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2018 75D home charging circuit breaker

Hpnewport

Member
Apr 6, 2015
32
2
Npb, CA
Just got new 75D. apparently charging cable is 'smaller' gauge and won't charge as fast-no problem. However, when I plug it in to my outlet and then to the car, the circuit breakers trips on the cord. When I look at the panel in the car it says 48V. I manually reduce it to about 20, unplug/replug at the wall outlet and it works fine, then I can increase the 20V to 32V and fine. But every time I plug in, it resets to 48V and circuit breaker trips??

I had a P85D for 3 years using same exact wall outlet and never had a problem. Don't think its the outlet so not sure what to do next.

Advice?
 

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boaterva

Supporting Member
Apr 2, 2016
7,565
3,737
Northern Virginia, USA
What says 48V? The car itself?That's the one photo you didn't give us. :) If the car is showing it's getting 48 Volts, then the UMC is bad, but that doesn't make sense for a new piece of equipment.

You should try it with the 120 V plug just to be sure that it works at all. It could be a loose connection from the pigtail to the UMC; this is most likely when it says 'low voltage' and the 14-50 on the wall was used before for the other car.

And the new Gen2 UMC's are all limited to 32 Amp (from 40 Amps) to reduce risk of fire, etc. It shouldn't matter to most people as they charge overnight.
 

Hpnewport

Member
Apr 6, 2015
32
2
Npb, CA
Just got new 75D. apparently charging cable is 'smaller' gauge and won't charge as fast-no problem. However, when I plug it in to my outlet and then to the car, the circuit breakers trips on the cord. When I look at the panel in the car it says 48V. I manually reduce it to about 20, unplug/replug at the wall outlet and it works fine, then I can increase the 20V to 32V and fine. But every time I plug in, it resets to 48V and circuit breaker trips??

I had a P85D for 3 years using same exact wall outlet and never had a problem. Don't think its the outlet so not sure what to do next.

Advice?
Yes, the car display says 48v until I manually reduce it. Thanks for the advice I will try the 120
 

goto10

Member
Mar 6, 2018
182
240
Provo, UT
Are you confusing volts and amps? The voltage should always be 120 or 240 and amps can be 32, 40, 48 (and other values). Amps is the value you can adjust in the car.
 
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boaterva

Supporting Member
Apr 2, 2016
7,565
3,737
Northern Virginia, USA
Are you confusing volts and amps? The voltage should always be 120 or 240 and amps can be 32, 40, 48 (and other values). Amps is the value you can adjust in the car.
Yeah, this is why I wanted the photo, there is no way the Gen2 UMC puts out 48 anything that can be reduced to anything.... Max Amps is 32 Amps. and Voltage can't be adjusted (for the OP).
 

Hpnewport

Member
Apr 6, 2015
32
2
Npb, CA
Are you confusing volts and amps? The voltage should always be 120 or 240 and amps can be 32, 40, 48 (and other values). Amps is the value you can adjust in the car.

Ha! Yes. 48A,32A, etc

I saw a post about the car recognizing it’s location and adjusting itself up/down in amps based on that so wonder if it has something to do with that
 

goto10

Member
Mar 6, 2018
182
240
Provo, UT
The car communicates with the UMC (the charging cable) to determine the maximum amperage it can draw. The UMC that came with your car is capped at 32A so if the car is trying to draw 48A then either the UMC is faulty and not reporting the correct max amps or there is a problem in car itself where it's not respecting the value from the UMC. Location-based charge settings should not override that.
 

ucmndd

Well-Known Member
Mar 10, 2016
6,551
12,318
California
Sounds like you have a bad UMC that isn’t properly communicating its max amperage to the car. You should never be able to see or set a 48A charge rate using the UMC.
 
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Hpnewport

Member
Apr 6, 2015
32
2
Npb, CA
The car communicates with the UMC (the charging cable) to determine the maximum amperage it can draw. The UMC that came with your car is capped at 32A so if the car is trying to draw 48A then either the UMC is faulty and not reporting the correct max amps or there is a problem in car itself where it's not respecting the value from the UMC. Location-based charge settings should not override that.
Ok I understand. The strange thing is that even
If I manually reduce it to
32A it still trips the UMC until
I reduce it to about 24A. Then once it starts charging I can increase it to 32Aand it charges fine... I’ll call service Monday!
 

boaterva

Supporting Member
Apr 2, 2016
7,565
3,737
Northern Virginia, USA
'Tripping' the UMC still sounds like a bad connection to the 14-50 pigtail. I'd either remove and replace (with itself, I mean :) ) that, or try the 120 V one as we were talking about. A bad connection to the pigtail explains the trips. Nothing explains the 48 Amps since as the label says it only goes to 32.. :D

And as was said, that's it. Location charging is below this, not above it. It can't exceed the maximum of the hardware.

And, yes, post more pictures of it doing this as it does it. We'll get it figured out one way or another!
 
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Qbenjamin

Frugal But Classy!
Jan 7, 2017
1,145
681
Bravos
I'm having a similar issue when going from the Gen 1 UMC, to the Gen 2. The Gen 1 UMC charges our M3 with no problem, but the Gen 2 trips the GFI within minutes of us plugging it in, regardless of the charging amps. I'm forced to slow charge right now, only have a standard outlet atm.
 

boaterva

Supporting Member
Apr 2, 2016
7,565
3,737
Northern Virginia, USA
I'm having a similar issue when going from the Gen 1 UMC, to the Gen 2. The Gen 1 UMC charges our M3 with no problem, but the Gen 2 trips the GFI within minutes of us plugging it in, regardless of the charging amps. I'm forced to slow charge right now, only have a standard outlet atm.
Wonder what (or how much) they changed in the components.... a 120V outlet, of course, can be on a GFCI circuit, where the EVSE/high current 14-50 isn't. But you shouldn't be seeing the kind of current imbalance to trigger the GFCI.

Have you tried resetting the GFCI? Some that don't get reset in years have issues and they should tested monthly (and almost never are).

Don't want to turn this into a general electrical troubleshooting thread, but this might be useful. :D
 

Qbenjamin

Frugal But Classy!
Jan 7, 2017
1,145
681
Bravos
Wonder what (or how much) they changed in the components.... a 120V outlet, of course, can be on a GFCI circuit, where the EVSE/high current 14-50 isn't. But you shouldn't be seeing the kind of current imbalance to trigger the GFCI.

Have you tried resetting the GFCI? Some that don't get reset in years have issues and they should tested monthly (and almost never are).

Don't want to turn this into a general electrical troubleshooting thread, but this might be useful. :D
Yep, we even had an electrician come out and change out the GFCI, but it still tripped it and my neighbor. I live on a military base atm, so there's no telling how crappy the actual wiring job was (wouldn't be surprised if every GFI in the house is daisy chained on the same circuit).
 

whitex

Well-Known Member
Sep 30, 2015
6,566
7,891
Seattle area, WA
@Hpnewport ,
  1. What amperage if your breaker?
  2. Is there anything else connected to the same breaker?
  3. When you say UMC trips, do you mean the breaker trips or the UMC kills the charging?
Typically it is not recommended to draw over 80% of the breaker current for sustained, long periods of time. Maybe Tesla got cleaver and they do a quick "test spike" to 40A to ensure that they are running on a minimum 40A breaker before drawing 32A safely? This would help them not burn down places which have a NEMA 14-50 on a 30A circuit (and breaker), which might not trip at 32A.

@Qbenjamin , do you have a NEMA-14-50 with GFCI, or are you talking 120V 15A or 20A plug?
 
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Hpnewport

Member
Apr 6, 2015
32
2
Npb, CA
ok, got home tried to plug in as usual but washed the dash which said 48A. It did drop to 32A immediately but then the UMC cycled twice through the green letters, then snap and red light comes on UMC and the ring around the car charging point. The dash readout goes back up to 48A.
I manually reduce the charge current to 25A. Same thing- the UMC green twice then red.
I reduce it to 20A and viola, it starts charging. I then go to dash and increase to 32A (won't go further up) and it stays charging fine.
I also tried the 120V adapter into a 'regular' outlet and it works but obviously very slow at 12A.
pics aren't necessarily in order of my description...
 

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Hpnewport

Member
Apr 6, 2015
32
2
Npb, CA
I'm having a similar issue when going from the Gen 1 UMC, to the Gen 2. The Gen 1 UMC charges our M3 with no problem, but the Gen 2 trips the GFI within minutes of us plugging it in, regardless of the charging amps. I'm forced to slow charge right now, only have a standard outlet atm.

mine isn't tripping our house breaker, just the umc circuit breaker...
 

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