toroidal transformers

[wjfiles]

What would cause a toroid to fail.
The transformer is a toroid 12v -12v in series 230 volt input
and driving a HobbyCNC board and a 24v fan. I would have thought this would not overload the power supply. There is no output.
Worked fine yesterday. Switch on today , NOTHING ???
Total time of use would be about 100 hours.
Is there something I should check before replacing.

Thanks in advance
WJF

[smarbaga]

hello
there is only 2 things you can do to check a transformer.
1. check the primary winding.
2. check the secondary winding.

1. make sure the primary winding(s) has the correct voltage going into it.
2. make sure the secondary winding(s) has the correct voltage comming out of it.

this is done with your meter on ac volts and on the correct voltage sacle.
you should have a burt smell or signs of overheating if the transformer is gone.
good luck garry

[wjfiles]

Thanks for the reply smarbaga,
Input voltage measures OK.
Primary coil has no continuity. Secondary coil has.
Now where did I put the checkbook.
WJF

[smarbaga]

hi there
you can always remove the transfo and unwrap the mylar tape.
perhaps you will find a burnt open spot in the primary.
the primary is usually wound first, therefore the secondary is overtop of it.
or put this transfo on the shelf for something to do at a later date.
move it around for five or 10 years then throw it out.
thats what i do and it works every time. :-)

[Al_The_Man]

It is very rare for a Transformer to go open without any prior indication.
I would tend to think the primary lead to winding connection has failed for some reason, some of the imported transformers have a thermal fuse buried in the primary, but I have never come across one in a power toroidal.
As suggested, it may be worth removing the secondary which should only be around 30 turns of bifilar wound secondary.
This should allow more investigation of the primary, at this point you have nothing to lose.
Al.

[smarbaga]

as mentioned the primary lead itself could be faulty.
if you don't have a terminal on your prim. leads,
in toirdial's, this will be part of the winding itself,(solid copper)

[Al_The_Man]

Originally Posted by smarbaga in toirdial's, this will be part of the winding itself,(solid copper)

Many are also single conductor stranded external leads that are either soldered to the primary or spot welded.
Antek & Plitron use either method.
Al.

[wjfiles]

Thanks for the responses,
I held a post mortem and found an AUPO thermal switch on the input lead.
A resistance check showed no continuity, maybe rigor mortis
How much is scrap copper these days
Cheers
WJF

[Al_The_Man]

Originally Posted by wjfiles Thanks for the responses, I held a post mortem and found an AUPO thermal switch on the input lead. A resistance check showed no continuity, maybe rigor mortis How much is scrap copper these days Cheers WJF

Why not just jumper out the thermal fuse and fit an external fuse, I suspect the transformer is ROC origin, as these are the only ones I have come across with the thermal fuse in them,
Al.