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Power transformer. Is this OK for electrostatic shield?
Power transformer. Is this OK for electrostatic shield?
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Old 20th December 2017, 07:59 AM   #1
Elerion is offline Elerion  Spain
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Default Power transformer. Is this OK for electrostatic shield?

Hello everyone.
I'm building my first large power transformer.
By "large", I mean bigger than 100 VA.
I'm using a split bobbin, but there're three secondary windings.
So I decided to add an electrostatic shield between primary and one of the secondaries (which go together on one side).

I used a strip of adhesive copper foil, with a wire soldered on one end, and the other one just half a centimeter appart from making a complete loop. Is it OK?
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Old 20th December 2017, 09:28 AM   #2
infinia is offline infinia  United States
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You've completely defeated the advantages of a split bobbin for creepage and isolation !
The primary copper seems small proportionally. or I wonder if the oversized copper on all the secondaries pushed your XFMR design over the edge, so to speak. Did you ever find out the max VA's for your core size?
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Last edited by infinia; 20th December 2017 at 09:42 AM.
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Old 20th December 2017, 09:53 AM   #3
Elerion is offline Elerion  Spain
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Quote:
Originally Posted by infinia View Post
You've completely defeated the advantages of a split bobbin for creepage and isolation !
I know, but this is the bobbin I have for this stack size.
It is a 150 VA for tube amplifier. One of the secondaries is high voltage, and bigger than the primary.
There will be some bobbin height left, but not as much as you might think.

The question is, is the electrostatic shield a valid one? Will it work?
Would it be OK if the copper foil ends touch each other?
I know that many people just lay a single layer of wire and connect only one end to ground (and it is important to not connect the other end). But it is easier for me to do like this.
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Old 20th December 2017, 10:03 AM   #4
Kay Pirinha is offline Kay Pirinha  Germany
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Quote:
Originally Posted by Elerion View Post
Would it be OK if the copper foil ends touch each other?
No. The ends need to overlap, but with isolating material in between.
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Old 20th December 2017, 03:51 PM   #5
AndrewT is offline AndrewT  Scotland
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a balanced design would have equal volume of primary to total of all the secondaries.

Your primary should fill the first window.

All your secondaries should fill the second window.
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Old 20th December 2017, 04:22 PM   #6
infinia is offline infinia  United States
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Quote:
Originally Posted by Elerion View Post
I know, but this is the bobbin I have for this stack size..
I like split bobbins, I think they provide superior isolation over an electrostatic shield for low to mid-band. My point being is you should use it properly E.g. keep the secondaries only on one side.

Electrostatic shields are often a waste of effort with a poor overall (system)grounding /measurement plan. what is yours ?
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Old 20th December 2017, 05:03 PM   #7
Elerion is offline Elerion  Spain
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Quote:
Originally Posted by AndrewT View Post
Your primary should fill the first window.

All your secondaries should fill the second window.
Sure. But I have only limited variety of wire and bobbins.
Also, all secondaries won't fit in this core/stack.
This design is the best I could come out with.
If it works fine, then that's ok for me at this point
More and better will follow
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Old 20th December 2017, 05:10 PM   #8
noSmoking is offline noSmoking  United States
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Power transformer. Is this OK for electrostatic shield?
Hi,
Try this google homoludens transformers
The link went 404 when I tried to put it up here
Lots of good reads on this site.
I built my first transformer from this information !
Have fun I do !
Merry Christmas !
NS

Last edited by noSmoking; 20th December 2017 at 05:17 PM. Reason: link went 404
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Old 20th December 2017, 05:24 PM   #9
noSmoking is offline noSmoking  United States
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Power transformer. Is this OK for electrostatic shield?
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Quote:
Originally Posted by noSmoking View Post
Hi,
Try this google homoludens transformers
The link went 404 when I tried to put it up here
Lots of good reads on this site.
I built my first transformer from this information !
Have fun I do !
Merry Christmas !
NS
Maybe this will work....... Homo ludens electronicus
look under
Tutorials and other stuff

Last edited by noSmoking; 20th December 2017 at 05:27 PM.
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Old 20th December 2017, 07:11 PM   #10
Elerion is offline Elerion  Spain
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Yes, very interesting page. I already knew about it, and I also recommend it!
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