Electronics > Projects, Designs, and Technical Stuff

20W 50Hz isolation transformer

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Benta:
I my opinion, you're wasting your time. Send the specs to a transformer manufacturer and he'll roll one for you just like that. He won't even calculate it, but just select from his own standard table of cores and winding specs.
And go for 400/230 V instead, then it's universal for many countries and will still work as 380/220.

soldar:

--- Quote from: ali_asadzadeh on April 26, 2019, 02:09:02 pm --- It's  not a measurement error, I have measured it with my good Latron RLC meter,
--- End quote ---

275 mH is too low and the no-load current would be too high, probably saturating the core. You need to review your measurements.

What happens when you measure straight resistance (Ohms)?

What happens when you connect it to 230 Volts? What current does it draw?

IMHO, if you want to learn then learn first and if you want a transformer then buy it but you are not equipped right now to complete this job safely and successfully.

soldar:
Another interesting page: Calculating mains frequency power transformers

http://www.giangrandi.ch/electronics/trafo/trafo.shtml

ali_asadzadeh:

--- Quote ---Another interesting page: Calculating mains frequency power transformers

http://www.giangrandi.ch/electronics/trafo/trafo.shtml
--- End quote ---

 :-+ :-+ :-+

Zero999:

--- Quote from: soldar on April 26, 2019, 02:57:47 pm ---
--- Quote from: ali_asadzadeh on April 26, 2019, 02:09:02 pm --- It's  not a measurement error, I have measured it with my good Latron RLC meter,
--- End quote ---

275 mH is too low and the no-load current would be too high, probably saturating the core. You need to review your measurements.
--- End quote ---
Yes.

XL = 2πLF = 2*3.1416*50 = 314Ω
I = V/X = 220/314 = 0.7A.

0.7A is far too higher magnetising current for a 200VA mains transformer. If your measurement is correct, then the transformer is bad. It most likely has a multiple shorted turns and should be scrapped.

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