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Door Bell Chime Transformers - UK

Discussion in 'Power Electronics' started by john2k, Mar 25, 2019.

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  1. john2k


    Jun 13, 2012
    I have a hard wired door bell chime. It's been running for about 10-11 years since it was installed in my new-build house. I removed the cover to inspect the transformer and the transformer is rather hot. I've been inspecting it for a few weeks now and it's always hot. Not hot that it will burn you but rather hot. Is this normal? I'm wondering if I should just change to battery operated chime with a wired bell
  2. Tha fios agaibh

    Tha fios agaibh

    Aug 11, 2014
    It should be warm to the touch but not so hot it will burn you if you leave your hand on it.
    Make sure your door buttons are not sticking on which would make it get hot by continuously drawing current.

    You can try taking off a wire off the low voltage side (wire to chime)and touch it back on the terminal screw. If you see a slight spark, it indicates that it is drawing current when idle and likely a door switch is not releasing.
    Martaine2005 likes this.
  3. dave9


    Mar 5, 2017
    With wiring already in place, I wouldn't want the extra recurring burden and expense of replacing batteries, and depending on location, distance and metal obstructions, and RF noise in the area, some wireless doorbells may have spotty results.

    If it is the type that is encased in a metal shell, those do tend to run hotter by adding the additional insulating layer of that and since it is metal will feel hotter to the touch than another material would.

    If it continues to work I would not change it, unless you had some very strict energy conservation needs for example living off grind and running everything on solar/wind/etc generated battery power. Even then I would consider using a switch adapter in place of the linear transformer for improved efficiency instead of going with device self-contained batteries.
  4. JohnnyO


    Mar 12, 2019
    Most mains powered door bell circuits will have a permanent 220v supply which will draw a small residual current in its primary which will produce a small rise in temperature in the transformer. Some bell circuits also have a bulb in the bell push button and if this is the case then the transformer core will have a further rise in temperature. In this case check if there is some heat in the chimes plunger coil. IF there is heat noticed then there is current draw in the secondary and it is likely that this is caused by the push button lamp and as such is normal.
  5. duke37


    Jan 9, 2011
    The core loss will depend on the voltage on the primary, not on the secondary current. Load current will produce loss in the secondary and additional loss in the primary, the core loss will not change significantly but will drop a smidgeon.


    May 20, 2017
    Low power mains transformers tend to have poor regulation and have a tendency to run a bit warm. It is down to core and copper losses. Can you measure the temperature of the core?
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