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Old 13th Feb 2018, 1:50 pm   #21
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 4,534
Default Re: HT / filament transformers from Aliexpress

Good test plan!

I doubt there will be any issues with insulation resistance, to be honest. Though it is a good thing to check.

Unloaded temperature rise - you may want to check every few minutes at first, the 'Can I put my hand on it' and 'Can I smell it' tests are good indicators.

As for temperature rise itself, you can use the primary winding to do this. Measure resistance cold (assume room temperature is 20 deg C); measure resistance after soak test, immediately after switching off. Work out the percentage increase. Then, temperature rise = % resistance increase x 2.54. Add the 20 deg C room temperature starting point and you'll get the final temperature in the heart of the transformer, which could be several degrees hotter than the outside.
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