Question about toroidal transformers - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 17th November 2008, 09:40 PM   #1
00940 is offline 00940  Belgium
diyAudio Member
 
Join Date: Sep 2003
Location: Paris
Default Question about toroidal transformers

A simple question, but I couldn't find any quick answers by searching.

I've got a 30VA 2X18VAC toroid. I'm drawing about 15W out of it.

Is it possible to just wind an enamelled wire around it in order to create a new CT 25-0-25 secondary, to draw around 50mA ? I've around 15m of 0.6mm enameled on hand would this be suitable ? Due to space constraints, it's not really possible to add another xformer.

Thanks for any answer
__________________
Ben.
  Reply With Quote
Old 17th November 2008, 09:49 PM   #2
diyAudio Member
 
Join Date: Mar 2007
Location: Canandaigua, NY USA
I'd think if you can fit enough turns on it, and it's running at a reasonable temperature, why not? That's one nice thing about toroids- it's easy to add extra windings.
__________________
May the root sum of the squares of the Forces be with you.
  Reply With Quote
Old 17th November 2008, 10:32 PM   #3
diyAudio Member
 
Stuart Easson's Avatar
 
Join Date: Oct 2002
Location: Santa Cruz, CA
Send a message via MSN to Stuart Easson Send a message via Yahoo to Stuart Easson
Default yup...

...the wire you describe would be more than adequate.

Ideally you'd space the new windings evenly around the core. When I do this I unwind the tape wound over the top of the secondaries, add the new windings, then reapply the tape.

You can also count the turns on the secondaries which will let you know how many you need to wind. In all the transformers I've (re)wound there was between 2 and 3 turns per volt.

You have a few options, depending on what you intend to use the new secondaries for:

1) Wind entirely new secondaries, just as it sounds. These should/will have complete isolation from the originals. Done this way you get 18-0 18-0, 25-0 25-0.

2) Augment the existing secondaries, this saves winding, but means the secondaries will each share a ground with one of the originals. Basically it means adding just enough new turns to get the voltage you want in series with the existing secondaries. In this case two independent 7v windings, each in series with 18v. Done this way you end up with 25-18-0 25-18-0.

3...) Permutations of the above...

Have fun

Stuart
  Reply With Quote
Old 17th November 2008, 10:42 PM   #4
00940 is offline 00940  Belgium
diyAudio Member
 
Join Date: Sep 2003
Location: Paris
Thank you a lot.

Another question. Should I wind the two wires side to side or wind them in opposite directions ? Side to side would be easier but if they go on opposite "sides" of the toroid, a possible short would be less dramatic.

Any advice ?
__________________
Ben.
  Reply With Quote
Old 17th November 2008, 11:51 PM   #5
diyAudio Member
 
Stuart Easson's Avatar
 
Join Date: Oct 2002
Location: Santa Cruz, CA
Send a message via MSN to Stuart Easson Send a message via Yahoo to Stuart Easson
Default Winding

If shorts are a possibility separated windings will perhaps work better...but...

If shorts are a possibility you should consider fixing whatever makes them a possibility ;-)

Hence my recommendation to unwind the insulating tape, then rewind it over the top of your new turns.

You can only control your windings, and my experience with toroids is that the originals are quite tightly packed, so "fixing" your new windings isn't really fixing very much...

I think optimal winding would space the turns evenly around the core, direction is more or less irrelevant, since you can simply reverse your connections to get the relative phases correct. Of course it looks much neater if the pigtails are all entering the transformer at approximately the same point, so you may get a cooler looking result by over-spacing the windings. If you want to wind two strands at a time you may find it easier to twist the two together to begin with. I recently did this with 3 strands at a time. The required 14 gauge was too stiff for my fingers, so I wound 3 thinner, more flexible strands. I used a makita cordless drill, some furniture and a dental pick to twist them together.

If you are not in too much of a hurry you can play and practice the process by simply using normal insulated multi-strand wire to judge how many turns give you what voltage etc. Plus you can try it out with wire that is more rugged and less likely to snap just because you looked at it funny. Once you have it down you can do it with the real wire and be done faster, safer with a cooler looking result.

My buddy Neil and I liked the look of the last ones we made enough to pot them in clear resin...of course then we hid them in a cool aluminum chassis...sigh.

HTH

Stuart
  Reply With Quote
Old 17th November 2008, 11:57 PM   #6
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Adjacent turns have as little as half a volt between them. Even if one of the enamel coatings is damaged the other undamaged one can easily insulate against that tiny voltage.

However, take care with wrapping windings that have a high potential between them. The insulation is really starting to work and you want as much undamaged enamel as possible between adjacent windings and between the beginning and end of the same winding.

The polyurethane used for the coating is quite tough, but don't take liberties and particularly avoid kinking your enameled wire and avoid scraping it.
__________________
regards Andrew T.
  Reply With Quote
Old 20th November 2008, 07:23 PM   #7
00940 is offline 00940  Belgium
diyAudio Member
 
Join Date: Sep 2003
Location: Paris
I just tried with the wire I've got on hand. Winding half of my wire around half of the toroid only gave me 4.5VAC (unloaded)... I'll have to order way more wire I think.
__________________
Ben.
  Reply With Quote
Old 20th November 2008, 10:33 PM   #8
aandy is offline aandy  United Kingdom
diyAudio Member
 
Join Date: Mar 2007
Location: in UK unfortunatly
important to wind around 360 deg of the transformer or the transformer will be very noisy.
This is a mistake some transformer makers do.
and they make rubbish Toridals

  Reply With Quote
Old 17th February 2009, 03:01 AM   #9
4me2ctv is offline 4me2ctv  Canada
diyAudio Member
 
Join Date: Oct 2006
More on the topic of DIY toroid secondaries. I could buy toroid cores with the primaries wound and then wire my own secondaries. The question: I need multiple secondaries capable to withstand something like 5000V for filaments for a high voltage tube bridge. So each secondary winding needs to be insulated separately to withstand high voltage. Is it possible to do this on a toroid? I think that adding all that insulation might cause a heat disipation problem? The voltage is low at 6.3V and 3 or 6 amp which makes the wire quite large. The filaments draw about 90VA total. Thanks in advance for any advise.

Adrien.
  Reply With Quote
Old 17th February 2009, 08:46 AM   #10
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
the low voltage from each winding means that turn to turn insulation is not a problem.
You have a winding to winding insulation problem.
The standard toroid is tested to about 1500V to check for winding to winding isolation. You are far in excess of this.

Use a second wrap of Mylar tape around the primary. ensure each tape wrap has >=55% overlap at every turn of tape and go around a second time. This guarantees 4 layers of insulation in addition to the standard primary insulation.

What is the voltage between the secondary windings? Do they need to be 5000V isolated from each other?
__________________
regards Andrew T.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
FS toroidal transformers royboy5033 Parts 0 22nd June 2009 08:46 PM
Toroidal SE transformers zogu Tubes / Valves 22 28th February 2007 09:28 PM
Toroidal transformers scottw Power Supplies 19 17th November 2006 10:09 AM
Best Transformers (Encapsulated Toroidal or Open Frame Toroidal) Rixsta Pass Labs 10 23rd April 2004 03:41 AM
toroidal transformers nbcd Parts 2 2nd May 2003 08:36 PM


New To Site? Need Help?

All times are GMT. The time now is 01:57 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2