[TCML] Subject: Overheated Secondary

[mark olson]

At 07:44 AM 12/31/07 -0800, you wrote:


>>The xfmr is dead. case is swollen. Should I bother to de-pot it and 
>>attempt a rebuild / shunt removal?
>>
>>
>>Thanks again,
>>Marko
>
>Sorry to hear about your transformer - those are hard to come by. Note 
>that when operating such a transformer with capacitive load of suitable 
>size you can draw a lot more than rated current from it - what had you 
>measured? Another question - were you using a variac to adjust primary 
>voltage and was it set to provide more than 120 volts? You might just have 
>overheated the windings due to excess core loss and the swollen case 
>sounds like overheating rather than voltage breakdown. Another possible 
>reason for fuse blowing if you're using a big variac is that it can draw a 
>very large starting current if it's switched to the line at the wrong part 
>of the cycle.
>
>Ed

Hi Ed,

I am using a 20A variac wired for 140 volts.  I never threw the switch with 
the variac above minimum.  The fuses
would blow after a few seconds of running @ 140 v.

I depotted my transformer and began cleaning it up.  It does not look like 
the one Bart photographed.  My
transformer has two primary coils in parallel and two secondaries in 
series.  One secondary overheated.
It never went open (until I worked on it) .  The insulation is gone from 
the outer layers of the winding.
Not sure how deep the damage goes, it is too cold to work on it lately.

Thanks,

Marko