It is true that the engineering of the UMC plays a part in the adapter's reworking. That said, even a properly-engineered UMC wouldn't have stopped the garage fire that resulted in this feature's insertion. That was due to a loose wire on the back of an outlet. Even if you install it properly, breaker screws and outlet screws can work their way loose over time (I just fixed a loose neutral in my outside shed this weekend - and yes, I can guarantee I installed it correctly 15 years ago) and when you couple that with continuous loads, you can end up with fires.
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It is true that the engineering of the UMC plays a part in the adapter's reworking. That said, even a properly-engineered UMC wouldn't have stopped the garage fire that resulted in this feature's insertion. That was due to a loose wire on the back of an outlet. Even if you install it properly, breaker screws and outlet screws can work their way loose over time (I just fixed a loose neutral in my outside shed this weekend - and yes, I can guarantee I installed it correctly 15 years ago) and when you couple that with continuous loads, you can end up with fires.
FlasherZ - It seems to me that if what you say is correct, and I assume it is, then Tesla should have figured that out sometime between 2003 and 2012 (when Model S went into production). It also seems to me that it might have been more prudent to either overdesign the UMC as was apparently the case with the Roadster, or design the charging session to NOT be a continuous, sustained load (ie. 40A for 20 minutes, then 20A for 5 minutes to cool, then repeat). Afterall, these are smart guys (Stanford, etc.). You have to design a product with a FULL understanding of the environment it will be operated in, blemishes and all. Either they didn't agree with the criticality of your statements, or they weren't as smart as we all assume they are.
Tesla, or anybody else for that matter will not be able to eliminate house wiring fires completely. Just like ICE car fires cannot be eliminated completely. What you are asking for is perfection, which doesn't exist.
The only reasonable solution I see to this problem is a better UMC(even if it costs extra), and the current limiting software, BUT with an override, coupled with a warning message. A company cannot take away features that have been paid for, especially when that feature is the most important aspect of the vehicle.
No, it's neither... just like any other product, they couldn't possibly anticipate every single electrical installation or grid attachment out there. The Roadster MC / UMC / HPWC has nothing to do with it. There were only 2,500 of the Roadsters manufactured (compared to 16x that in Model S today), and the customer base was less diverse. They didn't run into some of the same issues that they are running into with a much larger, more diverse customer base today. They are also more prominent -- being under the microscope means having to be more careful, hence the titanium plates or the charging back-off algorithm.
The continuous load aspect really can't be changed without increasing charge time, and that's a trade-off Tesla must make. Rather than forcing everyone to have an average of 37.5A as you suggested, they chose to address the risk by allowing those installations that "look good" in terms of the ohm's law profile to work at continuous, and for those that look marginal, they back off the charging current.
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Sorry, I'm boggled by the response. It's not like Tesla is just deciding to screw with you and backing off the current arbitrarily. It sees a significant fluctuation that points to a problem in the electrical system where you're charging. Just because you don't believe that, or just because the segment from your meter to your receptacle is good, doesn't make it untrue. Do you really consider it a bad thing that the manufacturer of the largest kWh load your home will ever see is protecting you?
I've said it several times, I'll say it again - just because something works doesn't mean it's safe. Placing an override there will cause the average person to hit it every single time, regardless of whether he understands the risks or the physics of the situation -- "my electrician said my side was safe, so why not?" Just the fact that someone would ask for an override without being able to explain precisely why the Tesla detects that profile and backs off is proof why it is needed.
It has been established that a manufacturer *CAN* take away features that have been paid for, when they're unsafe. This happens in child toy recalls all the time. There were several examples cited in the "low" suspension thread. Charging works at the full rate when the infrastructure is there to support it. Fix your infrastructure, and the product works as designed.
The FAQ (below) has the appropriate troubleshooting steps. Call in your power company, explain what you're seeing. Have them talk to Tesla about the voltage fluctuations that are seen. My power company was happy to hear that I was going to give them more business and upgraded, no questions asked. If, however, the answer is not satisfactory, file a complaint with the PUC -- some PoCo's are living in the 1960's where we only used power for incandescent light bulbs, refrigerator and sawmill motors, and resistance heating, and they have to be sync'ed up with the reality of the world. That 10 kVA transformer serving 3 houses isn't going to cut it anymore, and they need to be held accountable, not Tesla.
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Finally found the post I was looking for:
Smokin' transformers
In this case, I'm sure Adelman's home wiring was just fine... the transformer was horribly undersized. I think that protection is a good thing.
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Note that this could also be a hardware problem with the car. I had called Tesla with this problem, they checked my logs and told me they needed to bring it in. They picked it up this morning and are still trying to figure out why the car forces a drop to 30 amps.The loaner (same 5.9.44 as my car) they dropped off charges at 40 amps.
Like I said, I'm still on 5.8(.24) so this does not affect me at all. We must have differing opinion on what "significant fluctuations" are, because I have looked at fluctuation graphs posted here when the software current limit happened, and it was not significant. Let's say a Model S owner lives near a power plant which inevitably leads to fluctuations and current limit. Not an unsafe scenario, but the Power company will laugh when one tells them what you suggested. If that Model S owner has a long commute, he is screwed, even though he paid big money for a feature that was there, and then got taken away.
Again, companies can TRY to take things away that they sold, until someone gets pissed off enough to seek action. Not too far fetched. You cannot compare child toy recalls to $100k cars. Two opposite ends of the spectrum.
From what I have seen from both owners that are not experiencing it and those owners that are, I can tell you that these fluctuations are pretty significant when the Tesla drops back. Help me define what you consider "not significant". My voltage fluctuates 2-5v during any given charge session, and my voltage drop is ~3-4%, and it does not back off. The 1960's standards used by the power companies may tell you it's not significant, but they're thinking oven elements, motor loads, and light bulbs.
They both involve the life safety of the person using the device. I don't consider them opposite. But we can rule that out for a second, the suspension thread had a couple of examples of car manufacturers removing a feature during a safety recall.
FlasherZ - The biggest part of the problem is that Tesla didn't publish the old specs or the new specs for unacceptable "voltage fluctuations". By not making that information available to either the homeowner or the power utility, both entities are spending time and money guessing at what the problem might be. Tesla could help their customers by making this information available, but they won't. And that's what really upsets me. If the power utility knew what "condition" was in "Tesla's New Tolerance" to avoid backing off to 30A, they would know if the problem was on the transformer side or the homeowner side. So when the electrician says "everything's wired up right" and the power utility rep says "we are within our tolerance", the Tesla customer is screwed because he doesn't have anything to hang his hat on.
If I remember correctly it was between 2-7V. This was with FW 5.8.4, and Tesla might have changed the software tolerances. There is no way to tell though, so I'll stay on the my current FW for now.
I know exactly how much that current limit affects charging, as the UMC will dial back to 30-32A, when the "brick" portion gets any sunlight while the car is charging. It can be a significant amount of extra waiting time added to a charge when on the road, even when using a safe outlet.
It's amazing how much slack Tesla is given for their POS UMC design, even from experts in the field. It actually harms the company more than it helps. Tesla made a superb car, but the mobile charging solution is just junk engineering, to put it mildly.
This I agree with. I'm sure if you connected Tesla with the PoCo they'd be willing to help. I suspect it's more of an issue of Tesla still tweaking the parameters based on their data during minor software revisions. Some have reported that their back-offs were reduced with 5.9, others haven't.
Even if Tesla did release its specs for backing off, you may be stuck with the PoCo saying "within specs" anyway. That doesn't automatically create a license to blow away safety -- it just means perhaps that the PoCo doesn't understand. It may require a PUC complaint and hearing, to get the PoCo's engineering arm to look at it vs. the guy who sticks his analog meter and says "it's +/- 10%".
Actually, they have avoided direct contact with the power company. Can you imagine how bogged down they would be if they had to work with hundreds of power utilities for thousands of Model S owners who can no longer charge at 40A? That would be a bigger pain than just shipping 30,000 better quality UMC cable/adapters. What are they gonna do anyway when the fuseable link in your brand new adapter breaks connection and you can't charge at all? That's even worse than charging at 30A.
First, there is no evidence that there are "thousands" of Model S owners who can no longer charge at 40A. This poll at the top is worse than non-scientific, because it's not a representative sample. Unfortunately, there seems to be this belief that 30% of Tesla Model S owners are experiencing this backing off... that's just simply not the case. The thread title will only draw those who have interest in charging or who experience the specific problem. It will not draw in those who don't have the problem (or at least will only attract a disproportionate number). At worst, you know of ~60 people who have had charging current back down. Then, to make matters worse, you ask people who are not experts in electrical infrastructure to make a determination as to whether it "rightly" or "falsely" backed current down. I *guarantee* you that a good number of the people who claim that they have "falsely" been subjected to back-down have an infrastructure problem. It might not be in their house, but it will be in their transformer, or on their service conductors.
This is not a "bigger pain", because only in a few circumstances will you run into the issue where Tesla and the PoCo need to converse. Only if you run into a condition where the PoCo refuses to do anything and says everything is just fine do you need to consider this. When I've helped others track down this issue, EVERY time we've found the issue without needing to call the power company. I look up and see a 10 kVA transformer feeding 2-3 homes, one with an HPWC; or I see that their incoming service conductors are 2/0 or 3/0 for a 200A service. If the power company refuses to deal with it, then you tell them you'll file a PUC complaint. Follow through with the PUC complaint if that doesn't fix things.
With that said, I can't help you any more if you somehow believe your infrastructure is perfect and that the Tesla is just backing the charge current off for the hell of it, so my best to you. I wish you luck if you choose to engage the PoCo; I wish you happiness if you just want to sit and stew and watch your current decremented by 25%.
mnx
2018 M3P
FlasherZ I take it you haven't experienced the car dropping you down to 30A? I'm willing to bet the % of owners experiencing this issue is higher than you think.
I've only seen it happen a handful of times and I believe all those times were during peak/mid peak hours. It hasn't been an annoyance yet for me, although I have had trouble a couple times charging off a 120V outlet and been very annoyed. I'm not sure if it's 5.8.4 related or not.
FWIW, I contacted the utility before I installed anything and asked if a 40A continuous load for EV charging would be ok. They told me it wasn't a problem, but if I decided to install an 80A HPWC that I'd need to give them advance notice so they can preform some upgrades.
I've only seen it happen a handful of times and I believe all those times were during peak/mid peak hours. It hasn't been an annoyance yet for me, although I have had trouble a couple times charging off a 120V outlet and been very annoyed. I'm not sure if it's 5.8.4 related or not.
FWIW, I contacted the utility before I installed anything and asked if a 40A continuous load for EV charging would be ok. They told me it wasn't a problem, but if I decided to install an 80A HPWC that I'd need to give them advance notice so they can preform some upgrades.
The algorithm seems to trigger on different things, one of which appears to be a fixed voltage threshold. It appears to always trigger at 190V. Surely that's inappropriate if the open circuit voltage upon connect was only 200V in the first place. It causes the CS-90 at Hotel Mortagne in Boucherville (south shore of Montreal) to always back down from 70A to 50A. This makes a huge difference to your charging time, effectively neutering a rare high power Level II station.
The other thing that seems to trigger it is voltage fluctuations. Unfortunately the grid has voltage fluctuations all the time. That said, it appears less likely to trip on variations if your voltage is higher rather than lower. I don't know for sure what their algorithm is, but I don't think it's entirely well thought-out. Certainly it is too sensitive.
The other thing that seems to trigger it is voltage fluctuations. Unfortunately the grid has voltage fluctuations all the time. That said, it appears less likely to trip on variations if your voltage is higher rather than lower. I don't know for sure what their algorithm is, but I don't think it's entirely well thought-out. Certainly it is too sensitive.
FlasherZ - It doesn't matter what you or I believe. It's a fact that Tesla believes there is a problem. That's why they changed the software in 5.8.4. But that's a band-aid solution as we all know. It's also a fact that Tesla believes there is a problem with the hardware (UMC), that's why they redesigned the adapter and are shipping it out to all the customers. Another band-aid solution. Everyone agrees a better solution would have been an integrated adapter that's not removable from the cord. It's amazing that your only suggestion in response to these known problems is for the un-electrically educated customer to spend time and money attempting to troubleshoot his own install. It's great that you have this expertise. But the majority of Model S customers do not (nor should they be expected to have this expertise).
No - my car has, to the best of my knowledge and looking through the REST data collection logs, never dropped to the 75% mark -- at the airport, at the lake campground, at home, at my father-in-law's, and at J1772's at Illinois State University. That's a pretty broad base of chargers in many different environments (e.g., the St. Louis airport is @ 199V, 16A). I do have empathy, though - I have had to back down my charging on a faulty breaker once that would trip far before its load was truly reached; I don't blame Tesla for that.
I don't know what the actual %age of owners is, but I do know that assuming 30% based upon the poll in this thread is far off the mark. I've taken the opportunity to ask owners (in Facebook, in the St. Louis Enthusiasts' Group, and elsewhere), and it doesn't seem to be as prevalent as 30% or even 10%. Tesla knows, though - and that will give them the opportunity to look it over.
What I do know is that if your utility connection is sized correctly and your wiring is good, the car never backs down from charging at 100%. PoCo's are all different -- some, like mine, are really accommodating and the operations manager spent some significant time working with me on my requirements (and we re-engaged them the other day for any prep-work for Model X & a second HPWC -- they felt comfortable that I am within design capacity). Some, like PG&E, are a pain in the ass - see the post I linked above where PG&E claimed that Adelman would have to pay for the upgrade because of PG&E's excuse that his transformer was just fine and his solar PV system was the cause of transformer stress. You may have to file a complaint with the PUC (by the way, I had an acquaintance need to do this in PG&E land about 15 years ago, and it's amazing how responsive utilities can become when you threaten to do that, and follow through). Residential capacity management to many PoCo's is "wait until the transformer explodes/fails, then replace it" - evidenced by the many 1970's transformers still up on poles in neighborhoods around the US. The transformer serving my parents' home (built in 1884) is a 1970's vintage unit - I don't even know what the rating is but from its size, I'd guess about 5 kW.
Bottom line: the blame on Tesla for the safety provision in their software is misplaced. Just because it "worked fine" before doesn't mean that something wasn't overloaded and that it will continue to work. Perhaps they can tweak it to make its effects less pronounced in some infrastructure situations, but your charging load is different than traditional loads in the home. I do agree that they should release the technical specs that triggers a back-down so it can help troubleshoot the issue with the PoCo.
I don't know what the actual %age of owners is, but I do know that assuming 30% based upon the poll in this thread is far off the mark. I've taken the opportunity to ask owners (in Facebook, in the St. Louis Enthusiasts' Group, and elsewhere), and it doesn't seem to be as prevalent as 30% or even 10%. Tesla knows, though - and that will give them the opportunity to look it over.
What I do know is that if your utility connection is sized correctly and your wiring is good, the car never backs down from charging at 100%. PoCo's are all different -- some, like mine, are really accommodating and the operations manager spent some significant time working with me on my requirements (and we re-engaged them the other day for any prep-work for Model X & a second HPWC -- they felt comfortable that I am within design capacity). Some, like PG&E, are a pain in the ass - see the post I linked above where PG&E claimed that Adelman would have to pay for the upgrade because of PG&E's excuse that his transformer was just fine and his solar PV system was the cause of transformer stress. You may have to file a complaint with the PUC (by the way, I had an acquaintance need to do this in PG&E land about 15 years ago, and it's amazing how responsive utilities can become when you threaten to do that, and follow through). Residential capacity management to many PoCo's is "wait until the transformer explodes/fails, then replace it" - evidenced by the many 1970's transformers still up on poles in neighborhoods around the US. The transformer serving my parents' home (built in 1884) is a 1970's vintage unit - I don't even know what the rating is but from its size, I'd guess about 5 kW.
Bottom line: the blame on Tesla for the safety provision in their software is misplaced. Just because it "worked fine" before doesn't mean that something wasn't overloaded and that it will continue to work. Perhaps they can tweak it to make its effects less pronounced in some infrastructure situations, but your charging load is different than traditional loads in the home. I do agree that they should release the technical specs that triggers a back-down so it can help troubleshoot the issue with the PoCo.
cschock
Member
I use a newly installed (just before getting the Model S) by Solar City 50 amp breaker running new proper gauge wiring to a NEMA 14-50 connection in my garage. If I set the system to charge at 40 amps it will start out that way and then always at some point in the charge drop down to 30 amps.
There is no sign of heat damage or other problems with either the UMC or plug/receptacle.
I always charged at 40 amps until 5.8.4 without issue (again using same setup.)
Voltage appears pretty stable under charge but then I am not sitting and monitoring it for the full charge time.
I reported this as a false positive and look forward to getting the new 14-50 adapter and being able to charge at the rated speed of the outlet again.
There is no sign of heat damage or other problems with either the UMC or plug/receptacle.
I always charged at 40 amps until 5.8.4 without issue (again using same setup.)
Voltage appears pretty stable under charge but then I am not sitting and monitoring it for the full charge time.
I reported this as a false positive and look forward to getting the new 14-50 adapter and being able to charge at the rated speed of the outlet again.
It seems that we've now hit the point where the points are all out on the table and what's left are disagreements: whether this is Tesla's problem to solve or an infrastructure problem with particular installs; whether there should be an override so that a consumer can, upon having checked that everything south of the meter, override the limit; or whether there's infrastructure problem at all. So this should be my final post here.
There are two different problems, you're conflating them.
The first is the issue of melting UMC adapters, a local issue caused by a product design. On this, you and I agree it's a problem and needs to be solved. Tesla solved it by placing thermal protection into the adapter. I do not agree with you (contrary to your assertion that everyone agrees a better solution would have been an "integrated adapter that's not removable from the cord") because it would severely limit the adaptation ability of the UMC. Not everyone uses only the 14-50, and the Roadster's solution of having multiple cords would be difficult for me to manage. We will only know if this continues to be an issue if we see the reports of melted UMC's changing to reports of charging that stops all the time because of bad contacts in the adapters, and it's too early to determine. Perhaps heat was causing a runaway effect with the old adapters that just made things worse, perhaps we'll see a bad mechanical design fail in a safer way (stops charging vs. melts) and the root cause is yet to be fixed. Let's set this one aside because it has nothing to do with this thread and the charging back-off.
The second is the issue of continuous loads and potential infrastructure issues. The garage fire that triggered the 5.8.4 software fix had nothing to do with the UMC or its adapters. It was the result of a loose screw on the back of the NEMA 14-50. Tesla uses ohm's law to determine when it appears there might be a high-resistance problem in the infrastructure. This serves to protect the infrastructure (whether wiring in the home, overloaded transformer, etc.) I disagree that "we all know" this is a "band-aid" solution - I certainly don't agree with that statement on the 5.8.4 feature.
The only cross-point of these two problems is that when it involves a loose screw at a NEMA 14-50 receptacle feeding a UMC--you might get lucky enough that the heat generated in that junction will travel through the prongs of the 14-50 to the adapter where the heat link may cut off the power. That's not guaranteed to happen, though. And it most certainly won't happen if the loose screw is a breaker screw, or a loose lug in a meter pan, or a bad connector in a junction box, or in an HPWC, far away from that adapter. That's why it's my belief Tesla will never remove this feature (but may tweak it so that the impact in certain cases, like Doug's below where voltage starts outside of tolerance already, may be lessened).
Tesla added a safety feature. Those who are affected by this safety feature because something in their infrastructure is undersized are claiming that a) Tesla is wrong about it being undersized, and b) are demanding that Tesla remove a safety feature for their (40A) convenience, both without fully investigating the problem at hand and coming to a full conclusion as to why the car is backing down. I side with Tesla on this one, because I've seen people lose their houses and family members due to electrical infrastructure fires. The car is not arbitrarily backing down, so figure out what infrastructure problem is causing it to back down.
Finally, the final bad assumption I'd like for you to stop making is that I'm asking all of the "un-electrically educated customer to spend time and money attempting to troubleshoot his own install". First, if you don't like the backing off, you will have to invest time, money, and perhaps both... because there's something wrong with your infrastructure. If you're able to troubleshoot, you'll minimize money at the expense of time. If you don't have the time, but have the money, you can engage people (electricians) who can help. I offer suggestions for people to find out where the problem is within their infrastructure. My first suggestion in the FAQ says that if you're uncomfortable with it, you call people who can help.
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ANSI C84.1-2011 specifies a nominal voltage of 120V above ground for each leg with a 5% tolerance. On a three-phase 208Y/120V system, this means that the official voltage tolerance is between 197V and 218V for L-L phase voltage. If you're seeing 199V even before a load is applied, then something is undersized -- perhaps it's a long run to the charger from the distribution panel or transformer. Larger conductors will minimize that, or the transformer should be adjusted to provide a slightly higher voltage, or a boost transformer is required.
I think this is an area where a tweak to the algorithm might be appropriate, if there is a hard voltage threshold. It might be ok to look purely at voltage drop when load is applied, and ignore an out-of-spec voltage, considering it's a switching supply and can handle anything from 85V to 265V (277V in Superchargers). Perhaps Tesla will make this tweak in the future.
I don't know the specifics, either, but in each case that has been solved it has come down to something that was undersized or overloaded. It may not be in the home or "south of the meter", but it has been there.
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See the FAQ in my signature, especially the question about this. This algorithm can't determine whether it's infrastructure inside your home, between your transformer and your home, or in the distribution grid -- it just knows that based on ohm's law, there appears to be a higher resistance than expected somewhere. Could be overloaded transformer, could be undersized service conductors, could be overload (even if temporary) in the primary distribution grid to your transformer.
There are two different problems, you're conflating them.
The first is the issue of melting UMC adapters, a local issue caused by a product design. On this, you and I agree it's a problem and needs to be solved. Tesla solved it by placing thermal protection into the adapter. I do not agree with you (contrary to your assertion that everyone agrees a better solution would have been an "integrated adapter that's not removable from the cord") because it would severely limit the adaptation ability of the UMC. Not everyone uses only the 14-50, and the Roadster's solution of having multiple cords would be difficult for me to manage. We will only know if this continues to be an issue if we see the reports of melted UMC's changing to reports of charging that stops all the time because of bad contacts in the adapters, and it's too early to determine. Perhaps heat was causing a runaway effect with the old adapters that just made things worse, perhaps we'll see a bad mechanical design fail in a safer way (stops charging vs. melts) and the root cause is yet to be fixed. Let's set this one aside because it has nothing to do with this thread and the charging back-off.
The second is the issue of continuous loads and potential infrastructure issues. The garage fire that triggered the 5.8.4 software fix had nothing to do with the UMC or its adapters. It was the result of a loose screw on the back of the NEMA 14-50. Tesla uses ohm's law to determine when it appears there might be a high-resistance problem in the infrastructure. This serves to protect the infrastructure (whether wiring in the home, overloaded transformer, etc.) I disagree that "we all know" this is a "band-aid" solution - I certainly don't agree with that statement on the 5.8.4 feature.
The only cross-point of these two problems is that when it involves a loose screw at a NEMA 14-50 receptacle feeding a UMC--you might get lucky enough that the heat generated in that junction will travel through the prongs of the 14-50 to the adapter where the heat link may cut off the power. That's not guaranteed to happen, though. And it most certainly won't happen if the loose screw is a breaker screw, or a loose lug in a meter pan, or a bad connector in a junction box, or in an HPWC, far away from that adapter. That's why it's my belief Tesla will never remove this feature (but may tweak it so that the impact in certain cases, like Doug's below where voltage starts outside of tolerance already, may be lessened).
Tesla added a safety feature. Those who are affected by this safety feature because something in their infrastructure is undersized are claiming that a) Tesla is wrong about it being undersized, and b) are demanding that Tesla remove a safety feature for their (40A) convenience, both without fully investigating the problem at hand and coming to a full conclusion as to why the car is backing down. I side with Tesla on this one, because I've seen people lose their houses and family members due to electrical infrastructure fires. The car is not arbitrarily backing down, so figure out what infrastructure problem is causing it to back down.
Finally, the final bad assumption I'd like for you to stop making is that I'm asking all of the "un-electrically educated customer
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ANSI C84.1-2011 specifies a nominal voltage of 120V above ground for each leg with a 5% tolerance. On a three-phase 208Y/120V system, this means that the official voltage tolerance is between 197V and 218V for L-L phase voltage. If you're seeing 199V even before a load is applied, then something is undersized -- perhaps it's a long run to the charger from the distribution panel or transformer. Larger conductors will minimize that, or the transformer should be adjusted to provide a slightly higher voltage, or a boost transformer is required.
I think this is an area where a tweak to the algorithm might be appropriate, if there is a hard voltage threshold. It might be ok to look purely at voltage drop when load is applied, and ignore an out-of-spec voltage, considering it's a switching supply and can handle anything from 85V to 265V (277V in Superchargers). Perhaps Tesla will make this tweak in the future.
I don't know the specifics, either, but in each case that has been solved it has come down to something that was undersized or overloaded. It may not be in the home or "south of the meter", but it has been there.
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See the FAQ in my signature, especially the question about this. This algorithm can't determine whether it's infrastructure inside your home, between your transformer and your home, or in the distribution grid -- it just knows that based on ohm's law, there appears to be a higher resistance than expected somewhere. Could be overloaded transformer, could be undersized service conductors, could be overload (even if temporary) in the primary distribution grid to your transformer.
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FlasherZ - Yes we disagree on numerous issues. But the problem associated with backing down amperage to 30A is clearly something initiated by Tesla with 5.8.4 (for whatever reason). I'm not debating the merits of their decision, just the implementation. You know banks provide protection for their customers at ATM machines by limiting withdrawals to $400 or $500 per 24 hour period. They could give customers even more protection by limiting withdrawals to $50 per 24 hour period. But the overall benefit of having an ATM would be diminished if banks were to do that. So after allowing me to charge at 40A for one year without incident, Tesla has decided to "protect me" and themselves from legal action (presumably), by diminishing the utility of their product (40A to 30A) for me and many of their other customers. The implementation of the additional "protection" is flawed. Even you and I agree that Tesla should publish the specs that trigger the backing off event, so electricians and power utility personnel can effectively troubleshoot. But if they published the specs I'm sure some would question the reasonableness of those specs. So better to not publish them - I guess.
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