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Kizmo

Sun Jul 22 2007, 03:28PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

Sulaiman wrote ...

1) Clean the laminations with a solvent such as petrol (gasoline) rather than scratch them up

2) Clean up and save the secondary wire - thick rectangular copper for winding is very useful
.....Coilgun, ring launcher, Tesla Coil primary ........

3) Decide what I want the final transformer for.
Here are a few suggestions with possible output requirements;
3.1) Jacobs Ladder. 5-0-5 kVrms to 10-0-10 kVrms

3.2) Spark Gap TC. 5-0-5 kVrms to 10-0-10 kVrms

1. Done
2. Done, got several meters of 8x3mm copper wire

Something like TC powersupply or Jacobs ladder (or both..) are in my mind. 10-0-10 kVrms could be done under oil?

Here are some measures from naked core before disassembly:

I saw somewhere this kind of setup with UI core:

I could use same kind of structure?

EDIT: I just realized that im running out of space here so 5-0-5 is more doable IMO

Sulaiman

Sun Jul 22 2007, 04:22PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Yes you could do that;
if you re-assemble the cores nicely there's no need to re-do the primary,
just put two 5kV (or 10kV) windings on the other side.

Marko

Sat Jul 28 2007, 06:46PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hey, this is a beautiful core.
I would definitely save the primary (it is very nice) and build the secondary completely on the other side. Why you think to use half of the primary? Don't you have 230V available?

If you have the remaining bobbin you could also use it as a base for your secondary, although it will need a lot more insulation to be safe.

Kizmo

Sun Jul 29 2007, 05:57PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

I will use the old primary which has 229 turns to be exact. It is wound with quite thick wire (measures with lacquer slightly over 2mm). New secondary will be done with .20mm wire. How primary winding wire thickness affects to transformer features?

I had little shopping moment and already have these:
- 3.6kms (2.23 miles) .20mm (AVG 32) copper wire
- 0.05mm mylar sheets
- Thin urethane based lacquer for metal/plastic surfaces

My homemade winding machine (old lathe) is also operational, i have cheap step counter as turn counter. I Will take some pictures when things get rolling. (Ill start by making one half of sec winding)

Sulaiman

Sun Jul 29 2007, 06:44PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

The amp.turns for the secondary are usually a tiny bit less for the secondary than the primary,
and the current capacity of a wire is proportional to it's cross-sectional area,
so assuming your 0.2 mm wire is (like mine) actual copper diameter
and the primary is 1.8mm actual copper diameter
Then Ns = Np x (1.8 / 0.2)^2 = Np x 81
So an "ideal" transformer using 0.2mm wire would have 229 x 81 = 18549 turns
and a no-load voltage of 230 x 81 = 18630 Volts rms.

I'd be tempted to go with TWO secondaries of 10,000 turns each,
with an output voltage of 10-0-10 kVrms.
Under oil this transformer should be ok to 2500 W easily.

Kizmo

Mon Oct 01 2007, 07:03PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

Well, back to the old topic :)

I dont have anymore that core which i planned to use (actually i have it but it works as ballast now)

BUT i got even bigger core and some new ideas. I made one prototype like this:

Primary winding has too much turns still (im aiming to around 0.9V/turn). Each 'loop' has cross-section area of 18cm^2 -> inside the primary winding 36cm^2. MOT secondary represents HV winding and brown 2-turn coil is for measuring volts/turns ratio. Primary is done with AWG12 copper wire mainly because it was very cheap (10eur/200m from flee market).

So, what do you think, is there possibility that this could work, plan is that there will be 4 separate 5kV windings, two per 'loop'

Sulaiman

Mon Oct 01 2007, 08:13PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I wouldn't split the core like that;
I'd do it like in the drawing that you posted Sun Jul 22 2007, 04:27PM

why?

each secondary winding in your new arrangement would get 1/2 the primary flux
so each secondary would require 2x the number of turns compared to the drawing of Sun Jul 22 2007, 04:27PM
for a given voltage.
You will be using more wire than neccessary hence heavier, costlier and most importantly, less efficient.
AND
the flux coupling between primary and secondary would not be as good
so the output will appear to have some inductance in series with it
reducing the maximum output.

The old true and tried methods are often best!

Shaun

Mon Oct 01 2007, 11:57PM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

There's a reason why E-core transformers have both windings on the center part (see MOT). If you trace out the magnetic circuit in the core(s) you will see that half of it is essentially a "short". As Sulaiman said, the secondary only gets half possible flux.

Kizmo

Sat Jan 26 2008, 12:04PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

Now its finally time to actually *do* something, not just speculate :)

Recently i acquired even bigger core, this time it has a lot of space for windings. This will be the final thing:
http://koti.mbnet.fi/kizmo/misc/muhennin/220108/kokovertailu.jpg

It measures outer dimensions of 25cm x 25cm x 8cm and has cross-section area of 40cm^2.. and weights like hell for my broken back.

Today i will assemble that core with polyester resin. I haven't decided yet will it be 'dry' or oil insulated thing, it depends which i will get easier; high voltage mylar/kapton plastic or proper transformer oil. I have build several tools for assembling this core, it wont be easy to align laminations exactly when you have only 10 minutes before resin starts to harden. So everything *must* be dead-on planned and built.

Main points of design:

- 240V/400V primaries
- Total secondary voltage 15kV-20kV
- It must be constructed so that if(when) sec. insulation fails, i can disassemble it for repair without jackhammer
- Oil is not problem, but it does make things a bit oily.. eww

Dr. Dark Current

Sat Jan 26 2008, 12:29PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Kizmo, that's scary, where did you get that core? O_o

And what do you plan to use the xfmr for when it's finished?

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