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Andre

Tue Dec 11 2012, 11:35PM

Registered Member #6921 Joined: Wed Sept 26 2012, 07:47PM
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I'm building the secondary of the transformer, and it seems the smaller the width the lower the current on the primary, how many turns per layer should be in the secondary without having to put tape in between layers? is there a formula to calculate that?

Patrick

Wed Dec 12 2012, 04:08AM

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

Andre wrote ...

how many turns per layer should be in the secondary without having to put tape in between layers? is there a formula to calculate that?

i use planar ferrites for high cross section, but low magnetic path length...

but yes, your talking about layer to layer insulating. that means the breakdown of your mag wire, times the volts per turn between any layer and the next layer its in cotact with. typically youd find your Volts per turn, then the two farthest turns arprt that still youch each other, and your de-rating of the breakdown for your insulation.

so if your : (just an example)
V per T = 10v
turns = 70
Vbrk = 3kv

then youd choose your derating factor, lets say 1/3 of Vbrk.
then 10 * 70 =700v which is less than 1000v. so in this case you might get away with no layer to layer insulation.

however in principle, i always use interlayer insulation (and vacuum drawn oil or epoxy, if possible), its just too iffy to make some difficult transformer then burn it down.

single layer transformers are easier to make and effective as Steve Ward has demonstrated, but you need big cores for high V per T, and a long enough central leg to get enough turns to be useful. but for single turn transformers, you only need turn to turn, end to end, and end to core insultating condition to be met.

remember, transformers are proportional compromises of advantage and disadvantage from and of many factors.

Andre

Thu Dec 13 2012, 03:36PM

Registered Member #6921 Joined: Wed Sept 26 2012, 07:47PM
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so what voltage should not exceed per layer? I have a flyback transformer that I open it has about 40 layers with tape in between and it has 63 turns per layer, is there a formula, or how do you pick the magnet wire for it. how do you decide when to put tape and whats the width it would work the best to get to 40KV cause I will like to do with less insulation as possible not to put it every single layer

Ash Small

Thu Dec 13 2012, 04:09PM

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

Andre wrote ...

so what voltage should not exceed per layer? I have a flyback transformer that I open it has about 40 layers with tape in between and it has 63 turns per layer, is there a formula, or how do you pick the magnet wire for it. how do you decide when to put tape and whats the width it would work the best to get to 40KV cause I will like to do with less insulation as possible not to put it every single layer

Well, first thing is to ascertain the breakdown voltage of the insulation (the enamel coating on the wire).

This varies considerably. Manufacturers commonly produce enamellel wire with 1, 2 or 3 coats of enamel.

I did describe recently in another thread how to add more layers of enamel to wire.

Until you've ascertained the breakdown voltage of the enamel coating on the wire you intend to use, it's difficult (impossible) to do any further calculations regarding added insulation between layers.

Andre

Thu Dec 13 2012, 04:24PM

Registered Member #6921 Joined: Wed Sept 26 2012, 07:47PM
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I'm using the quad coating, if you look in this datasheet

and scroll down to MW83-C that's the one I'm using
I couldn't find the breakdown of the enamel

Ash Small

Thu Dec 13 2012, 06:03PM

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

Maybe you should try E-mailing the manufacturer at **link** and ask them?

Otherwise it's time to devise a method of checking the breakdown voltage for yourself.

Andre

Thu Dec 13 2012, 07:25PM

Registered Member #6921 Joined: Wed Sept 26 2012, 07:47PM
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the minimum voltage breakdown is 3.4KV, so how many turns I can do per layer without insulation to get to 20kV? or to have the minimum amount of insulation

Ash Small

Thu Dec 13 2012, 08:34PM

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

Andre wrote ...

the minimum voltage breakdown is 3.4KV, so how many turns I can do per layer without insulation to get to 20kV? or to have the minimum amount of insulation

Well, the next question is 'how many volts per turn?'

This will mainly depend on the cores you decide to use, and their cross sectional area. The larger the CSA, the higher the volts per turn.

I can't remember the formula offhand, but I'm sure someone here will, otherwise there are several threads here on the subject. There is also 'google'.

Andre

Thu Dec 13 2012, 09:14PM

Registered Member #6921 Joined: Wed Sept 26 2012, 07:47PM
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Ash Small wrote ...

Andre wrote ...

the minimum voltage breakdown is 3.4KV, so how many turns I can do per layer without insulation to get to 20kV? or to have the minimum amount of insulation

I have no idea what you are talking about , I will think the widest the transformer the highest the Voltage per layer, so I was looking the maximum turns I can do per layer before it breaksdown. or the maximum voltage I can have per layer,

Ash Small

Thu Dec 13 2012, 10:38PM

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

Andre wrote ...

I have no idea what you are talking about , I will think the widest the transformer the highest the Voltage per layer, so I was looking the maximum turns I can do per layer before it breaksdown. or the maximum voltage I can have per layer,

Well, the maximum turns per layer will depend on the volts per turn. If you have 1V per turn you can have ten times as many turns per layer than you can have if you have 10V per turn.

But, if your cores are only good for 1V per turn, they will have 1/10 times the CSA as a core that allows 10V per turn, so you'd be very unlikely to be able to fit ten times as many turns on it, due to it's smaller size.

As someone else pointed out above, if you go for very large cores, you may get away with only one layer, if the diameter of your wire is small enough, but there then comes a point where the voltage could be high enough to jump along the one layer and short.

I'm currently working on an Xformer that will hopefully give 50kV on the secondary, but I'm having to sandwich two sets of the largest cores I could get, in order to get 30V per turn, although this won't be driven in flyback mode.

I think you'd need to specify other parameters, like the current you want, which will determine diameter of wire, size of available cores, which will determine volts per turn, etc.

Until you know the volts per turn, diameter of wire, dimensions of core, etc, it's impossible to ascertain much else.

EDIT: most of the HV Xformers built here have pancake secondaries, to cut down capacitance. They have several secondaries connected in series, so the voltage between layers isn't a great deal.

Maybe you should read up on what others have done here first?

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