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Molten Mobile Connector, does 30A help?

Discussion in 'Model S: Battery & Charging' started by Olle, Oct 6, 2017.

  1. Olle

    Olle Member

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    My UMC receiver for the wall plug has melted. See picture. I was always charging at 40A. I have read in several threads that people have reduced their current to 30A to prevent them from melting. Why 30, why not 5, or 35? This seems such a random recommendation that I've never seen explained.
    I just find it hard to believe that Tesla would keep making these and set them to default charge at 40A if they can only tolerate 30.:confused:

    The short cable from wall plug to box was so hot that you couldn't touch it and I always thought this was normal because that's how it had always been or if it had become gradually hotter must have happened so slowly that I didn't notice. After it melted I started using a different UMC and it doesn't get hot at all, at 40A, now I realize the heat wasn't normal.

    I am still a bit uneasy /scared of fire since the melting occurred, so considering lowering to 30A. Could this be safer or is it only "lemon UMCs" that get really hot and eventually melt? Obviously don't want to charge slower if there is no benefit to it.

    So, other than general personal opinions; does anyone actually have a solid theory or evidence showing that lowering the current to 30A actually helps?





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  2. ran349

    ran349 Member

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    I've been charging for 2 1/2 years with my UMC at 40 amps and it gets barely noticeably warm. So if you have a good UMC cable, you shouldn't have to worry about charging to 40 amps. At 30 amps it will run cooler, but if I had a cable that gets that hot at 40 amps, I wouldn't use it at all.
     
  3. Rocky_H

    Rocky_H Active Member

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    Heh, that is not quite an "either/or" kind of question. It's a little bit of both. There are apparently a noticeable quantity of bad ones that get really hot at 40A. That is Bad(TM). But, even with the generally "good" ones, I would still confidently use the word most get noticeably pretty warm at 40A. It seems it was built for that as a maximum, and just barely covers that if it's made well. That is also why they came out with the newer corded mobile connector that has a 14-50 plug wired onto the end of it. 40A through those tiny pins of the interchangeable connectors is apparently pushing it a bit too much.

    It is a real thing that heat, and especially heat cycling--going from cold to hot to cold every day--is bad for the long term life of electronics. 30 isn't some magic number, though. In about 4 years on two Tesla forums, I hear of 34, 36, 31, 32, etc. Basically turning it down just a little bit into the 30's somewhere seems to really cut that heat down and keep it cool. I think I have mine at 31 or 32--forget which. It fills in just a couple of hours overnight anyway since we do fairly little driving, and there is just no benefit at all (for me) to charging faster than that, when I would rather just keep the equipment cool to make it last longer.
     
  4. JHawk

    JHawk Member

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    I had to be same thing happen to the UMC that come with my CPO 2013 P85. Tesla replaced the UMC under warranty. When I looked at mine it looked like a poor connection somewhere in the 14-50 adapter caused the issue but can't be sure. I've also replaced my 50A breaker for my 14-50 outlet too within about 6mo of having it installed. I was charging at 40A nightly but after those two issues I have lowered my nightly charging to 30A and have not had any additional problems.

    I can't say whether one of the issues above caused the other. But when charging at home over night I have decided that it's better to charge at the lower amps to reduce the load and wear on the total system. When I plug in at 9pm at home every night, I've learned that I don't care whether it takes 3hrs or 5hrs to recharge.
     
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  5. vgrinshpun

    vgrinshpun Supporting Member

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    #5 vgrinshpun, Oct 7, 2017
    Last edited: Oct 7, 2017
    Reducing current will result in lower current conductor temperature according to the formula from NEC listed below. The question is what is maximum ambient temperature in your garage (if the outlet indoors) or outside (if the outlet you are using is mounted outside). Also, if outlet you are using is outside, is it mounted in a way that exposes the plug to unshaded sun?

    EDIT: Reducing current to 30A will absolutely lower the temperature of current carrying conductors and their insulation.

    upload_2017-10-8_1-0-42.png
     
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  6. Rocky_H

    Rocky_H Active Member

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    Good points, plus to elaborate just a little further--any of that heat that is warming up the electronics box in the cable or the wires or rubber insulating jacket, etc. is just wasted energy going out in heat. Using a slightly lower level keeping it cooler is less waste.
     
  7. dgpcolorado

    dgpcolorado high altitude member

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    Is it though? My assumption is that the reduced loss from heat at a lower amperage is made up for by a longer charge time at the lower charge rate. And the longer charge time likely means additional energy losses in the car from pumps running and the like.

    I run my UMC at about 30 amps because I think that the reduced heat might put less wear on the device over the long term and charge speed at home is essentially irrelevant.
     
  8. Olle

    Olle Member

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    Yes you lose more energy from the UMC at higher current as the increased temperature increases resistance, meaning it is not fully compensated by shorter time.
    But like you said the longer run time of the equipment in the car might still make slower charging less efficient all together.
     
  9. Saghost

    Saghost Active Member

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    30A is safer and will lower the heating in any UMC and should make them last longer. Properly built parts should have no problems running at 40A indefinitely.

    If there are times when having the faster charging rate is helpful to you, I would probably continue to use it. If the charging rate never really affects you use of the car (my case,) then a lower rate is likely a little more efficient from the attempts folks have made to measure it here and certainly easier on the hardware.
     
  10. vgrinshpun

    vgrinshpun Supporting Member

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    Provided that specified ambient temperature is not exceeded. Even though the max ambient temperature of UMC is pretty high at 50 deg. C (122 deg. F), it could be easily exceeded if the UMC is, for example, exposed to the direct sunlight. Hence was my question about the ambient temperature in the post upthread.
     
  11. Olle

    Olle Member

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    Our garage used to be extremely hot but since we became an all EV family we insulated it and installed A/C its between 78 and 80 F all the time
     
  12. vgrinshpun

    vgrinshpun Supporting Member

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    This confirms that the melted adapter was indeed due to a defect.

    BTW, while UMC is rated for an ambient temperature of 50 Deg. C, the house wiring is usually not. NEC ampacity tables which are typically used by electricians without any consideration for a posibility of high ambient temperature are based on 30 Deg. C (86 deg. F). For applications with higher ambient temperature wiring need to be derated, especially for a continuous applications.

    The temperature in my garage, for instance, easily exceed 30 deg. C during summer. To address this I charge at 30A during summer, using 40A during fall / winter / spring. Based on NEC formula linked upthread reducing current from 40A to 30A will allow for the same temperature of current carrying parts as with the ambient which is 13.2 deg. C higher than the typical home wiring rated ambient of 30 deg.C, i.e. is good up to 43.2 deg C (110 deg. F)
     
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  13. EchoDelta

    EchoDelta Member

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    Maybe on a sidenote, do folks here have any recommendations for adapters NEMA 14-50 to NEMA 14-30 or 10-30?
    I am temporarily having to share the charger (I jesla’d mine)but the car doesn’t have a current limiter and things are getting too hot. Long story short , like discussed in the thread, I want to throttle charging current down to 24A, 5.7kW , but I need to do it from the UMC.

    I was wondering if such an adapter (NEMA 14-50 to NEMA 14-30 or 10-30, to be used together with a post-recall UMC 14-30 plug thingie) exists, but the internet seems full of offers for 14-50 to tt30 which is definitely not what I need. With the commonality of miswired 14-50s (Canada?) I thought this adapter may be more commmon that it is. Or maybe I should get a Canadian UMC 14-50 adapter that has a different current throttle resistor? Is that easy from the US?

    Thanks in advance.
     
  14. davewill

    davewill Member

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    You can simply cut or remove the neutral pin on the adapter. Then the 14-30 adapter will plug directly into a 14-50.
     
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  15. Cosmacelf

    Cosmacelf Active Member

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    Third party adapters from a 14-50 to 14-30 do not change the UMC's reported current rate (stays at 40A),which is why you have to turn down the current in the car. Your best bet in this case is to try to get a Canadian 14-50 adapter which will tell the UMC to charge at 32A.

    I am assuming that you are stuck using a 14-50 receptacle, correct?

    Actually the post above also had a good idea. Use a 14-30 Tesla adapter, and use a hack saw to cut off the neutral pin (its the L shaped one opposite of the round ground pin). That will allow the 14-30 adapter to plug into the 14-50. It then will charge at 24A.
     
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  16. Rocky_H

    Rocky_H Active Member

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    @EchoDelta If you're looking for good plug adapters, one of the best places, and highly recommended, is www.evseadapters.com. They have a section for Tesla charging plug adapters.

    If you want the current limited to some other levels, then you need to get the specific kind of Tesla official adapter to give the right current signal.
    Canadian 14-50 will limit to 32A.
    14-30 will limit to 24A. (And yes, cut off the neutral pin if you want it to be able to plug into those EVSEAdapter 14-50 receptacles.)
     
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  17. EchoDelta

    EchoDelta Member

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    Yup.

    Doh! didn't think of that (facepalm). And I guess that pin is disconnected anyways.

    The Canada adapter path seems less... cheesy? I'll call the SC to see how to get one.
    Thanks @Cosmacelf & @Rocky_H
     
  18. Cosmacelf

    Cosmacelf Active Member

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    Yes, Tesla adapters ignore/don't use the neutral pin in the 240V adapters.
     
  19. Cosmacelf

    Cosmacelf Active Member

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    Hey, who are you calling cheesy? ;)

    Capture.PNG

    (This is a modified 14-50, but you get the idea...)
     
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  20. strider

    strider Active Member

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    I have also noticed some melting of my UMC run at 40A. I noticed it when I took a trip and needed to destination charge on 120V - was a bear to get the 14-50 plug adapter off. I have since limited my charging to 30A.

    30A is not arbitrary as this is the amperage that Tesla reverts to if the voltage drops too low at 40A. Their selection of 30A may be arbitrary but we as user's are not pulling a number out of the air.
     

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