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after how many turn on a HV transfomer you start insulation

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Andre

Mon Oct 15 2012, 03:49AM

Registered Member #6921 Joined: Wed Sept 26 2012, 07:47PM
Location:
Posts: 109

so how this transformer running at 60hz can provide 70kv?

what's the trick?
and is very small

Dr. Brownout

Mon Oct 15 2012, 04:15AM

Registered Member #2405 Joined: Fri Oct 02 2009, 12:59AM
Location: Wisconsin
Posts: 140

Its like I said a few posts back, it takes very fine wire, you are looking at probably 40 gauge or smaller wire, I dont know what core you are looking at using. However if the wire fits in the window and the flux density is below the knee saturation curve then your good to go. That small gauge wire is not easy to wind. It breaks and stretches very easy.

But like I said it can be done you have to have some pretty large end margins and as you can see on the video for that size wire you can see the exaggerated end margins, those margins take away from winding space so you must take that into account , it also looks like they are mylar layer insulation as I stated before.

Yes it can be done, its going to take a lot of wire and careful handling of the winding when you stack the core after you get the secondary wound. If you are using a stacked core make sure there are no gaps, use keepers, if you are going to weld it make sure your welds are not deep and keep them placed close to the corners ( Flux does not fill out to the corners) and you should be fine.

You did not mention what regulation you needed that also will have an effect on the size and layer insulation. The trick to good regulation is use as close as possible the same CMA(circular mills per amp) on each winding. Meaning if you are choosing wire size based on 700 circular mills per amp on the secondary do the same on the primary. You will find that you cannot always do that so you will use the next size larger and then spacing and layer insulation start playing a larger part in the regulation.

So a lot of calculations and some time but not impossible.

genious 7

Mon Oct 15 2012, 04:19AM

Registered Member #2887 Joined: Sat May 29 2010, 11:10PM
Location: Panama City, Panama
Posts: 107

For beginners, the core you linked is made out of ferrite (or so I think, didn't really checked the specs deeply). Ferrite will never work at a transformer at 30 hz. That transformer you linked uses iron laminations, which are better suited for low frequencies.

Second: bear in mind these transformers are used for Xrays in medical applications; they are typically on for periods of less than one (or maybe a few) second (whatever the exposure time is). They are not meant to be run continuously for extended periods of time

Pinky's Brain

Mon Oct 15 2012, 06:29AM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837

Andre wrote ...

and is very small

Small? I'd say the core area is about 100 times of the one you linked ...

GrantX

Mon Oct 15 2012, 09:00AM

Registered Member #4074 Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335

Andre wrote ...

so how this transformer running at 60hz can provide 70kv?

(youtube video)

what's the trick?
and is very small

I own that exact transformer, purchased on eBay from the maker of this video. It is very fragile, and must only be operated at its full voltage after being submerged under oil and having a vacuum pulled. Its designed to deliver about 7mA with a duty cycle of less than one second. Ballasted to around 80VA input its secondary windings get very hot very quickly. It also pulls an enormous unloaded current (around 6 amps IIRC) due to saturation at its full input of 120VAC. It's secondaries are wound with thousands upon thousands of turns of hair-thin wire (less than 0.1mm).

That transformer is currently beyond the capabilities of our workshop at the transformer manufacturing company I work for.

EDIT: Also it is important to note that the 70kV figure is the zero-to-peak voltage, at open circuit it produces about 49kV AC RMS at 120V input.

Steve Conner

Mon Oct 15 2012, 10:28AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

The moral of the story is, if you're going to build an HV transformer, build a big one!

Andre

Mon Oct 15 2012, 04:27PM

Registered Member #6921 Joined: Wed Sept 26 2012, 07:47PM
Location:
Posts: 109

so if I reverse enginering this transformer, this would be my calculation
N = V / (4*f*B*Ae)
V=110
f=60hz
B= about 1T for nickel iron core

Ae = I'm guesing .0004m2

N = 110 /(4*60*1*.0004)
N = 1146 on primary
from the pictures I think it runs 2 secondaries at 35KV
(35000/110)*1146 = 364363 Turns on each secondary. since it peaks at 70KV it can be 5% less turns

would this be about right?

Steve Conner

Mon Oct 15 2012, 04:38PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

The core will be grain-oriented silicon steel, they are probably pushing it nearer 2T than 1.

Andre

Mon Oct 15 2012, 04:51PM

Registered Member #6921 Joined: Wed Sept 26 2012, 07:47PM
Location:
Posts: 109

Steve Conner wrote ...

The core will be grain-oriented silicon steel, they are probably pushing it nearer 2T than 1.

but is that the correct calculation?

teravolt

Mon Oct 15 2012, 07:23PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

Hi Andre, why not use a neon sign transformer and a dublier or a ZVS flyback driver. Depending what your end result is for a thyraron and a PFN circuit to create your square pulse. What is the purpace of your output

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