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Thread: Why did this Transformers fail. Is it this due to the low 230VAC rating..?

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    Default Why did this Transformers fail. Is it this due to the low 230VAC rating..?

    Hi all,

    As you might recall I had three alarm clocks and the PS of the bar fridge fail a few weeks ago.
    I opened up the clocks and - with my level of expertise - deducted that the transformers had failed, as the bar fridge one as well.
    I'm pretty sure that the old 5KW inverter had a 'surge/peak'.

    My new 6KW unit is supplying 241VAC into the house (as I type this).

    So I borrowed a working bar fridge PS - EXACTLY - the same as my 'gone' one and thought I'd find out why, by having both powered up at the same time and comparing them side by side on the bench.

    On the working PS, the underside photo, 240VAC is present and the 'double 12VAC' pads are measuring 14 - 15VAC.
    The failed PS also has 240VAC going in but ZERO on the 12VAC.
    Only took me 5 minutes to work that out, super skills...

    So what has actually 'gone' inside the transformer?
    I understand that there are multiple copper windings [very thin]. So what has 'broken', not allowing the electricity through? A physical break, caused by what?

    A new PS is only $40. As I have already bought one anyway, I thought about finding a bare transformer, just to see if it is indeed the transformer. They cost $1 each, but I don't need 5,000qty of them...


    Why is it classed to only 230VAC? So ok to handle 240VAC continuously?
    But would a peak of eg:247VAC take it out?









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    The primary is the 'flimsyest' winding so I'd go for an open circuit there being more likely than the secondary but an ohmmeter will prove which side is the culprit. As it's a 6VA rated transformer the primary current will be around 25-30mA max so expect a winding of around barely 0.1mm Cu being required. There's also the chance that a thermal fuse is embedded in the winding for fire protection and it's blown (not worth trying to fix it).

    The 230V rating shouldn't be a factor, ambient temperature is usually the culprit.
    Last edited by Skepticist; 13-04-19 at 06:23 PM.

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    Definitely a thermal fuse failure.
    Cut the cover away from the mains wiring, should be the yellow tape, and you will see the thermal fuse.
    These are cheap. If there is a mains fuse, just bypass the thermal fuse.
    Last edited by Reschs; 14-04-19 at 12:34 AM.

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    To clarify 230 Vac rating. Old standard 240 V has been changed to make Australian market more compliant to world-wide norm of 220 V.
    In fact when you see 230 Vac the device should be capable to work within -6% to +10% range. Your transformer should be able to work without problems from 216.2 V to 253 V..

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