It drops 10 amps to reduce the heat bring generated somewhere in the circuit, to prevent a fire. Dropping by 1 amp at a time wouldn't accomplish that. The charging is being reduced for safety, not to see the max number of amps the circuit can do. Best to find where your wiring problem is and correct it.
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Frankman60
Member
Yes, but why does it always automatically reduce the charge rate by 10 amps even though it can be manually adjusted by 1 amp increments using the screen in the car? Ten amps is a pretty big decrease in the charge rate given that the electrical circuit supports 40 amp charging and normally works fine at 40 amps. Many people may not even know this is happening because normally the chargin occurs overnight and as long as it is completed by the morning all is well.
Presumably it does it because ten amps reduces heat by a significant amount, which is what is wanted in a safety system.
Softwizard
Member
I typically see this reduction when there is a new software update. I think they are related, moreso than blaming my wiring, etc.
Frankman60
Member
Today my charger faulted with three red LED blinks on the charger, and a red ring on the charge port. Tesla phone support says it's a bad charging unit. The charger won't work with the 120V adapter, or the NEMA 14-50 adapter. This may be why I have noticed the drop from 40 amps to 30 amps on a 50 amp NEMA circuit in my garage. Initially it would consistently charge at 40 amps but then I began noticing that it automatically changed the setting to 30 amps. So my advice to anyone that sees their charging decrease to 30 amps when it should be charging at a higher rate, report this to Tesla because the problem may be the charger and not the wiring or anything else in the electrical circuit.
Yours may have been the charger in the car, but it's almost always an electrical supply issue when you get the charging reduction to 30A.
Easy way to distinguish this before calling Tesla-- try charging somewhere else.
Frankman60
Member
After Tesla replaced my mobile charger today it began charging at 40 amps again without any problems in the same NEMA 14-50 outlet. In my situation, initially I could charge at 40 amps without a problem. Then it began down rating to 30 amps for no explainable reason. In this situation, I think that the charger would be the likely cause. But in situations where the charger could never achieve 40 amps consistently, then the problem is more likely with something else in the circuit.
I think we have some confusion in terminology here. The charger is in the car. That's what I thought you meant when Tesla said you had a bad charger. The thing you plug into the car is the UMC (Universal Mobile Connector), not the charger. You had a bad UMC.
When the current drops from 40 to 30A, there is something wrong with the electrical supply and the car is sensing a voltage drop. Although in your case it was a defect in the UMC, experience here in dozens of posts on this topic over the years shows it's much more likely to be a problem in the home electrical supply. Anywhere from the transformer all the way to the 14-50 outlet.
When the current drops from 40 to 30A, there is something wrong with the electrical supply and the car is sensing a voltage drop. Although in your case it was a defect in the UMC, experience here in dozens of posts on this topic over the years shows it's much more likely to be a problem in the home electrical supply. Anywhere from the transformer all the way to the 14-50 outlet.
roblab
Active Member
Mine downrated to 30 amps just after a software upgrade, which obviously was designed to sense resistance in the charging circuit. I pushed it up to 32, but then figured that I have plenty of time overnight to charge what I need, and the lower amps are better for the battery. My charge cord works at 40 amps at my daughter's house, but my circuit is about 60', which is longish, so I don't mind it cutting the amps down.
CmdrThor
Active Member
The Wall Connector used to cost $1,200, then dropped to $750, now is only $500 or $550 depending on cable length. It is really a no brainer to install a hard wired EVSE to charge your Tesla. The Mobile Connector should be exactly what its title suggest, to be used when you are mobile. I use mine at my in-laws, 120V charging at hotels when I can, etc. 90% of my charging is either at a J1772 station at work, or my Wall Connector in my garage.
So basically, if you are having the amps reduced with your Mobile Connector, you might want to consider installing a Wall Connector.
So basically, if you are having the amps reduced with your Mobile Connector, you might want to consider installing a Wall Connector.
No, Mobile is a capability, not a use requirement or even a suggestion. Tens of thousands of Tesla owners use the UMC for daily charging at home.
That's exactly right and when you take delivery unless you have a dual charger Tesla recommends you use the UMC at home and on road trips. The second charger (wall charger) is an additional expense that most people don't need. Convenient but not necessary.
Frankman60
Member
I normallly charge the car overnight when the utility rates are lower. That is one of the reasons I didn't see that was charging at 30 amps right away. But the test yesterday with the new UMC was during the middle of the day, and only for 5 minutes but it sustained 40 amps during that time. Last night the car charged overnight for a few hours and the my calculations are that it charged at a rate of 29 miles per hour.
Frankman60
Member
Are there any other benefits from buying a wall charger other than the extra 8 amps (48 amps) charge rate and to be used as a backup if the UMC fails? For example, is it more heavy duty and made to last a long time with better materials? Because my UMC failed within 3 months I'm wondering what the average expected life is of the UMC if it is used daily. I guess a poll on this topic may help answer this question.
The HPWC is designed for 80 Amps, so it is more heavy duty than the UMC. It also is convenient.
It is not a necessary expense, but if you can afford it, then it is nice to have. Tesla has reduced the price over the years, it is much less expensive than competitive EVSEs, and it is a very good value.
Since the HPWC is hard wired, the 14-50 outet and plug are eliminated. That is a few less connections that could cause a problem, causing the car to reduce charging current.
GSP
It is not a necessary expense, but if you can afford it, then it is nice to have. Tesla has reduced the price over the years, it is much less expensive than competitive EVSEs, and it is a very good value.
Since the HPWC is hard wired, the 14-50 outet and plug are eliminated. That is a few less connections that could cause a problem, causing the car to reduce charging current.
GSP
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Redmiata98
Member
ColBatGuano
Member
I have had charging issues at home since I took delivery in July. I have had a loaner while Tesla checked my car out and it charged just fine on the same 14-50 plug that my car wouldn't (also won't charge on multiple 5-15 circuits). I have checked the breaker to plug section and the wiring and connections are correct. I have found that if I turn on the double oven in our house or now that it is cold and the heat pump is running in the evening the car charges just fine. Our home is in the country and our transformer is maybe 400 feet from the panel. When the car won't charge I see a 4%+ drop in voltage as the current is applied. I can sometimes 'feed in' by manually starting at 5-7A and raise the amps only as the voltage stabilizes. I've never found any of the connections to be hot and the problem doesn't occur once charging. I think the problem is low load on the transformer and the car ramping up the charge thinks it sees faulty wiring. From my poor discription does my conclusion sound reasonable?
Frankman60
Member
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