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Winding multilayer coils is a big PITA...

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LAN_403

IntraWinding

Wed Apr 14 2010, 09:10PM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

Very neat! Bear in mind the viscosity and setting time when choosing a potting compound, although I should think it will get into the glass fibre tape quite easily. Are you using vacuum potting?

Alan

Patrick

Thu Apr 15 2010, 02:18AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

use a vacuum on such a nice coil Jpsmith!!!

DAM it !!! i wish i had a lathe even half that nice!

i do believe overhead transperemncies are polyester not mylar mylar is to dam good (and i would kill to get some mylar) for such a simple use. ive held off 12kVac 60Hz witha single sheet 4.5 mils thck so figuer a useful 2000-1500 volts per mil for safety factor.

-patrick

hboy007

Thu Apr 15 2010, 04:47PM

Registered Member #1667 Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 374

Here are my two cents about vacuum potting with epoxy resin: use slow-hardening expoy (24h) and you can pull a nice trick once you get a fast heater/cooler. Allow the epoxy to settle for 15 minutes under vacuum, then heat to 80Â°C for 3-5 minutes, followed by rapid cooling down to 0-10Â°C (vent the vacuum chamber, make sure the cooling process is non-condensing).

When epoxy is heated, its viscosity is drastically reduced, allowing it to soak the last few gaps when atmospheric pressure is reapplied. The temperature also boosts the polymerisation process. Starting polymerisation when the workpiece is still hot creates mechanical stress and cracks and must be avoided, hence the forced cool-down.
After cooling down, the actual polymerisation may still take the rated timespan. I've been using clear epoxy so far because I haven't found softer resin for electronic components yet (at least affordable epoxy)

jpsmith123

Thu Apr 15 2010, 05:52PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843

Well the coil came out so nice there had to be something wrong...and there was...

For a quick test, I put it on a core and drove it with a sine wave. Unfortunately, the output started rolling off at about 16 khz. (I expect it would be even worse after potting).

Since I had planned on driving the transformer at a frequency in the range of 25 to 30 Khz, I am probably not going to use this coil for anything, although I may follow through with potting it, just to get the experience.

So now I'm "back to the drawing board".

I'm going to test an experimental layer wound coil I made with teflon insulated wire, later today. If the results are not much better, then it seems the only alternative would be some kind of "pie" winding.

Patrick

Thu Apr 15 2010, 06:28PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

what are the construction numbers for this coil, ferrite diameter, wind hieght, turns per layer, layers, wire awg , and your expected volts per turn? and the like?

-Patrick

hboy007

Thu Apr 15 2010, 07:08PM

Registered Member #1667 Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 374

jpsmith123: you might want to check out the thread about intra-winding capacitance,

I think you can blame much on the core you were using

jpsmith123

Thu Apr 15 2010, 08:10PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843

@Patrick

The coil has about 70 turns per layer, and six layers; for a total of about 420 turns. Thus in order to get the 10 kv peak I was aiming for, I would need to run at about 24 v peak, per turn.

I used 28 gauge magnet wire (with a measured diameter of 0.014"), and, for layer insulation, I was using two layers of glass cloth tape (1.25" x 0.007").

The core is a ferroxcube double "U" core (U100/57/25), with a cross sectional area of 6.45 cm^2.

@hboy007

Yes, I'm quite familiar with the parasitic capacitance problem, and discussion threads about it here.
Winding this coil was an experiment that gives me a baseline to work from...it gives me a "road feel" for what I'm dealing with here.
I'm not sure what problems you're attributing to the core.

Patrick

Thu Apr 15 2010, 11:03PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

is your A sub L (nH) value to high to give you low impedeance? forsuch a large cross section?

Arcstarter

Thu Apr 15 2010, 11:43PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Patrick wrote ...

use a vacuum on such a nice coil Jpsmith!!!

DAM it !!! i wish i had a lathe even half that nice!

i do believe overhead transperemncies are polyester not mylar mylar is to dam good (and i would kill to get some mylar) for such a simple use. ive held off 12kVac 60Hz witha single sheet 4.5 mils thck so figuer a useful 2000-1500 volts per mil for safety factor.

-patrick

Mylar can standoff quite high voltage, but at high frequency it gets hot and fails very quick. It is really terrible with corona formation, so carbon tracking is inevitable. Even with 60Hz, a homemade mylar cap had tremendous corona at 12kvac.

But, if you want some thick mylar, you can check at a hobby store. They sell them for cutting stuff on, i believe. You can get a sheet about 10 inches by a foot or more that is pretty thick, likely 10 mils or more, for around 3-5 bucks. I got mine from a store called Hobby Lobby.

Patrick

Thu Apr 15 2010, 11:53PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

i need to know more about your coil! if yours doesnt work, niether will mine!

no matter how i crunch the numbers for your coil i get 0.97 Henerys of inductance and at 16Khz that equates to 1.7nF of capacitence! crap Steve Ward may have been right!!!

A sub L for your core is 5.5uH so 5.5uH X 420^2=0.97H and 1/(2*PI*root(0.97*1.7*E^-9)=16kHz

maybe you and i need to switch to aircore non-resonant transformers driven like an SMPS with CMC?

DAM IT!!!

-Patrick

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