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  1. #1
    Join Date
    Oct 2015
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    Blew up a transformer today.. how?

    So I went to a service call for a rheem rooftop unit.
    M/N: RKKA-A060YL13E
    600v gas heating.

    Board is giving 2 flashes for pressure switch not closing.
    Check voltage at ventor motor, getting all kinds of weird readings, got 347v once even.

    Found that the step down transformer had a blown fuse on 1 leg. This is where things went to shit.

    I figured blown fuse is the reason the wrong voltage is going to ventor motor and go to buy a fuse, get back and it pops right away.

    Now I notice there are 2 different fuses on the transformer that are different.. cant be right, so I call up rheem to find out which ones to use.
    They inform me that that transformer does not even go into that unit, somebody had put the wrong part in.

    I finally get the right transformer, it has 2 leads going in and 3 coming out, L1, L2, com connect the 600v side and connect L1,L2, and common on the board.

    In my haste and inexperience I set the transformer down on top of the rooftop unit where it would be touching paint instead of back into its proper place.. I'm guessing it was no longer grounded because of this and that's why it exploded as soon as I flipped the disconnect? Feel free to crucify me and joke all you want if this Is the case but at least let me know that's what did it haha

    If not what am I missing? Transformer was for sure rated for 600 down to 230

    Thanks in advance, any help would be greatly appreciated as I am going back tomorrow morning

  2. #2
    Join Date
    May 2014
    Location
    Bay Area California
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    Most likely, the transformer died because it had too much load. There is an off chance it was bad out of the box, but best not to bank on that.

    Not grounding the transformer would not cause a transformer to fail. Other problems, yes often. But not a catastrophic failure.

    Something is shorted, or similar.

    Best to have fuses on hand. Especially wire a fuse into the new transformer to protect it.
    If you were a real tech, you'd solder a relay on that board and call it good to go.

    I do a triple evac with nitro to remove non condensables.

    I use 56% silver on everything except steel.

    Did you really need the " If you were a real tech " ??

  3. Likes CEAS-AC-TECH liked this post
  4. #3
    Join Date
    May 2014
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    Bay Area California
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    Best thing to do at this point is use your meter to check for high current at the transformer. With one hand on the disconnect.
    If you were a real tech, you'd solder a relay on that board and call it good to go.

    I do a triple evac with nitro to remove non condensables.

    I use 56% silver on everything except steel.

    Did you really need the " If you were a real tech " ??

  5. #4
    Join Date
    Jun 2019
    Location
    So Cal
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    600 volts?

    What country you in?

    I doubt it was the lack of "ground" that made it explode. Are you sure you didnt connect the primary side incorrectly? If your transformer is a multitap that works with different voltages this could happen if connected incorrectly. Last time we had a student connect the primary side of the transformer incorrectly which exploded as soon as power was applied, it was literally on fire.

    His mistake was connecting L1 to 120 and L2 to 240 rather than L1 to Comm and L2 to 120 or 240.

    Either way, I'm sure it was quite the experience. Stay safe out there.

  6. #5
    Join Date
    Oct 2015
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    Thread Starter
    Checked voltage coming into the contactor that closes to send voltage to the transformer. Was 600 or 601 across all 3 legs. Transformer said it was rated for 600v .

  7. #6
    Join Date
    Aug 2015
    Location
    Buffalo,NY
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    Everyone has had those days. It won’t be your last either. My guess is you wired it wrong honestly? Having it on top of the unit wouldn’t cause you to blow it up. Where are you located for 600v?


    Sent from my iPhone using Tapatalk

  8. #7
    Join Date
    Oct 2015
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    Thread Starter
    I'm in canada. There is no way I connected the leads wrong. It wasnt the type with multiple options.. just a straight 600v to 230 transformer. 2 wires in. 3 wires out

  9. #8
    Join Date
    Oct 2015
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    Thread Starter
    If I'm getting 600 or 601 across all 3 legs of the voltage on input side of contactor.. wouldn't it be impossible for voltage to be higher at the transformer? Could lower voltage break it?

  10. #9
    Join Date
    May 2014
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    Bay Area California
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    What does the transformer feed?
    If you were a real tech, you'd solder a relay on that board and call it good to go.

    I do a triple evac with nitro to remove non condensables.

    I use 56% silver on everything except steel.

    Did you really need the " If you were a real tech " ??

  11. #10
    Join Date
    Jun 2019
    Location
    So Cal
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    3 wires on the secondary side?? never seen that.

    Does it step down to 2 different voltages?

    If you for sure didnt connect the primary side incorrectly you must have a pretty big short somewhere.

    Like BB asked, what does the transformer feed?

  12. #11
    Join Date
    Jun 2001
    Location
    San Diego, CA
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    I might be wrong but the one 480/230 3ph stepdown transformer I installed did require a ground reference. Voltages prior to throwing the 230v disconnect were as you described - wierd.

  13. Likes CEAS-AC-TECH liked this post
  14. #12
    Join Date
    Jan 2010
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    The ninth digit in the model is the voltage, which in this case is 575 volts / 3 Phase / 60 Hz.

  15. #13
    Join Date
    Sep 2005
    Location
    Atlanta GA area
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    Hmmm...

    An unit rated for 575V... and getting 600V...

    Reminds me of a rooftop many many many years ago...
    Rated for 460V, getting about 495-500V... was within the margin.

    Did I read in the OP... that this Xformer drives the draft inducer motor???
    Is the motor functional??? Does it turn freely???
    Check the ohms on the motor... might find something...
    GA-HVAC-Tech

    Your comfort, Your way, Everyday!

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    *Installation is more important than the brand of equipment
    *The duct system keeps the house comfortable; the equipment only heats and cools (and dehumidifies)
    *Cheap is not good, good is not cheap; however expensive is not a guarantee of quality!
    Choose your contractor wisely!

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