Simple Workings of a Transformer

Discussion in 'Electrical Forum discussion & Blog' started by DJhandy, Aug 27, 2007.

  1. DJhandy

    DJhandy New Member

    Messages:
    12
    Location:
    FLORIDA
    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
  2. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    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.
  3. DJhandy

    DJhandy New Member

    Messages:
    12
    Location:
    FLORIDA
    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
  4. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,837
    Location:
    Cave Creek, Arizona
    voltage

    is there any voltage between the two red wires?
  5. Chris75

    Chris75 Electrician

    Messages:
    608
    Location:
    Litchfield, CT

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

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,153
    Location:
    New England
    Measure between the two red wires, tape off the white wire unless you have a need for half the voltage.
  7. Furd

    Furd Engineer

    Messages:
    446
    Location:
    Wet side of Washington State
    A transformer will output AC voltage. Are you sure that your application does not require DC?
  8. DJhandy

    DJhandy New Member

    Messages:
    12
    Location:
    FLORIDA
    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. HandyAndy

    HandyAndy General Contractor, Farmer

    Messages:
    68
    Location:
    Haxtun, CO
    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. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,153
    Location:
    New England
    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.
  11. DJhandy

    DJhandy New Member

    Messages:
    12
    Location:
    FLORIDA
    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. snafflekid

    snafflekid Electrical Engineer

    Messages:
    45
    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. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    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. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,153
    Location:
    New England
    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.
  15. 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
  16. Rancher

    Rancher Guest

    AC transformers are spec'd at their full load current (or 80%, I forget) so if you bought a 1 Amp, 12 Volt CT (center tapped) transformer, the open circuit voltage could well be 15 volts as you have discovered, or 14 volts under load, or 12 volts under full load that the transformer was spec'd at.

    Rancher
  17. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,540
    Location:
    North Carolina

    nd DC, DC. ??????????

    Have you learned how to transform DC?
  18. Rancher

    Rancher Guest

    Sure you can transform DC, 12 Volts DC into one side of the transformer, 0 Volts DC out the other side.

    Rancher
  19. abikerboy

    abikerboy DIY Senior Member

    Messages:
    202
    Location:
    VA
    Yea...it's called an "inverter"...lol!!! In the early days of electronics, it was called a "vibrating coil"... it was used to synthesise ac voltace out of a dc input by creating a chopped sign wave. Sorry guys, I just couldnt resist!
  20. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,540
    Location:
    North Carolina
    Does not an inverter work by reversing the polarity of the DC voltage applied to the transformer or in other words by alternating the polarity of the DC voltage.
    Last edited: Aug 30, 2007
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