Temperature UMC vs Wall Connector

[GJ79]

GJ79,

Good idea. I remember other owners doing that and posting the results here at TMC years ago, so data for normal UMCs should already be available. As others have said, yours doesn't sound normal.

If the Tesla service folk are saying the problem is your wiring, try measuring the voltage at your 14-50 outlet while charging. That should show where the Voltage drop is: in your UMC cabling, or the house wiring.

Even if you get your UMC replaced and everything works to spec, you still may want to buy the HPWC for peace of mind. Tesla designs to the edge of what is possible. For example, I believe the relays in the UMC are rated at 30 A by their supplier, and Tesla runs them at 40 A continuous. Running the 80 A HPWC at 40 A provides a nice fat design margin for long life and peace of mind (and you can just keep the UMC in the trunk).

Good Luck

GSP

My voltage drop is less than 5 Volts and ranges anywhere from 247 and 242 - perfectly normal.

 

[GJ79]

I'm an EE by trade too, but got sucked into I.T. long ago so most of my head thinks in 1's and 0's, not amps/volts... I couldn't tell for sure from the thread, but have you be able to swap out your UMC for a different one and see if your particular cable might have some high impedance defect? Also, if you have access to an amp meter, clamp on style, you might be able to see if there is some imbalance or over current draw on one of the conductors.

Sorry about the house fire. I can understand how you feel about leaving "charging" items unattended. I would dial down the amps from the car until it seems not so hot (whatever that is) and until a solution can be found. Good luck.

That is what I have been doing for a while now. To be honest I was planning to use the UMC as my regular charging solution as I am perfectly fine with charging overnight and the way it's set up at my house it looks just as nice as the Wall Connector. But this heat issue makes me reconcider.

My Clamp meter got lost in the said house fire years ago and I never bought one again as I got sucked into IT as well and never needed one again.

 

[GJ79]

My "classic" S has Dual Chargers (no longer available) and my HPWC is set to 80A on a 100A circuit. The cable can get warm when charging but I would not describe it as "hot". I use my UMC occasionally on trips and it can get quite warm at 30A but I don't think I have ever used it at 40A.
I respect your professional qualifications, and I have no electrical expertise (I work with current flows in humans, not machinery ;-) but I would point out that with over 100,000 Teslas in use I am only aware of one garage fire (in Canada somewhere) that occurred with a Tesla plugged in at home. Probably there are a handful of other incidents but I am not aware of any fire that was demonstrated to have been caused by a UMC while charging. So it seems that the UMC is safe, in my non-expert opinion at least on a statistical basis. And as you point out the UMC is UL and TUV certified of course.

Statistics for only 100k Chargers that are less than 4 years old say nothing. Wait till these get older and the insulation starts to deterioate from the constant hot and cold. Your statistics will change - I promise. Products that are heavily used on a daily basis should be designed as such and you should not be pushing the limits. Especially when you risk peoples lifes while they are sleeping. The previous owner of my car had the original UMC replaced because the plug melted. And from what I found researching this issue he was not the only one. Sounds very safe to me !!!!!!! From what I learned in the past is that that current flow in humans also stops once enough carbon monoxide is inhaled.

 

[GSP]

My voltage drop is less than 5 Volts and ranges anywhere from 247 and 242 - perfectly normal.

If that 242-247 V measurement is at the outlet, while charging at 30-40 A, then it pretty much proves the problem has to be in the UMC (or the car, but that is less likely). You did say the car was automatically limiting the charge current, if I understood correctly (I might not have). If so, the voltage at the car must be reduced well below 240 V.

If your 242-247 V measurement was from the car's charging screen, then I have no idea what is going on. I would think it would be impossible for there to be much heat from your UMC cable, and still have such high voltage at the car while under load.

GSP

 

[GJ79]

If that 242-247 V measurement is at the outlet, while charging at 30-40 A, then it pretty much proves the problem has to be in the UMC (or the car, but that is less likely). You did say the car was automatically limiting the charge current, if I understood correctly (I might not have). If so, the voltage at the car must be reduced well below 240 V.

If your 242-247 V measurement was from the car's charging screen, then I have no idea what is going on. I would think it would be impossible for there to be much heat from your UMC cable, and still have such high voltage at the car while under load.

GSP

It is measured ready from the cars screen. I think the UMC also reduces the current when it senses a temperature, correct ?

 

[GSP]

I think it is the car's software that limits current when it senses low voltage. This was added as an over-the-air update some time ago. I have no idea why it would limit current at 242 V or more.

The UMC sends a pilot signal (PWM, per SAE J1772 recommended practice) that tells the car what the max safe current is supposed to be (12, 16, 24, 32 or 40 Amps). The UMC alters this signal depending on what plug adapter is being used (the different plug adapters have different value resistors that are sensed by the UMC).

Good Luck,

GSP

 

[GJ79]

hmm, ok. I thought the UMC would also alter the pilot signal based on it's temperature.

 

[LoL Rick]

@GJ79 - you can try out my UMC if you want for comparison. It mostly just sits in the trunk since I have a HPWC.

 

[ArtInCT]

I have a later HPWC (Feb 2016) wired with #2 copper to a 100A SquareD breaker. The HPWC is located about 14 feet from the panel with a Hubble switch between the breaker and the HPWC so I can turn off the HPWC should the need arise. My S has a single charger so It pulls 40A at 220v. The HPWC cable and handle is never hot or even warm. Charging is always at full 40A capacity to my Feb 2016 built S. I also have a 14-50 wired to a 50A SquareD breaker as a backup circuit for the UMC but frankly, other than for a test, I have not used the UMC as it stays in the car with the adapters. Hope this data point helps?

 

[GJ79]

@GJ79 - you can try out my UMC if you want for comparison. It mostly just sits in the trunk since I have a HPWC.

I might take you on on this. I think I saw you on plugshare very close to me. I live in Wesley Chapel.