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Selfwound 50hz HV transformer

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LAN_403

Omicron

Thu Mar 02 2006, 02:07AM

Registered Member #131 Joined: Fri Feb 10 2006, 09:25PM
Location:
Posts: 185

Remember how high current these things are. At high voltage one shock could be your last, on the outer hand have fun!

Steve Conner

Thu Mar 02 2006, 10:51AM

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

Thanks Omicron, but we know HV transformers are dangerous. I had a MOT when I was thirteen, but my dad wouldn't let me plug it in. However, Reaching has already built several successful Tesla coils without blowing himself up, so I'm really not worried about him.

I'll take this opportunity to remind folks that excessive current can never saturate a transformer core: all it can do is overheat the windings. It's only excessive voltage, or too few turns, or DC, that causes saturation. If a transformer buzzes loudly under load, it's more likely due to stray flux or Lorentz forces.

Reaching

Sat Mar 11 2006, 12:02PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

hehe, a few days ago, i came across a EI 170B Core with 800watts, for about 1â‚¬ on ebay

. i thought it would make a great high voltage transformer for teslacoil use.i want something like 10kV 80mA or so. heres a pic in comparisation with my first hv transformer

John

Wed Aug 02 2006, 07:23PM

Registered Member #327 Joined: Sat Mar 18 2006, 07:47PM
Location: Belgium
Posts: 6

I tried rewinding a transformer, but after a short time it flashed through between the outer winding and the core. Any suggestion what's best to use for insulation ? It's used at 10 Kv/50 Khz.

Kinds regards
John

Steve Ward

Wed Aug 02 2006, 08:32PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

I'll take this opportunity to remind folks that excessive current can never saturate a transformer core: all it can do is overheat the windings. It's only excessive voltage, or too few turns, or DC, that causes saturation.

But Steve, voltage and current are tightly knit here with ohms law

. You can look at the saturation point as determined by the V*s/turn product, but i often prefer to simply calculate the maximum current that should be passed through the winding that causes saturation (because its often easier for me to hook up a CT than it is to isolate my scope and look at the voltage directly). Though i admit, even this has its flaws.

Reaching, why dont you wind a test 10 turn primary (you can simply remove your bobbin, and just wind the 10 turns on there, nothing else), and make a plot of input current vs input voltage. If the core isnt saturated, it should look linear (V=iZ), but once it starts saturating, you should see current increase much faster than the voltage. If you make a visual graph of this, it is easy to see what the maximum V/turn should be at 50hz. Remember, you will only need a few 10's of VAC input for this test!

Anyway, nice transformer. I make my own too, but i use ferrite instead

Hazmatt_(The Underdog)

Wed Aug 02 2006, 11:34PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

If you want to know more about the properties of a transformer, I have written up an article for the wiki. You will need a wattmeter for the analysis though.

J. Aaron Holmes

Thu Aug 03 2006, 01:36AM

Registered Member #477 Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546

Wow, sweet! Great to see some success with amateur transformer making, Reaching! I've often thought about trying my hand at it, however finding a good core seems like an issue. Dialing the geekiness down a bit and buying a big C (C-I?) core from a local transformer manufacturer might make life easier. I've seen big neon bombarders built on cores like that. That way you could just wind the thing right on the steel and dispense with the mandrel.

I sawed the windings off a 15kVA pole pig some years back, thinking I'd use the core laminations for a ballast choke, however with the way they're bent into C's, getting anything useful out of them turned out to be really hard! Most of the lower-V higher-KVA cores I've seen (240-, 480-, 600V distribution transformers) are always coated with something, so I've always dismissed the idea of trying to reuse one of those for anything.

I'll have to check with a couple of the local custom transformer joints and find out how much they want for a C core capable of a few KVAs and with a really big window for some serious stacking of windings

It'll probably be more than I want to pay, but it can't be *too* terrible, right? That would sure make experimenting with transformer winding a breeze!

Regards,
Aaron, N7OE

Simon

Thu Aug 03 2006, 04:13AM

Registered Member #32 Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549

I gave Part Scavenger some instructions for transformer making (with formulae). It seems like he's done about as much with them as me so far: very little.

If any of you would like to try this guide, PM me. I'd really like to have someone give it a good go and tell me how well it works.

I know that sounds lazy of me but I also know there are others on this board with more time for this who'd be enthusiastic to try.

dan

Thu Aug 03 2006, 04:55AM

Registered Member #223 Joined: Mon Feb 20 2006, 06:42PM
Location: Ottawa, Ontario, Canada
Posts: 125

Hmmm... Let me think about this for a second. Winding 10kâ€™s of turns by hand sounds like hours of fun. Grin

Unless I came up with something automated or at least semi-automated I don't think I would want to make my own HV transformer. Maybe I could build a rig that uses steppers to do the winding part and just have a buzzer ring every time it's done a layer so I can add the insulation and hit start again. It would be something interesting to try assuming I could find the materials/time.

Nik

Thu Aug 03 2006, 05:40AM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

I have a core from a ligthing ballast (400w) and only after I had it unwound I fond there was a peice punched out. Can any one tell me if this will severaly limit the amount of power I can put throug this? (there are 2 shunts that were between the windings that are not in the picture)

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