primary coil

Discussion in 'General Electronics Chat' started by adamclark, Nov 13, 2013.

  1. adamclark

    Thread Starter Member

    Oct 4, 2013
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    Ive got a few transformers and they have no writing on them at all.. How do I find the primary coil from the secondaries??
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If they are mains transformers generally and step down, then a resistance check would be a rough indication.
    The next problem would be the voltage rating and the Va.
    Max.
     
  3. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Throw in all of the disclamers you can think of.
    If you can see the laminations, .5 mm to 1 mm probably 50Hz to 60 Hz. finer than .3 mm might be audio.
    Line side frequently has two black leads, sometimes red & black, with higher resistance than other pairs leads. Three lower resistance leads may mean a centertapped winding, sometimes green, CT may be yellow/green.
    If you have decided on a primary, start with a lower AC V, say 24 V, & check for heat rise. That is as far as I can go.
     
  4. adamclark

    Thread Starter Member

    Oct 4, 2013
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    well.. the one I like has some writing.. its a Marantz ts1850403.. looks like it has 4 coils altogether and a center wire.. I googled it and its a power transformer for an old home stereo amp.. again its a pwer transformer.. but that's all the info I can find on it...im about to find which wires belong to each coil, but I still don't know how to tell the primary apart from the rest...
     
  5. adamclark

    Thread Starter Member

    Oct 4, 2013
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    ok the first coil are red and blue wires and they measure 3.3 ohms, the next coil are yellow wires and they are 5.8 ohms, both of those coils are on the bottom of the transformer.. at the top the next coil are green wires and they measure .5 ohms, the last coil is orange wires with a white wire, they all show continuity to each other the orange wires measure 1.1 ohm, the outside orange and the white measure .7 ohms, and the inside(middle) orange and the white wires measure .7 ohms... does any of this mean anything? im thinking the red and blue wires are the primary, the yellow and green coils are secondary and the orange are center tapped witgh the white? I just want to determine the primary so I can plug it in and measure the sec. voltages..
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I am guessing this is an old tube amp power transformer, if so the two orange & white are the H.V. secondary, the yellow pair and green pairs are L.V. tube heater source.
    The primary is usually the first winding on the core. Red Blue?
    Max.
     
  7. adamclark

    Thread Starter Member

    Oct 4, 2013
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    I really cant tell if the red blue is the first winding or not, Its a good sized transformer. but it does have the highest impedance.. I measured my smaller transformer and the primary on it had the highest also, so am I to assume that's it? What would happen if I put 120vac to it and its not the primary? and what is the difference between the h.v. and l.v.? so would that make the white wire center tapped with the orange H.V. sec.?
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Transformers are pretty rugged devices, put a fuse in any line when testing.
    The low voltage are usually put on last, tube filament for a tube amp were often 5v and 6.3v
    A variac is usually the best way to test if you have one.
    Max.
     
  9. adamclark

    Thread Starter Member

    Oct 4, 2013
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    ok,, so heres the findings.. the red/blue are primary, the orange with white center is the sec H.V. and it meters 44.5 vac/62.47 vdc, the yellow coil measures38.5 vac/54.05 vdc, and the green coil is 8.1 vac/11.37 vdc... I grabbed this transformer for my psu project I am working on.. I have a bridge rectifier (pn:mb354-w), Its 40-100v 35 amp.. I think this transformer is pretty well suited for my rectifier, What do you think? I want my psu to be variable rate 4a.. The voltage regulator I plan on building is from the lm317-t data sheet and it uses 3 317's in parallel to achieve 4a max current.. sound like im on the right track so far?
     
  10. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
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    I do have a variac, but I have no idea how to use it.. it came with my current psu, I paid 20 bucks for both at a yardsale a few weeks ago..
     
  11. ronv

    AAC Fanatic!

    Nov 12, 2008
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    The tougher question is how much current can your transformer supply. A 4 amp one at 40 volts will probably weigh 6 pounds unless it's a toroid.
     
  12. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Think of a Variac as a transformer with a variable turn secondary.
    IOW the turns ratio, and hence output changes with a rotation of the knob.
    It is however a auto-transformer, so there is no isolation between supply and output.
    Max.
     
  13. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
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    its every bit of 6 pounds, 3.5 inches tall and 4 inches wide. its a pretty stout transformer. its a Marantz power transformer, I ran the numbers on it and it went to a Marantz home audio tube amplifier so It should be able to do a fair amount of current..
     
  14. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
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    makes sense,, I wondered what the big knob on top was for. Its big,green and has all kind of numbers on it.. could I use that to drive a tesla coil? I seen a video of a 4 foot tall one and it had one of those connected to it..
     
  15. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The maximum ACV output is usually 25% above the supply voltage.
    Max.
     
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