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H8erade

Fri Sept 02 2011, 08:58PM

Registered Member #3451 Joined: Sun Nov 28 2010, 11:13PM
Location: United States
Posts: 100

the mad scientist wrote ...

CWs are tons of fun and easy to make i made 3 of them and i can use one to power the other

You must have had to add extra inverter circuitry, right?

the mad scientist

Fri Sept 02 2011, 09:23PM

Registered Member #3768 Joined: Tue Mar 22 2011, 12:46AM
Location:
Posts: 107

yea

Herr Zapp

Fri Sept 02 2011, 11:49PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

TMS -

Can you provide a more detailed description of your multipliers ...... how many stages, what components were used, especially info on the inverter design.

Photos would be be great.

Herr Zapp

GrantX

Sat Sept 03 2011, 03:25AM

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

Hmmm, yes I can see the problem, there's no way I could justify the cost of that many monster caps. Are there any other methods of generating a 100kV (this figure is not important, I just want lots of voltage for my own amusement ;)) apart from a Tesla Coil or huge-arse transformer?

I have a feeling it is difficult to produce a higher voltage using an NST, correct?

the mad scientist

Sat Sept 03 2011, 03:38AM

Registered Member #3768 Joined: Tue Mar 22 2011, 12:46AM
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Posts: 107

10 stages 20kv caps each, and 10~16kv diodes, ill give more info later k

Proud Mary

Sat Sept 03 2011, 08:59AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

XravenorX wrote ...

Hmmm, yes I can see the problem, there's no way I could justify the cost of that many monster caps. Are there any other methods of generating a 100kV (this figure is not important, I just want lots of voltage for my own amusement ;)) apart from a Tesla Coil or huge-arse transformer?

I have a feeling it is difficult to produce a higher voltage using an NST, correct?

Capacitors have a property called reactance, which you can think of as being resistance to the passage of an AC current at a given frequency. The symbol for the reactance of a capacitor is XC and the value is given in ohms.

For a given capacitor, reactance rises with a decrease in frequency, and falls when the frequency is increased.

Xc = 1/2Ï€fC

Using this formula, you'll see that the 10nF caps I use in my microamp full-wave tripler, the reactance of each cap is 318.31kÎ© at 50Hz - high resistance to the flow of current.

In Henning's giant C&W, his 100nF capacitors are ten times larger than mine, so his 50Hz reactance is ten times smaller at 31.831kÎ©

So for most practical purposes, C&W voltage multiplers (VM) are not used at 50 Hz. Typical C&W drive frequencies are between 15 kHz and 50 kHz, though frequencies up to 100kHz are sometimes used.

Using the formula above, you'll see the reactance of my 10nF capacitors at 50Hz is 318.31kÎ©, but at 50kHz this falls to a mere 318.31Î©, a resistance 1000 times smaller which is a thousand times less obstructive to the flow of current.

GrantX

Sat Sept 03 2011, 09:29AM

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

Proud Mary wrote ...

Capacitors have a property called reactance, which you can think of as being resistance to the passage of an AC current at a given frequency. The symbol for the reactance of a capacitor is XC and the value is given in ohms.

For a given capacitor, reactance rises with a decrease in frequency, and falls when the frequency is increased.

Xc = 1/2Ï€fC

Using this formula, you'll see that the 10nF caps I use in my microamp full-wave tripler, the reactance of each cap is 318.31kÎ© at 50Hz - high resistance to the flow of current.

In Henning's giant C&W, his 100nF capacitors are ten times larger than mine, so his 50Hz reactance is ten times smaller at 31.831kÎ©

So for most practical purposes, C&W voltage multiplers (VM) are not used at 50 Hz. Typical C&W drive frequencies are between 15 kHz and 50 kHz, though frequencies up to 100kHz are sometimes used.

Using the formula above, you'll see the reactance of my 10nF capacitors at 50Hz is 318.31kÎ©, but at 50kHz this falls to a mere 318.31Î©, a resistance 1000 times smaller which is a thousand times less obstructive to the flow of current.

Ah, thank you thats very informative. we are currently going over reactance and inductance in my course, so I'm pleased all the hypothetical problems I've gone over in class are paying off :D

So, as I understand it: It is feasbile to build a CW that will provide a huge voltage boost from an NST, but because of the very low frequency the output current will be very small unless I use huge 100nF+ caps? So If I took a similar approach to you and build a CW with 10nF caps it would still function without exploding in flames, but the output current would be tiny and the voltage sag/ripple would be extreme?

In a full wave tripler are the caps meant to be rated at 2 or 3 times the input voltage? Is it the same for the diodes?

Ash Small

Sat Sept 03 2011, 10:59AM

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

Proud Mary wrote ...

. Typical C&W drive frequencies are between 15 kHz and 50 kHz, though frequencies up to 100kHz are sometimes used.

Can anyone give any more information regarding the limiting factors for multiplier frequency?

I've recently realised that I'll need to increase frequency from the 25kHz I was originally planning to run at in order to get more current from the multiplier, but what are the factors that actually limit the upper frequency?

Proud Mary

Sat Sept 03 2011, 11:00AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

XravenorX wrote ...

So, as I understand it: It is feasbile to build a CW that will provide a huge voltage boost from an NST, but because of the very low frequency the output current will be very small unless I use huge 100nF+ caps? So If I took a similar approach to you and build a CW with 10nF caps it would still function without exploding in flames, but the output current would be tiny and the voltage sag/ripple would be extreme?

My little 50Hz C&W tripler will produce 1mA at 20kV, but the sag is so bad that it struggles to produce 200Î¼A at 30kV i.e. if I put a load on it that would draw 1mA at 30kV,
the output voltage falls to about 23kV. But for most of the things I do, which often involve accelerating electrons and then stopping them suddenly, this is all I need.

As always, you must first determine the power needs of an application before you can design a power supply for it.

XravenorX wrote ...

In a full wave tripler are the caps meant to be rated at 2 or 3 times the input voltage? Is it the same for the diodes?

This here Vishay Application Note will help you with further questions:

Using Rectifiers in Voltage Multiplier Circuits

Adam Munich

Sat Sept 03 2011, 01:13PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

If you just want a hardy HV supply, an xrt + a variac might be a good option.

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