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Old 2nd Apr 2010, 2:09 pm   #12
bob_rich
Retired Dormant Member
 
Join Date: Mar 2010
Location: Chelmsford, Essex, UK.
Posts: 16
Default Re: Testing a transformer for shorted turns

Hi Folks.

I have tested numerous transformers for a shorted turn (or other maladies) by simply feeding mains power to the mains winding via a 100W to 200W tungsten filament bulb in series with the supply to the transformer primary. A cold bulb has a very low resistance so the transformer magnetising and loss current will not usually light the bulb and increase its resistance so a dim bulb suggest the transformer may be OK. With a totally shorted turn the impedance of the transformer under test will be low and the bulb will light up --thus liming the current . If the bulb does not light then the transformer should be OK and its ratio can be checked by using a voltmeter on the primary and secondary winding. For very small transformers use a lower power bulbs.

Idea can work on audio output transformers in this case feed the speaker winding from a low voltage transformer say 12V rms with a car stop light bulb as the series limiter (21W/6W) most audio transformers are usually OK at 50Hz.

The only problem I find with this idea is getting filament bulbs!!! not sure what would happen with low energy ones!

hope this helps

Bob
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