box, thanks for pointing that out. I'll open it up again to investigate further. I've also ordered a Hubbell NEMA14-50 outlet and plan to replace it in about a week once it arrives.

Thank you for your help and patience.
 
  • Like
Reactions: golferguy
my neighbor has a non-tesla L2 station mounted outdoors, connected to the car with a mennekes type2 cable.

he suspects that when the car is receiving less than the 32A the box is capable of handling, it is due to thermal issues on the box -- which also has a black colored external housing. he tested this by placing a shoebox over the charging box to cover it from direct sunlight and says amperages goes back right up.

hes since swapped the black housing with a white one and is receiving full current again.
 
  • Like
Reactions: Tronguy and Tagar
Not arguing too hard. two possibilities:
  1. Honest to golly high temperatures in the handle. This could be caused by:
    1. Bad wired connection in the handle, resulting in high temps.
    2. Bad connector contact between the connector in the handle and the connector in the car, resulting in high resistance and lots of hot temps.
  2. Bad temperature sensor.
If I'm not mistaken, the Tesla itself has a temperature sensor in the car's connector. Which might help figure out exactly what is wrong.

In any case: If I were you, when you've got a spare minute or three, unplug the handle and, with a flashlight, take a good gander inside the car's and the handle's connectors. Any grunge in there? No problem if there's not, but an eyeball check wouldn't hurt.

If there is grunge, a little denatured alcohol on a Q-tip might do wonders to clean it out.

All bets are off if there's loose/broken bits of metal.
Just an update since installing the new Wall connector front end. Handle Temps are down! Would easily climb into 150F after less than 30 mins and then cutback to half load (24 of 48A). Been holding steady at 111F max for over an hour even though it’s hotter outside and in garage.
 

Attachments

  • IMG_4919.jpeg
    IMG_4919.jpeg
    218.3 KB · Views: 5
Just an update since installing the new Wall connector front end. Handle Temps are down! Would easily climb into 150F after less than 30 mins and then cutback to half load (24 of 48A). Been holding steady at 111F max for over an hour even though it’s hotter outside and in garage.
Cool. Looks like you had a no-kidding bad NACS handle. Whether it was a badly connected wire->connector joint, something wrong with the connector, or just an old-timey bad temperature sensor, looks like the problem's solved now.

Interesting about the 111F being read off the handle. I'm always good for a hypothesis, especially the idiot kind.

One of two things: The interior of the car is cool, the NACS is plugged into the car, and copper is a much better conductor of heat than plastic and all that. So you get the temperature of the car, plus some.

Other possibility is that the temperature sensor is not the World's Most Accurate. At work I play with thermocouples. On those, the voltage across the two dissimilar metals that actually are the thermocouple is set by the Laws of Physics; how accurate a temperature measurement one gets is usually a function of a voltage reference inside the meter itself. But there are other means of measuring temperature. For example, if one has a garden variety 2N2222 or 2N3904 transistor and one connects the base and collector together, the P-N junction of the base and emitter is a standard diode with Very Good Characteristics. If one then runs a calibrated current through the diode, then another, 10X calibrated current through the diode, and samples the diode voltage both times, there's a straightforward way to calculate the temperature of the diode. There are chips, actually, that can sense the temperatures of multiple diodes this way, automagically. Usually accurate to a degree F or C or so.

And then there's thermistors, which are resistors with a (nominally) calibrated temperature coefficient. Least accurate, but they're cheap :).
 
I was thinking it is an RTD type. The dynamics temperature responses I’ve seen of the sensor are slow characteristic of RTD and due to the temperature range, the RTD could provide better accuracy than a thermocouple.

I like you like to get into the hardware side of things. When I first had thr problem I tried to find the Tesla NACS spec to see how the wires are terminated in there and where is the sensor in the handle. Thought maybe I can open it up and find something to fix. But couldn’t find anything that’s wasn’t behind some paywall with the new SAE J3400 standard that took place. Some specs used to be on Tesla’s website but once SAE took it over for NACS, its not there.

If you find something, please share.
 
I was thinking it is an RTD type. The dynamics temperature responses I’ve seen of the sensor are slow characteristic of RTD and due to the temperature range, the RTD could provide better accuracy than a thermocouple.

I like you like to get into the hardware side of things. When I first had thr problem I tried to find the Tesla NACS spec to see how the wires are terminated in there and where is the sensor in the handle. Thought maybe I can open it up and find something to fix. But couldn’t find anything that’s wasn’t behind some paywall with the new SAE J3400 standard that took place. Some specs used to be on Tesla’s website but once SAE took it over for NACS, its not there.

If you find something, please share.
Well, I am a hardware design engineer and had a career doing this and that with temperature sensors, fans, thermocouples, and all that. So, not that I've ever tried to disassemble a Tesla, I kinda know how these things go. I believe you about the RTD.

I dunno about that handle, though. It has the looks of Nothing Repairable By A Mere Human, what with all that heavy rubber and no fasteners visible, anywhere. I imagine that a determined individual with a sharp Xacto knife and No Cares Whatsoever if stuff gets sliced can get into one and see what can be seen. But the end result of that, even with a discovered and clean repair, still means that one has a handle with 240 VAC on it and.. maybe not such a great job of insulating the high voltage from a human. Especially if it gets rained upon.

Unless you had to send your TWC back to Tesla (I suppose they might want it, for FMA, but who knows?), you could do the Xacto knife trick, with the understanding that this is for curiosity's sake only, and you're Never Going To Apply Power To That Thing Again, darn it!

Besides, as I pointed out before - it might not be the handle that's faulty, but maybe corrosion or cold solder joints on the chip that measures the temperature. Oddly enough, I have had to contend with that particular failure case before. Dirty, these central offices can be.
 
Well, I am a hardware design engineer and had a career doing this and that with temperature sensors, fans, thermocouples, and all that. So, not that I've ever tried to disassemble a Tesla, I kinda know how these things go. I believe you about the RTD.

I dunno about that handle, though. It has the looks of Nothing Repairable By A Mere Human, what with all that heavy rubber and no fasteners visible, anywhere. I imagine that a determined individual with a sharp Xacto knife and No Cares Whatsoever if stuff gets sliced can get into one and see what can be seen. But the end result of that, even with a discovered and clean repair, still means that one has a handle with 240 VAC on it and.. maybe not such a great job of insulating the high voltage from a human. Especially if it gets rained upon.

Unless you had to send your TWC back to Tesla (I suppose they might want it, for FMA, but who knows?), you could do the Xacto knife trick, with the understanding that this is for curiosity's sake only, and you're Never Going To Apply Power To That Thing Again, darn it!

Besides, as I pointed out before - it might not be the handle that's faulty, but maybe corrosion or cold solder joints on the chip that measures the temperature. Oddly enough, I have had to contend with that particular failure case before. Dirty, these central offices can be.
There was a big difference in touch temperature so something was getting very hot. The wire bundle going to the handle was especially the hot spot and you did not want to touch it with your hand. New one feels cooler and just like how I remember when new, 2 years ago.
 
  • Like
Reactions: Tagar
I have a 6-50 outlet for welder use that is limited by a 40 Amp breaker. To get around a truck in the driveway, I used the welder's extension cord. After a few months I got a drop in current to half. There was a message in the notices saying there was an overheat at the plug.

After a bit of experimentation I found I could charge at up to 28 Amps, but no more before a trip to half power. None of the building wiring was getting warm. Just the extension cord end was getting warm. So I used it at only 20 Amps charge rate, which was a bit faster than the 16 after a trip. The car could then understand the right time to start charging to be ready at X time.

I've since replaced the extension cord end with a good Hubble one. It cost more than the extension cord originally did.
 
  • Like
Reactions: Tagar
I have a 6-50 outlet for welder use that is limited by a 40 Amp breaker. To get around a truck in the driveway, I used the welder's extension cord. After a few months I got a drop in current to half. There was a message in the notices saying there was an overheat at the plug.

After a bit of experimentation I found I could charge at up to 28 Amps, but no more before a trip to half power. None of the building wiring was getting warm. Just the extension cord end was getting warm. So I used it at only 20 Amps charge rate, which was a bit faster than the 16 after a trip. The car could then understand the right time to start charging to be ready at X time.

I've since replaced the extension cord end with a good Hubble one. It cost more than the extension cord originally did.
So.. Don't know how much of the thread you've read through, but the Tesla Mobile Connector (TMC) maxes out at 32A. This may or may not be Tesla cheaping out; turns out that the NEC (as you've discovered) allows for a 40A breaker, 40A wire, and a 50A socket, a NEMA14-50, as you've discovered. The apparent reason for this is that 50A wire is expensive, electricians run into 40A loads from time to time that could use 40A wire, but there's no NEMA connectors in existence that are rated for 40A on the nose. Since a TMC can't tell if it's got a 50A circuit or a 40A circuit, in the interests of preventing House Fires (not joking) it's thought they assume the smaller current circuit; the max draw (jiggered into the TMC) is then 80% of 40A. And that's 32A.

As far as the heating.. The general Tesla rule is No Extension Cords. With 120 VAC circuits, this is pretty obvious: The "Heavy Duty" extension cords that one finds at Home Depot are only "heavy" in that they use a lot of plastic, but as little copper as they can get away with. Plastic being cheap and copper being expensive.

In general, when one uses copper, copper has resistance, and the resistance is greater the thinner the wire is. Let's say the resistance of the extension cord is R.

The voltage drop across the wire is going to be 2*R * Amps (There's a "2" in there since there's one drop from the socket in the wall to the other end of the extension wire on one hot, and the same drop from the end of the extension cord on the neutral/other hot back to the socket.). A Tesla will happily measure the voltage when first plugged in with no current flowing (and no drop), and remeasure under load. If there's 'way too much drop, it'll simply not charge; if there's some drop, it'll reduce the current draw, in the interests of Not Catching Things On fire.

On Fire? Yeah, well, to a first-order approximation, the power dissipation in the extension cord is P = 2*(R * Current). Put your hands on the cord for a running vacuum cleaner and, yup, it's warm, and That's Why. If one gets the wire in said extension cord hot enough from this, one can cause the insulation to either burn (bad news, but not typical) or simply degrade. "Degrade" means the plastic insulation is breaking down and, when it finally goes, blowing breakers/house fires R Us. None of which is good for one's health, especially if one is charging overnight and is asleep.

Along those lines: Suppose the insulation finally decides that This Is The Evening That It's Going To Die. It gets hot enough to trip the TMC, which is nice, and the TMC goes off, which is also nice. Fine: The TMC is off, but the insulation is leaking current. And you've got a 40A breaker on this thing. Suppose 8A at 240VAC is what's leaking: That 1.92 kW right into the copper wire. We're going to get flames. Suppose this thing is lying up against the wall. The wall catches fire. Without a single breaker being popped. Um. This is a hazard to life and property. I'm saying this seriously, now: It's one thing if you risk your own life in the dead of night by not having a decent extension cord, but what about your loved ones?

Seriously, given that you're playing literally with fire, I would strongly suggest ditching that extension cord and finding one that is Truly Duly Rated for 40A for the length of wire. And not just intermittent use by a welder.

Or, even better, getting an electrician in there to move your 40A socket from wherever you've got it close enough to the car that you can use the TMC sans issues. Yeah, it might be a couple hundred bucks. But how much is your life worth?