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Author Topic: DIY Mains Transformers  (Read 2463 times)
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metal
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« on: August 17, 2012, 02:43:35 14:43 »

Hi,

It all started here, and the full description can be found here. The nice thing is that this guy created a software as well. I think that the software can produce both, RMS and peak calculations, it depends on the application for the which the transformer is made. The site also offers bobbins plans, I found errors in these plans, so I corrected them, added useful images at the end and attached in this post.

Other pages I found interesting are Winding Your Own Transformers and DIY TRANSFORMERS. These sites have different wire gauge/ current from the Portuguese DIY page. I don't know the reason for this difference in the charts!?

Finally, I found a software that I think is the best. It deals with different lamination types, and gives true wire gauge based on peak current, not RMS, which will result in larger cross-sectional transformer area.

I am truly confused!!! Calculations are kinda different, the Portuguese guy has his own wire gauge charts!?
« Last Edit: August 18, 2012, 04:26:50 04:26 by metal » Logged

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solutions
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« Reply #1 on: August 18, 2012, 06:52:45 18:52 »

The Portuguese guy's wire charts seem to be exactly half the power dissipation (I^2) of the WYOT site.

This implies either a lower temp rise due to insulation limits (one may be bare wire, the other enamelled) or a safety factor of 2. With that, I'd say the Portuguese table is BARE wire and the WYOT is enamelled.

But I'm guessing, beyond the 2x power observation.
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borberk
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« Reply #2 on: August 18, 2012, 07:18:51 19:18 »

Transformer Coil Former can be asembled from 6 parts.
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solutions
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« Reply #3 on: August 18, 2012, 07:42:23 19:42 »

Does anyone have drawings for a coil winder? One you've used and that is good for many types of cores (ideally with a turns counter)?
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metal
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« Reply #4 on: August 18, 2012, 08:43:28 20:43 »

The Portuguese guy's wire charts seem to be exactly half the power dissipation (I^2) of the WYOT site.

This implies either a lower temp rise due to insulation limits (one may be bare wire, the other enamelled) or a safety factor of 2. With that, I'd say the Portuguese table is BARE wire and the WYOT is enamelled.

But I'm guessing, beyond the 2x power observation.

Gauge 25 in Portuguese chart has spprox. the same current for gauge 24 in WYOT chart. I don't know if you have already noticed that the current in WYOT chart is divided by approx. 1.414 compared to the Portuguese chart, what do you think? So, gauge 24 in the Portuguese chart is 0.8A / 1.414 = 0.567A in WYOT chart. I still can't guess what insulation grade the Portuguese guy used.

Looking at the first example given in the Portuguese page, he needs 60V 4A, so the transformer power is 240W. Why did he divide peak power on RMS voltage? Does this justify the currents he used in his chart?

I am really confused to be honest. When I use the Mains transformer calculation software with B = 1 and J = 3, the results are different. I am still not sure how to determine the current density i.e. J for the transformer.
« Last Edit: August 18, 2012, 08:45:52 20:45 by metal » Logged

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kiltro
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« Reply #5 on: August 25, 2012, 02:13:48 14:13 »

Hello!
I'm new to the forum..
I know a page full of good infos for transformer calculations.. unfortunately it is in Italian but if you ask I can help with translations (it's my first language)
http://digilander.libero.it/giunchifabrizio/

Does anyone have drawings for a coil winder? One you've used and that is good for many types of cores (ideally with a turns counter)?

I have 2 pdf for this, one come from the same page and it is in italian of course.. (it's the "bobinatrice" file under the "scarica" section), the other is in english but I've seen it's already posted here:
http://www.sonsivri.to/forum/index.php?topic=2224.0

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metal
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« Reply #6 on: August 25, 2012, 10:03:05 22:03 »

This page seems to be for audio output transformer.

I think it is OK to follow the Portuguese plans, provided the transformers are used for Audio amplifiers, not class A, of course. If any one needs more help on the topic, please put questions here. It is also important to read this page to understand how things really work.

Any way, I came across a nice plan for a coil/transformer winding machine that uses a digital display to show the windings number, I have been trying to find it again for more than a week now... silly bookmarks..

BTW, this page is very important because at some phase, you will buy the magnet wire, the guys will ask you about the weight, and will look at you in a strange way when you mention the length ; )
« Last Edit: August 25, 2012, 10:07:22 22:07 by metal » Logged

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kiltro
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« Reply #7 on: August 26, 2012, 09:39:31 09:39 »

This page seems to be for audio output transformer.

If you refer to the Italian page it also contain infos for PTs, auto transformers, and 3 fase transformers
http://digidownload.libero.it/giunchifabrizio/_private/Manuale%20Trasfo.pdf
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Tech_n
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« Reply #8 on: November 08, 2012, 08:21:59 20:21 »

For those who understand German.

http://www.jogis-roehrenbude.de/Transformator.htm


I used plain baking paper as insulation between every winding layer.
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Gallymimu
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« Reply #9 on: November 08, 2012, 09:09:14 21:09 »

For those who understand German.

http://www.jogis-roehrenbude.de/Transformator.htm


I used plain baking paper as insulation between every winding layer.

Typically you would use NOMEX, but I guess baking paper is great if you don't need any safety approvals Smiley
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« Reply #10 on: November 08, 2012, 09:28:52 21:28 »

Well, if i had access to better insulators at that time, sure i would use them. But the paper insulation was put between ever layer of windings. I seems unnecessary when using good enamel wire, but I did it for sure. I havent seen this style of insulation on newer transformers. For the insulation between primary and secondary winding I used some paper and then some wraps of a heavy wax impregnated cloth.

I checked the insulation with about 2kV AC.
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Gallymimu
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« Reply #11 on: November 08, 2012, 10:43:37 22:43 »

Well, if i had access to better insulators at that time, sure i would use them. But the paper insulation was put between ever layer of windings. I seems unnecessary when using good enamel wire, but I did it for sure. I havent seen this style of insulation on newer transformers. For the insulation between primary and secondary winding I used some paper and then some wraps of a heavy wax impregnated cloth.

I checked the insulation with about 2kV AC.

I was just teasing, honestly the baking paper is a great idea!  I've actually had issues with large mains transformers that didn't have at least mylar wrap around each set of windings.  The enamel is pretty delicate.  I think our problem was transformer survival through shipping with bare enamel coating between layers.  These were big 60lb toroid transformers we were working with so small bumps could have big impacts.
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