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Charging safely at 9/12 amps?

Discussion in 'Model 3: Battery & Charging' started by RossianSpy, May 14, 2019.

  1. eprosenx

    eprosenx Active Member

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    So I am going to take a slightly different tact on this conversation than most have commented on so far.

    Yes, 120v charging is not optimal.
    Yes, plugging into a circuit with lots of connections is not optimal.
    Yes, plugging into a non dedicated circuit is not optimal.

    Now, with all that being said, if there is *truly* no realistic way to push for a better setup, I would take nine amps of charging over nothing. At least it will offset vampire losses.

    So here is my thesis: I am making the assumption that this is a 20a circuit (generally required in a commercial building), and that all the wire is run in metal conduit, and that the garage is made of concrete walls/floors/ceilings. I am also assuming the wiring is generally of reasonable quality (the conduit is properly grounded) and the building has proper smoke detection and fire suppression systems.

    If all of that is true, then I guess I am not too concerned about the dangers of using that receptacle. Likely the worst case is some connection melting (because of a bad connection) and shorting out to the conduit and blowing the breaker. The repair work would likely be just pulling new conductors in that conduit. Commercial wiring is often times a lot more resilient than residential.

    I was about to say that the voltage drop described is not that horrible given that distance, though I just ran some math and it is a bit lower than I would expect (though it is possible that the panel that circuit comes off of could also be a long way from the feeding service/transformer). If the voltage drop can be completely explained simply by the wire distance calculations then I actually would not be that worried about charging a Tesla off of it. Yes, it is dissipating that energy as heat, but over more than 200 feet of conduit that is not a lot of energy as long as it is not all dissipating at a single joint or connector.

    This is not like a synchronous motor which when the voltage drop it just draws more current to keep spinning at the same speed (which increases the load on the wire further). The Tesla will draw a fixed amount of amps regardless of the voltage (it is computer controlled...). If the voltage is lower, it just charges slower.

    The Tesla sounds like it is backing off to 9 amps (is it giving you errors when it does this?) because it sees the voltage drop delta between when you start charging and after it runs for a minute or two. The Tesla assumes if this drop is large it is due to a loose connection which could catch fire. If it is just because of a really long wire run it can't tell the difference.

    What is the voltage when you first plug into the car (after not having charged for a while) but before the car actually ramps up charging? I am curious what the unloaded circuit voltage is vs. the loaded circuit.

    Btw, you are totally fighting total resistance of the entire circuit which is causing the voltage drop. Your 14 gauge extension cord is not helping. I would absolutely upgrade that to a 12 gauge extension cord (if not 10 gauge - though that is probably overkill).

    I would also replace all the light bulbs on that circuit with LED bulbs. That might give you more overhead and keep you from blowing that breaker. ;-)

    Can you post pictures of all the conduit and such that you have access to and the panels, etc? I am curious if there might be a relatively inexpensive way to upgrade that circuit with basically no visible impact to the building. If there is conduit all the way back to the panel you may be able to have an electrician pull more wire into the existing conduit (could be as little as a single additional wire and using a shared neutral and ground) to give you a dedicated circuit with no extra connections in it.

    EV charging is very much the future, so building owners are going to have to get onboard with it. If I owned the place, I would totally be willing to spend some $$$ to get a good charging solution. It will increase resale value!

    Good luck!
     
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  2. cbutters

    cbutters Member

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    In the meantime if you do continue to use this socket; dial the amps down to 5-6 at the very least.
     
  3. RossianSpy

    RossianSpy Member

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    Thank you for that detailed post. I will try to get some pictures up for you and I will try to direct connect it instead of using extension cord. I know for sure that the amps going to 12/12 for a split second but then it drops down to 9 amps. The building is fairly new like 2006 I think so everything should be probably run at 20 amp circuits. It is all run with pipes covering the lines and everything is concrete with each closet having a sprinkler system installed. I know there is a nema 5-20 outlets setup on some of the walls in fact one of the cars is parking right next to it so my other goal is to figure out who this person is and ask to trade spots. The board is really hard to get a hold of here from what I heard, so I would want to keep that as the last resort to this by asking them to do things. I will update you tho.
     
  4. RossianSpy

    RossianSpy Member

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    I also forgot to mention, that there is a bike that is not being used at all so far. Pretty sure it just sits out till it gets warmer out so its always plugged in with some kind of trickle charger, I assume that would affect the voltage drop a decent amount as well. Those are usually 4 amps I think tho.
     
  5. eprosenx

    eprosenx Active Member

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    If it is a decent lead acid battery tender it should use basically zero power most of the time. A motorcycle battery can’t take too much current or you will destroy it.

    Even if it’s max output is four amps, that is four amps at 12 volts which is only 48 watts, so like half an amp of AC at 120v.

    I would worry more about lighting load on the same circuit.
     
  6. RossianSpy

    RossianSpy Member

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    Okay so I have connected it directly and the initial voltage goes to 114v then drops down to 103 and it says that charging speed reduced check extension cord or bad wiring. So I looked at how far away the electrical room is and I'll upload the pictures as well as the inside of it
     
  7. RossianSpy

    RossianSpy Member

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    #27 RossianSpy, May 22, 2019
    Last edited: May 22, 2019
    So the first garage picture you will see my red model 3 all the way at the end. Then the 2nd image continues where first left off and third shows the opposite side of the garage where the electrical room would be behind the wall. So my question is maybe the UMC is dropping it on purpose to safe levels if it feels that the line is not strong enough to go at higher speeds, so would it be safe to just charge or should I drop even lower amps to like 7-8?
    Also I have no access to the panels unfortunately
     

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  8. quantumslip

    quantumslip Member

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    Just curious if you get a volt meter (or look at the voltage when the car is just starting or set to very low amps) how many volts does the socket have? Wondering what you're getting in the first place before the load is applied.
     
  9. RossianSpy

    RossianSpy Member

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    I'll test out tonight
     
  10. RossianSpy

    RossianSpy Member

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    So just now I just tried to set before charging max amps to 5 which is lowest it gets and when connected it gave me 115 volts at the start and about 110 drop a few minutes later. Then with every 1 amp increase it went down in voltage. At 9 amps went down to 104-105. Interesting enough it never gave me any messages saying to check wiring or cable. I could keep increasing the amps to higher and see if it drops but for me getting 3 mph is totally fine as long as I can sleep at night without thinking the place is going to melt
     
  11. dhanson865

    dhanson865 Active Member

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    I'd set it to 5 amps and leave it until they upgrade or replace the wiring. Higher amps would only be more efficient if the wiring were up to spec. You are losing a lot to heat if you go up in amps and down in volts. And the more heat the higher chance something melts or starts a fire.

    If 5 amps x ~109 volts is too slow for you I'd go elsewhere to charge on a public charging station or to a friends house or work. Anything to avoid turning up the amps on that substandard wiring.
     
  12. RossianSpy

    RossianSpy Member

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    I turned it down to 6 amps. Getting 108 -109 volts @ 2mph. I'll take that since it's better than nothing.
     
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  13. 233.3

    233.3 Member

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    I too think you have a problem with the circuit you are trying to use. A lot of posts are suggesting a new circuit for good reason. I would seriously consider investing your own money to make it happen.

    If you have to pay to have an outlet installed go as big as you can afford or as big as they will allow (in other words the highest amperage they will allow or the panel can handle). The material cost will increase with the amperage because of the larger wire needed. You should go with 208 or 230 volts over 110v. As already pointed out the cost is the same as 110; however, you charge twice as fast. The only difference is that you need a 2-pole breaker in the panel instead of a single-pole. The wire color changes but otherwise the same stuff is needed for 120v as 2XXv. The 2-pole will take up more space and if the panel is already full that could be a problem.

    Consider asking if you can move your parking space to a location closer to the panel to save on the cos of the circuit. Not only will that mean shorter wire but the wire can likely be smaller because it will not need to be oversize to avoid voltage drop. Electricians will almost always give quotes for free. So, if you think there is hope for approval, you can get a quote so you know how much money would be involved.
     
  14. eprosenx

    eprosenx Active Member

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    Thanks for the pictures!

    It is hard to tell if that drop you are seeing is just due to the distance, or if it is also due in part to a bad connection somewhere in the chain. Troubleshooting that might be a pain (take voltage readings at each storage unit receptacle along the way while you car is putting load on the circuit). Probably would require an electrician to check every junction box where the wire is spliced.

    If the drop in voltage is due to the overall length issues, it would almost be tempting to get a 5-20 NEMA adapter from Tesla for the UMC and an adapter to let you plug in to that 5-20 adapter into a 5-15 receptacle so you could then still set the draw to 12 amps and maybe it would not execute its backoff as severely due to it thinking it was already backed off? Or maybe that would have the opposite effect on its aggressiveness?

    That looks like 1/2 in EMT conduit to me. If it goes all the way back to the panel and it only had one hot conductor in there plus a neutral, you might be able to have two more wires pulled in to give you a 208v dedicated circuit (separate from the lights, but using the same conduit run). But that would require building cooperation (also they may want you to pay for the power). The electricians would need to ensure the feeding panel had enough physical spots and capacity to do this (I suspect it does).
     
  15. RossianSpy

    RossianSpy Member

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    Thanks for the info. So Im very sure that all other closets have basic lamp fixtures without any built in outlets in them. Seems that people just screw into the bulb socket another adapter that gives them a 120v no ground 2 prong outlet. (I'll take photo of my old one). So I'm wondering if maybe the maintenance guys didn't install my outlet well enough or it's just the distance. I would be very surprised to have bad wiring in such a new building that's right downtown across the city hall area in a decently wealthy area. I got a few electricians friends that I'll consult, just not sure how much they know about Tesla charging. In meantime is 109v @6 amps safe enough? How much drop is allowed? I also can test out other outlets that are in the walls to do see what they read. I did test the 5-20 outlet and that was at 12/12 amps but I think it had 117 volts only.
     
  16. MaryAnning3

    MaryAnning3 Supporting Member

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    great advice.
     

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