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Author Topic: Help needed to wind my own EHT  (Read 1082 times)
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Unhappy
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« on: March 14, 2014, 10:22:27 22:22 »

Dear all I wish to improve upon my tesla coil using old colour TV (CRT) EHT
which I wish to use in my colleagues sons' (ozone project) studying in second year of undergraduate course in electronics
Primary is rated for 90v to 110v 16KHz
Secondary 20Kv to 25Kv 4mA (Approx)
My problem is it is getting hot and primary burns of after 30 to 40 minutes of operation with single IRF840 driven.
I wish to increase the primary coil volts rating to be doubled for/to 220v and 1 Amp
So that it is safe for operating continuously up to two hours On time
I have tried many of the drivers available on internet but what I see is either they get costlier and Bulky/Heavy in size/volume   
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solutions
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« Reply #1 on: March 15, 2014, 10:28:00 10:28 »

So, right now,it's burning up at 100W and you want to push 200W into it?
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« Reply #2 on: March 15, 2014, 11:06:13 11:06 »

So, right now,it's burning up at 100W and you want to push 200W into it?
yeah either that or Embarrassed
I want it to not blow either the primary winding or the Driver switch working with input of 220v 16KHz
It should work for two hours at a stretch and repeat the same after a pause of say same two hours
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« Reply #3 on: March 16, 2014, 10:34:43 10:34 »

Leave the system as is at 110V and rewind the secondary, using 50kV rated insulation (yeah - good luck with that). Drop it into mineral oil for good luck.

Don't know if you realize it, but that secondary can kill you as is, let alone doubling its power output  Shocked

By the time you're done f-ing around, you would have been better off buying the right coil,IMO, because the odds of you coming out with something that meets your specs is,oh, let's say 1E-18  Smiley
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« Reply #4 on: March 16, 2014, 01:55:59 13:55 »

Leave the system as is at 110V and rewind the secondary, using 50kV rated insulation (yeah - good luck with that). Drop it into mineral oil for good luck.

Don't know if you realize it, but that secondary can kill you as is, let alone doubling its power output  Shocked

By the time you're done f-ing around, you would have been better off buying the right coil,IMO, because the odds of you coming out with something that meets your specs is,oh, let's say 1E-18  Smiley
Thanks for all the comments, dear.
Can you suggest me how to calculate the primary turns(I just need to increase the current rating in primary coil)
Secondary here is not the issue as it is already rated as per my requirement
Ferrite cores used in TV EHTs image of EHT core attached
Diameter of cyl.limb=14mm
Air Gap between limbs is =14mm
rect. limb area = 14mmX10mm

In short I wish to know how to calculate the number of turns for a particular ferrite core size/shape being two C facing each other like (2* []), accordingly I can calculate my Primary/secondary if required as I know the voltages
Pri V=220v 16khz Sec. V=25KV
« Last Edit: March 16, 2014, 02:25:04 14:25 by Unhappy » Logged
Gallymimu
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« Reply #5 on: March 16, 2014, 03:19:44 15:19 »

Thanks for all the comments, dear.
Can you suggest me how to calculate the primary turns(I just need to increase the current rating in primary coil)
Secondary here is not the issue as it is already rated as per my requirement
Ferrite cores used in TV EHTs image of EHT core attached
Diameter of cyl.limb=14mm
Air Gap between limbs is =14mm
rect. limb area = 14mmX10mm

In short I wish to know how to calculate the number of turns for a particular ferrite core size/shape being two C facing each other like (2* []), accordingly I can calculate my Primary/secondary if required as I know the voltages
Pri V=220v 16khz Sec. V=25KV


Looks like a UR core to me.

At that frequency I'd imagine your limiter is your core flux density.  Certainly if you want to increase the primary voltage your saturation flux density will be an issue.

Typically on the primary you are looking at applied volt-seconds.  This is what increases flux in the core, and as the core reaches saturation the core loss increases non-linearly.

As a first order approximation, if you double the voltage you double the number of turns to maintain the same max flux in the primary.

If your windings are getting hot, then you can certainly increase the gauge of the wire.

using 2 cores in parallel is another way to reduce the flux density and therefore your core loss at the cost of transformer size and increased use of wire, though otherwise there isn't much of a downside.

If you need a precise magnetizing/leakage inductance then it is a different set of calculations from the ones involved in the above comments.

This isn't the best resource but it has some of the equations you need and is easier than my trying to type them in this window!!!

http://www.onsemi.com/pub_link/Collateral/TND350-D.PDF

On page 16 is the basic equation for voltage, turns, and flux.  That's the only page from the PDF I'd really bother with.

This also has a decent explanation of the basic core equation for flux vs turns etc.

http://www.onsemi.com/pub_link/Collateral/TND350-D.PDF
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« Reply #6 on: March 16, 2014, 03:29:06 15:29 »

have you thought of a diode cap ladder?
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« Reply #7 on: March 16, 2014, 06:44:03 18:44 »

Looks like a UR core to me.

At that frequency I'd imagine your limiter is your core flux density.  Certainly if you want to increase the primary voltage your saturation flux density will be an issue.

Typically on the primary you are looking at applied volt-seconds.  This is what increases flux in the core, and as the core reaches saturation the core loss increases non-linearly.

As a first order approximation, if you double the voltage you double the number of turns to maintain the same max flux in the primary.

If your windings are getting hot, then you can certainly increase the gauge of the wire.

using 2 cores in parallel is another way to reduce the flux density and therefore your core loss at the cost of transformer size and increased use of wire, though otherwise there isn't much of a downside.

If you need a precise magnetizing/leakage inductance then it is a different set of calculations from the ones involved in the above comments.

This isn't the best resource but it has some of the equations you need and is easier than my trying to type them in this window!!!

http://www.onsemi.com/pub_link/Collateral/TND350-D.PDF

On page 16 is the basic equation for voltage, turns, and flux.  That's the only page from the PDF I'd really bother with.

This also has a decent explanation of the basic core equation for flux vs turns etc.

http://www.onsemi.com/pub_link/Collateral/TND350-D.PDF

Thank-you Gallymimu, You made my day.
Exactly,This is what I was looking for

I hope information provided in this document will solve my problem, will report the results as soon as I can

have you thought of a diode cap ladder?

Yes, I did, but that again is not feasible as the Diodes/capacitors to be used in EHV ladder
are not easily available here where I live
« Last Edit: March 16, 2014, 08:26:50 20:26 by Unhappy » Logged
Gallymimu
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« Reply #8 on: March 17, 2014, 01:14:31 01:14 »

Thank-you Gallymimu, You made my day.
Exactly,This is what I was looking for

I hope information provided in this document will solve my problem, will report the results as soon as I can


I hope it helps man!!!! good luck!

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fpgaguy
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« Reply #9 on: March 18, 2014, 08:47:37 20:47 »

how about an ignition coil ?

as example:

http://www.summitracing.com/parts/msd-8202

It's already packed up and you get to use safer voltages on the input half of the circuit

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