Transformer Question

Discussion in 'General Electronics Chat' started by Flyinb, Feb 24, 2006.

  1. Flyinb

    Thread Starter New Member

    Feb 24, 2006
    5
    0
    Hi folks...Looks like a place someone could answer a few of my questions:).
    I put togather a hot wire cutter to use on my cnc machine to cut foam using a transformer from MPJA http://mpja.com/productview.asp?product=7846+TR Its 120v~240v in and 24v 10amp out ct. It has 4 wires on the input side, i used 2 of them for my 120 input using a dimmer switch to regulate, took the 2 blue output wires and use them to heat my 24" cutting wire with 24 volts ac and capped off the yellow ct wire. It woks fine but the transformer gets hot and smells after 10 min or so. Pulling about 5~6 amps. Afraid to bun it up so i quit using it. Is it normal to get that hot? Would using a rectifier on the output help? Mayby its just a bad transformer.

    Thanks guys
    Bruce
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    See if you can't find a connection diagram for your traansformer. It has two primary windings. They need to be hooked in parallel for 120 volt operation. It's getting hot because the one winding you're using is overloaded. Connecting them in parallel will allow the transformer to handle the 6 amp load without overheating.
     
  3. alim

    Senior Member

    Dec 27, 2005
    113
    1
    Hi no arectifier would not help. the 4 wires on the primary side would indicate 2 separate 120 volts coils,using one coil as you did,is using 1/2 of the transformer,you ought to wire the 2 coils in parallel, observing the polarity of the leads(start to start finish to finish) but why you use adimmer switch,is this on the input not clear?
     
  4. Flyinb

    Thread Starter New Member

    Feb 24, 2006
    5
    0
    Thanks guys...Yes there is a diagram on the transformer that shows two coils, 120 volts each, each haveing one black wire and one red wire, i will try both coils in parallel and see what happens. I suppose both reds togather and both blacks togather=parallel? Man i get so frustrated with electronics as that is my weak point, but i am very good with mechanical stuff.

    Thanks again
     
  5. Flyinb

    Thread Starter New Member

    Feb 24, 2006
    5
    0
    OK...I did a bit of experimenting. Connected both red wires (one from each coil) togather and the 2 black wires (one from each coil) togather, connected to my 120ac and blew the fuse on primary. Connected one red and one black togather and connected the other black and red to 120. Now i get 12V out of the secondary insted of 24 but it dont get hot or blow fuse.
     
  6. alim

    Senior Member

    Dec 27, 2005
    113
    1
    Hi I do not figure how the fuse blew,maybe there is a bridge between 2 of the leads. Can you measure the resistance between the different leads, say which 2 leads you used initially, and we can take it from there.
     
  7. Flyinb

    Thread Starter New Member

    Feb 24, 2006
    5
    0
    [attachmentid=1220]Ok...The resistance is 4.9 on both sets of wires. here is a picture of the trans. wire dia. Maybe i need to use 220 to get my 24 volts?
     
  8. alim

    Senior Member

    Dec 27, 2005
    113
    1
    Hi I recognise the transformer,but some info in your third post does not "add up",the xformer has 2 primaries if placed in // is for 120 volts, if placed in SERIES is for 240 volts,the sec. is CT. this is really a12 volt transformer @10 amps or 24 volts @ at5amps(CT unused) hope this helps.Not clear why the fuse blew.
     
  9. Flyinb

    Thread Starter New Member

    Feb 24, 2006
    5
    0
    alim...Thanks for your time and help. 12 volts @ 10 amps will work fine for my app. I get 12 volts on the two secondarys and 6 volts between one secondary and CT when connected to 120volts in what i would call series so i will see what happens with my hot wire.

    Bruce
     
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