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Thread: Simple Workings of a Transformer

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    DIY Junior Member DJhandy's Avatar
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    Default Simple Workings of a Transformer

    I ordered a 115 volt primary, 12 volt secondary transformer. I received it and this is my problem: Has 2 wires for primary got that, has 2 red wires and one white wire on the secondary. When I connect to 115v and check the secondary Ground to white and check each red wire I have 7.5 volts out of each read wire. I need 12 volts, am I missing something? Why does it have 2 red wires? How do I get the 12 volts I need?

    Reply appreciated

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    Plumber jimbo's Avatar
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    Whatever you are calling ground does not enter this equation.

    Without actually seeing a diagram of that unit, I would suggest that the secondary is the two red wires. You would see about 15 volts ( open circuit). That is about normal to give you 12 volts under load. The white wire is the center tap, hence 1/2 the voltage from each red to the white.

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    DIY Junior Member DJhandy's Avatar
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    Default Transformer

    It has 2 black wires on the primary side. One white and two reds on the secondary side. If I connect meter: One leg to the white and one to either red I get 7.5 volts. How do I connect it to get 12 volts? I need it to connect to a govenor control box on a generator. I have two connections on the control box to connect the transformer too. The govenor control needs 12 volts to operate.

    Thanks
    DJ

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    Moderator & Master Plumber hj's Avatar
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    Default voltage

    is there any voltage between the two red wires?

  5. #5
    Electrician Chris75's Avatar
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    Quote Originally Posted by DJhandy
    I ordered a 115 volt primary, 12 volt secondary transformer. I received it and this is my problem: Has 2 wires for primary got that, has 2 red wires and one white wire on the secondary. When I connect to 115v and check the secondary Ground to white and check each red wire I have 7.5 volts out of each read wire. I need 12 volts, am I missing something? Why does it have 2 red wires? How do I get the 12 volts I need?

    Reply appreciated

    What brand and model so we can look it up online...

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    Measure between the two red wires, tape off the white wire unless you have a need for half the voltage.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Engineer Furd's Avatar
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    I need it to connect to a govenor control box on a generator. I have two connections on the control box to connect the transformer too. The govenor control needs 12 volts to operate.
    A transformer will output AC voltage. Are you sure that your application does not require DC?

  8. #8
    DIY Junior Member DJhandy's Avatar
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    Default Transformer

    Yes I need 12 volt AC it is a replacement transformer. The old one had various voltages 6-9-12 I believe and the 12 was used. The model# 41FG300 is what was sent(no name or origin) as replacement and it states Pri: 115v Sec: 12.6 v
    It supplies the signal to the governors board from the generator to control the engine speed. The wires from the transformer goes to a ground terminal and to signal in on governors board. The replacement transformer as stated previously has 2 black wires for primary, secondary has 2 red and one white wire. Power across both reds are 14-15 volts, from either red to white is 7.5 volts. I need 12 volts from single wire to connect to board and a ground wire to board. I've always used transformers that gave me the voltage I needed out of one wire. What do I need to accomplish what I seek?

    Thanks for your help

  9. #9
    General Contractor, Farmer HandyAndy's Avatar
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    Default

    first:
    there is no such animal, you need two wires (paths), to make a complete circuit,

    even a cars coil, (which is a transformer) is actually a two wire (paths) unit, the high voltage wire running to the spark plugs and the case of the coil which attaches to the bock of the motor and the spark plugs are also attached to the block of the motor, thus two wires even tho you only have (one visible wire) in other words there needs to be a complete circuit, which takes two avenues of path, (wires),

    there is two wires,(paths) in the primary side of the transformer, and there are two or more paths, (depending on the taps) on the secondary side of the transformer), but each voltage needs a complete circuit to travel thus (for sake of better description) a path out of the transformer coil and one back in to coil. Now like in the cars coil the case of the coil is the other path (wire),

    ~~~~~~~~~~~~~~~~
    two: apparently the transformer you have is different than the one that is in the generator, and you may need to go and get actual parts for that model


    three: it sounds like to me you may be wise to take it to a an actual repair place that understands the workings of the generator and get fixed and checked out by some one who understands what is going on in the unit,

    if you get it hooked up wrong you may end up costing your self much more than the price of the transformer,

  10. #10
    Retired Defense Industry Engineer jadnashua's Avatar
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    You might be able to attach one of the reds to the system ground and use the other lead as your hot. It doesn't matter which one.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  11. #11
    DIY Junior Member DJhandy's Avatar
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    Thumbs up Transformer Solved

    I contacted the manufacture Precision Governors (Chad a fine fellow)and jadnashua (moderator) you win the bragging rights and a big thank you.

    One red goes to the + input and the other to the -terminal and wala 14.5 volts as needed.

    I personally don't understand when u bench test an item and have 7.5 out of each lead and if you connect one leg to ground that 7.5v ends up in the positive leg giving 14 v. I've read and read about transformers. Can someone explain this in layman's terms??

    Thanks to all for your help
    DJ
    Ready now Generator good to go it's a Diesel Isuzu 15KW

  12. #12

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    One red wire to the white wire is a transformer tap for 7.5V

    The white wire to the other red wire is another identical transformer tap for 7.5V

    So, one red wire to the other red wire is like two taps in series, the voltages add and that makes 15V, or about 14.5 in your case.

  13. #13
    Plumber jimbo's Avatar
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    There is no positive and negative on AC voltage , so you are mixing up the terms a little. I hope your device actually needed an AC voltage, and not 12 VDC

  14. #14
    Retired Defense Industry Engineer jadnashua's Avatar
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    The transformer secondary winding in your device has a tap in the middle (the white wire). While not an exact analogy, think of a variable resister with the wiper arm set exactly midpoint. If you run voltage through it, measuring from one end to the other, you get the full voltage; measure from one end to the middle, you get half.

    this is the same idea as the power coming into your house...it is really 220vac, with a tap in the middle (your neutral), so you get 110 on each half referenced to the middle.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  15. #15
    Homeowner geniescience's Avatar
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    Default

    Quote Originally Posted by DJhandy
    Diesel Isuzu 15KW
    Isuzu 15KW VAC Diesel
    gives me more search results than
    Isuzu 15KW VDC Diesel
    so without any more thinking,
    I'll guess you have an AC thingie.

    Transformers keep AC as AC
    and DC, DC.

    David

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