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Why do I sometimes only draw 30 amps instead of 40?

Discussion in 'Model S: Battery & Charging' started by Mickie, Sep 10, 2016.

  1. Mickie

    Mickie Member

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    I'm running the NEMA 14-50 setup. Most times when I plug in, I draw 40 amps, but sometimes, only 30. Why is that?
     

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  2. TexasEV

    TexasEV Active Member

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    You have a wiring problem. Search for charge reducing to 30A and you'll find dozens of posts explaining it.
     
  3. kirkbauer

    kirkbauer Member

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    It isn't necessarily a wiring problem. I had this happen at two houses now. One I had an electrician do the 50-amp outlet, the other I did it. Basically if there is any sort of brownout during charging the car will reduce the amperage. I keep mine at 38amp and it stays there pretty well.
     
  4. Mickie

    Mickie Member

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    Thanks guys. I think this makes more sense as I believe I might me approaching my 100 panel's limitations.

    I'll do another search for more info. I tried that first but I guess I was wording it goofy.
     
  5. kirkbauer

    kirkbauer Member

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    That could be the case, but it just happened to me at my new house with a 400A panel... I know it wasn't overloaded (at night) so it was likely a small power drop from the power company.
     
  6. SabrToothSqrl

    SabrToothSqrl Active Member

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    Step 1. inspect wiring.
    Step 2. blame power company
    Step 3. give up and charge below 40 amps, or after 9 PM...
    Step 4. calculate time between charging at 30 amps vs. starting at 9PM
    Step 5. make a stiff drink, because the power company won't do _____ about it.
     
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  7. Mickie

    Mickie Member

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    Yeah, it happened to me again midday yesterday with basically nothing else running in the house. Hoping it's ComEd because I'm otherwise baffled. The electric work was done tight and by the book, permit approved and all. Central A/C is the only other high draw appliance (natural gas range and dryer) and again, that stuff was all off while I was only achieving 30 amps while charging.
     
  8. Rocky_H

    Rocky_H Member

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    As cynical as it sounds, @SabrToothSqrl is basically right. I have seen several threads of people trying to chase this down. Try it around 35A or so. With less draw, it will not be pulling on the voltage quite as hard, and it may be able to stay up and not get interrupted and cause it to kick in that safety system.
     
  9. Mickie

    Mickie Member

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    Will do. Just to echo the sentiments of most folks perplexed by this issue, I can get by fine with 30 amps 90% of the time, but it's irksome not getting the 40 that you expect.
     
  10. Rocky_H

    Rocky_H Member

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    Eh, like he/she said: blame the power company, and just add it to the list. The stop lights are longer than we would like, the traffic is more than we would like, food costs more than we would like, etc. Things aren't perfect.
     
  11. SabrToothSqrl

    SabrToothSqrl Active Member

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    This used to bother me a lot too.. I used visible Tesla to track/log, watch voltage readings, etc etc.

    Even had PP&L put a 'monitor' on my meter... which had the accuracy of a hand grenade. Basically they said everything was in spec, and handed me a PDF of an 8.5x11 reading of voltage for a 7 day week. Which was about as useful as a Samsung phone in an airplane.

    SO, yes, after many months of checking wiring, plugs, connectors, Tesla, etc. etc. If your house isn't getting enough from the grid, because your neighbors are running a heatpump/dryer/well pump/their own tesla, etc etc.... there's not much you're gonna do about it.

    Now, I am however hopeful that when my wife gets a Tesla, we can draw enough between 2 cars, (80 amps) + dryer (25) + water heater (17) + heat pump (8) = 130 amps + lights = enough to brown out my neighbors... and basically force PP&Ls hand with the issue.

    and if that's not enough, I can get a HPWC and pull 80 on my car... bringing the total to, 170 amps!

    And if anyone has a S, I actually have 3 14-50 outlets at the house, moving it to, 210 amps ! (which, yes, my main breaker is a 200 amp)...

    so, yea, charge at 30, when you see it change push it to 40, but go do something less stressful with your time :)
     
  12. gaswalla

    gaswalla P4201/85/airsusp/pano/19i

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    I had this exact thing happen for about a year... Kept on lookin for a panel issue. It was the UMC - they were not designed for everyday charging (on terms of durability). I recommend taking your umc to the service center and getting it checked out.
     
  13. SabrToothSqrl

    SabrToothSqrl Active Member

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    Did that.. no issues.
     
  14. TexasEV

    TexasEV Active Member

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    That's kind of a strong statement. Most UMC use is everyday charging. Mobile is a capability, not a requirement.
     
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  15. Skipdd

    Skipdd Member

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    Like others have said, fluctuations in the current cause it to drop back to 30. This happens periodically to me and then I manually adjust the car back to 40 which fixes it. I used to have really bad power at the house. Power company denied it, did what SabrToothSqrl said and put honking huge meter on it to PROVE THEY were right. After blowing HVAC electrical circuit boards twice, I had an electrician wire circuit breaker before main power into house and also before compressor on outside, which eliminated that problem. Then a couple of years ago Power Company replaced outside underground cables and what do you know they "discovered" that my cables had been spliced - poorly I'm sure.. If I were to have a recurring issue with the car, I would probably consider putting some kind of grooming unit in front of the UMC.
     
  16. Mickie

    Mickie Member

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    My electrician briefly mentioned a line cleaner, to clean the dirty power coming in from the electric company. I wonder if that would've made any difference.

    To Sabr, I just leave it at 48 all the time, and it normally just goes to 40 from my 14-50, unless it's doing that 30 amp nonsense.
     
  17. wycolo

    wycolo Active Member

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    Assuming good wiring, connections and breaker the rate of charge (amps) that is negotiated is solely determined by the voltage present. Voltage is what you need to look at as you are plugging in - not easy to do from where you are standing. The 236v shown in the photo is totally nominal (117v x2). If your house shares a transformer with a neighbor you may have voltage swings that will setup a 30A charge instead of 40A.
    --
     
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