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Old 15th June 2003, 01:12 PM   #11
AJT is offline AJT  Philippines
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circlotron,
i agree with what you said 100%, i handbuilt all the trannies used in my amp projects, i started out with solid state amps in the late 60's or early 70's while still a freshman in college. that time, the shops making transformers do not yet understand the solid state transformer requirements as tube amps were still very much in season then...so i had no choice but to make my own. having knowledge of transformer theory helped me make up my own trannie...though i had to dismantle a good transformer meant for tube amps to get the desired turns ratio, figuring out wire size was easy....i have built a torroid transformer which i used for a low powered leach amp...the biggest i made so far is one with an EI core with 2 1/4 center leg and stacked to about 5.5 in depth, all made by hand....
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Old 15th June 2003, 03:17 PM   #12
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Default stack depth

How deep can you stack the laminations?
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Old 15th June 2003, 04:51 PM   #13
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Default Here's the lamination that I'm interested in:

With 11 gauge wire, how deep do you suppose the stack can be?
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Old 15th June 2003, 05:08 PM   #14
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Default Re: stack depth

Quote:
Originally posted by carpenter
How deep can you stack the laminations?

I see Joan2 rolls bigger than me. The maximum I've done is EI 150 (1 1/2" center leg) with a stack of 3 1/4") I would generaly limit the stack to about 2 times the center leg size.

Last year I made 2 transformer of this size for my Aleph 4 rated at around 750 VA each. Secondaries were 12 ga.

Regarding the bobbin former what I usualy do when doing non standard stacking is splitting a standard plastic former with a jacksaw put it over the wood mandrel and fix it with some tape and I'm ready to start winding.

Big bobins should have an internal hole about 0.005" oversize regarding the lamination core to accept the poor gometry of the bobin.

If doing a non standard bobin or in instances that I don't have a standard plastic bobin former I make a former using Fish paper usualy 0.010" thick as you can see a small bobin on one of the previous pics.

The following pics show tranies for the Aleph..
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Old 15th June 2003, 05:12 PM   #15
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Bottom view...
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Old 15th June 2003, 05:21 PM   #16
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Default Re: Here's the lamination that I'm interested in:

Quote:
Originally posted by carpenter
With 11 gauge wire, how deep do you suppose the stack can be?

John, those are huge laminations, what do you intend to do?

These are for 3KVA or more, I may venture.
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Old 15th June 2003, 05:35 PM   #17
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Default Re: thanks Joe......

Quote:
Originally posted by carpenter
I've been trying to discover a way to fabricate my own large chokes using the E/I laminations approach. I've ordered 80 lbs. of 11 gauge magnet wire and will be procurring 4 very large E/I sets next weekend. Digi-key want about $250.00 each for a 100mH/10amp 35 lb choke. I hope to make four of them for $300.00. They'll create the current source for my balanced Zenlites. I'll use the inductors instead of the lightbulbs. This should boost the efficiency from 8 percent to around 40+. With the 11 gauge wire I may find that I have less inductance and more amperage capability. Time will tell.

OK now it's clear.

Still they seem a little big, but you can play with the stack hight to size them correctly.

I hope your amps are monoblocks!!!

PS,
John, you are a bold guy!!!
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Old 16th June 2003, 05:14 AM   #18
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Default I was thinking.....

Yes, I can vary the stack depth. Also, if the stack is large, this equates to more wire and then I can run more voltage before saturating. More voltage, more output.....

should be a kick

John
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Old 18th June 2003, 05:55 AM   #19
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Default well now.....

I ordered 750 I/E sets in a smaller size (7.5" x 6.5") #26 gauge. The order stacks out to roughly 14" which gives me a stack height of 3.5" apiece for the four chokes. With shipping (140 lbs cost me $65.00!!) the cost comes to $272.51. The 11 gauge wire cost me $160.00. Everything combined, I'm investing $432.51, which is a bit more than the $300.00 I had originally planned on spending. Still, four of these chokes would probably cost $1200.00 to $1400.00 from Hammond if I were to gauge cost by weight. So I'm cutting the cost by about 2/3s. I'll keep you folks posted on my results.

John Inlow
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Old 18th June 2003, 05:38 PM   #20
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Default Re: Well, I'm certainly impressed!

Quote:
Originally posted by carpenter
In fact, I might be able to fabricate a devise such as yours. Would you care to discuss further the winding technique? i.e. is it necessary to isolate with paper (or what have you) the winding layers on a choke that will see 45 volts? Do you have to oversize the bobbin to allow the E/I laminations to fit more easily. And, how do you create an air gap? If I were more well read I could ask more questions; afraid I'm still in the learing curve. I'm all eyes!

Coming back to some of your questions, tis is the way I do it, so feel fre to experiment.

Layer interleaving with craft paper or 0.002 mylar is always a good idea but I only do this for output transformers or voltages over 200/250V. Interlayer voltage difference with 45V total should be very low. To put this in perspective you see bobins in high power electric motors rated for 220VAC winded ramdomly without any winding insulation (except the varnish of the original magnet wire), but they do varnish the whole stator when bobins are finished.

On magnet wire varnish you will find different qualyties and materials though, and also doubled varnished types. But for our type of work I find the regular single varnish type good enough, at least on what I can get arround here.

If you care to varnish your finnished chokes buy a galon of air drying electrical varnish and dip the whole assembly on it. A good idea is to heat the chocke first, hanging from a piece of wire over an electrical heater to something arround 50°C or more, this will dry most moisture and will help the varnish to penetrate the winding.

Air Gap:
The way to create an air gap with EI laminations is simple, just put all the "E" from one side of the bobin and all the "I" to the other side in order to close the magnetic path.

To create the gap you just need to put a nonmagnetic separator between the E and the I. Doing this you will be creating a double gap since you are sepatating the central core (full magnetic path) plus both 1/2 outer magnetic path.

So, if your able to calculate a certain gap you should divide by 2 to get the correct physical amount of the gap for EI chockes.

The problem you will have is to hold the magnetic structure. The esay way is to use a frame as you can see on commercial products, but on big and nonstandard pieces such as you are doing this will be something you will have to work on your own. Not difficult though.

I'll show a pic of a gapped choke, for a LP filter, I did reacently. this was for testing purposes but I still have it like this.
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