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Charging at home at 16 amps instead of 32

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Hi! My MY started charging from time to time on 16amps instead of 32amps.
I have schedule to charge for the car to be ready by 9am.
So it started missing 9am deadline to be charged to the target level and still charges when I come over in a morning.

Had this setup for over a year (the NEMA14-50 outlet was from a previous EV).

I wonder if one of the phases contacts is no good? Could be some other reason?

Tesla does a quick test when I plug the car is and shows this correctly as level 2 charger / 32 amps.
But then somehow goes down to 16amps.
Is this something Tesla should be able to help? Not sure if it's a car or a charge problem.
There are no tripped circuit breakers or something like that
 
Um. On various Teslas capable of charging at 48A, it turns out that there's three actual rectifier blocks, each capable of 16A.

When one first plugs the car into a 48A circuit (I happen to have that, here) one will see the charge current go from 0A to 16A; stay there a bit, then pop up to 18A, then drop down to 10A, ramp up to 32A, stay there a bit, pop a bit, then drop to 28A or so, then ramp from 28A up to 48A and stay there.

Clearly, the software is turning on one rectifier at a time.

On TMC, there has been the occasional case where one (or more!) of the rectifiers in the car fail; in which case, if one has a 48A circuit, suddenly the car's charging only at 32A. Of, if more than one of these rectifiers has died, 16A. Or, I guess if all three have died, Supercharging works fine (that bypasses the rectifiers) by AC charging is kaput.

Standard Range Teslas that have smaller batteries have on-board AC chargers that are sized for that smaller battery, saving the user money on both the battery and rectifiers. Those cars max out at 32A, having but two 16A rectifiers.

In any case: As an old-timey general electronics and telecommunications hardware troubleshooter, my Main Mantra is, "I hate intermittents."

Teslas do keep fault logs; so it's possible that if one of the rectifiers died, even intermittently, that may have been logged. In which case opening a service ticket, describing the problem, and asking plaintively, "Does the car keep a log of such events?" may get a tech to remote into the car and Look.

In terms of other problems: Both the Tesla, Ye Typical Wall Connector, and the Tesla Mobile Connector all have thermal sensors. Like, all over. If something goes overtemperature, the Car Gets Informed. It's well known that the car will reduce current draw if:
  • The AC voltage droops.
  • The temperature sensor in the plug of the Tesla Mobile Connector gets too hot.
OK: In the above cases, what we're talking about is Resistance, as in Too Much Of It. Say.. for example.. that the NEMA14-50 socket you're using has developed a case of the worn-out contacts. The resistance goes up. This can potentially cause two things:
  1. Vdrop = Amps * Resistance. The the resistance of ye typical connector (plug + socket) is on the order of 10 milliOhms, at 32A this would be a voltage drop of 0.32V. So, in stead of getting (say) 240V, you'd get 239.68, which nobody would care about. But suppose it gets up to, I dunno, 0.5 Ohms? Then you'd have a V drop of 32A * 0.5 = 16V - and believe you me, the car would notice that and either stop charging or drop the current, a lot.
  2. Power dissipation. As a first order handwaving, power dissipation in a resistor at (more or less) constant current goes as Amps*Amps*Resistance. Take the 10 milliOhm case. At 32A, Pdissipation = 32A*32A*0.010 = 10.24W. Um. Ten Watts isn't huge, but the contacts in this case will get Warm and the plug and socket will both warm up. If it gets to the point where it gets dangerous (fires, anybody, and, no, I'm not kidding), the TMC will detect it, tell the car, and the car's answer will be to drop the current. Which, given that were talking (A^2)*R, is actually pretty effective: Going to 16A will drop the power dissipation by a factor of four.
So.. things to try.
  1. With the car charging at 32A, carefully put one hand on the plug and around the socket. If you have to pull your hand away, fast, lest it get burnt, STOP CHARGING IMMEDIATELY. This is life-or-death stuff here, you do not want an electrical fire, which is what you're going to get if the situation isn't rectified.
  2. If you don't have an immediate heat issue, then get into the driver's seat and stop the car from charging using the control screen. Note the displayed voltage. Start charging and watch the voltage. In my case, the breaker box is in the garage, there a TWC on the wall with a 60A circuit, and there's no appreciable droop. If you see more than a volt of droop as the car works its way up to 32A, STOP CHARGING IMMEDIATELY. You may have a bad breaker, loose wire, or some other nasty.
  3. If everything is fine and dandy.. consider how hot your garage is getting. We had a case last summer where some yahoo discovered that aiming a house fan at the NEMA14-50 socket did the trick. Is it warm in your garage?
  4. As I said initially, I Hate Intermittents. If you can reliably trick the car into doing its low-current trick somehow, take yourself and the car to some J1772-based public charger at the local parking lot. Most of those do 32A. Try it there, using the J1772 adapter that came with the car. If, after a few tries, you're still getting 16A - it's not the TMC, it's the car. Service ticket time. If you take the car to Tesla (with their permission) to try one of their Wall Connectors, you may get some additional help. If they're not too busy.
Finally: NEMA14-50 sockets that one tends to find in Home Depot and the like are designed for the likes of clothes driers and electric stoves. In both of those cases, a plug gets inserted and left there for years, if not for the life of the house. There's not a lot of physical wear and tear.

However, when using a TMC, where it gets unplugged on a regular basis and thrown into the trunk, then reinserted later when one gets home, Wear Out Is A Real Thing. I'm too lazy to go looking right now, but there's been some spectacular pictures of melted/burned/shorted NEMA14-50 sockets around these parts over the years..

There are industrial grade NEMA14-50 sockets - and they're a lot more expensive. But not melting down in the middle of the night causing house fires, well, there's a certain cachet to that kind of thing. The industrial grade sockets have MUCH bigger hunks of metal in them with large contacts that, while they do wear out eventually, it's sure a lot longer than the cheapie Home Depot specials. (And, yeah, recently Home Depot's been stocking better sockets. Explicitly for BEV charging.)

There's a bit of another thing. You implied that the NEMA14-50 in your place was put in there by a previous owner. Hm. My understanding from reading these forums (and being an electronics engineer/techie) was that there was a change in the National Electric Code that stated that NEMA14-50 sockets in garages in particular needed to have GFIs (Ground Fault Interrupters) attached. That's roughly the same technology one finds in the 120 VAC sockets in one's bathroom or kitchen (for obvious reasons), but the 240 VAC circuits for BEV charging require that the breaker on that circuit be of a GFCI type. And those, I've heard, are expensive.

For the above reasons, given that a new installation requires both an expensive GFCI breaker as well as an industrial grade socket, the additional cost to go to Wall Connector, hardwired to the breaker panel, doesn't require a GFCI breaker, and Doesn't Have Problems with wear-out gets very attractive. Around here, we all usually recommend going with a Wall Connector - it's cheaper and safer.

Good luck!
 
Um. On various Teslas capable of charging at 48A, it turns out that there's three actual rectifier blocks, each capable of 16A.

When one first plugs the car into a 48A circuit (I happen to have that, here) one will see the charge current go from 0A to 16A; stay there a bit, then pop up to 18A, then drop down to 10A, ramp up to 32A, stay there a bit, pop a bit, then drop to 28A or so, then ramp from 28A up to 48A and stay there.

Clearly, the software is turning on one rectifier at a time.

On TMC, there has been the occasional case where one (or more!) of the rectifiers in the car fail; in which case, if one has a 48A circuit, suddenly the car's charging only at 32A. Of, if more than one of these rectifiers has died, 16A. Or, I guess if all three have died, Supercharging works fine (that bypasses the rectifiers) by AC charging is kaput.

Standard Range Teslas that have smaller batteries have on-board AC chargers that are sized for that smaller battery, saving the user money on both the battery and rectifiers. Those cars max out at 32A, having but two 16A rectifiers.

In any case: As an old-timey general electronics and telecommunications hardware troubleshooter, my Main Mantra is, "I hate intermittents."

Teslas do keep fault logs; so it's possible that if one of the rectifiers died, even intermittently, that may have been logged. In which case opening a service ticket, describing the problem, and asking plaintively, "Does the car keep a log of such events?" may get a tech to remote into the car and Look.

In terms of other problems: Both the Tesla, Ye Typical Wall Connector, and the Tesla Mobile Connector all have thermal sensors. Like, all over. If something goes overtemperature, the Car Gets Informed. It's well known that the car will reduce current draw if:
  • The AC voltage droops.
  • The temperature sensor in the plug of the Tesla Mobile Connector gets too hot.
OK: In the above cases, what we're talking about is Resistance, as in Too Much Of It. Say.. for example.. that the NEMA14-50 socket you're using has developed a case of the worn-out contacts. The resistance goes up. This can potentially cause two things:
  1. Vdrop = Amps * Resistance. The the resistance of ye typical connector (plug + socket) is on the order of 10 milliOhms, at 32A this would be a voltage drop of 0.32V. So, in stead of getting (say) 240V, you'd get 239.68, which nobody would care about. But suppose it gets up to, I dunno, 0.5 Ohms? Then you'd have a V drop of 32A * 0.5 = 16V - and believe you me, the car would notice that and either stop charging or drop the current, a lot.
  2. Power dissipation. As a first order handwaving, power dissipation in a resistor at (more or less) constant current goes as Amps*Amps*Resistance. Take the 10 milliOhm case. At 32A, Pdissipation = 32A*32A*0.010 = 10.24W. Um. Ten Watts isn't huge, but the contacts in this case will get Warm and the plug and socket will both warm up. If it gets to the point where it gets dangerous (fires, anybody, and, no, I'm not kidding), the TMC will detect it, tell the car, and the car's answer will be to drop the current. Which, given that were talking (A^2)*R, is actually pretty effective: Going to 16A will drop the power dissipation by a factor of four.
So.. things to try.
  1. With the car charging at 32A, carefully put one hand on the plug and around the socket. If you have to pull your hand away, fast, lest it get burnt, STOP CHARGING IMMEDIATELY. This is life-or-death stuff here, you do not want an electrical fire, which is what you're going to get if the situation isn't rectified.
  2. If you don't have an immediate heat issue, then get into the driver's seat and stop the car from charging using the control screen. Note the displayed voltage. Start charging and watch the voltage. In my case, the breaker box is in the garage, there a TWC on the wall with a 60A circuit, and there's no appreciable droop. If you see more than a volt of droop as the car works its way up to 32A, STOP CHARGING IMMEDIATELY. You may have a bad breaker, loose wire, or some other nasty.
  3. If everything is fine and dandy.. consider how hot your garage is getting. We had a case last summer where some yahoo discovered that aiming a house fan at the NEMA14-50 socket did the trick. Is it warm in your garage?
  4. As I said initially, I Hate Intermittents. If you can reliably trick the car into doing its low-current trick somehow, take yourself and the car to some J1772-based public charger at the local parking lot. Most of those do 32A. Try it there, using the J1772 adapter that came with the car. If, after a few tries, you're still getting 16A - it's not the TMC, it's the car. Service ticket time. If you take the car to Tesla (with their permission) to try one of their Wall Connectors, you may get some additional help. If they're not too busy.
Finally: NEMA14-50 sockets that one tends to find in Home Depot and the like are designed for the likes of clothes driers and electric stoves. In both of those cases, a plug gets inserted and left there for years, if not for the life of the house. There's not a lot of physical wear and tear.

However, when using a TMC, where it gets unplugged on a regular basis and thrown into the trunk, then reinserted later when one gets home, Wear Out Is A Real Thing. I'm too lazy to go looking right now, but there's been some spectacular pictures of melted/burned/shorted NEMA14-50 sockets around these parts over the years..

There are industrial grade NEMA14-50 sockets - and they're a lot more expensive. But not melting down in the middle of the night causing house fires, well, there's a certain cachet to that kind of thing. The industrial grade sockets have MUCH bigger hunks of metal in them with large contacts that, while they do wear out eventually, it's sure a lot longer than the cheapie Home Depot specials. (And, yeah, recently Home Depot's been stocking better sockets. Explicitly for BEV charging.)

There's a bit of another thing. You implied that the NEMA14-50 in your place was put in there by a previous owner. Hm. My understanding from reading these forums (and being an electronics engineer/techie) was that there was a change in the National Electric Code that stated that NEMA14-50 sockets in garages in particular needed to have GFIs (Ground Fault Interrupters) attached. That's roughly the same technology one finds in the 120 VAC sockets in one's bathroom or kitchen (for obvious reasons), but the 240 VAC circuits for BEV charging require that the breaker on that circuit be of a GFCI type. And those, I've heard, are expensive.

For the above reasons, given that a new installation requires both an expensive GFCI breaker as well as an industrial grade socket, the additional cost to go to Wall Connector, hardwired to the breaker panel, doesn't require a GFCI breaker, and Doesn't Have Problems with wear-out gets very attractive. Around here, we all usually recommend going with a Wall Connector - it's cheaper and safer.

Good luck!

Thank you @Tronguy - super helpful. Will follow the recommendations.
Few quick notes:
- I've put the electric line from the panel to the garage myself, including the NEMA14-50 socket (yes it was bought in HD). I like electric work! And hate drywall work, although had to do both to install the L2 charger 6 years when I had a Leaf.
- I am pretty sure it's not wear and tear in NEMA14-50 as I was religiously tried to avoid plug-unplug cycles on it for reasons you stated -- maybe had 10-20 total cycles in the 6 years I had that electric socket there.
Will follow your recommendations to try to narrow down root cause here. Thanks!!
 
If it's voltage droop, the car may cut current by 25% to maintain the charge, not 50%. A tracking service like TeslaFi will log the charging amp/voltage every 60 seconds and see what's happening.

If the receptacle "wears out" it is likely to overheat, the gen2 UMC will notice this and should stop charging. But 32A over a 14-50 isn't much. HD still sells Leviton 14-50 receptacles, but they're a slightly different design than the ones that failed a few years ago.
 
Hi! My MY started charging from time to time on 16amps instead of 32amps.
I have schedule to charge for the car to be ready by 9am.
So it started missing 9am deadline to be charged to the target level and still charges when I come over in a morning.

Had this setup for over a year (the NEMA14-50 outlet was from a previous EV).

I wonder if one of the phases contacts is no good? Could be some other reason?

Tesla does a quick test when I plug the car is and shows this correctly as level 2 charger / 32 amps.
But then somehow goes down to 16amps.
Is this something Tesla should be able to help? Not sure if it's a car or a charge problem.
There are no tripped circuit breakers or something like that
I tried and found the Be Ready At charging schedule is poor at best. Save yourself some frustration and set manual charging times.

Most likely something somewhere between the circuit breaker and the car is overheating. Likely culprits would be the outlet or the EVSE itself.
The OP may want to charge for an hour or more then use one of these to look for hot spots.

IMG_3255.png
 
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I am pretty sure it's not wear and tear in NEMA14-50 as I was religiously tried to avoid plug-unplug cycles on it for reasons you stated -- maybe had 10-20 total cycles in the 6 years I had that electric socket there.
The Leviton outlets from Home Depot are known to fail and melt even without frequent plugging and unplugging. Just unscrew it from the box and see if anything looks melted. That’s very easy first thing to check before wasting time chasing down other culprits.

I tried and found the Be Ready At charging schedule is poor at best. Save yourself some frustration and set manual charging times.


The OP may want to charge for an hour or more then use one of these to look for hot spots.

View attachment 1051860
I haven’t had an issue with the scheduled departure charging setting until my 40 amp corded mobile connector started to fail and overheat.

But yes an IR thermometer was very helpful when I was trying to figure out what was overheating.
 
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I did a quick test tonight and it went to 16amps from 32amps eventually (don't know exactly when, but it was plugged for at least couple of hours).
The plug from the Tesla Mobile Connector (that goes into NEMA14-50) is warm, but not hot, probably 20F higher than ambient temperature - didn't do exact measurement.
The plug that goes into the car is not warm at all.
When I noticed the amperage drop, I unplugged the charger, waited a minute or two, then plugged back in and started charging again, it's still on 32amps after 30 minutes or so.
So scheduled charge has nothing to do with the issue.
My guess it takes 1-2 hours for the car to drop charging current from 32amps to 16 amps, and it started it doing so recently, maybe has been going on for at least several weeks, not much longer.
 
I did a quick test tonight and it went to 16amps from 32amps eventually (don't know exactly when, but it was plugged for at least couple of hours).
The plug from the Tesla Mobile Connector (that goes into NEMA14-50) is warm, but not hot, probably 20F higher than ambient temperature - didn't do exact measurement.
The plug that goes into the car is not warm at all.
When I noticed the amperage drop, I unplugged the charger, waited a minute or two, then plugged back in and started charging again, it's still on 32amps after 30 minutes or so.
So scheduled charge has nothing to do with the issue.
My guess it takes 1-2 hours for the car to drop charging current from 32amps to 16 amps, and it started it doing so recently, maybe has been going on for at least several weeks, not much longer.
Dunno. But that does sound thermal to me. Remember that when you’re feeling around, any heat has to get through plastic insulation and such to get to where you and your nerve endings are. On the other hand, copper doesn’t just conduct electricity really well, it also conducts heat extremely well (not a thermal insulator). So any temperature sensors buried in the plug will be much hotter than on the outside of all that insulation.

Two thoughts:

Sounds marginal. Aim a fan at the plug/socket and see if the current goes back up. If it does, pop the breaker, pull the socket out of the wall, and inspect it for damage. If you’ve got an ohmmeter, use it: resistance should be zero from the screws on the side to the contacts on the inside front. After zeroing the meter on the lowest scale. Even a tenth of an ohm above what you get when the ohmmeter leads are crossed is likely too much. If you’ve got any wire nuts in there, make sure they’re tight.

Second: you did say you wired this sucker yourself. Um. You did use the right gauge wire for 50A service, right? Too small a gauge will get you too much heat and door prizes for burning the house down..

There is this silly bugger thing in the NEC about NEMA14-50s. Seems that there’s NEMA connectors for 15A, 20A, 30A, and 50A, but there’s no NEMA connectors for 40A. Which is a problem for electricians installing 40A loads, like clothes driers and electric stoves, since they really don’t like paying $$$ for 50A service wires rather than $$ for 40A wires. Copper is expensive.

So the NEC allows using 40A wire, 40A breaker, and a NEMA14-50 socket. With a label, I guess. Which is odd, because usually they all have to match.

It’s thought that this is at least one reason the TMC is limited to 32A. Max load on a circuit when one has a heavy, steady load (hello, Tesla!) is 80% of the circuit rating. So the wire and breaker connected to my Tesla Wall Connector in the garage out back is 60A. Which allows the car to charge at its maximum of 48A (80% of 60A).

Since Tesla can’t tell if it’s plugged into a 50A circuit, in which case it could draw 40A, or a 40A circuit, in which case it could draw 32A, it assumes the latter.

But if you used, I dunno, standard ROMEX only good for 20A.. that would be Bad.

Third thought: have you tried charging at a public L2 charger, like a ChargePoint, yet? They’re usually good for 32A.
 
Dunno. But that does sound thermal to me. Remember that when you’re feeling around, any heat has to get through plastic insulation and such to get to where you and your nerve endings are. On the other hand, copper doesn’t just conduct electricity really well, it also conducts heat extremely well (not a thermal insulator). So any temperature sensors buried in the plug will be much hotter than on the outside of all that insulation.

Two thoughts:

Sounds marginal. Aim a fan at the plug/socket and see if the current goes back up. If it does, pop the breaker, pull the socket out of the wall, and inspect it for damage. If you’ve got an ohmmeter, use it: resistance should be zero from the screws on the side to the contacts on the inside front. After zeroing the meter on the lowest scale. Even a tenth of an ohm above what you get when the ohmmeter leads are crossed is likely too much. If you’ve got any wire nuts in there, make sure they’re tight.

Second: you did say you wired this sucker yourself. Um. You did use the right gauge wire for 50A service, right? Too small a gauge will get you too much heat and door prizes for burning the house down..

There is this silly bugger thing in the NEC about NEMA14-50s. Seems that there’s NEMA connectors for 15A, 20A, 30A, and 50A, but there’s no NEMA connectors for 40A. Which is a problem for electricians installing 40A loads, like clothes driers and electric stoves, since they really don’t like paying $$$ for 50A service wires rather than $$ for 40A wires. Copper is expensive.

So the NEC allows using 40A wire, 40A breaker, and a NEMA14-50 socket. With a label, I guess. Which is odd, because usually they all have to match.

It’s thought that this is at least one reason the TMC is limited to 32A. Max load on a circuit when one has a heavy, steady load (hello, Tesla!) is 80% of the circuit rating. So the wire and breaker connected to my Tesla Wall Connector in the garage out back is 60A. Which allows the car to charge at its maximum of 48A (80% of 60A).

Since Tesla can’t tell if it’s plugged into a 50A circuit, in which case it could draw 40A, or a 40A circuit, in which case it could draw 32A, it assumes the latter.

But if you used, I dunno, standard ROMEX only good for 20A.. that would be Bad.

Third thought: have you tried charging at a public L2 charger, like a ChargePoint, yet? They’re usually good for 32A.

Will test on a public L2 charger today. Totally makes sense the NEMA14-50 and the 80% current limitations, thanks!

I've noticed TMC blinks with red once in a while when and only when on 16amps New video by Ruslan Dautkhanov (the video doesn't show the second red blink right after the first one, the video is too short, so the pattern is 3-4 seconds no red blinking and then 2 blinks in 1-2 seconds, while the green leds still show as charging ). There is no red blinking when it charges at 32 amps normally
 
I believe in “Data is God”.

I recently troubleshooted my 48amp charge getting cut in half after some period of time.

Downloaded the app “Wall Monitor”, looked at all the streaming data and saw my charge handle temp hitting almost 150F after 20 mins and then cutting back. App also has numerous other temps, currents, etc.

It showed the fault “Charge Handle Rollback”.

Explained to Tesla issue and they sent me a new Wall Connector.

IMG_4787.png
 
I believe in “Data is God”.

I recently troubleshooted my 48amp charge getting cut in half after some period of time.

Downloaded the app “Wall Monitor”, looked at all the streaming data and saw my charge handle temp hitting almost 150F after 20 mins and then cutting back. App also has numerous other temps, currents, etc.

It showed the fault “Charge Handle Rollback”.

Explained to Tesla issue and they sent me a new Wall Connector.

View attachment 1053209
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.
 
If the receptacle "wears out" it is likely to overheat, the gen2 UMC will notice this and should stop charging. But 32A over a 14-50 isn't much. HD still sells Leviton 14-50 receptacles, but they're a slightly different design than the ones that failed a few years ago.
Home Depot sells both the Leviton 279-S00 (half size steel contacts, screw down wire clamping) and the Leviton 1450R (full size brass contacts, pressure clamping on the wires). The 1450R is one of the good receptacles, but the 279-S00 is far more common and apparently the most common receptacle in the "overheating receptacle" stories.

If you look into the plug blade holes and see something other than full size brass contacts, you may want to replace the receptacle with a better one.