Project: Transformer Checker

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Cool_buddy_57 said:
Yes i like it but.
What is the neon bulb?
A neon bulb mean LED or any thing else
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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.
 
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?
 
philba said:
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?
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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.
 
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_buddy_57 said:
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?
Click to expand...

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.
 
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.
 
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