20kv Cockroft walton generator

[John Steaver]

hi, I just want to know if this is right. ill have 2000v diodes with 1000v capacitors with a 250-500v input with 20 stages (to lower current). I hope this is right haha. thanks- John

 

[(*steve*)]

ac input I presume.

output will be about 20 times the peak input voltage at low currents.

 

[John Steaver]

ok good. and could you tell how much current that would be? just an estimate would be fine. thanks

 

[(*steve*)]

it depends on the capacitors and the number of stages.

here is a simple calculation

V_out = (V_in x 1.414 x n) - (I x (n³ + (9 x n² / 4) + (n / 2))) / (12 x f x C)

where

• V_out is the output voltage
• V_in is the input RMS voltage
  
• n is the number of stages
• I is the current draw in Amps
  
• f is the input frequency
• C is the capacitor in farads

So, for 20 stages, and a 350VRMS AC input, 0.1uF capacitance 60Hz...

Open circuit (zero current) will give you about 9.9kV

at 0.01mA, you'll have an output voltage of about 8.6kV

So you'd probably be safe draw up to 10uA without the output dropping to less than 80% of your expected voltage.

What value are your capacitors? What current do you need?

 

[dorke]

John,
1.I have a bit different term for the voltage drop.
Voltage drop ∆V = iload *(2/3 n³ + n²/2-n/6) / [f*c]

for n=20 we get ∆V(about )=5500*iload / [f*c]
you need to fill in f and C to get iload or vice versa.

2.Take very good care not to get yourself zapped!

3.The voltages of the diodes and capacitors is the same!
It is Vin(peak to peak) .
are you driving the multiplier from a line transformer?.

 

[(*steve*)]

I think both formulae end up with a very similar result.

Here is one relatively readable reference.

 

[John Steaver]

I don't know what the power source will be yet. and I only need 2-5milli amps (non-lethal) and I don't really know how much farads on the capacitor I will use. could u help me to find that out?

 

[Martaine2005]

John,
Nobody can help you!
If you don't know what input voltage you will be using, how can somebody answer your questions.
Did you read the link Steve provided? It has all the information you need.
The calculations have already been done for you above!!
In fact, this has already been explained in great detail to you in your "other" thread.

I seriously think you need to do a lot of reading before attempting this!!
It is NOT a Kindergarten project.

 

[John Steaver]

alright, thanks martaine

 

[John Steaver]

ok so, just one more question. will these work? 0.1UF/1000V Axial POLYPROPYLENE. I don't know if the axial polypropylene are the right ones. thanks

 

[(*steve*)]

they should be fine.

but there's no way you'll get anything as high as 2 to 5 mA. 2 to 5 uA is achievable.

And don't kid yourself that 2mA at 20kV is safe. Power supplies capable of outputs like that are typically labelled as LETHAL.

 

[John Steaver]

yea, but I heard that 2-7 or 10ma isn't VERY lethal however it will hurt if you if you touch it or it can kill if you have a heart condition etc. will 1uF be 1mA? thanks for your help

 

[John Steaver]

wait sorry no that's not right. I read that as 2 - 5uF haha. is there an equation to work out the mA from uF? I heard about the ampere second/volt.
How many microfarad in 1 ampere second/volt? The answer is 1000000. that's off a website but I cant understand how that works. thanks again.

 

[John Steaver]

wait no those are coulombs. I cant calculate the amps without the watts or ohms and voltage. and I cant calculate the watts or ohms without voltage and amps haha.