High Voltage PSU for functional Fusor

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Finn Hammer
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Re: High Voltage PSU for functional Fusor

Post by Finn Hammer »

Matt,
2CL2FP 30kV, 100mA diodes work fine in my multipliers. They start to heat at frequencies above 40kHz, so stay below that.
These Chinese diodes are good quality, and the only option you have, unless you want to pay 20$ a piece for US made VMI diodes.
Hope this helps.
Cheers, Finn Hammer
Ali_Hassan
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Re: High Voltage PSU for functional Fusor

Post by Ali_Hassan »

Matt,

You can fine many types of Rectifier Diodes from Ali Express.

Regards
Ali Hassan
Matt_Gibson
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Re: High Voltage PSU for functional Fusor

Post by Matt_Gibson »

I went with the 2cl2fm (20kV, 100mA, 100nS). I am running a CW VM calculator that I found: https://www.extremeelectronics.co.uk/ca ... alculator/

I see that the input current is much greater than 100mA. Does this need to be accounted for?

Edit: Should add that I chose 30mA as the load current.
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Finn Hammer
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Re: High Voltage PSU for functional Fusor

Post by Finn Hammer »

Matt,

The CW multiplier over at Derek's site is a good one, for a first pass, but:
It is a single wave multiplier, and you will get a lot lower ripple by using a full wave multiplier. This is not just a theoretical point of view, because you are going to be dealing with quite some power. You could soon exeed a kW. In an ordinary circuit, the full wave rectifier is the standard, and so it should be in a high voltage multiplying rectifier for power applications.

Linear Technology has an electronic simulator called LTSpice, it is the industry standard for simulating electronic circuits, and the one I use to predict the multipliers that I make.
When you have drawn the circuit and run the simulation, You get access to voltage and current probes, ground referenced and differential, and the benefit of plotting the response on a time line, exactly like if you were measuring the finished product with an oscilloscope.

By assigning parametric values to circuit components , you can change the value of all the capacitors, or all the resistors in one instance, run simulations, and find out which values will give you what ripple, peak current in the diodes, short circuit behaviour and whatever scenario you want to investigate.

Using LTSpice will prepare you for a better understanding of the multiplier.

The time spent to master LTSpice will pay you back in dollars, when you build your multiplier, and you will rightly feel, that you own the circuit.

Below are dumps of the screen from LTSpice, with a 5-stage multiplier I have built.

Get your copy of LTSpice, build your schematic, start playing around with values and features, you will not regret it.

Udklip.JPG
Udklip1.JPG

Hope this helps

Cheers, Finn Hammer
Matt_Gibson
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Re: High Voltage PSU for functional Fusor

Post by Matt_Gibson »

Hi Finn,

I’ll check out LTSpice.

Is a full wave multiplier necessary, or will a half wave suffice? I’ve only got enough of these doorknob capacitors for a half wave.

-Matt
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Finn Hammer
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Re: High Voltage PSU for functional Fusor

Post by Finn Hammer »

Matt,

Sure, a half wave will do.


Cheers, Finn Hammer
Matt_Gibson
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Re: High Voltage PSU for functional Fusor

Post by Matt_Gibson »

Finn,

From what I’ve read/understand, the benefit for going full wave vs half wave is essentially that I reduce ripple, needing less capacitance and lower frequency. Is that correct? In a nutshell…

I’m still waiting to get the LTspice downloaded (been on company travel), so still using the calculator. Half wave is requiring me to use larger capacitors and higher frequency to reduce ripple such that I don’t have to flash over my feed through just to get to a minimum voltage to the grid.

If this is correct, I’ll have to do a bit of cost-benefit here and price shopping capacitors/diodes to see which route gives me the best outcome.
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Richard Hull
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Re: High Voltage PSU for functional Fusor

Post by Richard Hull »

The higher the frequency of any AC supplied to any multiplier, the better, assuming you can get that AC with some real power behind it and have the componenets that will work with it. 25khz is a great point used by many modern HV switchers that do not put too much of a strain on easily obtained components.

Older linear system working off the 60 hz mains directly preferred full wave as that is 120hz filtering and reduced the required capacitance needed for filtering. Stored energy in such high voltage systems is horrendous and any arcing to ground will literally tear stuff up and vaporize the surrounding gear.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Finn Hammer
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Re: High Voltage PSU for functional Fusor

Post by Finn Hammer »

Matt,

I second what Richard wrote.
The frequency is limited by the diodes, the chinese ones, where 35kHz seems to be the maximum frequency. Go beyond that, and they overheat and fail.
As far as capacitors go, I have had good results with polypropylene film capacitors.
Based on experiences from the tesla coiling community some 15 years ago, it turned out that this kind of capacitors, with their inherent self healing properties, can be safely overvolted (to a point, of course), and therefore become financially attractive.
1600VDC capacitors can handle up to the double in AC, even at high currents, so in a fusor multiplier, they may well even last indefinitely.
Abusing capacitors like that is not for a consumer product, but in a hobby environment, it is your own choise. Polypropylenes die fast from overcurrent, overvoltage taken to an extreme will cause the capacitance to fall at a steady rate.
Forgive me, but I could talk about capacitors for hours.
You can read somethng about those caps, here:
viewtopic.php?f=11&t=13790&hilit=Finn+hammer
Matt_Gibson
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Re: High Voltage PSU for functional Fusor

Post by Matt_Gibson »

Finn and Richard, thanks for the reply!

I remember the Cde942c was the go to for Tesla coils (my former days were building Tesla coils and solid state lasers)
I am looking at the WIMA fkp1 6000v capacitors. 3 in series should be good for 18kV. Any experience with these type?

I know the VMI diodes cost a hell of a lot more (a bit less on eBay), but would they be good for an actual 100nS?

-Matt
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Finn Hammer
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Re: High Voltage PSU for functional Fusor

Post by Finn Hammer »

Matt,
I asked VMI about a max. Frequency, they said 70kHz.
At the time, I was obsessed with the idea of making a supply at 100kHz, like a Spellman I once had access to, so I decided to go with the chinese diodes, and lower the frequency accordingly.
There are issues with the magnetics, which point in the same direction, and in the end, I just wanted something that could run cool enough without oil, so I ended at 33kHz as a good compromize.

Cheers, Finn Hammer
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