sheldonstv

a transformer can only fail in a few ways-oc primary,oc secondary or shorted turns -shorted turns primary will soon result in an oc winding,the same thing may also happen with the secondary.
if you need to check the transformer is ok,check it by applying ac to the primary,set your meter to read ac volts and connect it to the transformer secondary-if there are any faults with the windings they will show up when checking in this way(without a load on the tx the secondary volts will be a little higher than usual,but not by a great deal)
if you want,you could always ring the tx primary and check the secondary waveform with your scope.....but why make things too complicated when a simple continuity test or voltage test will suffice?
regards mike

Nigel Goodwin

This simple tester does ring the transformer, that's how it works - and you don't need a scope to use it. You also don't need to ring the primary and check the secondary, a ring test will detect any windings with shorted turns on the same core.

You seem to be limiting the testing to mains transformers?, but the ringing test can be used on many more, audio transformers, switch-mode transformers, non-mains power transformers, line output transformers etc.

It's a far more useful test than a simple ohms test, and faster and safer than a mains test.

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sheldonstv

there are times when i need to use a scope to check whats going on with a tx-for example when testing lopts for go-nogo due to shorted turns(eht overwind etc)........also scancoils are sometimes checked in the same way.......

Nigel Goodwin

Yes, using a scope for that is a VERY old technique, certainly more than 50 years old, some old scopes even had a timebase output you could use to ring the transformer. But it's a LOT easier to use a handheld tester, I build one from a kit that came from Dick Smith Electronics, it's really useful - and was quite cheap as well!.

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sheldonstv

:lol: you will have to forgive me as far as ringing transformers goes-be they audio,smps or flyback(and deflection coils )i am very much old school and set in my ways in that respect.
hand held testers are handy to use ,ive built one specifically for testing flyback transformers and scan coils-it also will check audio txs etc-but being able to view the resultant signal on the scope is sometimes very much a necessity.
regards mike

Cool_buddy_57

Yes i like it but.
What is the neon bulb?
A neon bulb mean LED or any thing else

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Cool Jasim

Nigel Goodwin

It means a 'neon bulb', it's a very common old component, they require a high voltage (about 70V to 90V to strike) - nothing else will do. If you really can't find one, try old switched mains sockets, those that have a red/orange light, they use a neon bulb.

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philba

maybe this is a dumb question but how often do transformers fail with a short inside the coils? I guess if they really got cooked and melted the insulation on the wires it could happen but wouldn't that be pretty obvious from a visual inspection?

Nigel Goodwin

It's a common failure mode, particularly in line output transformers, but also in modern cheap mains transformers - however, modern transformers usually have internal (non-replaceable) heat fuses, and the heat generated by the shorted turn will usually blow the heat fuse.

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Cool_buddy_57

Ok Dear u say Right
But u say that neon bulb require 70V to 90V to stike. And in transformer checker circuit 6V battery is used. What u saying about this?

__________________
Cool Jasim

Nigel Goodwin

That's the entire point behind the project!, when the current is discontinued a high back EMF is generated, it's that high voltage that causes the neon to strike. If there's a shorted turn in the transformer this will damp the back EMF, and the neon won't light.

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jkr6211

very ingenius method

speakerguy79

The transformer will easily create a high voltage pulse and light the LED/neon bulb when you release the switch.

I had a transformer with a 1mH coil that I was switching with a MOSFET (ignition coil primary) that was being charged with 12V. The voltage spike at the drain of the low-side-switch n-channel mosfet was >200V.