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Kizmo

Sat Jul 21 2007, 05:21PM

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

I decided to take laminations apart, it was a lot easier than i first thought:

Sulaiman

Sat Jul 21 2007, 05:55PM

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

GOOD !

Now is the tine to look for a suitable container for the transformer and oil.
To save on oil and weight the container should be as small as possible.

That's a fantastic core and primary you've got there
worth making a good transformer.

Kizmo

Sun Jul 22 2007, 08:55AM

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

Transformer is now fully disassembled and it was success, all laminations are ok. Now i need to scrap all loose lacquer away.

Lets talk about transformer design, i know that there is a lot of math involved.

Specs of this core are following:
- 30.5cm^2
- 50Hz
- transformer was rated at 1200VA

I have lots of 0.20mm copper wire and im planning to make secondary HV winding with that stuff. What i need to know (or calculate) to get values for primary winding? Good www-site about transformer design for dummies would be great :)

Dr. Dark Current

Sun Jul 22 2007, 09:16AM

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

Kizmo wrote ...

What i need to know (or calculate) to get values for primary winding? Good www-site about transformer design for dummies would be great :)

(edit, I probably got something wrong)
Wrap 10 turns around the core, turn the transformer on, measure voltage across these 10 turns, divide by 10 and you have the volts/turn for your core.

Finn Hammer

Sun Jul 22 2007, 10:23AM

Registered Member #205 Joined: Sat Feb 18 2006, 11:59AM
Location: SkÃ¸rping, Denmark
Posts: 741

I am wondering about 2 things you wrote in the first post:

You write that there are 90 turns on the primary and that you intend to use half of it.
90 turns sounds unreal, a core like this will support around 0.9 volts per turn, so for 240 volts in, there should be 270 turns.

How to determine the total voltage sec. out:

You have 0.2mm wire, which probably measures 0.24 with lacquer?
Get some 0.05 mylar sheets to insulate each layer.
Each layer will fill 0,3mm
Measure how thick the total coil can be and divide with 0.3, you have number of layers.

Amount of turns per layer:
You cannot wind all the way to the end, but need to make some space for insulation. so the bottom layer will be like 10mm shorter than the core window, and the top winding will be like 40mm shorter.

________ooooooooooooo_________
_______oo ooooooooooooo________
______ooooooooooooooooo_____ __
_____ooooooooooooooooooo______
____oooooooooooo ooooooooo_____
___ooooooooooooooooooooooo____

In average, the windings will be 25mm shorter than the window length.
Subtract 25mm from window length, and divide by 0.25 to give windings per layer. now multiply by total layers, to give total amount of turns.
Multiply by 0.9 to give RMS winding voltage, and 1.41 to give peak voltage.

Hope this helps.

Cheers, Finn Hammer

Kizmo

Sun Jul 22 2007, 01:02PM

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

Finn Hammer wrote ...

You write that there are 90 turns on the primary and that you intend to use half of it.
90 turns sounds unreal, a core like this will support around 0.9 volts per turn, so for 240 volts in, there should be 270 turns.

I was wrong with that, i thought first that there were only 1Â½ layer of primary winding but there was 3Â½ layers. So target should be around 0.9V/turn.

I haven't fully understand how important that Volts/turn ratio is. Im guessing it has something to do with efficiency/iron losses?

Sulaiman

Sun Jul 22 2007, 01:56PM

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

A couple of thoughts;

1)
Do you really need 20 kV rms
less voltage = much easier insulation.
Consider the final design of whatever it is that this transformer is going to power.

2)
No matter what voltage you decide on
it would be much easier to insulate/protect from corona
if you split the secondary in two.
e.g. Instead of one 20 kV winding (0V and 20kVrms)
use two windings, with a center-tap to ground/earth/0V (10-0-10 kVrms)

Kizmo

Sun Jul 22 2007, 02:03PM

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

Well, as you can see, this is my 1st DIY transformer project so please be patient - and im open for ideas - how you would do this :)

Finn Hammer

Sun Jul 22 2007, 02:39PM

Registered Member #205 Joined: Sat Feb 18 2006, 11:59AM
Location: SkÃ¸rping, Denmark
Posts: 741

Kizmo wrote ...

I haven't fully understand how important that Volts/turn ratio is. Im guessing it has something to do with efficiency/iron losses?

It has to do with flux density in the core.
A ferromagnetic material has a high permeability, therefore it increases the inductance of the coil that surrounds it. This permeability is linked to the flux density, in a way that is described by the B-H curve.
Initially, the permeability is low, than it increases and stays high untill the flux density reaches typically 1.6 Tesla (typical nos for transformer lams.)
Beyond 1.6 T, the iron saturates, and the permeability starts to drop.
If you apply more volts per turn than the core can handle, the flux density increases beyond the saturation level.
Then the inductance starts to drop, the inductance decreases, and too much current starts to flow.

The volts per turn ratio is the only parameter you need to know, to make a 50Hz transformer work.

The real beauty of a transformer is, that the primary coil has enough inductance to keep the current low, when the load reflected from the secondary is low.

How long is the winding window, and how wide is it from secondary core to primary winding.?
I`d like to teke a shot at a layout.

Are you still determined to put it under oil?

Cheers, Finn Hammer

Sulaiman

Sun Jul 22 2007, 03:03PM

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

I would;

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

3.3) Isolation Transformer. Dis-assemble a second transformer and use two primaries on one core for 230:230 Vac

3.4) Experiments with inductance; Bolt all the "U" sections together and bolt all the "I" sections together,
Put back the primary and secondary windings on the "U" section

3.4.1) with a 1.5V battery feel how powerful the "I" section is attracted to the "U" section for the two different coils.
3.4.2) put a neon across the 230V winding and briefly apply a 1.5V battery to the 12V winding,
with and without the "I" sections.
3.4.3) measure the current into the coil using 230Vac on the 230Vac winding
with different airgaps between the "U" and "I" sections
Consider how this could be used in series with a second transformer for current-limiting.

Requires current limiting

Anyone else got any good ideas for Kizmo ?

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