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Service voltage drop.

Discussion in 'Model S: Battery & Charging' started by GarrickS, Jul 10, 2016.

  1. GarrickS

    GarrickS Member

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    Hi all, my new car can't maintain a charge rate at 40amps. At the main panel, I see a voltage drop from 233 down to 215 or so. This tells me that service to my house is inadequate. (Let's assume everything in my house is fine).

    Has anyone else ever had to call your power company for this? Any luck?
     
  2. ABCCBA

    ABCCBA Member

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    @GarrickS

    Are you using a HPWC or a 14-50?

    Where are you measuring the voltage drop? On the main panel buss or on the load side of the breaker feeding your charger?

    What is the Main Breaker size for your panel?

    What size service feeds your house? 200A? 100A?

    To try and duplicate the voltage drop, turn your AC on, clothes dryer on and electric oven on at the same time and measure the voltage.

    If you do not see a voltage drop on the panel, then you can have an issue with your breaker or worse yet, the conductors feeding your charger could be undersized.

    I'd be glad to help troubleshoot more, if you are interested. The above questions would be starters. Pictures would be helpful, too.

    - Mike

     
  3. Barry

    Barry Member

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    Not necessarily a problem with your service. Could be too small diameter copper for the length of the run and current draw.
     
  4. miimura

    miimura Active Member

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    If the utility meter itself is indicating this voltage drop, I would definitely call your utility.
     
  5. GarrickS

    GarrickS Member

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    Hi all, it's a 200amp panel. I'm measuring the voltage drop in lots of places: across the mains on the line side of the main breaker, load side of the 50amp breaker, each leg separate and together, and at the 14r-50. The phases are well balanced. I ensured nothing else was on in the house to influence my measurements.

    I'll try to reproduce the same drop with the other house appliances, but I'm not sure what that would prove.

    I don't see volts on the meter itself.

    But has anyone ever actually called their utility about low voltage in their area?
     
  6. ABCCBA

    ABCCBA Member

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    #6 ABCCBA, Jul 11, 2016
    Last edited: Jul 11, 2016
    @GarrickS I had a company that serviced the electric utilities. Yes, you can have 'low' voltage in an area. It can be for a number of reasons. In the summertime, utilities go into 'load control'. Part of that is lowering the voltage at the substation by lowering the Voltage Regulators. Additionally, utilities use Voltage regulators outside of the substation, on remote feeds where the run is so long that there would be a voltage drop near the end of the line, so they install a regulator and step the voltage up. So, there are numerous reasons why voltage could be 'low' from the utility. FWIW, 215 is on the very low side of where a utility would want to have the service voltage.

    However, in your original post, you stated that you are seeing the voltage drop from 233 to 215. My assumption in your wording was that you were measuring the voltage, started charging the car and the voltage dropped. If that is the case, the voltage drop is isolated to the equipment from Power Company transformer serving your house to your 14-50 outlet. You electric car cannot cause a voltage drop for your whole neighborhood.

    Why try other electric appliances? By measuring the voltage at the service feed or the service conductors into your breaker panel, if the voltage drops there with your car charging and/or if it drops with all of the electric appliances on, you most have a problem with the power transformer, service conductors or meter base. If you do not have a voltage drop on the incoming side of the panel, but rather only on the 14-50 circuit, then your problem is either your breaker, the conductors feeding the outlet or the outlet itself.

     
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  7. GarrickS

    GarrickS Member

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    When you put it like that, it seems rather obvious :)

    However, each house doesn't get it's own transformer on the pole. I don't know how many houses are served by that big can on the pole, but I think it's at least a dozen.

    This morning I tried to replicate the problem without the car. Using my AC, water heater, and a water kettle (I forgot the dryer!), I was able to pull about 30A and measure a 10V drop above and below the main breaker. This is consistent with my findings from yesterday... 233V with little load, ~10V drop at 30A, ~20V drop at 40A... measured over and over again at various spots from above the main breaker all the way to the 14r-50. I haven't opened up the panel around the meter yet, but I will (nor have I climbed the roof to measure the top of the service drop).

    I might just ask my neighbors if I can measure the voltage at their houses. I wouldn't even need to open their panel. Probing an exterior 110v socket would be enough.

    Thanks @MikeJr74, this is all good food for thought.
     
  8. ABCCBA

    ABCCBA Member

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    @GarrickS Since you were able to duplicate the voltage drop with just 30A of current draw, you definitely have an issue. The issue is somewhere from the power transformer to your main breaker. I would call your local utility and explain to them that you are seeing a 10 - 20 volt drop with just under 40 amps of load. They will send a line crew out to test your service from the transformer to the meter base. From the meter base into the house is your responsibility.

    As far as the number of homes on a transformer, it is typically 4 to 6 200A drops. depending on the size of the transformer 25KVA to 50 KVA.

     
  9. brantse

    brantse Member

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    Low voltage would certainly be an issue worth contacting them about; but on the contrary, I've actually alerted my utility about high voltage.

    Although it's more of a blessing than a problem, I just wanted to make sure it was clearly documented if I ever had tesla come back and tell me that high voltage damaged my charger. It normally runs 252-257V, which I've read the chargers are rated to 260V.
     
  10. David99

    David99 Active Member

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    I think it's worth calling your power company. 233 Volt without load is already pretty low. I'm getting 245 and it drops to maybe 239 Volt when charging at 40 Amp. I'm one foot from the panel, though.

    Tesla is using the chargers in their Superchargers where they are fed by 3 phase 277 Volt. I remember a post here where someone used a transformer to up the voltage from 240 to 280 (or something around that) to increase his charge rate.
     
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  11. GarrickS

    GarrickS Member

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    Thanks everyone for your input. I've just called it in to the SCE. Hopefully it's something they will fix.
     
  12. ABCCBA

    ABCCBA Member

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    @GarrickS Please let us know the outcome.

     
  13. SomeJoe7777

    SomeJoe7777 Marginally-Known Member

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    Yes, definite problem.

    As a reference point, I charge at 80A on a HPWC, and I typically see about 5V of drop (243 -> 238). I also have 200A service.
     
  14. Barry

    Barry Member

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    High voltage is far from a blessing. It will cause light bulbs and electric appliances (eg., the heating elements in an electric stove or oven) to burn out prematurely.

    I had a similar problem in a previous residence. The utility put a recording voltmeter on my mains for 24 hours, confirmed what I reported, and made an adjustment at the dropdown transformer.
     
  15. tnt1971

    tnt1971 Member

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    I have a NEMA 14-50 outlet at work and home. My office is in Queens, a borough of NYC, and my home is just over the Long Island border, about 12 miles away line of sight. At home I routinely get 238 to 242 volts. At work I routinely get 209-213 volts. Time of day, year, and load seems to make almost no difference. I asked the electrician and he told me it was because of the infrastructure in NYC that was old. The amps are identical at the locations at 39-40.

    It makes a significant difference in charge rate. I get 25-6 at work and 29-30 at home. I did not know you could call to get the utility to measure the voltage. I will look into that.
     
  16. Barry

    Barry Member

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    At work, it's most likely a 3 phase circuit, whose nominal voltage is 208. That's what I have at home, as I live in a mixed use residential/commercial building.
     
  17. mikeash

    mikeash Active Member

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    I see 236-247V at home. Charging at 40A typically reduces it by 1-2V. The biggest variable seems to be air conditioner use in the neighborhood. I see the low end in the middle of hot days when everybody's AC is blasting, and I see the high end when things are cool.
     
  18. tnt1971

    tnt1971 Member

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    When it first starts charging I see 245 volts but it always ramps down to the 240 right away as the amps ramp up. I had the home charging installed in April when there was no air conditioning going on. Yesterday I was charging mid day and it was close to 90 out. I did not notice any drop in voltage from the norm.
     
  19. GarrickS

    GarrickS Member

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    SCE guys came by this morning, took one look at the service wire from the pole and said, "nope, that's not gonna work. That's gauge 4 with waaay too long a run." They are coming back in the morning to replace the wire from the transformer to the house with gauge 0.
     
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  20. SomeJoe7777

    SomeJoe7777 Marginally-Known Member

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    4 gauge feeder from the transformer? And you haven't had any problems up until now?

    You should go buy a lottery ticket. :D
     
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