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Stepdown Transformer Hum

Discussion in 'Electronic Repair' started by Erik Archer, Oct 31, 2004.

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  1. Erik Archer

    Erik Archer Guest

    Hello,

    I have a Modine gas Heater in my garage on a dedicated 110v/15A
    circuit. (USA 60 Hz)
    When the Thermostat is off, I can here a distinct hum from the main
    power transformer in the unit. (110v to 24v Step down).
    (It appears to be a 4" iron square, mounted directly/enclosed within
    the metal casing of the heater. 2 wire 110v in, 2 wire 24v out).

    It is not a loud hum by any stretch, you could only hear it if you
    stand quietly by the unit.
    My question is, is the hum ok / normal?

    (The heater itself is 4 years old and ran every winter, the previous
    owner said it did not hum, but I doubt he would have noticed
    this hum, or even paid attention to it).

    I googled archived groups and similar questions about hum have
    been asked, with just about any answer you could imagine.
    Some posts say replacement, others say it is normal, problem is
    most are directly related to A/V equipment and I don't know that
    garage heaters fall within such a exacting specification.

    Other posts said to remount/isolate the transformer from it's current
    mounting to help isolate transmitted vibrations.
    My question then being, if I remounted it, should it/what if, it is
    insolated from the heater chassis? Ok?

    Others mentioned dirty AC line voltage, but the garage construction
    is new, and the rest of the electronic equipment in the house has
    shown no indication of poor/dirty power.

    Suggestions appreciated.
    -Erik
     
  2. Ol' Duffer

    Ol' Duffer Guest

    The mechanical vibration is caused by the magnetic field
    in the transformer making the core laminations and other
    parts alternately repel or attract each other and relax.
    These transformers are rather cheaply constructed and
    tend to rattle or buzz. Also, they tend to be mounted
    to sheet metal, which can act as a sounding board.

    The hum is not an indication of a problem, but if it
    really bothers you, it might be eliminated or reduced,
    depending on how much you are willing to spend and to
    what lengths you are willing to go.
     
  3. << When the Thermostat is off, I can here a distinct hum from the main
    power transformer in the unit. (110v to 24v Step down).
    (It appears to be a 4" iron square, mounted directly/enclosed within
    the metal casing of the heater. 2 wire 110v in, 2 wire 24v out) >>

    Erik-

    As Ol' Duffer stated, it is normal. The effect he described is called
    "magnetostriction".

    There is also a possibility that the transformer's stray magnetic field is
    interacting with the metal it is mounted to. In addition to acting as a
    sounding board for the mechanically-coupled vibration, it could be generating
    more in reaction to the magnetic field.

    Fred
     
  4. NSM

    NSM Guest

    |
    | Hello,
    |
    | I have a Modine gas Heater in my garage on a dedicated 110v/15A
    | circuit. (USA 60 Hz)
    ....
    | My question is, is the hum ok / normal?
    ....

    Yes. It's not a problem. Sometimes you may have a loose lamination in the
    transformer and it will really buzz but this is not a problem either unless
    it keeps you awake. It isn't broke - don't try to fix it.

    Real transformer faults:
    1) Open winding. Result: It won't work.
    2) Shorted winding. Result: It won't work, and other bad things will happen
    (burning smell, blowing fuses).

    N
     
  5. CJT

    CJT Guest

    Probably. Unless it's running hot, I wouldn't worry about it.
    Sometimes the noise level increases if for some reason a transformer
    is overloaded (or has internal shorts) -- I would expect it to also
    get quite warm or hot in that case. If it's cool or only somewhat
    warm, rather than hot, I'd ignore it.
     
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