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New Model S 75 UMC GEN2 issues.

Rocky_H

Well-Known Member
Feb 19, 2015
6,097
7,069
Boise, ID
Just received a replacement gen 1 UMC cable today, my second. 9 months old MS 75D. Logs showed issue with the cable.

I noticed a few times that the charge rate on the MCU increases to 48amp despite manually setting at 32 amp. This trips the 50amp breaker.
Wait a second, further explanation please? The UMC gen 1 can't go any higher than 40A. So it can't draw 48A from the outlet to trip the breaker, no matter what the car asks for.
 

Kalex

Member
Oct 1, 2017
149
110
New York
Wait a second, further explanation please? The UMC gen 1 can't go any higher than 40A. So it can't draw 48A from the outlet to trip the breaker, no matter what the car asks for.
Wait a second, further explanation please? The UMC gen 1 can't go any higher than 40A. So it can't draw 48A from the outlet to trip the breaker, no matter what the car asks for.

When I checked the MCU after the breaker tripped, it was showing 48A. The logs also showing the fluctuations, that’s why they replaced it with a new one. Don’t know why.
 

Rocky_H

Well-Known Member
Feb 19, 2015
6,097
7,069
Boise, ID
When I checked the MCU after the breaker tripped, it was showing 48A. The logs also showing the fluctuations, that’s why they replaced it with a new one. Don’t know why.
Ooooh, I think I get it. There will be two numbers with a slash between them, like XX/XX. Do you mean the second numbers went up to 48? That would make sense. Those numbers are like "this many amps being used out of this many amps possible". So if the mobile charge cable is connected, it will signal to the car that 32A are available, so you might see 32/32 or 30/32. But if there is no cable connected to your car at all, then the car will just be showing the highest possible amps the onboard charger can handle, so that would be 48. You said the breaker tripped, so that would appear as disconnected. So as far as the car can see, there is no cable connected anymore, and it's just going to default back to showing what the charger can do, so 0/48.
 

EdinSD

Member
Apr 12, 2018
6
2
San Diego county
I have noticed that we seem to have more success when charging is scheduled for later. If I plug in at 8pm, but it doesn't start charging right then because charging is scheduled for midnight, then we usually don't get any errors. Anyone else have experience with that?

Also, the Tesla mobile tech is supposedly looking for a Gen 1 cable for us.
 

EdinSD

Member
Apr 12, 2018
6
2
San Diego county
Update: The mobile tech worked with someone else in Tesla that looked more in to our vehicle logs. They were seeing voltage and amperage fluctuate, although I'm not so sure that isn't normal. But they did come up with this technical note that said the car might be demanding more amperage than the cable can handle.
So as a experiment, we set the car to max of 30 amps instead of 32. Since then I have not had the charger fault. We are also still using the schedule to start at midnight, so there are really two variables changed here. But the end result is several days without a fault.
So maybe some of the rest of you that have been having this problem could try setting the max amps to 30, and setting up scheduled charging and see what happens.
 

BHCLUC

Member
Nov 7, 2017
232
168
Chicago
Interesting. Much like the OP, and some of the rest of you, I received my car in mid December. I have had no issues with my UMC gen 2. I was having some other issues with my vehicle, and they sent out a ranger to update my firmware today and take a look, which I thought odd since the firmware can be deployed remotely.

Anyway, once in site, he wanted to see my UMC. I wondered what this might have to do with my problem, and he said my VIN was flagged as receiving a possibly bad UMC and to replace it. He didn't know why, or what issues it may have caused, only that the serial number fell within a range of those that were supposed to be replaced.

Strangely I had my car in for service in April, and this was not mentioned. So it seems they may have found a defect in the early batches of the gen 2 UMC and are replacing them.
 

BHCLUC

Member
Nov 7, 2017
232
168
Chicago
Also interesting is that the ability to update the UMC firmware was released somewhere around the same time that these UMC issues must have been solved. Perhaps a way to diagnose and log the UMC issues remotely for replacement?

I know there was some speculation as to what those updates may be, but it would be too coincidental to be unrelated.
 

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