transformer trix

scottw · 14th October 2009, 08:36 PM

At a hamfest the other day, I couldn't pass up an unused pair of about 500va EI transformers. Trouble is the secondaries are 50-0-50v, which is about 2x the voltage I would typically play with (might work on some mosfet project?). They are single primary 120v.

Being that they are a pair, what would happen if I hooked the pair up in series with 120v mains, would this halve the output voltage? Sorry if this sounds remedial to some of you, as I'm still learning what you can and can't do with transformers.

Thanks,

Scott

zigzagflux · 14th October 2009, 09:00 PM

You could, but it won't work well. There is no guarantee they will share the voltage equally, so one output might be 40-0-40 and the other 10-0-10. The load you place on each will affect this even worse.

I suppose you could parallel the secondaries and series the primaries, but then you'd probably have some var flow to balance things out. Still not the right solution, but at least they're identical units. That would give you 25-0-25. Might be a fun experiment, if nothing else.

scottw · 14th October 2009, 10:40 PM

Thanks, I figured it was a long shot.

"...you could parallel the secondaries and series the primaries..."

I had seen this done somewhere which made me wonder if it would work without the secondaries in parallel. Guess not. I'll find a project for them someday.

Maybe connect secondary to secondary add some caps and make a line conditioner for low power source equipment.

Scott

igwt · 15th October 2009, 01:15 AM

Scott,
If you unwind the secondaries. each turn in the wire removed drops the voltage,as you proceed check the output until you reach the desired voltage. The tranny can be fine tune to the desired voltage with no consequence to the va rating. Not difficult at all.

Good Luck,
Brent

star882 · 15th October 2009, 06:03 AM

They'll work nicely as isolation transformers for testing switching power supplies. They'll output about 17% below normal line voltage, which would stress switching power supplies more than usual. Probably desirable for testing.

picowallspeaker · 15th October 2009, 06:56 AM

Or just drop in a pair of power transistors to have a regulated PSU.

14th October 2009, 08:36 PM	#1
scottw diyAudio Member Join Date: Feb 2004 Location: Kalifornia	transformer trix At a hamfest the other day, I couldn't pass up an unused pair of about 500va EI transformers. Trouble is the secondaries are 50-0-50v, which is about 2x the voltage I would typically play with (might work on some mosfet project?). They are single primary 120v. Being that they are a pair, what would happen if I hooked the pair up in series with 120v mains, would this halve the output voltage? Sorry if this sounds remedial to some of you, as I'm still learning what you can and can't do with transformers. Thanks, Scott __________________ "The Adobe Updater must update itself before it can check for updates. Would you like to update the Adobe Updater now?" -Adobe Updater

14th October 2009, 10:40 PM	#3
scottw diyAudio Member Join Date: Feb 2004 Location: Kalifornia	Thanks, I figured it was a long shot. "...you could parallel the secondaries and series the primaries..." I had seen this done somewhere which made me wonder if it would work without the secondaries in parallel. Guess not. I'll find a project for them someday. Maybe connect secondary to secondary add some caps and make a line conditioner for low power source equipment. Scott __________________ "The Adobe Updater must update itself before it can check for updates. Would you like to update the Adobe Updater now?" -Adobe Updater

15th October 2009, 06:03 AM	#5
star882 diyAudio Member Join Date: Mar 2007	They'll work nicely as isolation transformers for testing switching power supplies. They'll output about 17% below normal line voltage, which would stress switching power supplies more than usual. Probably desirable for testing. __________________ "Fully on MOSFET = closed switch, Fully off MOSFET = open switch, Half on MOSFET = poor imitation of Tiffany Yep." - also applies to IGBTs!

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14th October 2009, 09:00 PM	#2
zigzagflux diyAudio Member Join Date: Oct 2006	You could, but it won't work well. There is no guarantee they will share the voltage equally, so one output might be 40-0-40 and the other 10-0-10. The load you place on each will affect this even worse. I suppose you could parallel the secondaries and series the primaries, but then you'd probably have some var flow to balance things out. Still not the right solution, but at least they're identical units. That would give you 25-0-25. Might be a fun experiment, if nothing else.

15th October 2009, 01:15 AM	#4
igwt diyAudio Member Join Date: Mar 2009	Scott, If you unwind the secondaries. each turn in the wire removed drops the voltage,as you proceed check the output until you reach the desired voltage. The tranny can be fine tune to the desired voltage with no consequence to the va rating. Not difficult at all. Good Luck, Brent

15th October 2009, 06:56 AM	#6
picowallspeaker diyAudio Member Join Date: Apr 2007	Or just drop in a pair of power transistors to have a regulated PSU.

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