Welcome to Tesla Motors Club
Discuss Tesla's Model S, Model 3, Model X, Model Y, Cybertruck, Roadster and More.
Register

Home charging now stepping down to 24 amps during the charging session

This site may earn commission on affiliate links.
My M3 (rear wheel long range) will be two years old next month (August). When I charge it, exclusively starting at midnight due to rates, and using a Tesla wall connector, I receive a text when charging starts and when it ends along with the mile range when it starts and finishes. The first year or so, I regularly looked at those texts and calculated, based on time and miles of range added, what my range per hour being added was. It has consistently been 44-45 miles of range added per hour. No exceptions.

Haven't been as diligent looking at these texts recently, but last week, I happened to notice one pair of texts that implied it took way longer than normal to charge (picture attached). Doing the math, it was 27 miles of range added per hour. So I watched it closely the next time I charged. Again, it was very low.

So yesterday I plugged it in during the day for about five minutes and observed the display. 44 miles @ 48 amps which is what it should be. Charged it last night starting at midnight. I woke up at 12:20 AM and checked the app. 44 Miles at 48 amps. All is good. Woke up again at 2:18 AM and checked the app again. 22 miles at 24 amps. It cut the amps in half and thus the miles. Went to the car to look at the screen (picture attached) and it showed 24 amps, but the plus sign to increase the amps was greyed out (see red box on picture). This implied to me that it wasn't able to go beyond 24 amps at that time.

To further test, I stopped charging, unplugged the cable, waited about 10 seconds, plugged the cable back in and started charging again. It ramped right back up to 44 miles and 48 amps (see picture). Went back to bed and 20 minutes later I checked the app (picture attached) and it was at 45 miles and 48 amps. All good. But this morning, when I looked at the start and stop texts for this last charging session (picture attached), it works out to 38 miles of range per hour. My guess is it stepped down to 24 amps again sometime during the charging session.

Any clue why this is happening? I don't know if it's the car, Tesla wall connector or electrical feed. Although I don't think this is it, it's worth noting that I got solar for the house back in April. I can't imagine that would have an impact but just throwing it out there anyway. The lights on the Tesla wall connector still do the same thing they always have - green blinking in a downward direction.

Thanks in advance for any advise.
 

Attachments

  • First Notice.jpeg
    First Notice.jpeg
    763.1 KB · Views: 1,042
  • Step Down to 24A.jpeg
    Step Down to 24A.jpeg
    327.6 KB · Views: 570
  • Restart.jpeg
    Restart.jpeg
    291 KB · Views: 529
  • 20 Minutes Later OK.png
    20 Minutes Later OK.png
    1,003.7 KB · Views: 550
  • Restart Slowed Down.jpeg
    Restart Slowed Down.jpeg
    713 KB · Views: 647
  • Like
Reactions: Gasaraki
I don't have much to back up this claim other than my gut, but I would think the car is fine and there's a problem with your wall connector, or its power supply. The screenshot shows 24/24 indicating the connector is limited to 24 - I would suspect it would say 24/48 if the car was limiting the current. Not sure why you're not getting a warning message like bbell did though.

Having solar installed COULD HAVE caused a problem if the circuit breaker was moved within your panel to make room for the solar circuit. Simply HAVING solar wouldn't cause a problem though. If the electrician didn't tighten everything back down, you could be overheating the connection points and seeing voltage drop causing the wall connector to lower its current draw. And of course the wall connector could have a problem.

Do you have other means of charging? (another location with a wall connector, a UMC with a high power outlet?) I have a feeling you're going to want to switch over until this issue is resolved to your satisfaction since there could be a safety issue here. Maybe manually turn down your charge current to 24 until you get it resolved.

did you happen to feel the wall connector when it was charging for awhile to see if felt hotter than normal? Maybe do the same at the circuit breaker panel?
 
I don't have much to back up this claim other than my gut, but I would think the car is fine and there's a problem with your wall connector, or its power supply. The screenshot shows 24/24 indicating the connector is limited to 24 - I would suspect it would say 24/48 if the car was limiting the current. Not sure why you're not getting a warning message like bbell did though.

Having solar installed COULD HAVE caused a problem if the circuit breaker was moved within your panel to make room for the solar circuit. Simply HAVING solar wouldn't cause a problem though. If the electrician didn't tighten everything back down, you could be overheating the connection points and seeing voltage drop causing the wall connector to lower its current draw. And of course the wall connector could have a problem.

Do you have other means of charging? (another location with a wall connector, a UMC with a high power outlet?) I have a feeling you're going to want to switch over until this issue is resolved to your satisfaction since there could be a safety issue here. Maybe manually turn down your charge current to 24 until you get it resolved.

did you happen to feel the wall connector when it was charging for awhile to see if felt hotter than normal? Maybe do the same at the circuit breaker panel?
I think it's the wall charger or electrical feed as well. What's perplexing to me is that it starts out at 48a and then eventually (after at least 20 minutes in both my cases tested), it drops down. And if I restart, it immediately goes back to 48a.
 
Sounds like a thermal problem to me. Initial charging works normally but then something gets hot and the HPWC throttles back. I'd suspect the electrical wiring/breaker.

I assume that you are using a 60A breaker to be charging at 48A. It's something that I'm considering doing with my soon-to-be HPWC installation. I'm planning to put in a 60A breaker, set the Gen 2 HPWC to deliver 48A, and also wire in a transfer switch to a 14-60 outlet. That way I have the option to use my mobile connector in case the HPWC goes kaput.
 
  • Like
Reactions: ElectricIAC
Sounds like a thermal problem to me. Initial charging works normally but then something gets hot and the HPWC throttles back. I'd suspect the electrical wiring/breaker.
But when it's dropped to 24a, and I unplug, wait about 10 seconds, and plug back in, it goes back to 48a for at least 20 minutes and all looks fine. It seems if something got too hot, it would stay too hot over a period of less than 20 seconds and it thus would stay at 24a, or would quickly revert back to that if something was too hot.
 
unrelated - but in a hot Texas garage (96F...) my UMC set to 32A (the max it does) will get too hot after an hour and a warning message appears and the unit automatically dials it back down to 16A to let it cool off..... Setting the charging limit to just 24A solved this as the UMC doesn't overheat. I'd rather do 24A overnight consistently than the 32A to 16A reduction.
 
But when it's dropped to 24a, and I unplug, wait about 10 seconds, and plug back in, it goes back to 48a for at least 20 minutes and all looks fine. It seems if something got too hot, it would stay too hot over a period of less than 20 seconds and it thus would stay at 24a, or would quickly revert back to that if something was too hot.
Not true, when the charge current drops the temperature drops as well back into the "safe" zone and so when you re-initiate the charge at high amperage the temperature goes back up. Also, if the circuit is already hot it will not detect the voltage drop because the voltage drop occurs as the circuit heats up. If you re-initiate charging and the circuit is already hot you could induce even more heat which would lead to a safety concern.
 
Not true, when the charge current drops the temperature drops as well back into the "safe" zone and so when you re-initiate the charge at high amperage the temperature goes back up. Also, if the circuit is already hot it will not detect the voltage drop because the voltage drop occurs as the circuit heats up. If you re-initiate charging and the circuit is already hot you could induce even more heat which would lead to a safety concern.
OK. Got it. A thermal problem does make sense. I don't think it's a weather heat problem cuz it's not that hot here right now and it's been plenty hot many times before with no problem. Next time I have a chance to monitor the charging better, I will see if the wall connector or anything else gets hot.
 
unrelated - but in a hot Texas garage (96F...) my UMC set to 32A (the max it does) will get too hot after an hour and a warning message appears and the unit automatically dials it back down to 16A to let it cool off..... Setting the charging limit to just 24A solved this as the UMC doesn't overheat. I'd rather do 24A overnight consistently than the 32A to 16A reduction.

Sounds like your house's wiring isn't capable of supporting 32A continuous. Capping permanently at 24A seems very sensible.
 
  • Like
Reactions: Dmagyar
Any clue why this is happening?
You can isolate the problem by swapping out parts:

1. Try the car at a different 48A TWC away from home, or bring a another car to charge
2. If you can, charge using your mobile connector at 32A at home

FWIW, I am a fan of looking for simple things first. I would probably cut the juice to the EVSE and open it up to check the wiring and torques. A loose wire would make a lot of sense since the connection would heat up with use, and all the merrier at high Amps.

The following sounds logical to me ... but less safe than what I wrote above. It is as safe as continuing to use the EVSE as you have been:
Let the EVSE charge at 48A until the trip down to 24Amps. At that point disconnect, shut down the juice to the EVSE, then open it up and scan it with an IR gun to look for an over heated component or connection.

In you shoes, I would dial down the car charging to 24 Amps until the problem is resolved in case this is over heating.
 
Last edited:
I agree with @SageBrushResistive gearing is a function of current squared.

Say what? Resistive gearing? I’m assuming that’s an autocorrect error.

According to science, Voltage = Current x resistance (V = I x R), Power dissipated = voltage x current (Pd = V x I), and thusly Power dissipated = current x resistance x current or Pd = I^2 x R.

But most people don’t really know any of that even means or how it relates to charging or temperature.

I didn’t see what SOC or target SOC was set in the car. It may have been reducing the current to do cell group balancing. Each time you unplugged, you reset the software algorithm which then needs to pull the full current for a while, then throttles back automatically to perform the balance.

Tesla may not do this at all SOCs (like below 80 or 90%). I’m just throwing it out there.
 
Last edited:
Also might want to check your voltage under load. I’ve noticed that if TWCs detect significantly low voltage, they back off the amps. I’ve seen this at hotels that have the destination TWCs. At home, I can see the voltage drop a few volts (<5) when the AC units cycle on/off.