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Transformer power?
Transformer power?
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Old 15th November 2019, 07:55 PM   #11
nenad88 is offline nenad88  Serbia
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It says 230V 50hz
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Old 15th November 2019, 08:12 PM   #12
FauxFrench is offline FauxFrench  France
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Many thanks, that won't give us a hint.
If the maximum input power is stated and no important consumption outside of the transformer is known, I assume the transformer power to be 80%-90% of the maximum input power.
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Old 15th November 2019, 09:02 PM   #13
nenad88 is offline nenad88  Serbia
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yea probably
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Old 15th November 2019, 10:04 PM   #14
Elvee is offline Elvee  Belgium
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Search this forum and the WWW: there are many hints, based on weight, dimensions, resistances.
A recent example found here:
Age-old question: reverse, perverse engineering of surplus power xfmrs.
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Old 16th November 2019, 05:03 AM   #15
LateraLiz is offline LateraLiz  United States
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Quote:
Originally Posted by DF96 View Post
Weigh the transformer. Compare with catalogue figures.
Is this ballpark 'accurate', have you used this method to gauge the power rating of a mystery xmfr? Seems almost too easy to be true, ha!
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Old 16th November 2019, 06:52 AM   #16
PRR is offline PRR  United States
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Power transformers are historically 5VA/pound.

The properties of iron have changed little (in ways that matter for our types of iron) and copper has changed not at all. Insulation is better and commercial pressure is much higher, so ratings/pound have gone up from 5VA/lb. But comparable types will all fall in a narrow band. E-I versus torroid makes some difference. Cheap-junk versus lasts-forever can be a big difference. Industrial transformers often fall under industry guidelines and may seem under-spec for the weight (but will stand hours of overload).
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Old 17th November 2019, 08:38 AM   #17
nenad88 is offline nenad88  Serbia
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Transformer with no load gives me 14.5-0-14.5 and after rectifier filter board -20-0-20 or 40v. I assume this is 12-0-12 transformer because voltage would drop to 12-0-12 unrectified under load. Am I correct?
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Old 17th November 2019, 10:48 AM   #18
FauxFrench is offline FauxFrench  France
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Quote:
Originally Posted by nenad88 View Post
Transformer with no load gives me 14.5-0-14.5 and after rectifier filter board -20-0-20 or 40v. I assume this is 12-0-12 transformer because voltage would drop to 12-0-12 unrectified under load. Am I correct?

Sounds right. Nominally some 13Vac. The 20Vdc rectified is unusually high for nominally 12Vac but you may have peak rectification of some spikes as well. With a slight loading of the 20Vdc it should drop to some 18Vdc.
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Old 20th November 2019, 10:28 PM   #19
PRR is offline PRR  United States
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> 20Vdc rectified is unusually high for nominally 12Vac

He reports 14.5VAC no-load. Times root-2 makes 20.5V peak. Allow a half-volt for a no-load Silicon rectifier, the math works out clean.

I would expect it to droop to 15VDC-17VDC depending on load and size of iron.
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Old 21st November 2019, 07:24 AM   #20
FauxFrench is offline FauxFrench  France
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I evidently agree with your math. But, the question was if it is a (nominally) 12-0-12 transformer. My impression is that " 20Vdc rectified is unusually high for nominally 12Vac". The nominal value is rather 13Vac-14Vac.
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