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DC Resonant Charging Tesla Coil

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Ash Small

Sat Mar 07 2015, 01:41PM

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

A DC flyback has several internal diodes connected in series with the windings.

I think you could use an AC flyback and doubler with the series resistor instead of using resonant charging. I think it makes more sense if using a flyback, this would avoid the need for a choke and de-Q-ing diode, but see what others think

Edit: I'll post a schematic of my design later if you like. I'm posting via my phone at the moment

ZakWolf

Sat Mar 07 2015, 07:02PM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

Ash Small wrote ...

A DC flyback has several internal diodes connected in series with the windings.

I think you could use an AC flyback and doubler with the series resistor instead of using resonant charging. I think it makes more sense if using a flyback, this would avoid the need for a choke and de-Q-ing diode, but see what others think

Edit: I'll post a schematic of my design later if you like. I'm posting via my phone at the moment

Thanks Ash, Im confused now though. Why use a doubler when I can use the choke to double the voltage? I guess the doubler would be much easier and cost less. In any case I want to play around with different options and see how each of them perform.

I rolled some caps, there bigger then my hand. 130cm L x 50cm Dia (5 1/4"L x 2" Dia)

Ash Small

Sun Mar 08 2015, 12:46AM

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

I rolled my own caps too and they worked perfectly. I think you'd be wasting your money on a choke, but see what others think. By all means do it to experiment with inductors, I do that myself

I'll post my schematic tomorrow when I'm sober for you to look at, maybe you wonn't be so confused then

ZakWolf

Sun Mar 08 2015, 01:28AM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

Ash Small wrote ...

I rolled my own caps too and they worked perfectly. I think you'd be wasting your money on a choke, but see what others think. By all means do it to experiment with inductors, I do that myself

I'll post my schematic tomorrow when I'm sober for you to look at, maybe you wonn't be so confused then

Thanks Ash, appreciate it

I measured the capacitance it read 11.57nf, that's with two layers of overhead projection sheets. From what I read roughly each sheet is rated for 14kv??? Im pretty sure that rating varies when used with different frequencies, what would you say a good voltage rating would be with two sheets ?

Ash Small

Sun Mar 08 2015, 11:27AM

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

Here's my schematic I drew this from memory ten years after I built it. The only bit you need is the tank circuit, etc.

I've not used OHP capacitors, so can't really advise on them. I used polythene.

I don't see any reason why you couldn't use, for example, an AC flyback and tripler from an old TV, maybe?

(My circuit was designed to 'fire' under argon, so didn't need to be as high a voltage as your's will need to be.)

ZakWolf

Mon Mar 09 2015, 01:52PM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

Ash Small wrote ...

Here's my schematic I drew this from memory ten years after I built it. The only bit you need is the tank circuit, etc.

Thanks Ash, although i dont think i really understand whats happening there. Can you explain it.

Also, what is a good cap. size for HV filtering? I have never made one before and I just want to do a little smoothing after its rectified.

Ash Small

Mon Mar 09 2015, 04:39PM

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

There is no need for a smoothing capacitor in my design as the tank capacitor gets charged up instead.

When the voltage on the capacitor is high enough the gap fires, and the tank 'rings down', transferring all the energy from the primary tank capacitor to the secondary and top load.

The primary tank capacitor then charges up again from the flyback and the sequence repeats.

The resistor isn't of high enough value to restrict the capascitor from charging, but it is sufficient to stop the HF as the tank rings down, protecting the diodes, etc. You could use an AC flyback and tripler (or any number of multiplier stages) or you could just use a DC flyback. It depends on what voltage you want to charge the primary tank capacitor to.

In mine I had a 1:1 ratio between primary and secondary, but you will want a much higher turns ratio in order to achieve the voltages required for 'breakout' in air at STP.

Also, I'd suggest using a more powerful flyback driver that the single 2N3055 driver that I used.

See if you can now come up with a schematic based on the above

EDIT: As for tank capacitor value, I used 20nF, but anything from 10nF to 50 or even 100nF should be ok.

EDIT 2: This is the bit you need to look at. This has a DC flyback, but an AC one and doubler, tripler, etc would be a lot simpler than resonant charging

(It takes several cycles of the flyback to charge the primary tank cap. Newton Brawn once worked out how long it takes to 'ring down', it was a surprisingly short period.)

I might even build one of these using one of Fiddy's flybacks and a doubler or tripler.

ZakWolf

Thu Mar 12 2015, 04:29PM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

Ash Small wrote ...

There is no need for a smoothing capacitor in my design as the tank capacitor gets charged up instead.

When the voltage on the capacitor is high enough the gap fires, and the tank 'rings down', transferring all the energy from the primary tank capacitor to the secondary and top load.

The primary tank capacitor then charges up again from the flyback and the sequence repeats.

The resistor isn't of high enough value to restrict the capascitor from charging, but it is sufficient to stop the HF as the tank rings down, protecting the diodes, etc. You could use an AC flyback and tripler (or any number of multiplier stages) or you could just use a DC flyback. It depends on what voltage you want to charge the primary tank capacitor to.

In mine I had a 1:1 ratio between primary and secondary, but you will want a much higher turns ratio in order to achieve the voltages required for 'breakout' in air at STP.

Also, I'd suggest using a more powerful flyback driver that the single 2N3055 driver that I used.

See if you can now come up with a schematic based on the above

Ash the schematic you posted is what Im going for, except that the resistor will be my HV Choke.

As far as the maths go I dont think i can perform any till i get an oscilloscope... I am at a loss as far as calculations go. I know that im making a DC resonate Tesla coil so that must require the primary to be tuned (by the HV cap) to res. frequency of the secondary. Im not to sure how the inductor comes in to play as far as resonate charging goes. I know that it builds up a field while the cap is charging and at the moment the current stops flowing through it, collapses and causes it to almost double the voltage before the spark gap fires.

So, what calculation would i need to perform/what is the point of having an "X value" inductor. Is it really specific or is it just a minimum Henry rating?

I now have a multimeter and an LCR meter, still working on getting that scope though.

Ash Small

Thu Mar 12 2015, 05:05PM

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

Resonant charging is normally used with something like a couple of MOT's, around 2kW of power. Your flyback will put out ~1/1000th of that. The MOT's re-charge the capacitor 100 times a second. While a choke 'may' provide protection for the charging circuit, it will not serve any other purpose if used as you are describing. unless the smoothing capacitor is much larger than the tank capacitor.

I don't think that a flyback can keep the smoothing cap charged sufficiently to sustain resonant charging. I think a better way would be to use a doubler to get the same voltage, and charge the tank capacitor directly. The coil will 'fire' each time the tank cap voltage exceeds the breakdown voltage of the gap. I guess it will still fire several times every millisecond, certainly in that ballpark.

My design does work, I used it in my HF TIG welder, but you will need a higher voltage to achieve 'breakout' in air at STP. (This is just a question of increasing the spark gap, the flyback will charge the capacitor until the breakdown voltage is achieved. and, obviously, having a lot more turns on the secondary.)

The choke and large smoothing capacitor are not required, in my opinion.

Others may have other views

EDIT: The easiest way to 'tune' the primary tank circuit is to adjust the inductance of the primary coil. You will have to do some maths first, though.

EDIT: I think I need to re-read Ritchie's page before I'm certai that what I stated above is correct. I'll re-read it and then re-post or further edit this post.

EDIT: Yerp, I'm as sure as I can be that I'm correct.

TeslaHighvoltMan

Tue Mar 24 2015, 01:41PM

Registered Member #54545 Joined: Mon Mar 02 2015, 12:35PM
Location:
Posts: 2

Anybody already checked out this 12kW DC resonant charging system? Seems to have an amazing performance:

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