# Interesting charge issues with UMC - 16 vs 32 amps



## GDN (Oct 30, 2017)

So I've had an interesting charge issue pop up with the 2018 AWD with the home UMC. The car is approaching 3 years old and the UMC at 32A is the primary charging device other than a Supercharger every couple of months. However on Friday morning we decided we wanted a road trip that afternoon. The car was at about 165 miles of range and I wanted a full charge in 3 hours to leave the house. So I pulled the plug from the WC across the car and plugged in at 48A. This was the first time I'd ever plugged in to the WC on this car. I got the perfect full charge I wanted in 3 hours with the 48A. It shut off at 100% about 30 minutes before we left.

Over the next 7 hours we only drove 142 miles, but had the AC on 100% of the time, we did a lot of sitting in the car waiting (we were out chasing the Union Pacific steam engine coming through North Texas). When I got home and plugged in I went back to the UMC at 32A. It charged for almost an hour at 32A and then stepped down to 16A. I only noticed as I checked on the status before going to bed and the time to finish charging was way too long. I unplugged and plugged it back in, it went back to 32A and completed the charge to 80% where I typically keep it.

The car is still plugged and has not been driven for about 36 hours. I got a notice a bit ago charging had started. I looked and the battery had dropped about 2% so it was topping it off, however only at 16A on the UMC.

I'll watch the charging this week, but if the charging continues at 16A I'll open a service ticket. It's just interesting that it started after using the WC at 48A the first time. Maybe I need to plug the WC back in there to see if I can still get 48A. If I recall there are 3 modules/converters in the car 16A each that handle the charging conversion - perhaps one of these is going out? Other thoughts?

Another small tidbit, my max range dropped by a couple of miles after the long day of the car being on, but the top up charge this morning brought it back to the 282.


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## iChris93 (Feb 3, 2017)

GDN said:


> If I recall there are 3 modules/converters in the car 16A each that handle the charging conversion - perhaps one of these is going out?


That's my guess. I think @Mike has experience with this.


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## Mike (Apr 4, 2016)

GDN said:


> Maybe I need to plug the WC back in there to see if I can still get 48A. If I recall there are 3 modules/converters in the car 16A each that handle the charging conversion - perhaps one of these is going out? Other thoughts?


Based on my experience and ultimate replacement of the line replaceable unit (the "power conversion system" which has three 16 amp parts inside the unit) I would try charging with your WC at 48 amps until further notice.

Here is my background story on this issue:

https://teslaownersonline.com/threads/my-tm3-throttled-home-charging-from-48-amps-to-32-amps.16521/
At 48 amps, it works out to 15% recharge per hour and if it drops to 36 amps, it becomes painfully obvious.

*Edit*: *for clarity.*


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## GDN (Oct 30, 2017)

Thanks for the replies. I've read through @Mike's thread and can see similarities. The interesting part is I'm also the one with the LTE module that likely needs to be replaced and I've not opened a service ticket on it yet. @Mike has pointed me to that - so likely will address both issues at once.

I will experiment with the charging over the next two weeks swapping between the UMC and the WC. So far the WC was OK at 48. It was going back to the UMC expecting 32, which stepped down to 16. I think the key here, regardless, the step down was in a 16A increment which points to 1/3 of the charging unit potentially having a fault. I don't know how it decides which 2/3 to use when using a UMC if it varies or if it is always the same 2/3.

I do not recall any messages in the car, but I didn't look. I do have specific times from my Teslafi logs, so I will capture those and Tesla can review if needed.


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## Ed Woodrick (May 26, 2018)

If the wall charger woks well, but the UMC has some issues, I'd turn to the UMC circuit. Could be some loose wires or a socket going bad.


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## GDN (Oct 30, 2017)

Ed Woodrick said:


> If the wall charger woks well, but the UMC has some issues, I'd turn to the UMC circuit. Could be some loose wires or a socket going bad.


Thanks - I can't and shouldn't rule out a circuit, however there are 2 model 3's in the garage, one charges exclusively off the UMC (14-50 installed over 3 years ago) and logged in Tesla fi and has never had the step down issue. The other car charges on the WC (installed about 2 years ago) and has never had a step down issue. It could all be timing, it just seemed odd to have an issue after charging the one from the UMC with the WC to have an issue show up like this.

The electrical panel, the 14-50 and the WC are all on a west facing brick garage wall which no doubt builds up some afternoon heat with the TX sun bearing down on it. The car had also been "on" for over 7 hours. It hit 100 degrees in the garage a couple of weeks ago and right now both cars report 91 degrees in the car, so no doubt it all gets hot out there. While charging, I know the wiring gets even much hotter than that. I'll watch and consider pulling things apart to check connections, the last thing I need is a fire.

I've got a second UMC from the other car so I can do a lot of testing and swapping equipment and charging to see if the problem recurs and where it happens. I just knew I'd heard of similar issues. The issue seems a little interesting.


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## Ed Woodrick (May 26, 2018)

GDN said:


> Thanks - I can't and shouldn't rule out a circuit, however there are 2 model 3's in the garage, one charges exclusively off the UMC (14-50 installed over 3 years ago) and logged in Tesla fi and has never had the step down issue. The other car charges on the WC (installed about 2 years ago) and has never had a step down issue. It could all be timing, it just seemed odd to have an issue after charging the one from the UMC with the WC to have an issue show up like this.
> 
> The electrical panel, the 14-50 and the WC are all on a west facing brick garage wall which no doubt builds up some afternoon heat with the TX sun bearing down on it. The car had also been "on" for over 7 hours. It hit 100 degrees in the garage a couple of weeks ago and right now both cars report 91 degrees in the car, so no doubt it all gets hot out there. While charging, I know the wiring gets even much hotter than that. I'll watch and consider pulling things apart to check connections, the last thing I need is a fire.
> 
> I've got a second UMC from the other car so I can do a lot of testing and swapping equipment and charging to see if the problem recurs and where it happens. I just knew I'd heard of similar issues. The issue seems a little interesting.


But the NEMA 14-50 has a plug and a socket. Some sockets are notorious about degrading over time. Also check the Tesla side of the plug and make sure there are no issues.


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## garsh (Apr 4, 2016)

GDN said:


> I do not recall any messages in the car, but I didn't look. I do have specific times from my Teslafi logs, so I will capture those and Tesla can review if needed.


Try to also take a report from inside the car the next time you experience one of these charging issues.


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## JasonF (Oct 26, 2018)

GDN said:


> Maybe I need to plug the WC back in there to see if I can still get 48A.


This is the place to start. If it can maintain more than 32 amps on the Wall Connector, then the car's on-board chargers are ok, and looking at the Mobile Connector more closely is next. If it can't maintain at least 32 amps on the Wall Connector, the on-board chargers need service.

You could also pull the plug head off of the MC and re-attach it, making sure it's seated correctly. Those can come loose and generate heat, which causes the MC to slow down or even shut down. Or it could be the plug in the wall that has loose connectors or has become damaged, so it's heating up. Or it could be the wires inside the wall getting hot, or the circuit breaker not seated correctly. Work backwards from the car, and you'll find it.


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