Hey all,
For a tube based project, I am needing a transformer to supply 0-640v@100ma secondaries...
I have a 100 - 120VA Toroid that has 120v primary and 21v secondaries....and reason to beleive I cannot use this toroid backwards?
Have not tried it yet...thought to ask those far smarter first...
For a tube based project, I am needing a transformer to supply 0-640v@100ma secondaries...
I have a 100 - 120VA Toroid that has 120v primary and 21v secondaries....and reason to beleive I cannot use this toroid backwards?
Have not tried it yet...thought to ask those far smarter first...
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Where will you connect the 21V secondaries to? Not the mains I hope - that would fry the transformer.
Jan
Jan
Whoops...Thank Jan, you saved me a transformer...was blindly looking at step up/down ratio
But dont we run toroidal transformers backwards all the time?
EDIT - OK, I see that if the pri/sec voltages awere a bit closer, running reverse could work... I have used a Triad N68X backwards (120v - 240v) for a preamp years ago....
But dont we run toroidal transformers backwards all the time?
EDIT - OK, I see that if the pri/sec voltages awere a bit closer, running reverse could work... I have used a Triad N68X backwards (120v - 240v) for a preamp years ago....
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240+240+120 would get you close. I have no problems with putting three transformers in series….
But a single 2x320V would likely be as cheap. Or cheaper.
But a single 2x320V would likely be as cheap. Or cheaper.
Yes. Power transformers normally run close to the max induction the core is designed to.
Connecting a 21V winding to 230V will completely saturate it and the inductance collapses and there's nothing to limit current except the winding ohmic resistance.
Jan
Connecting a 21V winding to 230V will completely saturate it and the inductance collapses and there's nothing to limit current except the winding ohmic resistance.
Jan
Yup, understood...I will get the correct transformer..
I have an Edcor XPWR178-120...just need another one...
I have an Edcor XPWR178-120...just need another one...
A transformer has an idle current which is determined by the voltage and the inductance. A 21V winding has a relatively small inductance that would not limit the mains idle current, and the transformer core would saturate, causing a huge ~short circuit current. Toroidal transformers are wound with just enough inductance to prevent saturation under normal conditions, but even a zero-crossing startup can temporarily saturate the core. A cheap transformer will be wound with a minimum inductance in order to be able to claim higher power handling, but it will be prone to inrush current problems. For reliability, it is a good idea to de-rate the winding voltage, ie use a ~130V transformer at 120V.
steveu - yes, thank you for the full explaination...I thought since I was needing only 100ma@640v, backwards could work since it was rated for double the VA.... but now understand otherwise
rdf - yes, that tranny could work, but still need two...and I have the one Edcor...just need another...
rdf - yes, that tranny could work, but still need two...and I have the one Edcor...just need another...
Could also use the 2x325V 300 VA unit - less $ if you don’t need or have room for the 800VA. They are pretty big. With the 2x325 you also have a center tap available. The 650 could go to 1300 if needed (series or parallel).
Only problem with Antek trafos is they are butt ugly. Might have to buy the metal can. At least they offer them now. One of the attractions of EI’s is the pretty end bells.