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InTheShadows
Active Member
If you know the building wiring and the feeder circuits are good and you have the UMC. take the 14-50 plug off of the UMC and look for signs of melting. If you see any at all (or can't get it apart because it's melted together) call your service center and request a new one. I was having problems with mine and it turns out it was melting inside and reducing the charge current.
It's bigger than just building wiring and feeder circuits. Voltage fluctuations can sometimes go all the way back to the substation, if a distribution node is overloaded. This is why troubleshooting is important.
Troubleshooting can be complicated here, because it can be a factor of transformer overloading, or distribution circuit overloading, or service conductor overloading, or a not-quite-torqued service conductor... and complex interdependencies can exist - for example, you may not see that your service conductor is overloaded until you have the Tesla charging and suddenly your A/C compressor kicks in, drawing the voltage down because of high resistance there. But is that an issue with your service conductor, or perhaps is it the start capacitor or compressor motor on your A/C compressor going bad that makes it draw 200A for a few seconds instead of a fraction of a second?
Start local and work your way back. First, inspect the UMC - it's the easiest thing to check. Then, check your branch wiring - that your outlet is tight, that your conductors are the right size, that the breaker is tight, and that there is no damage along the branch circuit. Then you have to start narrowing potential problematic loads in the building - turn off all breakers but the Tesla charging one and see if it still backs off. If it does, then you know it's not anything related to loads inside the house but likely something with the power company. If it doesn't, begin turning on your loads, starting with the largest, and work through them slowly to see when the car backs off. Narrow down the potential problematic appliances on the load that seems to trigger the back-off and try to isolate it. A repair might be necessary there. If it doesn't seem to be isolated to a single appliance, you may have an aggregate load problem on the service conductors, transformer, or distribution network. Your power company will have to help you, and you may have to connect them with Tesla to figure out what might be triggering it.
A good electrician will be able to help diagnose this for you if you don't feel comfortable doing it.
The one thing I do know is this: I have a 2-4V fluctuation the entire time I'm charging, and the car doesn't back off. It takes a pretty good fluctuation to make the Tesla back off, and it's an indictor that *something* is wrong. You just have to work with the power company, Tesla, and perhaps an electrician to find it. Public chargers aren't immune to these problems, either, sometimes they're on an overloaded transformer or an undersized run, etc. But most importantly, I am happy knowing that at least Tesla wants to ensure the safety by having a check on the infrastructure rather than blindly drawing what will be the largest load seen in 95% of our homes.
Ok - now that we've had 5.9 out there for a little while, time to revisit this topic. For those of you who said that the car had "falsely" backed away from the max charge current, have any of you received the 5.9 update and has the behavior changed for you (i.e., does it no longer back down)?
Forty Creek
Member
5.9 just installed and I am going to be checking this issue very closely. Since December's software update, I've been experiencing reduced charge rates with my HPWC. The HPWC has been replaced once, as was the car's charge port. The car seems to charge successfully at the service center, so the cause must be local. I have had our hydro utility out once to check the power to the house and they could not detect any problems (we are rurally situated, so I suspected a possible problem with power from the street). I routinely do schedule charges which start at 2:00 AM when nothing much else is drawing power. The house has a 200 amp electrical panel with a 100 amp breaker dedicated to the HPWC. The hydro people tested the line to the house without the car plugged in so I am wondering if the 79-80 amp load could cause enough drop in voltage to trigger the set back? They offered to come back if the problem wasn't resolved and so I'll arrange it sometime when I can actually be there with the car plugged in. The folks at Tesla Service in Mississauga have been great by the way in trying to help. The issue has simply been elusive.
dirkhh
Middle-aged Member
Yes and yes
5.8.x would drop down about once a week. 5.9 not a single time since I've had it.
efxjim
Member
Forty Creek
Member
Had my first charge since 5.9 and it didn't back off. The graph shows my home's power usage with a 2:00 AM scheduled charge. Anything around 19 kwh tells me all is well. Will keep an eye on it in the coming days.
mnx
2018 M3P
I was charging my Model S this past Sunday afternoon and it dropped to 30A from 40A... I've never had a problem charging overnight however.
I charged at the Hotel Mortagne in Boucherville Quebec a couple of days ago. It has a CS-90. Unfortunately the voltage is rather low there, and the predictable result is that it always falls back to 50A, even though there's absolutely nothing wrong with the circuit.
Good thing I was staying overnight. The last time I was there I waited for three hours for a charge. That would have increased to 4.2 hours with the current reduction. That's kinda like the anti-Supercharger. Adds over an hour to your wait!
I complained to ownership and they said they downloaded the logs and were looking into it.
Good thing I was staying overnight. The last time I was there I waited for three hours for a charge. That would have increased to 4.2 hours with the current reduction. That's kinda like the anti-Supercharger. Adds over an hour to your wait!
I complained to ownership and they said they downloaded the logs and were looking into it.
islandbayy
Active Member
I had same issue, even on 5.9 I got downgraded to 30 amp the other night. Install is perfect. Just a lot of houses on my transformer and I'm at the end of the long string of homes.
The thing can and does trip on utility fluctuations. One of the owners I was talking to in Montreal said he could charge at full power at night, but if he tried to do it during peak demand hours it would always back off.
Prediction: once the rollout of replacement NEMA 14-50 adapters is complete, they'll quietly remove the "feature".
Prediction: once the rollout of replacement NEMA 14-50 adapters is complete, they'll quietly remove the "feature".
Yeah, I have 5.9 and the car still backs down to 30A. Doesn't do it every time. Only about 1/3 the time. I had a great year of use with my UMC cable (prior to 5.8.4), no errors, no melting, 40A whenever I wanted. Then the software changed, no specs were published, and 30% of the owners have to be inconvenienced. I'm guessing the local transformer has fluctuations (within the utility's tolerances), but the new software updates don't like it. All my other major appliances don't seem to care, and operate normally. I guess we're waiting for software update 6.0, along with my center console, and my new adapter. On the brighter side, I did get the titanium shield installed yesterday. - babysteps . .
Please read the FAQ (in my signature below) for why the "back-down" is critical and some of the troubleshooting steps you can take. Just because something works doesn't mean it's safe, and when you're dealing with electrical current this large, safety is an issue because of the intense heat that can be generated.
All of your other appliances don't seem to care because they are either a) resistive heating devices which don't care or b) typically draw less than 2 amps and therefore produce 1/400th the heat at the same resistance.
The car backs down because *something* is overloaded or undersized in your particular case, which creates a fluctuation that looks like a high-resistance heating point.
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I doubt it. They may loosen the sensitivity, but I can't see them removing it. It is needed at currents this high. The fused 14-50 doesn't stop a fire from developing at a bad wiring junction elsewhere, a loose screw on a breaker, a subpanel lug, etc. It only deals with a local problem at the specific receptacle, whether a loose adapter on the UMC or a loose screw on the outlet.
Can you imagine if someone's electrical panel caught fire because of a loose screw at the breaker, and it was discovered that Tesla's safety feature may have stopped it by backing down the current but that the feature was removed? That's why I don't see it ever being eliminated.
All of your other appliances don't seem to care because they are either a) resistive heating devices which don't care or b) typically draw less than 2 amps and therefore produce 1/400th the heat at the same resistance.
The car backs down because *something* is overloaded or undersized in your particular case, which creates a fluctuation that looks like a high-resistance heating point.
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I doubt it. They may loosen the sensitivity, but I can't see them removing it. It is needed at currents this high. The fused 14-50 doesn't stop a fire from developing at a bad wiring junction elsewhere, a loose screw on a breaker, a subpanel lug, etc. It only deals with a local problem at the specific receptacle, whether a loose adapter on the UMC or a loose screw on the outlet.
Can you imagine if someone's electrical panel caught fire because of a loose screw at the breaker, and it was discovered that Tesla's safety feature may have stopped it by backing down the current but that the feature was removed? That's why I don't see it ever being eliminated.
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FlasherZ - "The car backs down because *something* is overloaded or undersized in your particular case, which creates a fluctuation that looks like a high-resistance heating point."
That's possible. But it's also possible, and more likely (given the high percentage of owners experiencing the backoff), that "fluctuations" are simply coming from the transformer and are no more dangerous on the Tesla circuit, than they are on your electric oven circuit, or your heat pump circuit. I don't believe that 30% of all installs involve loose connections or undersized wiring as you suggest. I give electricians more credit than that. I also don't believe that those 30% of owners did their own electrical work, and that 100% of those installs are botched.
FlasherZ - " b) All of your other appliances don't seem to care because they typically draw less than 2 amps and therefore produce 1/400th the heat at the same resistance."
A 40A oven circuit draws a lot more than 2 amps. Likewise with a heat pump. That's why they are on 30A and 40A circuits. And I know all about startup spikes that some appliances have. Many major appliances have an initial surge when they cycle on, but then running amps are lower.
That's possible. But it's also possible, and more likely (given the high percentage of owners experiencing the backoff), that "fluctuations" are simply coming from the transformer and are no more dangerous on the Tesla circuit, than they are on your electric oven circuit, or your heat pump circuit. I don't believe that 30% of all installs involve loose connections or undersized wiring as you suggest. I give electricians more credit than that. I also don't believe that those 30% of owners did their own electrical work, and that 100% of those installs are botched.
FlasherZ - " b) All of your other appliances don't seem to care because they typically draw less than 2 amps and therefore produce 1/400th the heat at the same resistance."
A 40A oven circuit draws a lot more than 2 amps. Likewise with a heat pump. That's why they are on 30A and 40A circuits. And I know all about startup spikes that some appliances have. Many major appliances have an initial surge when they cycle on, but then running amps are lower.
This is taking it too far IMO. There is risk in everything we do. The world doesn't live in a bubble, and electrical problems exist even without EV's in the mix. Tesla's UMC design deserves most of the blame, as the Roadster UMC, and the Roadster Foundry units never had these issues(they were by far much more safety oriented, and had oversized components).
Tesla sold the car with a 10kw charger and a UMC capable of charging at that speed, they either need to keep it at 10kw, or advertise the car having only 7kw charging capability.
BTW, software doesn't have the capability of differentiating between safe and not safe. It's just a guess.
You're mistaking my use of "undersized wiring" to mean only the conductors. Undersized wiring also includes the size of the wiring in the transformer -- i.e., transformer size. An undersized transformer is a safety hazard - it generates extra heat and in some cases will boil the oil right out the top. It *is* a problem.
You left out my a) qualifier. A 40A oven circuit is an intermittent resistive heating device. It doesn't care because the nichrome wire element does exactly what Tesla is trying to protect against. Furthermore, these circuits are not used with continuous loads - an oven or range cycles its elements intermittently, and never draws the full 40A for hours on end all at once. With regard to heat pumps, they are motor loads and almost always draw nowhere near the circuit breaker's capacity. Both of them are non-continuous loads.
I know that those of you who are affected by this really would like for it to go away, but wishing it away does not get rid of the safety issues associated with high-current, continuous load applications. I have seen first-hand the results of the problems, and I applaud Tesla for the safety intelligence they've added.
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It's not a wild-ass guess, but rather an educated comparison to a known electrical pattern aligned with ohm's law. The new AFCI requirements are also the same - they look for the electrical loading patterns that represent an arc flash characteristic of a broken appliance. Likewise, the Tesla looks for the electrical loading patterns that represent a high-resistance or overloaded component.
A 40A continuous load is not the same as an oven circuit, or a heat pump circuit, or a handful of computer server appliances. There are some things that it does come close to -- and there was a thread here previously on one of them. For 95% of homes out there, the Tesla represents the largest kWh load the home will ever see.
See this post:
Incoming utility cable capacity - A cautionary tale
When installed properly, and when the capacity is managed properly, the Tesla can charge at 10 or 20 kW. No need to rate it at 2, 5, 7, 8, or 9, when the infrastructure is properly installed and rated for the load offered. In my case, had I kept my old 15 kVA transformer before installing my HPWC, it would likely be backing down right now because I would have stressed the ~60A limit of the transformer with the Tesla alone.
Many people make the assumption that just because they have a 200A rated service to their home, that the infrastructure will happily support 200A. My 200A service had 2/0 aluminum service cable, which the NEC rates to ~135A. My transformer was rated at 15 kVA (~60A). They had to be upgraded - and even today, my 400A service is the sole service connected to a 37.5 kVA transformer rated for ~150A. There is no doubt that many Tesla owners here are connected to transformers rated at less than 200A, *and* there are 3-5 homes connected to them.
The Tesla is backing down because it sees a high-resistance signature. Yes, it may be in a transformer out on the street that is high on a pole and is relatively safe (save from boiling oil falling from the pole) from the issue at hand -- but it's still overloaded.
The right thing to do is to follow the troubleshooting steps, involve the PoCo, and connect them with Tesla if you have to do this. Tesla would be stupid to pull off a (IMO smart) safety feature and open themselves to liability when a loose breaker screw causes an electrical panel to catch fire. Not a stove - cycling elements allows for components to cool; not a motor - inrush current vs. operating load allows for components to cool; it's a continuous load.
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I agree with most of your observations, but just because a range, welder or any other appliance is not a continuous load, doesn't mean that the outlet for those cannot handle a continuous load. Sure there are shoddy installations, but that is not the norm. I also don't need the software to make an educated guess for me, I'm smart enough to determine if an outlet is safe to charge from, or not.
Having said that, I have absolutely no experience with any of this software backing current off stuff(just going off others miserable experiences), as I'm still on 5.8(.24), and will continue to be as long as this nanny feature is there. I think that everyone here that has any kind of electrical experience can agree that if the Model S UMC was engineered properly, very few, if any of these melting issues would have happened.
Having said that, I have absolutely no experience with any of this software backing current off stuff(just going off others miserable experiences), as I'm still on 5.8(.24), and will continue to be as long as this nanny feature is there. I think that everyone here that has any kind of electrical experience can agree that if the Model S UMC was engineered properly, very few, if any of these melting issues would have happened.
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