Miller Thunderbolt Yellow Plastic A/C Port Cover Melted Off
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  1. #1
    Join Date
    Jul 2013
    Location
    IL
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    14

    Miller Thunderbolt Yellow Plastic A/C Port Cover Melted Off

    I have a Miller Thunderbolt welder and have an issue with it. This actually happened a few years ago. At the time I just threw it in the corner and used my dial arc. When it happened I don't remember if I was tig or stick welding. I think I was stick welding in DC using 3/32 7018 so would've had it set around 85 amps. Anyways,while welding, I flipped my hood up and happened to noticed that the yellow plastic port cover on the ac melted and fell off. The welder has 3 ports for ac. One is labeled "work" and the other two "electrode". The electrode ports are labeled 40-225 amps and the other 30-150 amps. The one that melted was the 30-150 amps.

    I pulled the cover off and nothing jumps out at me. No wires touching or chewed wires.

    Any ideas?

    Thanks

  2. #2
    Join Date
    Oct 2014
    Posts
    223

    Re: Miller Thunderbolt Yellow Plastic A/C Port Cover Melted Off

    It has a loose connection with resistance there somewhere to be making enough heat to melt the plastic. Ohm meter may find the culprit or look for carbon arcing traces.

    Is the inside of the port clean as well as the connector your plugging into it and fits snug ? The wire going in connector is in good condition and tight ?

  3. #3
    Join Date
    Jul 2013
    Location
    IL
    Posts
    14

    Re: Miller Thunderbolt Yellow Plastic A/C Port Cover Melted Off

    Quote Originally Posted by danielplace View Post
    It has a loose connection with resistance there somewhere to be making enough heat to melt the plastic. Ohm meter may find the culprit or look for carbon arcing traces.

    Is the inside of the port clean as well as the connector your plugging into it and fits snug ? The wire going in connector is in good condition and tight ?
    Thanks for the reply.

    The ports where the welding leads plug in were clean.

    I thought it was weird that the ac port melted even tho I was using DC and nothing was plugged into the ac port. I'm not really sure how these are wired but I guess power is still going to those ports even tho I wasnt plugged into them?

    I know how to use a multi meter but I have no idea what to ohm on the welder. As you suggested I'll look around for arc marks and check all connections again. I might go ahead and disconnect all connections and clean them up. Should I use dielectric grease on them?

    Thanks again

  4. #4
    Join Date
    Jun 2017
    Location
    AJO, ARIZONA
    Posts
    803

    Re: Miller Thunderbolt Yellow Plastic A/C Port Cover Melted Off

    Dielectric grease won't hurt a bit, and may help a lot, make sure everything is clean, if you were welding DC, then it makes little sense to me that the AC tap would heat like that, but what do I know!!
    NRA LIFE MEMBER
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    We didn’t pass it to our children in the bloodstream".
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  5. #5
    Join Date
    Jul 2013
    Location
    IL
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    14

    Re: Miller Thunderbolt Yellow Plastic A/C Port Cover Melted Off

    Thanks for the reply Cavemann.

    One thing that I forgot to mention or just plain forgot because it has been a few years is I believe the 110v cord female plug also melted. The welder was purchased used so I don't know if it came with the extension cord or if someone added it. I used it many times with a grinder. Nothing was plugged into it at the time it melted. The hot is just wired into one leg on the power switch and the neutral and ground are just grounded to the machine. On 110v circuits the neutral and ground are normally separate until the breaker box so don't know if it could be the culprit? Probably not but I might just get rid of it anyways.

  6. #6
    Join Date
    Mar 2011
    Location
    Western Washington
    Posts
    740

    Re: Miller Thunderbolt Yellow Plastic A/C Port Cover Melted Off

    Interesting..... got any pics of the melted ports and their associated wiring?

  7. #7
    Join Date
    Jul 2013
    Location
    IL
    Posts
    14

    Re: Miller Thunderbolt Yellow Plastic A/C Port Cover Melted Off

    I don't have the extension cord plug anymore but here is a pic of the lead port and of the wiring of the extension cord. The extension cord is the big wire coming out of the back middle of the welder.


    https://preview.ibb.co/drLzKz/20180915_165743.jpg
    https://preview.ibb.co/cLhqRe/20180915_165656.jpg

    Sorry about the triple posts. I wasnt sure which code to post so thought I was hitting preview post but must not have been.
    Last edited by MarineGrunt; 09-15-2018 at 06:07 PM.

  8. #8
    Join Date
    Jul 2013
    Location
    IL
    Posts
    14

    Re: Miller Thunderbolt Yellow Plastic A/C Port Cover Melted Off

    I don't have the extension cord plug anymore but here is a pic of the lead port and of the wiring of the extension cord.
    Last edited by MarineGrunt; 09-15-2018 at 06:04 PM.

  9. #9
    Join Date
    Jul 2013
    Location
    IL
    Posts
    14

    Re: Miller Thunderbolt Yellow Plastic A/C Port Cover Melted Off

    I don't have the extension cord plug anymore but here is a pic of the lead port and of the wiring of the extension cord.

  10. #10
    Join Date
    Oct 2014
    Posts
    223

    Re: Miller Thunderbolt Yellow Plastic A/C Port Cover Melted Off

    Ok wow I missed the part that you weren't plugged into the port that was melting. If it wasn't heating by shorting to the cabinet it seems it must have been the entire lead in there heating at the transformer and wicking up the wire to the port bezel. Only explanation I can think of.

    I would try to recreate the happening and use a lazer temp gun with the covers off to possibly try and see what is heating what and then maybe you can figure out why.

  11. #11
    Join Date
    Mar 2011
    Location
    Western Washington
    Posts
    740

    Re: Miller Thunderbolt Yellow Plastic A/C Port Cover Melted Off

    Only things I kin think of is something got spilled on the port and caused carbonization to ground....
    or
    there is a piggyback lead on the back of the port where the main wire feeds it and they both had a bad connection....

  12. #12
    Join Date
    Mar 2010
    Location
    Ceres, California
    Posts
    3,272

    Re: Miller Thunderbolt Yellow Plastic A/C Port Cover Melted Off

    First. thunderbolts should run on 230 volts. If what you were welding on was connected to earth ground and the AC receptacle was shorted to the case. ( cracked insulation) . Then we have a current path that could melt the yellow receptacle.
    All receptacles are always hot. Check them all for shorts to case. And anything melted.
    Replace with a new receptacle of correct color. retest and make sure not shorted to case. Follow instructions on how to assemble
    the receptacle. If you replace all your receptacles I would also replace the jacks on the weld leads.
    A bad connection in a jack can cause the receptacle to heat up and melt. allowing it to slide down and short to the case. Only has to move about 1/16 to 3/32 of an inch. Also check the transformer lugs and make sure they are not loose. some of these units just curled the aluminum lead into a loop and made that the lug. these have to be sanded and a aluminum connect grease
    wiped on before they are reconnected. Sanding and coating and assembly are all done with in 1 minute. or you have to clean the aluminum again.

  13. #13
    Join Date
    Jul 2013
    Location
    IL
    Posts
    14

    Re: Miller Thunderbolt Yellow Plastic A/C Port Cover Melted Off

    Thanks for all of the help and advice.

    I cleaned and greased all connections and also replaced the extension cord plug and yellow welder plug cover. I've been welding away and all is well. I did try and weld before cleaning the connections and it worked fine. As mentioned above I used a temp gun to keep an eye on things.

    Who knows...maybe the yellow plastic plug cover had a crack in it.

    I have it hooked up with 6 gauge wire on a 50 amp breaker so am running on 230.

    Anyways, it seems to be working for now. Thanks again for the help.

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