Making an isolation transformer

[Rigby]

Hi.  How hard would it be to make an isolation (1:1) transformer out of enameled wire & a ferrite core?

A lot of arcade monitors I work on require isolation transformers, and it seems to me that making them myself would be something I could enjoy slightly more than I would enjoy spending $25 buying them used.

I only need 1A out the other end, but I need the full voltage.  What size/shape of core would I need, and what wire gauge?  I have plenty of parts to experiment with, and I will experiment; I'm asking in case anyone else has done the work trying this.

[kripton2035]

some information here : http://ludens.cl/Electron/trafos/trafos.html
and here : http://ludens.cl/Electron/Magnet.html

[jaycee]

You are probably best to get some EI transformer which is not welded together, seperate the laminations, and wind an appropriate secondary. The factory would primary would remain. Winding your own primary requires knowlege of the core materials and a lot of other voodoo.

[Telequipment]

I'm really interested in this as I could do with a 600 ohm X 600 ohm 1:1  Isolation transformer, for a audio EQ to the balanced modulator on am Ham radio transceiver, and I wonder could I wind it on a toroid.

[Psi]

You can wind a toroid without needing to take it apart but it gets a bit boring having to keep pushing the wire end through the hole for each turn.

If the transformer is for audio you might want to just buy one. Audio transformers are specially designed to have a near flat response which is hard to do if you wind it yourself.

[Rigby]

You can wind a toroid without needing to take it apart but it gets a bit boring having to keep pushing the wire end through the hole for each turn.

If the transformer is for audio you might want to just buy one. Audio transformers are specially designed to have a near flat response which is hard to do if you wind it yourself.

It would be for driving an arcade monitor, in my case; many such monitors require isolation transformers.  1:1 voltage ratio, and the monitor spec sheets state that 1A of current should be available on the secondary.  I can buy them for about $20-$25 used but I don't know what kind of life is left on those when I buy them.  I'd probably wind up buying them in the end, but I think successfully making one would be a worthy endeavor. 

I am not even sure about what size/type of ferrite core to use, but I'm guessing that a simple cylindrical core would suffice to start.  I'll have to probably experiment significantly with winding count and wire gauge, though.

[WarSim]

PSI is right. 
Allot of tech is in Audio transformers justifying the cost. 
  Most important design factor is the intrinsic noise.  If you are making a white noise generator great for pure tones not so great. 
  Audio transformers are also designed for specific input and output impedance matching. 
To achieve the low noise some exotic materials are used.  I knew some of this stuff but not so much now. 
Yes you can wind your own but it will be trial and error.  Unless you get lucky, plan on investing in many cores and conductors. 

This is all I can remember at the moment:
Keep the harmonics and sub-harmonics of the self resonant frequency away from the audio frequencies.  Usually done by adjusting the lacquer thickness.
Stay below a certain low percentage of the saturation level of the core.  Causes clipping and squealing etc.
Air gaps have a secondary negative effect on audio transformers. 

There is allot more and there old be some else still doing this sort of thing here, that can help allot more. 

[johnwa]

I'm really interested in this as I could do with a 600 ohm X 600 ohm 1:1  Isolation transformer, for a audio EQ to the balanced modulator on am Ham radio transceiver, and I wonder could I wind it on a toroid.

Have you tried ripping a transformer out of an old modem? I think these should be a reasonable approximation of 600 ohms. I have used some of these to break a ground loop from my computer into my stereo. I was initially a bit concerned about degradation of the audio quality, but I think they ended up being fairly flat up to at least 20kHz.

To the OP: I presume you are talking about a mains power isolation transformer? It may be possible to make something by rewinding an existing transformer, but in the interest of safety, you should make sure whatever you come up with as adequate insulation from the primary to the secondary. Using a 'split bobbin' design would be necessary, and definitely don't go unwinding a transformer and re-using the wire!

[G7PSK]

You could take two microwave oven transformers apart and use the primary windings from both and reassemble into one. Not sure what the duty cycle would be but would run for half an hour or so at a time without over heating.