Old Transformer Humming

Discussion in 'FAQs' started by Buck62, Mar 29, 2006.

  1. Buck62

    Buck62 New Member

    I bought an old American Flyer No. 2 transformer (60 Cycles - 75 Watts) at a train show recently. I'm planning on using it just to light up a few of the lighted houses and buildings in my kids' layout. When I plug it in, it has a hum to it. When I hook it up to some of the lighted houses, it hums a bit louder as I crank up the power. Otherwise, it seems to work just fine.

    Is this normal for an old steel transformer?
  2. nachoman

    nachoman Guest

    yep. Perfectly normal. Transformers hum. If you have a big square transformer near your house, listen to it.

  3. ezdays

    ezdays Out AZ way

    As Kevin says, they do hum. The older they are, the more they tend to hum. What happens is that the insulation between the core laminates dries out and the laminates get loose. You are hearing them viberate 60 times a second. I have an old MRC dual throttle I've been using to test my lighting circuits with. It is about 30 years old and hums like the dickens. I will replace it really really soon.:D :D
  4. Buck62

    Buck62 New Member

    Okay, so then I can run my lights with this thing now? (.... as is?)

    Somebody told me today to short it out and it will sort of reset itself and hum less.

    Is that true?
  5. ezdays

    ezdays Out AZ way

    Uh, shorting it out isn't the best thing to do, depending on your power pack it could just do it in, then it will smoke a lot insead of humming.:eek: That's just a small risk since most power packs are designed to handle a short circuit mainly because that is a common occurence. But if it did make an improvement, it would only be temporary and it will never go away. I would just use it as-is. Like I said, I'm using one to run my lights right now, but the noise is got to go. along will that old power pack.:D
  6. jim currie

    jim currie Active Member

    you can dip the xformer in a high quality varnish and let it dry might help some.
  7. Buck62

    Buck62 New Member

    So, can I open it up and somehow re-insulate the inside?

    It has two big screws on the top that would allow me to pop it open and look into it.

    Good idea?.... Bad idea??

    How long might this thing last if I leave it "as is?"
  8. pgandw

    pgandw Active Member


    The thing will probably the last (and hum) rest of your life if not abused. Except for wire insulation "rotting" or going bad, there is not much to go wrong.

    The iron core laminations are difficult to reglue or fix because of the wire windings that go around them. It is the actual iron core laminations that are slightly loose. The iron pieces need to be as close as possible to conduct the magnetic field with less magnetic resistance. If you have to remove the wire windings for some reason - broken wire or cut in the wire insulation - then you can tighten the lamination stack.

    As you can see, dipping the core in varnish could help the iron laminations stick to together better while keeping the winding wire insulation intact.

    The only way a short circuit could help is to get everything hot enough to melt the old glue in the lamination stack. I would not want to try to figure out how much short circuit time between melting the lamination glue and melting insulation in the windings or other wiring, and finally starting a fire!

    Best bet if the hum is too loud is to buy a replacement.

    yours in transforming
  9. ezdays

    ezdays Out AZ way

    Don't know what the transformer looks like, but chances are that there is a metal frame around it so the edges of the laminents are not visable. Honestly, if you can stand the hum, use it as-is, it's perfectly safe to use for what you're using it for. If the hum is too distracting (mine is way beyond that) :rolleyes:, you can always buy a cheap plug-in transformer or converter. I never throw those away, even when the electronic device they power goes in the trash, they're still good. Just read the plug-in, it always tells what the input voltage, the output voltage and current or power output. I've got them ranging from 3.7 VDC (from a cell phone) to 21 VDC (drill battery charger), and a few AC ones as well.
  10. kf4jqd

    kf4jqd Active Member

    The hum you are hearing is the resonating AC in the coil. AC works on 60hz (like a radio frequency) A transformer is made of two sets of wire. A primary, where the AC is feed into from the wall. The secondary is the converting of the power. A step up transformer "steps up" or boostes the power out put. Model train transformers are step down. Which means the output power is lower than the input power.

    What does this all leads? The principle uses electro-magtism to do this conversion. In some cases this resonates the coils in the transformer. This is the hum you are hearing. There is nothing wrong. Might be annoying. All transformers hum, some more than others. Older ones really hum.

    I hope this is a good lesson for Gauge Members on basic electricity.

    You should hear my Astron Ham Radio power supply when I turn it on...."Bonk..Bong..." 13.8vdc at 35amps!
  11. kf4jqd

    kf4jqd Active Member

    A transformer is an electrical device used to convert AC power at a certain voltage level to AC power at a different voltage, but at the same frequency.

    The construction of a transformer includes a ferromagnetic core around which multiple coils, or windings, of wire are wrapped. The input line connects to the 'primary' coil, while the output lines connect to 'secondary' coils. The alternating current in the primary coil induces an alternating magnetic flux that 'flows' around the ferromagnetic core, changing direction during each electrical cycle. The alternating flux in the core in turn induces an alternating current in each of the secondary coils. The voltage at each of the secondary coils is directly related to the primary voltage by the turns ratio, or the number of turns in the primary coil divided by the number turns in the secondary coil. For instance, if the primary coil consists of 100 turns and carries 480 volts and a secondary coil consists of 25 turns, the secondary voltage is then:

    secondary voltage = (480 volts) * (25/100) = 120 volts

    A transformer may have multiple secondary coils to feed a number of electrical loads; however, power must be conserved, so the sum of the output power must equal the sum of the input power minus losses. Energy losses in transformers are due to a number of factors: these are copper losses in the coils themselves due to material resistance, core losses due to hysteresis (the reluctance of the material's magnetic domains to reverse during each electrical cycle), and eddy currents.

    Answered by: Eric Berg, Mechanical Engineering Senior, Colorado School of Mines

    Here's an advance summerary and picture:thumb:


    Attached Files:

  12. kf4jqd

    kf4jqd Active Member

    One last thing. It's about voltage and current (amps)
    When voltage goes up...amps goes down
    When amps goes up.....voltage goes down
    This principle applies to transformers.

  13. Buck62

    Buck62 New Member


    Thanx for all the advice and education on transformers, guys.

    It's nice to know that I'm not going to burn the house down by lighting up the layout! :thumb:
  14. ezdays

    ezdays Out AZ way


    Some great information there, a good basic dissertation on how a transformer does what it does. Like you say, all transformers hum, so more than others. That's why those transformers you see up on poles or on the ground in your neighborhood are filled with oil. Keeps them cool and keeps the humming down. But still, get close enough and you can hear it. The same goes for flourecent lights.

    The fact is, that older transformers hum more than others because they are old and they had different manufacturing technology. It's that electromagnetic field that is directed by the laminated core from one coil to the other that is causing the laminates to vibrate. They are separated by a thin sheet of insulation and are sometimes dipped in varnish to hold everything together. This varnish and the insulation dries out over time and the metal laminates become loose. As the field expands and contracts, so does the laminates resulting in the hum. Like you said, sometime when you turn on a transformer, especially one that has a load on it, you get a resulting "clunk" which of course is the field pulling all the laminates together.

    This all may be much more information than most people need. Suffice to say that it is an annoyance but not a harzard.:D :D

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