TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker and becoming a Supporting Member. For more info: Support TMC

Suddenly can't charge above 24 amps?

Discussion in 'Model S: Battery & Charging' started by Theflash95, Dec 17, 2017.

  1. Theflash95

    Theflash95 Member

    Joined:
    Sep 23, 2017
    Messages:
    111
    Location:
    Orlando, FL
    Hi Everyone,

    I've got a NEMA 14-50 outlet in my garage and have been charging my month old Model S with no issues from day 1. However, yesterday I noticed that the breaker had popped at my house and ever since I switched it back on my Tesla will only charge at 24 amps max. In the car settings I can change the setting to 40 amps, but moments after plugging in the cord it drops down to 24 amp. Any ideas what's going on?
     
  2. gregd

    gregd Active Member

    Joined:
    Dec 31, 2014
    Messages:
    2,464
    Location:
    CM98
    Is the voltage reported by the car still correct (normally 240v +/- a volt or two)? I'd check to see if the breaker is physically getting warm. It might be that the contacts aren't quite seated right, which could be "fixed" by cycling it manually once or twice. Or, the breaker could be faulty.
     
  3. Theflash95

    Theflash95 Member

    Joined:
    Sep 23, 2017
    Messages:
    111
    Location:
    Orlando, FL
    Yup, currently charging and showing 238v and 24/24 A... even though I've manually set the car to charge 40 A. Once the the connector is plugged in you can lower the amperage, but it won't let you change it to more than 24 A.
     
  4. TMeister

    TMeister Gearhead

    Joined:
    Oct 6, 2016
    Messages:
    263
    Location:
    Boise, ID
    Do you have a 50 amp breaker on that circuit? What is its value? What is the wiring capacity?

    Some 14-50 installations are actually wired as if they only supply 40 amps, not 50. Depending on code application, it was acceptable to use a 40 amp 8 gauge copper circuit and a 14-50 receptacle. Correct use is 6 gauge copper and a 50 amp breaker. Since charging is considered a continuous load you are only supposed to draw 80% of the breaker capacity which is then 40 amps. If you have a 40 amp circuit your continuous load capacity is 32 amps.

    Your scenario (blown breaker and car drawing 40 amps) would be unlikely with a 50 amp circuit

    My understanding... the car uses location to guide itself on capacity of the circuit. If you had an event during a session (i.e. the blown circuit breaker), the car will reduce and remember the current setting for that location. I don't know how you reset this other than several successful sessions. Maybe a UI or car reset or a power down/restart?
     
  5. Theflash95

    Theflash95 Member

    Joined:
    Sep 23, 2017
    Messages:
    111
    Location:
    Orlando, FL
    I had a licensed electrician do the install. There is a 50 amp breaker and 6 gauge wire. It has been charging all along for a month at 40 amps no problem and now suddenly it’s maxing out at 24 amps.
     
  6. BerTX

    BerTX Supporting Member

    Joined:
    May 2, 2014
    Messages:
    3,505
    Location:
    Texas/Washington
    Seems likely that you have a bad connection or a bad breaker. My guess is a bad connection. You might try changing the amps before plugging in, then plug in and quickly go watch the voltage drop.

    But you have a problem in the circuit and you should get that fixed.

    Edit: regrettably, electricians do not always use new breakers
     
  7. Solarman004

    Solarman004 Member

    Joined:
    Apr 27, 2016
    Messages:
    716
    Location:
    Colorado
    I had a similar situation. I found a loose connection at the terminal block in the HPWC where the main power lines connected. If you have a loose connection anywhere in the circuit from the breaker box to the HPWC, the car will sense the voltage drop and throttle back your current.
     
  8. Theflash95

    Theflash95 Member

    Joined:
    Sep 23, 2017
    Messages:
    111
    Location:
    Orlando, FL
    The thing is it’s showing 239 volts (just checked)... so that’s the right voltage it’s just not pulling more than 24 amps.
     

    Attached Files:

  9. BerTX

    BerTX Supporting Member

    Joined:
    May 2, 2014
    Messages:
    3,505
    Location:
    Texas/Washington
    As the system is loaded, the voltage will drop. The car sees the voltage drop and reacts by lowering the amperage until the voltage drop is acceptable to it. That's why I recommended disconnecting the car and raising the amps again. Then when you plug it in, the voltage will drop. The voltage dropping indicates that it can't handle that much current without a problem, so it reduces the amps. The voltage reading is OK because it reset the current.

    Think of it as a garden hose with a partial kink in it. You can still spray a long distance with the kink in it, but you have to put your finger over the end to reduce the amount of water leaving the hose to get the pressure up. The car is reducing the current to get the voltage up.
     
  10. Theflash95

    Theflash95 Member

    Joined:
    Sep 23, 2017
    Messages:
    111
    Location:
    Orlando, FL
    Thanks for that explanation BerTX. So is everyone in agreement then that I need to get my electrician back here to see what’s up with the work he did?
     
  11. SSedan

    SSedan Active Member

    Joined:
    Jul 24, 2017
    Messages:
    2,698
    Location:
    Greenville Wisconsin
    Seems like the prudent decision.
    As said sometimes electricians use used parts, sometimes connections can come loose from heat cycling.
     
  12. Theflash95

    Theflash95 Member

    Joined:
    Sep 23, 2017
    Messages:
    111
    Location:
    Orlando, FL
    I have the car set to 40 A... when I plug in my UMC it very quickly changes to 24/24 A and I can’t set it higher.
     
  13. Periokid

    Periokid Member

    Joined:
    Oct 8, 2016
    Messages:
    87
    Location:
    LI, NY
    Why doesn't the car say 24/40A?
     
  14. Theflash95

    Theflash95 Member

    Joined:
    Sep 23, 2017
    Messages:
    111
    Location:
    Orlando, FL
    if what everyone above says is correct and I’ve got a bad breaker or have some issue with the way the electrician ran the outlet then I would guess that the car always displays the maximum number of amps you can pull with the current connection. I’ve only owned the car for a month and have only charged at home so maybe someone else on here can verify that.

    Since it’s showing 24 amps maybe some part of the breaker failed and it’s behaving like a 30 amp breaker (80% of 30 is 24).
     
  15. gregd

    gregd Active Member

    Joined:
    Dec 31, 2014
    Messages:
    2,464
    Location:
    CM98
    The only other possibility that I can think of (besides a loose wire or bad breaker) is that your UMC (presuming that's what you are using) has a problem. Is there another 14-50 nearby, e.g. neighbor or campground, where you can try charging, to see if the problem repeats? It might be sensing the pigtail incorrectly. If cycling the breaker and re-plugging into the 14-50 don't help, maybe detach and reattach the pigtail to clean the contacts?

    If there is a loose wire somewhere, it should be getting noticeably warm, even at "only" 24 amps.

    Oh, and per the other thread, wiggle the connector going into the car. :)
     
    • Helpful x 1
  16. TMeister

    TMeister Gearhead

    Joined:
    Oct 6, 2016
    Messages:
    263
    Location:
    Boise, ID
    Since the wiring is supposed to be correct and the breaker popped that means something created a large load or the breaker is bad. The car probably didn't create that load so the breaker is bad and tripped at a 40 amp load. Yes, get the electrician back to diagnose.
     
  17. Brass Guy

    Brass Guy Active Member

    Joined:
    Jan 5, 2014
    Messages:
    1,097
    Location:
    Holbrook, MA
    This is the right question. I've had my car reduce current. It would show 30/40. The only reason the car would show 24/24 is if the UMC adapter is for a 30A receptacle. Assuming you still are using the 14/50 adapter, it is faulty and signaling the UMC that it is a 30A adapter.

    Bring your car and UMC with all its adapters to a service center. They'll test it and replace it under warranty if I'm right.
     
  18. GSP

    GSP Member

    Joined:
    Dec 28, 2007
    Messages:
    2,562
    My Model S displayed 24/24 A when it reduced current on a 30 A EVSE a few weeks ago. It initially displayed 30/30 for a minute or so.

    In that case, it was happening at multiple locations, and the car also would not supercharge. The service center replaced the master on-vehicle charger to resolve the issue.

    @Theflash95 - I would try charging at a different 14-50 outlet, as suggested above. If you have the same problem, then contact Tesla. If not, then have your electrician check your breaker and wiring.

    Good Luck,

    GSP
     
  19. BerTX

    BerTX Supporting Member

    Joined:
    May 2, 2014
    Messages:
    3,505
    Location:
    Texas/Washington
    I think the confusion here is the difference in the display when one manually lowers the amperage as opposed to when the car reduces the amperage.When the car reduces it, it displays the available maximum as its determined maximum. (24/24).

    I might go along with the idea of he defective reading of the adapter resistor if the car had not ever charged at 40 amps, but the OP says it did. Resistors don't often fail, especially not something just providing a signal .
     
  20. Brass Guy

    Brass Guy Active Member

    Joined:
    Jan 5, 2014
    Messages:
    1,097
    Location:
    Holbrook, MA
    I admit a failed resistor is not likely.
    Higher resistance is required for a lower current signal. I remember because I would have paralleled the resistor to use my 14/50 with a 30A outlet if that would have worked.

    It really needs to be tested on another receptacle that is known to be in working order, I still suggest the nearest service center. It'll most likely be either be something wrong with the UMC/adapter, or something in the car's charging system. Either way Tesla would take care of it.
     

Share This Page

  • About Us

    Formed in 2006, Tesla Motors Club (TMC) was the first independent online Tesla community. Today it remains the largest and most dynamic community of Tesla enthusiasts. Learn more.
  • Do you value your experience at TMC? Consider becoming a Supporting Member of Tesla Motors Club. As a thank you for your contribution, you'll get nearly no ads in the Community and Groups sections. Additional perks are available depending on the level of contribution. Please visit the Account Upgrades page for more details.


    SUPPORT TMC