Weird, unstable charging above 24 amps

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darco

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#1
I've noticed that, when doing normal level 2 charging, the charge rate on my Model 3 is unstable (wildly fluctuating up and down a few times a minute) when I first start charging unless I limit the charge current to no more than 24 amps. If I limit charging to 24 amps I have no problems, but if I only limit charging to 25 amps then it becomes unstable again.

Sometimes the charging will be unstable enough for the Model 3 to take notice and limit charging to 16 amps and throw an exception. Other times it eventually stabilizes but indicates a charge current which is higher than the maximum charge current than the station maximum (like "32/30 A"). In such a situation, if I adjust the maximum charge current to be 29, I'll see it fluctuate between 30 and 31; If I set it to 28 I see it fluctuate between 29 and 30... I checked with the charge station to see how much current it was indicating when my car was reading "32/30 A", and the station indicated just 30 A—which makes me wonder if I have a badly calibrated shunt resistor somewhere.

Supercharging seems unaffected. I've also verified this behavior at several different charge stations, as well as checking the connectors to make sure they are clean, and they are.

Anyone else seen issues like this? It feels like something strange is going on with the second 24 amp charger unit, but honestly I have no idea.

See pictures below:

img_0049-jpg.22261
img_0051-png.22262
 

Ed Woodrick

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#3
Check your adapter and check the plugs. Its very possible that you are having an electrical system issue, not in the car, but the house. What I hear is that if the current gets too high, then the car detects it, probably by dropping voltage, compensates for it. That sounds like something may be loose and sparking.
 

darco

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#4
This happens at multiple charger locations. I’ve checked the plugs and socket. They are perfect.
 

JasonF

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#5
24 amps sounds oddly specific. Are you sure the circuit, or the wiring in the circuit, isn't rated for just 30 amps? That would definitely cause it to start to heat up past about 25 amps.

EDIT: I was focused on the amps in the photo, and didn't notice...207 volts? That's two 103.5 volt legs, which is way below normal for a supposedly dedicated circuit like that. It drastically increases the possibility that the wiring is under-rated and it's heating up (the Mobile Connector will detect that and back off on amps).
 

darco

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#6
This happens at multiple charger stations at different buildings.

Supercharging works fine.
 

garsh

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#8
This happens at multiple charger stations at different buildings.
OK, good.
Next, I would try to borrow a different J1772 adapter, so that you can rule that out as a culprit.
If you still have the problem with a different adapter, then it's time to make a service appointment for the car.

Supercharging works fine.
Supercharging supplies DC power, so it bypasses the car's built-in AC charger (and of course, doesn't use the J1772 adapter either).
 

JasonF

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#10
208v is a normal 3-phase industrial service in North America.
https://ctlsys.com/support/electrical_service_types_and_voltages/
At the time I posted (see timestamps above) there wasn't anything indicating it wasn't a home charger.

If it's a commercial charger, it's probably either the J-1772 adapter not making contact well enough and heating up, or it could also be the charge port doing the same. Hopefully it's not a bad charger in the car, because I think that's inside the battery pack? Which might necessitate replacing the entire battery.
 

JWardell

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#11
It's the current higher than the limit that's boggling my mind and must be a bug. I would send these screenshots to Tesla.
All I can think of is that one of the current sensors is not calibrated correctly or faulty, and the UI is using that one but the PCS is using a different one.
 

darco

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#12
I have a service appointment for next week. We will see what happens.

I honestly think it is something wrong/miscalibrated with one of the two 24 amp charger modules in the car. This explains why 24 amps works great but anything more has instant trouble.

I’ve tried this with a commercially installed Tesla HPWC and got the same results. Seems unlikely to be the adapter.

Will post next week about what Tesla says.
 

garsh

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#13
I’ve tried this with a commercially installed Tesla HPWC and got the same results. Seems unlikely to be the adapter.
Yep, I had assumed you were only using J1772 EVSEs.
Time to make a service appointment. :)
 

JWardell

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#14
I have a service appointment for next week. We will see what happens.

I honestly think it is something wrong/miscalibrated with one of the two 24 amp charger modules in the car. This explains why 24 amps works great but anything more has instant trouble.

I’ve tried this with a commercially installed Tesla HPWC and got the same results. Seems unlikely to be the adapter.

Will post next week about what Tesla says.
Forgot there are two modules, I think your logic is correct