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Current fluctuation with new UMC

fsch

Member
Sep 21, 2015
151
177
Montreal, QC
Weird behavior of a new UMC that the Tesla service center gave me about a month ago in exchange for a perfectly working one.

As you can see in the video, 35 seconds after starting to charge, the current reaches the nominal value (32 A), but then, 1 min into the video, the current starts to fluctuate, and drops to 10 A, together with the maximum current (at about 1:20), then increases back to 32 A (just before 2 min) and then drops back to 10 A again, etc. Later it drops to 13 A or 14 A. It's not the power source since it did that at two different locations (both with the NEMA 14-50 connector), and it's not the car charger because it charges steadily at 40 A on the HPWC at home.

So I suspect something wrong with this new UMC. I'll try to see if, by any chance, the service center still has my old one.

Anyone else has seen that?

 

Lloyd

Well-Known Member
Supporting Member
Jan 12, 2011
6,321
2,123
San Luis Obispo, CA
Weird behavior of a new UMC that the Tesla service center gave me about a month ago in exchange for a perfectly working one.

As you can see in the video, 35 seconds after starting to charge, the current reaches the nominal value (32 A), but then, 1 min into the video, the current starts to fluctuate, and drops to 10 A, together with the maximum current (at about 1:20), then increases back to 32 A (just before 2 min) and then drops back to 10 A again, etc. Later it drops to 13 A or 14 A. It's not the power source since it did that at two different locations (both with the NEMA 14-50 connector), and it's not the car charger because it charges steadily at 40 A on the HPWC at home.

So I suspect something wrong with this new UMC. I'll try to see if, by any chance, the service center still has my old one.

Anyone else has seen that?

I would take the HPC back and try again. Try your existing one at the service center
 

scottm

Legacy account
Jun 13, 2014
3,070
2,236
Canada
Super strange that the available current (denominator) jumps around like that. With the NEMA 14-50 attachment it should stay steady at 32A or if its an older unit like mine, 40A. Especially since the voltage remains fairly steady and within a good range of 240 at all times.

Your denominator jumps around 32, 12, 10... ? It's like the UMC can't figure out what head is plugged onto it. Are you mixing the 14-50 head from your old unit onto this newer UMC? Tesla now makes a limited 14-50 head for Canadian market that only gets 32A.


Or one of the hot pins is not making good contact so the 240 VAC is dropping a leg and the UMC sees only 120 VAC ... when it is expecting 240 with the 14-50 head attached. That could throw it for a loop... But that's less likely because the voltage reading is pretty constant at 236..


Are you getting the message on the instrument cluster like "charging power has been reduced because of extension cord in use.." or whatever..?

Anyway, you need a better UMC ... why was your old one swapped away from you? Did they see it was an older 40A unit that they don't send to Canada anymore and wanted to take it back?
 
Last edited:

fsch

Member
Sep 21, 2015
151
177
Montreal, QC
Finally replaced; was BO for several weeks. The new works normally. A tech at the service center told me that it is a problem with one of the phases inside the UMC.
 
  • Informative
Reactions: mongo

tnt1971

Member
Feb 5, 2016
260
153
United States
I had the exact same issue with mine after using it for about a year. It was one of the 40 amp ones and it would start out at 40 and then drop into the high 20s after about 20 minutes or so and continue to fluctuate thereafter between high 20s and low 30s. The SC duplicated the problem and they said there was a bad resister in the UMC that was generating too much heat. Apparently there is a safety in there that throttles back the amps when it gets hot. Anyway, they replaced it and I have not had the issue since.
 
  • Informative
Reactions: fsch

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