Charging Amperage always 1A less than setting

[SSonnentag]

Has anyone else noticed that since the last update or two, the current readout is always 1A less than what the in-car setting is set for? I have my car set for 40 A and my app consistently shows 39/40A. If is set the car to 72A, the app shows 71/72A. I never saw this behavior before the 2018.4x series of updates.

 

[gavine]

What does the car display? Is it different from the app? My guess is that the car is displaying 39/40 also and the reason for that is because your voltage is so high. Charging is really measured in watts so 40A @ 240v should be 9600 watts. (W = V x A)

Since your voltage is 248, the car has to drop the amps down to 39 to stay within the wattage range that the onboard charger supports (248 x 39 = 9672). Your voltage might not always be that high so you'll probably notice 40A charging the next time your voltage drops closer to 240.

 

[rpo]

I literally posted about this glitch in the User Interface forum an hour ago. It does not matter what amps you choose...it's always 1 amp less. If I charge on a wall outlet at 12 amps, the app shows 11.

 

[SSonnentag]

My voltage was varying between 143 and 148. It didn't seem to matter, especially with the 72A onboard charger, it shouldn't matter. In-car display shows the same 1A discrepancy.

 

[Jan Fiala]

It's a known bug since 42.2 at least...

 

[gavine]

I literally posted about this glitch in the User Interface forum an hour ago. It does not matter what amps you choose...it's always 1 amp less. If I charge on a wall outlet at 12 amps, the app shows 11.

Correct. It is because you have a very high voltage. Mine does the same thing whenever the voltage is running high. Maybe you are close to the transformer and consistently get high voltages? That's not a bad thing.

In the end, you're still getting the same charge rate at the lower amperage because the total output is still the same (again, measured in watts which equals "power")

 

[SSonnentag]

Yeah, I'm not worried about it, it's just that this is a new phenomenon. My voltages are the same as they have been for the past year. It's the software on the car that has changed. You may be correct about the reason, but the software shouldn't have changed in my opinion as it just looks messy and may cause concern or confusion.

 

[Cosmacelf]

It happens even with low voltages. On my X I recently charged at 72A, 209V, and it showed 71A.

 

[Jan Fiala]

It has nothing to do with the power. The car shows the correct and preset amp which is +1 of what the app shows.

 

[SSonnentag]

It has nothing to do with the power. The car shows the correct and preset amp which is +1 of what the app shows.

Even the car reading is not always correct. Both our S and X often show -1A from the max setting. Another oddity is that it is often impossible to set the max Amperage to what it "should" be. For instance, I used to be able to set my max to 72A, but now I am often limited to 70 or 71A as the max setting, and then after a few minutes the max setting will increase to the full 72A. It's all very odd software behavior that didn't act this way until recently.

 

[gavine]

i didn't realize there was a recent bug. But, I have seen a few times in the past that the reported amperage drops when the voltage rises.

 

[rpo]

Correct. It is because you have a very high voltage. Mine does the same thing whenever the voltage is running high. Maybe you are close to the transformer and consistently get high voltages? That's not a bad thing.

In the end, you're still getting the same charge rate at the lower amperage because the total output is still the same (again, measured in watts which equals "power")

That only applies when you are exceeding the wattage limit of the onboard charger. That's definitely not the case below 46 amps on mine. Occasionally setting it to 48 will get it limited to 46 or 47.

 

[gavine]

That only applies when you are exceeding the wattage limit of the onboard charger. That's definitely not the case below 46 amps on mine. Occasionally setting it to 48 will get it limited to 46 or 47.

Good point. Come to think of it, I have only noticed my X drop from 48 to 47 but never from anything below that and I do charge at lower rates sometimes. Thanks for clearing that up.

Then again, the OP might only have a 40A onboard charger though.

 

[rpo]

Good point. Come to think of it, I have only noticed my X drop from 48 to 47 but never from anything below that and I do charge at lower rates sometimes. Thanks for clearing that up.

Then again, the OP might only have a 40A onboard charger though.

True, but I am experiencing this no matter what the amps are set to. It is always 1 amp lower on the mobile app than what the car shows at the same time. It's been happening for a couple of weeks now.

 

[jlv1]

I'm suspecting it's a bug in the remote API, since it only shows incorrectly in the mobile app and in services that query the car, like TeslaFi. It shows correctly on the dash. Right now my app is showing 205v & 31A, but the dash is correctly showing 32A.

 

[TMeister]

Mine shows 39/40 on both app and in car. My OpenEVSE L2 charger (set at 40 amps for the pilot signal) shows 40.2 amps being delivered. So the car is close but not correct. Measuring with a clip on amp meter I also get 40.2 amps delivered. Even destination chargers have most recently shown -1 amps from the max by the car and app. Have not measured those since I have to separate lines to do so.

There are upper power limits as well to keep in mind. Mine has a ~17 kW limit with it's 72 amp charger. Others have 48 amp, 40 amp, 80 amp each with their own power limits. But in this case I think the 39/40 is a truncation error (instead of rounding).

 

[dk1888]

FYI... I got this response from the remote diagnosic’s team:

" A firmware bug got introduced into 2018.39 and later (v9) that can cause the Tesla Mobile App to display the charging current as 1A less than requested.

If this issue is present, the vehicle UI will still display the expected value.

For example, the vehicle is charging using the Gen 1/1.5 UMC with a maximum charge current of 40A. The vehicle UI displays 40A/40A, meaning that the vehicle is charging with 40A out of available 40A. However, the Mobile App displays 39A/40A, suggesting that the vehicle is drawing less current.

This is a known firmware issue that is going to be resolved in 2018.44. Please note that this is only a visual issue in the Mobile App, the vehicle still draws the correct current as expected."

The pushed 2018.44 to me but I haven’t try charging on L2 since the update. It has nothing to do with the voltage.

 

[SSonnentag]

I can confirm that the official response from Tesla is INCORRECT. The in-car readout is also -1A from what the car is set to.

My HPWC is on a 100A circuit and is set to provide a maximum of 80A. My car has a 72A onboard charger. So there should be no problem charging at 40/40A, and yet both the car and app show 39/40A.

 

[whitex]

I noticed it back in May I think after switching to a new HPWC because the 2018 new MCU car would throw errors using Gen1 HPWC. When connected to the old HPWC the old car would show the correct amperage, but the new one shows usually 1 but sometimes 2A less than the max. Not only that, on the new 2018 car, even on new HPWC, the max often shows 47 instead of 48, so I see 47/47 and then occasionally it goes to 48/48 and then 47/48 and then back to 47/47. On my older (2015) car using the old Mobile adapter it always shows 40/40 and the old HPWC always showed 80/80, but the when connected to the new one it seems to often show one amp less (39/40 or 79/80) but the max doesn't change to less like the new car.

My guess is as long as it's chugging along and even at 1A less, it's far from top of Tesla's priority list to fix. If they had time and expertise to throw at it, they would have figured out the problem with new cars and Gen1 HWPC's, since there are a bunch of Gen1 HWPC's deployed out there as destination chargers, and a lot of new Teslas can't use them reliably.

 

[boaterva]

Posted in the other thread also, it's the same with percentages and I think it started with 42.2. Both our X and 3 do it, and what's weird is that the notifiications seem to be correct. I get a notification that the charging stopped at 90% and the car says 90, but the app right then says 89 (same for the other car we keep at 80). One goes between 90 and 87, the other between 80 and 77. 89 and 79 on the app. Drives this slightly OCD Engineer nuts.

I'm wondering if someone did a roundoff wrong, and truncated instead......