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Grooved Bobbins For Segmented Windings

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Patrick

Wed May 11 2011, 04:42PM

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

Dam, This wasnt meant to be a double post.

If you pot with silicone meant for heat dissipation, its better than air, but not as good as oil.
For wire related matters go here:

WireTronics. Even if you dont buy their wire, they give out a lot of spec information.

And you can use this tool which I use all the time for deciding wire issues:

look for this link on their main wire page:
***http://www.wiretron.com/wtsetup.exe***
(I didnt want it to be an auto-downloading link so I commented the button-link out.)

This program also gives explanations for the kind of coatings, chemical sensitivity, whether annealing or crazing is a possibility and other important factors too. (single, heavy, triple, quad and the dimensions there of etc.)

jpsmith123

Wed May 18 2011, 11:38PM

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

I took a few more measurements today: I measured the self-resonant frequency of three coils.

I very loosely coupled the signal generator (inductively) to the coil under test, and then swept the generator output while watching the scope. (I had a tektronix P6122 10x probe across the coil).

The 560 turn layer-wound coil measured about 205 kHz; the 600 turn segmented coil about 307 kHz; and the 360 turn layer-wound coil (with 26 gauge teflon insulated wire) measured about 485 kHz.

Assuming that the scope probe added about 11 pF (and subtracting that amount accordingly), this tranlates to an equivalent parasitic shunt capacitance of about 27 pF or so across the 560 turn layer-wound coil, and significantly less for the 600 turn multi-segment coil.

There's one more coil configuration that I didn't try yet, but I want to see what it looks like: a "tall and skinny" coil wound with 26 gauge teflon insulated wire. I'm going to make a different bobbin and wind one.

Ash Small

Wed May 18 2011, 11:55PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Keep us posted, IP.

jpsmith123

Fri Jul 15 2011, 01:57AM

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

Well my first attempt at epoxy encapsulation had to be aborted.

The resin and hardener should be mixed accurately, so I decided to use my digital scale. I bought the scale about a year ago and used it a few times, but I never had more than a few ounces on it. On the box, it says "500g capacity".

So I wanted to mix about 100 ml or so which would be about 210 grams. I poured what I thought would be the approximately correct amount into a cup, and behold the 500 gram digital scale turned out to be only a 100 gram scale. So I had to pour it back into the can. Of course it's so thick that I lost half of it (it stuck to the cup), and it's all running down the side of the can, and somehow it just got on everything...

And this stuff is thick. Way thicker than what I imagined it would be. It's just sloppy and gooey and messy and just a general all around PITA.

So now if I still want to do it (and that's a big if at this point), I have to go spend more money on a bigger digital scale.

Forty

Fri Jul 15 2011, 02:20AM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

couldn't you just slowly add the epoxy to the cup, and zero it at every 100g?
if the mixing directions have a volumetric ratio then you don't even need the scale, just some disposable measuring cups
the ratio doesn't have to be absolutely perfect, so long as it is mixed well.

jpsmith123

Fri Jul 15 2011, 02:28AM

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

Unfortunately zeroing the scale doesn't help. If I put more than about 105 grams on it, the display just says: "ovld".

According to the directions, the epoxy should be mixed by weight. The specific gravity is specified as being 2.1, so I can approximate it by volume, but after putting so much time and effort into the coils, I didn't want to take any chances with an inaccurate mixture.

2Spoons

Fri Jul 15 2011, 03:59AM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615

you may find the EPCOS ferrite design tool useful

,locale=en.html . Only has EPCOS cores in it of course, but still useful for getting ballpark figures for similar cores. Has a few nice things such as AC wire resistance, power transfer and air gap calculators

Patrick

Fri Jul 15 2011, 05:34AM

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

Im going to PM you soon, i have new ideas related to this thread for getting higher V/turn with fewer turns, now that im finished with summer Math-120! Im a little too tipsy at the moment! That Guinness and New Castle packs a wallop!!!

Ash Small

Fri Jul 15 2011, 08:39AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

2Spoons wrote ...

you may find the EPCOS ferrite design tool useful

Patrick wrote ...

. i have new ideas related to this thread for getting higher V/turn with fewer turns,.

Has anyone else looked at the EPCOS program yet?

I'm using these EPCOS N27 cores:

and I'm trying to work out how many primary turns I need (I'm assuming there is an optimum volts per turn ratio).

I'll be using rectified 240 V AC (peak 340 V DC), at 2.5kW per core, so I want a turns ratio of 150 (I think) for 50 kV.

I'm also puzzling over how many amps will be flowing in the primary, as, due to voltage ripple the voltage won't be constant, so it's not simply a case of using the peak voltage and power figures to calculate average current. (do I just use the RMS figure of 240 V, or will smoothing capacitors affect this?)

From looking at the EPCOS program, it would appear that I need to know all this in advance before I can input any relevant figures.

Any help would be appreciated. (Should this be in a new thread?)

EDIT: From what I can work out, the EPCOS program is telling me I need a single layer 160 turn primary of AWG 25, in order to transfer 2.5kW @ 25kHz, .No mention of volts and amps, though. I must be missing something.

EDIT EDIT: Is this where a series inductor is required, to help shape the pulse and limit the current?

jpsmith123

Fri Jul 15 2011, 03:35PM

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

That looks like an interesting tool, but for HV stuff, IMO, (especially when using the newest low-loss ferrites, at low to modest frequencies and low to modest flux densities), the most difficult issues are "mechanical" in nature; i.e., problems related to physical layout and construction and proper insulation...avoiding excessive stray capacitance and electric field enhancement resulting in corona.

2Spoons wrote ...

you may find the EPCOS ferrite design tool useful

Edit:

Ash, I think getting 50 kv off the secondary is going to be very difficult. It may be possible, but it will be a real challenge, IMO. Can I ask why so high? Is it intended to feed a CW multiplier?

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