Transformers, usually toroids nowadays, new and legacy has always been built around some spec. Also EI and other did. Back in the days they had more margins, that’s a feeling I have.
The perfectly normal thing in commercial production is to reach the specs to an as low production cost as possible. To sell more of course.
That probably means that the manufacturer does not make one extra turn on the primary if it holds the specs nominal.
Many trafos, new and older, vibrate, makes sounds, gets warm, barely holds output specs etc. Even without load.
A winder that doesn’t have the economic pressure adds enough winds, enough iron etc to make the product live an easy life for what it’s ment for.
What is your criteria when you evaluate a transformer for it’s purpose? How many degrees over nominal under load. Can it make sounds audible a meter away etc?
Not a purely scientific thread, just interested in your thoughts. Going over a lot of iron in my stash and pondering over what to ditch and what to keep.
The perfectly normal thing in commercial production is to reach the specs to an as low production cost as possible. To sell more of course.
That probably means that the manufacturer does not make one extra turn on the primary if it holds the specs nominal.
Many trafos, new and older, vibrate, makes sounds, gets warm, barely holds output specs etc. Even without load.
A winder that doesn’t have the economic pressure adds enough winds, enough iron etc to make the product live an easy life for what it’s ment for.
What is your criteria when you evaluate a transformer for it’s purpose? How many degrees over nominal under load. Can it make sounds audible a meter away etc?
Not a purely scientific thread, just interested in your thoughts. Going over a lot of iron in my stash and pondering over what to ditch and what to keep.
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There is more to it than mechanical vibration/noise, and heat.
What about regulation, sensitivity to saturation (for torroids), suppression of AC line noise ingress, suppression of leakage fields around transformer, etc.?
What about regulation, sensitivity to saturation (for torroids), suppression of AC line noise ingress, suppression of leakage fields around transformer, etc.?
<<Transformers, usually toroids nowadays...>> - unfortunately.
Power and audio transformers have contradicting requirements.
Toroids are good for audio, for the power supply you need U-I or C-core.
The primaries and secondaries must be separated in space as much as possible - the best
is to use one leg (and bobbin) for the primaries and the other leg for the secondaries.
At least, any one bobbin must be divided into two sections - to separate the primary and
the secondary windings (side-by-side) - typical.
Even E-I transformer - properly designed -will do the job, at a lower cost...
Power supply transformer must not buzz when connected to the supply line, and should not
have any added substance inside.
You hope that transformer rated for 120VAC (240V) will be better than the one rated for
110VAC (220V) (for the same market / grid frequency), but you can expect that only from
the serious professional manufacturer...
Power and audio transformers have contradicting requirements.
Toroids are good for audio, for the power supply you need U-I or C-core.
The primaries and secondaries must be separated in space as much as possible - the best
is to use one leg (and bobbin) for the primaries and the other leg for the secondaries.
At least, any one bobbin must be divided into two sections - to separate the primary and
the secondary windings (side-by-side) - typical.
Even E-I transformer - properly designed -will do the job, at a lower cost...
Power supply transformer must not buzz when connected to the supply line, and should not
have any added substance inside.
You hope that transformer rated for 120VAC (240V) will be better than the one rated for
110VAC (220V) (for the same market / grid frequency), but you can expect that only from
the serious professional manufacturer...
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Yea, I’m building a dummy load so I can go over them. Some actually behaves better when rectified and loaded, so I want to see how they do in real life.
The worst one so far was a brand new bought Elma TT IZ75 isolation transformer that gets searing hot after a few minutes unloaded. Old 220 volt primaries can sometimes get a little warm and give a slight vibration hum.
I’m thinking if they stay under 10 degrees C over ambient unloaded, 15 or so loaded and don’t give an audible hum except with the ear next to it, they are keepers. And then mark what they give on the secondaries.
The worst one so far was a brand new bought Elma TT IZ75 isolation transformer that gets searing hot after a few minutes unloaded. Old 220 volt primaries can sometimes get a little warm and give a slight vibration hum.
I’m thinking if they stay under 10 degrees C over ambient unloaded, 15 or so loaded and don’t give an audible hum except with the ear next to it, they are keepers. And then mark what they give on the secondaries.
You have set yourself a difficult task. A winding’s temperature rise is measured using what is called “Change of Resistance” technique. This requires an ohm-meter capable of accurate readings of values below one ohm using a “four-wire” setup. Both primary and secondary windings must be measured. You must disconnect the transformer from the loads and attach the test leads very quickly. If this takes longer than a few seconds you should periodically record resistance readings as the transformer cools and extrapolate backwards to the instant the load was removed.
Assuming no information is available for the transformers you wish to test, I would assume a 30 deg C temperature rise as a default. If the transformer under test caches fire before stabilizing at a 30 deg C rise you probably didn’t want to use it anyway, so no loss.
Assuming no information is available for the transformers you wish to test, I would assume a 30 deg C temperature rise as a default. If the transformer under test caches fire before stabilizing at a 30 deg C rise you probably didn’t want to use it anyway, so no loss.