Charging on 240 50 amp circuit

Charging on 240 50 amp circuit


I’m using a 240 outlet with a 50 amp circuit breaker, and I use to be able to charge at 40 amps an hour if need be.

Did Tesla change something on their end where now the car only lets me charge at 30 amps max.

Maybe I’m jumping the gun here, because in the colder months I’ve noticed I get a little less juice in my garage when I’d be up at 40 amps, the car would sometimes give me a charging error.

My model S was delivered in January of 2018

Thoughts? | March 11, 2019

No software changes.

If the car detects a voltage sag when pulling 40 amps, it automatically drops to 30 amps as a safety mechanism. If it used to work fine, you may have a poor connection at the breaker or at your NEMA 14-50 connector. You can touch the plastic parts of either item when charging - they should be cool to the touch. If hot, you've located the problem area.

p.c.mcavoy | March 11, 2019

I also had this happen once seemingly at random. Reset the charge amps in the car back to 40 amps and been fine. Could be something outside your home caused a voltage dip sufficient for the car to dial it back. In my case this has been once in 2.5 years of charging, was probably over 2 years ago, and never had it happen since.

Nexxus | March 14, 2019


Did you get a software update? We did and it automatically reset the charging limit to 30 amps. Check your charging screen and see if the limit is at 30 amps and reset to 40 amps and you should be fine.

jordanrichard | March 14, 2019

I have had an amperage drop a couple of times over the past 5 years. One time it wouldn't let me change it to 40 from 30, until I did a reboot. Most recently, it happened again and I simply raised it back to 40.

Half Dollar Bill | March 14, 2019

My Gen1 UMC recently died and the service center upgraded me to a Gen2 cable/combo. First time I plugged in I noticed that it maxed out at 32 amps. Tesla's website confirms that Gen2 limit.
Even though I'm taking advantage of Time-of-Use electric rates, I don't think it'll impact me in the long term; I figure I'll just be a little conservative and top off over the course of two days if I get home with a really low charge.
You didn't mention a cable change so I'm inclined to agree with previous posters about the software auto-lowering it due to a voltage issue. It's happened to me as well, infrequently, and is easily reset to the higher rate on the MCU.

stevenmaifert | March 14, 2019

I don't consider the Gen2 UMC to be an upgrade, especially when both my MS and M3 are capable of charging at 40A.

nothotpocket | March 14, 2019

For sure, the Tesla store agrees that it's not an upgrade from Gen 1 to Gen 2. Gen 2 costs way less :-)

Albatross | March 14, 2019

I asked the same thing when trading in my 2015 to 2018. It came with gen2. I was told the drop though was better for the batteries. Same drop happened with my wall charger (from 80 to 72). Have others heard that ? Otherwise would get a gen 1 again.

AERODYNE | March 14, 2019

FWIW, I am going to save my gen 1 for trips, and use my just purchased gen 2 at home. Now installing a 50A GFIC 240V breaker with a 4 foot run of 6/2 Romex in the garage wall, to an old work 34 cu in flush mount box, containing a NEMA 6-50 outlet.

Going to deviate from recommend practice by attaching a 50A 6-50, 20 feet long extention cord to the Gen 1. Will set the car to 24 A, as I only need 100 miles to be added overnight.

Thanks to Tesla Tap for excellent guidance on the TT site!

NKYTA | March 14, 2019

TT does do his due diligence.

I’ve got a road trip in May/June this year, my original 6+yr old UMC still works dandy and will give me 40A if needed (unlikely, given that the goal is SCs, but you never know). If I’m stopping for the night (cough, @BH, cough), chances are all I need is to plug in to a J1772 or and HPWC, one needs and adapter, one doesn’t.

No sweat.

Half Dollar Bill | March 15, 2019

Hey, NKYTA, the east coast is just as hospitable, cough, cough :)

NKYTA | March 15, 2019

Noted. :-)

stevenmaifert | March 15, 2019

@Albatross - Who told you that? If the battery can handle a 120 kW Supercharger, it can certainly handle a 10 kW Gen1 UMC.

p.c.mcavoy | March 18, 2019

Albatross | March 14, 2019
I asked the same thing when trading in my 2015 to 2018. It came with gen2. I was told the drop though was better for the batteries. Same drop happened with my wall charger (from 80 to 72). Have others heard that ? Otherwise would get a gen 1 again.

@Albatross - The drop from 80 to 72 amp with your HPWC would be due to 72 amps being the max limit of the on-board charger in newer vehicles. It has nothing to do with the design of your HPWC.

SUN 2 DRV | March 19, 2019

stevenmaifert, Your Model 3 should be capable of a 48 amp charge rate but you'll need a Wall Connector and a 60 amp circuit to achieve that.

Bighorn | March 19, 2019

Are you needing a place to cough charge overnight or just admitting a weakness in needing to sleep cough? I assumed the latter, but HDB thinks otherwise. We have a 10-30, but also a couple charging cords, but you know I have my own local supercharger.

NKYTA | March 19, 2019

But of course, King of Sheridan! Nah.
The closest we’ll get to Sheridan might be the wife on the way back to NorCal. My loss ;-)
She is headed home, and I am headed East.

@HDB, can you update the wiki to 401 for me, pretty please? Google sheet seems right, and I might mangle the wiki at this point.

Haggy | March 25, 2019

I had that problem early on, and got lots of replies suggesting voltage fluctuations. It turned out to be the on board charger.

tstolz | March 25, 2019

For what its worth .. I can charge at 80 amps in the winter as my service is more stable in the cold. In the summer my max is 50 amps else voltage fluctuates and the car dials me back.

murphyS90D | March 25, 2019

Your voltage is fluctuating in the summer because of all the air conditioner compressors on your street cycling on and off.