Amp setting chnges on its own from 24 to 48 amps

[ucmndd]

It's built for 32A in extreme conditions like being outside in direct sunlight, yet here we're likely in a nice cool indoor space, given we're using a dryer plug.
Anything built for broad consumer use in these conditions easily has a 1.5X safety factor.
You really think stuff inside is completely fine at 32A but would melt at 48A? Nothing in the safety critical consumer space is built with that little margin.
Do you really think that if you pulled 55A on a 50A rated wire in your house that the expected outcome is fire?

You should take a look at Tesla's 80A Wall Connector and the cabling there and really question if the UMC looks like it would just melt into a puddle at 1/2 the current.


The UMC is literally just a relay between the outlet and the car. It doesn't regulate power or convert it at all. When plugged into a 50A outlet, what would prevent it from "providing" 48A?

It appears people have a fundamental misunderstanding of what an L2 EVSE is and what occurs inside. It's just a relay/contactor so that the connector on the end can't shock a human and doesn't have any voltage on it until safely plugged into a car. It also signals to the car the max current that can be utilized based on what circuit it's connected to. It's up to the car to not draw more current than commanded, and the EVSE doesn't have to protect for overcurrent.

You are correct about the EVSE function regarding "providing current" and I stand corrected. But you're going down a needless and far-fetched rabbit hole to describe a failure scenario that should be impossible if the microcontroller in the UMC adapter is designed with any sort of safety and common sense "fail closed" design principles in mind.

What's likely happening has already been well documented in this thread. OP has a circuit problem that needs to be investigated and it's extremely unlikely that it's due to the UMC signaling more current availability than it should. It's not clear from the manual that the UMC does or doesn't have explicit overcurrent protection but it has at least 4 temperature sensors that would likely come into play if a device designed for 32 amps max is suddenly passing 48 for unknown reasons.

 

[gearchruncher]

Unlikely, but possible and doesn't require software issues or other weirdness. If you're convinced nothing else is hooked to the circuit that could be popping the breaker, then this is where I would start.

OP has a circuit problem that needs to be investigated and it's extremely unlikely that it's due to the UMC signaling more current availability than it should.

Yep, we agree.

it has at least 4 temperature sensors that would likely come into play if a device designed for 32 amps max is suddenly passing 48 for unknown reasons.

48A wouldn't clearly, suddenly cause unacceptable temperature rise. Those temp sensors are there to catch things like a high resistance connection in your outlet. In this case, resistance being 1.5X higher than nominal would be identical to current being 48A instead of 32A. And if you didn't get the temp rise, then what is the problem?

 

[Big Earl]

If the car is actually charging at 48 amps from the UMC, then something is wrong with the car. The UMC should limit it to 32 amps for gen 2, and up to 40 amps for gen 1.

Teslas will often display their highest available AC charging power when not connected to anything. In other words, a long-range car will usually display 48 amps when it isn't plugged in. As soon as you plug in, it should limit itself to either the highest available power from the wall connector or mobile connector, or the setting based on GPS location, whichever is lower.

I'm doubtful that the OP's circuit tripped because the car was charging at 48 amps on a dryer outlet. I suspect the OP's dryer is connected to a NEMA 14-50 receptacle on a 30-amp circuit. This would instruct a gen 2 UMC to charge at 32 amps, which exceeds the circuit rating. A 30-amp circuit can provide 24 amps continuously. There are cases where Teslas have forgotten about or otherwise not respected the touch screen setting, which is why it's important to have the proper charging equipment that sends the correct signal by default (correct receptacle and adapter for the size of circuit).

 

[RayK]

All of this is speculation until the OP provides photos of the breaker, the outlet, the Tesla UMC NEMA adapter being used and any other piece of gear that's between the outlet and the car.

 

[gearchruncher]

I suspect the OP's dryer is connected to a NEMA 14-50 receptacle on a 30-amp circuit. This would instruct a gen 2 UMC to charge at 32 amps, which exceeds the circuit rating.

This is a great point, and given tolerance on breakers is about +/- 25%, 32A on 30 breaker could likely work forever.
Home breakers are simple mechanical devices with massive tolerances from both manufacturing and the environment they live in. Home wiring is not a precise art, it's one with a ton of safety factor added in to make up for all the imprecision and lack of doing engineering on every circuit.

This is true in most civil engineering- it's easier just to build with a 5X safety factor than do the engineering, especially on a one off building that you can't test. Meanwhile, you go to build an airplane and can't afford extra weight, and in those cases we only use a 1.25 to 1.5X safety factor, but do a lot of really expensive engineering, testing, and quality control to prove that's the actual factor.

 

[Cosmacelf]

All of this is speculation until the OP provides photos of the breaker, the outlet, the Tesla UMC NEMA adapter being used and any other piece of gear that's between the outlet and the car.

Yes, this is yet another OP asks a question and then leaves letting the rest of us to provide tons of information and various speculation (since the OP never actually gives enough information). I'm actually getting annoyed at many OPs behavior these days. When you ask a question, stick around to listen to the damn answer!

Maybe I'm just getting old and grumpy.

 

[Rocky_H]

It's built for 32A in extreme conditions like being outside in direct sunlight, yet here we're likely in a nice cool indoor space, given we're using a dryer plug.

Heh, it definitely isn't. I have seen A LOT of threads here on the last few years, where they don't operate correctly and throttle down when they operate in direct sunlight. They only seem to be able to maintain that 32A when they are kept out of the sun and in relatively mild conditions.

You really think stuff inside is completely fine at 32A but would melt at 48A? Nothing in the safety critical consumer space is built with that little margin.

...except that Tesla's charging products have already had quite a history of that kind of problem. The data is there. The old Gen1 UMCs and the older Gen1 and Gen2 wall connectors had several reports of melting at their officially rated maximum levels of 40A and 80A, respectively. So yes, Tesla seems to build for right on the very bleeding edge of what they say it's rated for. That's why some people tried to run them a little less than their maximum rating, to try to give them that operating margin.

Do you really think that if you pulled 55A on a 50A rated wire in your house that the expected outcome is fire?

Entirely different world. That wire has to comply with NEC ratings for building code, which is made to have very large safety margins. Companies' products don't have to meet NEC levels of margin.

The UMC is literally just a relay between the outlet and the car. It doesn't regulate power or convert it at all. When plugged into a 50A outlet, what would prevent it from "providing" 48A?

Melting. It might try for a little bit, but the connections are probably not beefy enough to support that much significantly higher current for long.

It appears people have a fundamental misunderstanding of what an L2 EVSE is and what occurs inside.

No, but you seem to not be considering that any kind of wire connection can literally act as a fuse. It has a certain reasonable cross sectional area, which can reasonably support a certain amount of current it is expected to take at a reasonable temperature. If too much current goes through that small wire connection, it can melt and break just like a fuse.

and the EVSE doesn't have to protect for overcurrent.

It should, and in the physical sense, it definitely will at some point.

 

[RayK]

Yes, this is yet another OP asks a question and then leaves letting the rest of us to provide tons of information and various speculation (since the OP never actually gives enough information). I'm actually getting annoyed at many OPs behavior these days. When you ask a question, stick around to listen to the damn answer!

Maybe I'm just getting old and grumpy.

I've been checking into the OP's profile since yesterday. Last time they were on the forum was this morning at 8:28 PDT so they haven't disappeared just yet. But you're right; we haven't received answers to some very important questions.

As long as we are speculating, I'll throw my $0.02 into the ring....

Assuming that everything the OP has posted is true, and I don't doubt those facts, the member appears to have been charging a 2018 LR RWD for five years at home. They posted here back in Sept. 2018 looking for a 10-30 NEMA adapter, however that thread seems to be for a Gen 1 UMC. But let's assume (there's that word again) that their outlet is indeed an older 30A 10-30 outlet and that they have the Gen 2 UMC as was delivered with the 2018's. As per the OP, the last several years has been fine. Only recently has there been a problem (i.e, breaker tripping). I think that they are being fooled by seeing the 48A display on the screen after power has been disconnected and assuming that sometime during active charging, 48A was being delivered.

My guess at the cause of these problems is that the 10-30 outlet has finally given up. Probably because it's something like a Leviton brand outlet and the poor connections to the blade of the plug is causing problems. But that's just a guess...

 

[Cosmacelf]

I've been checking into the OP's profile since yesterday. Last time they were on the forum was this morning at 8:28 PDT so they haven't disappeared just yet. But you're right; we haven't received answers to some very important questions.

As long as we are speculating, I'll throw my $0.02 into the ring....

Assuming that everything the OP has posted is true, and I don't doubt those facts, the member appears to have been charging a 2018 LR RWD for five years at home. They posted here back in Sept. 2018 looking for a 10-30 NEMA adapter, however that thread seems to be for a Gen 1 UMC. But let's assume (there's that word again) that their outlet is indeed an older 30A 10-30 outlet and that they have the Gen 2 UMC as was delivered with the 2018's. As per the OP, the last several years has been fine. Only recently has there been a problem (i.e, breaker tripping). I think that they are being fooled by seeing the 48A display on the screen after power has been disconnected and assuming that sometime during active charging, 48A was being delivered.

My guess at the cause of these problems is that the 10-30 outlet has finally given up. Probably because it's something like a Leviton brand outlet and the poor connections to the blade of the plug is causing problems. But that's just a guess...

You are almost certainly correct. 10-30 outlets are old to begin with (14-30s came into vogue 20 or 30 years ago). It would have been a ”contractor” grade outlet (read, cheap). 5 years of charging at 24A probably means the outlet has degraded and has a lot more electrical resistance than spec, causing heat build up, but more importantly, drawing more than 30A at the breaker, causing the breaker trips. The car only sees 24A, but the breakers sees 30+A due to resistance at the outlet.

The breaker could be failing too.

Check both before you have a fire, OP.

 

[RayK]

I have a 10-30 outlet in my house for the my electric dryer. The house was built in 1970. I've never considered using it as a means of charging my car. Mostly because it's in a laundry room on the opposite side of a garage wall and the farthest away from the driveway where my car is parked. But even if the outlet was inside the garage, and that I had a gas dryer, and I actually used my garage to park a car inside of it, I'd still wouldn't use it with my UMC unless it was an emergency. I'd finally unbox the Wall Connector I had before my car and put it to use, grumbling at the higher cost of electricity from PG&E, compared to the $0.19/kWh I get from a local CHAdeMO stand.

 

[gearchruncher]

The old Gen1 UMCs and the older Gen1 and Gen2 wall connectors had several reports of melting at their officially rated maximum levels of 40A and 80A, respectively.

Can you point to some of these? All I am finding are cases where the outlet or the wiring melted, not the UMC or wall connector itself.

I have seen A LOT of threads here on the last few years, where they don't operate correctly and throttle down when they operate in direct sunlight.

Throttling down can be done to keep the safety margin. It doesn't mean it's about to melt.

 

[Cosmacelf]

Can you point to some of these? All I am finding are cases where the outlet or the wiring melted, not the UMC or wall connector itself.


Throttling down can be done to keep the safety margin. It doesn't mean it's about to melt.

Tesla actually had a campaign to replace the originally shipped/sold gen 1 UMC 40A 14-50 adapter due to ... melting issues. This would have been like in 2013/2014 timeframe.

Gen 2 UMC is much safer since it incorporates temperature sensors in both the adapter plug and the NACS car connector, unlike the gen 1 which did neither.

 

[gearchruncher]

Tesla actually had a campaign to replace the originally shipped/sold gen 1 UMC 40A 14-50 adapter due to ... melting issues.

https://www.tesla.com/support/adapter-recall

I think you mean 14-30. They specifically told you to keep using the 14-50 and never redesigned it.

In November 2016, we learned about two customers whose NEMA 14-30 charging adapters overheated. These are the only two such incidents that we know of anywhere in the world and neither resulted in any injuries or property damage. However, out of an abundance of caution, we’re replacing NEMA 14-30, 10-30 and 6-50 adapters that were made years ago by our original supplier.

If you have one of these NEMA 14-30 adapters and regularly use it, you will receive a replacement from us within the next couple of weeks. If you do not regularly use it you will receive a replacement as soon as possible. Until then, we ask that you stop using your current adapter, and that you instead charge your car in a different way, such as with a Tesla Wall Connector or NEMA 14-50 adapter (if you have one), or by Supercharging.

Although there have been no incidents with NEMA 10-30 or 6-50 adapters, they have some common elements with the NEMA 14-30, so we will be replacing those as well. These replacements will take about three months to develop and manufacture. In the meantime, since none of these adapters has ever overheated, you can continue to use them if you do not have another way to charge your car.

Yeah, doesn't sound very widespread, and Tesla continued using the UMC Gen 1 for years and an order of magnitude more shipments after that, until 2018, even for some Model 3's (Plus the UMC1 is 40A so it's much more useful than UMC2).

None of this makes me think a Modern UMC2 would melt into a "puddle" at 48A.

 

[Cosmacelf]

https://www.tesla.com/support/adapter-recall

I think you mean 14-30. They specifically told you to keep using the 14-50 and never redesigned it.



Yeah, doesn't sound very widespread, and Tesla continued using the UMC Gen 1 for years and an order of magnitude more shipments after that, until 2018, even for some Model 3's (Plus the UMC1 is 40A so it's much more useful than UMC2).

None of this makes me think a Modern UMC2 would melt into a "puddle" at 48A.

No I didn’t mean the 14-30. Just because you can’t find information on something that happened 10 years ago doesn't mean it didn’t happen. At any rate, it really doesn’t matter a whole heck of a lot right now.