Anyone Still Experiencing Charge Current Limiting (40A->30A)?

DavidM · Dec 29, 2014

Since the 5.8.4 software update, many Model S owners began to experience charging sessions where charging was randomly reduced from 40A to 30A. When it happens, there is usually a message on the dashboard that says "charging problems". The impact of this change is slower, and unpredictable refueling sessions. Personally, I have owned my Model S for 2 years. For a full year before the software change, I could charge at home (at 40A) unimpeded. Since the change, the software limits my charging to 30A (in most cases).

The power utility has checked the install and the transformer. Tesla has checked the install. Electricians have checked the install. Everything is within standard residential tolerances (but perhaps not within the new Tesla tolerances). Lots of head scratching. Tesla won't disclose the old (or new) tolerance levels to the power utility, which makes it difficult to troubleshoot the problem. I am using the Universal Mobile Connector (with the revised adapter).

Is anyone else still having this issue with the car randomly backing off to 30A while charging at home? If so, are you using the UMC cable, or the beefier Wall Connector?

studiojon · Dec 29, 2014

I have the same issue using the Tesla wall charger permanently installed in my garage.

shady · Dec 29, 2014

I would say it happens to me about once a month

scaesare · Dec 29, 2014

I get it every few weeks as well.

I've looked at the voltage sag when it happens, and I can't find any pattern to it.

It's a bummer, as in the winter I schedule my charges so they finish shortly before I leave in the morning, and occasionally I'l lend up with less range than I'd like.

Forty Creek · Dec 29, 2014

I have had the problem with my HPWC ever since the software update. Charge rate drops from 79 amps to 59 sometimes immediately and sometimes after 10 minutes or so of charging. Occasionally the charge rate holds through the entire charging session. It has nothing to do with what else is drawing power in my home. It happens even when I do a scheduled charge starting at 2:00 AM. In my case the voltage displayed in the car drops from around 238 to 221 as the amps ramp up. It seems very likely that the software detects this drop and lowers the charge rate. I suspect that your power utility will need to do their testing under load otherwise, everything 'looks' fine. Tesla was pro-active and offered to send out one of their electricians to look my problem but for a variety of reasons I haven't taken them up on it. I will in the next week or so, once the holidays are over.

qwk · Dec 29, 2014

What firmware versions are you guys on? 5.9 and later let's you toggle the amperage up after the software dials it back.

Forty Creek · Dec 29, 2014

qwk said:
What firmware versions are you guys on? 5.9 and later let's you toggle the amperage up after the software dials it back.

I have the latest update. No, you can't dial the amperage back up during a charging session where it has been reduced. You have to stop charging, then start charging again in order to get back to the pilot amperage (80 amps in my situation).

Cerie · Dec 29, 2014

It happened to me once before I started using scheduled charging. I think it was because I had too many other high voltage demanding things running at the same time (laundry machine, dishwasher, central vac) but since I moved scheduled charging to begin at midnight, it hasn't happened since. Try charging it in the middle of the night when nothing else is going on.

apacheguy · Dec 29, 2014

Happens periodically. Annoying that it requires manual intervention to reset.

DavidM · Dec 29, 2014

I suspect the changes that Tesla made to the software with 5.8.4 were overly aggressive, and as such, it detects what it thinks is a circuit problem, when no such problem exists. I've brought this up with Tesla Service several times, over an 8 month period. Both with my local service center, as well as with headquarters in California. At this point, California simply routes the issue back to my local service center. Now, they are silent on the whole issue. I have not received any indication that anyone is looking into the issue. Dealing with this sort of thing is why I have become sour on Microsoft over the years. They download updates to my computer. Many of the updates make my computer better and safer, but there is always one item that gets screwed up in the process. Something that worked perfectly fine before, and is now partially broken.

It's obvious that there are many Model S customers who are experiencing the same issue (to varying degrees).

sublimaze1 · Dec 29, 2014

I have noticed this as well.

I can get 40A most of the times, then it will drop to 30 and stay there unless I manually reset to 40.

I have a feeling it has to do with the adapter not fitting 100% into the car and when that happens, the feedback to the UMC (or wall charger) module detects it and steps it down. Not a big deal, as I charge every night and it doesn't get low. But when I do come in with less than 30-40 miles on the range, I make sure that it seats well and that I dial it up to 40.

Small price to pay - FWIW.

apacheguy · Dec 29, 2014

DavidM said:
Dealing with this sort of thing is why I have become sour on Microsoft over the years. They download updates to my computer. Many of the updates make my computer better and safer, but there is always one item that gets screwed up in the process. Something that worked perfectly fine before, and is now partially broken.

Well at least you can uninstall a Windows Update or better yet, restore your OS to an earlier date.

DavidM · Dec 30, 2014

sublimaze1 said:
I have noticed this as well.

I can get 40A most of the times, then it will drop to 30 and stay there unless I manually reset to 40.

I have a feeling it has to do with the adapter not fitting 100% into the car and when that happens, the feedback to the UMC (or wall charger) module detects it and steps it down. Not a big deal, as I charge every night and it doesn't get low. But when I do come in with less than 30-40 miles on the range, I make sure that it seats well and that I dial it up to 40.

Small price to pay - FWIW.

I hadn't thought about that. But that could be fixed with a better connector, or a software tweak. Neither has been attempted, or even suggested by Tesla. A few times I've returned home after a long trip with minimal range. I needed to run some additional errands before dinner, and would have appreciated the ability to charge at 40A (28 mi/hr), instead of 30A (21 mi/hr). But I agree that in most cases, charging at 30A overnight is adequate. It just bugs me to have paid for 40A, and now receive 30A. This after having 40A capability for over one year.

Forty Creek · Dec 30, 2014

DavidM said:
I hadn't thought about that. But that could be fixed with a better connector, or a software tweak. Neither has been attempted, or even suggested by Tesla. A few times I've returned home after a long trip with minimal range. I needed to run some additional errands before dinner, and would have appreciated the ability to charge at 40A (28 mi/hr), instead of 30A (21 mi/hr). But I agree that in most cases, charging at 30A overnight is adequate. It just bugs me to have paid for 40A, and now receive 30A. This after having 40A capability for over one year.

Just as a data point, I have had my HPWC replaced AND the port on my car replaced. Still experience the step down in charge rate nearly every time.

dan-l · Dec 30, 2014

If you are near the Tampa Bay region, I'd be more than happy to swap UMCs with you for a week to see if that helps your situation.

DavidM · Dec 30, 2014

dan-l said:
If you are near the Tampa Bay region, I'd be more than happy to swap UMCs with you for a week to see if that helps your situation.

Thanks a lot Dan! But in light of "Forty Creek's" comment, I doubt there is an issue with the UMC. Tesla gave me a loaner car several months ago, and I experienced the current reduction on that car as well. With so many owners experiencing this problem, I'm convinced that the software parameters are just too aggressive for standard residential electrical service.

scaesare · Dec 30, 2014

I ended up with a replaced HPWC as well... still no deal... so I don't think it's the HPWC.

Also supporting that conclusion is that according to Visible Tesla (and the dash displays when I've caught it), is that the HPWC is correctly reporting a pilot current of 40A:

smsprague · Dec 30, 2014

I have had this issue twice in my 6 months of ownership. Drop from 40 amps to 30 amps after about a minute. Both times Tesla replaced the master charger. Last time I was told I had a new design. Has been charging at 40 amps for last 6 weeks so I am hopeful

kennybobby · Dec 30, 2014

scaesare said:
View attachment 67541

So many numbers, and such precision of battery current to 0.1 amps, yet curiously absent is one of the most important
values--battery voltage...? And other important factors: pack and charger internal temperatures.

i would think that most EV chargers for lithium packs have conditions to limit power based upon simple electrical and thermal measurements.

scaesare · Dec 30, 2014

kennybobby said:
So many numbers, and such precision of battery current to 0.1 amps, yet curiously absent is one of the most important
values--battery voltage...? And other important factors: pack and charger internal temperatures.

i would think that most EV chargers for lithium packs have conditions to limit power based upon simple electrical and thermal measurements.

I don't believe battery voltage is something Tesla supplies via the API. But the chargers ramp the voltage up to whatever the battery requires, and then limit the current based on what the battery profile requires. SO not seeing battery voltage shouldn't be a problem.

As for pack temp... it's understood that charging at 1/8C or so shouldn't put any real thermal stress on the battery that would likely limit it.. and if so, the cooling system kicks in. In any case, this is in my garage where it's 40-ish degrees, so there's no real thermal issue here at the moment...

Anyone Still Experiencing Charge Current Limiting (40A->30A)?

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