# Cockroft Walton Voltage Multiplier Problems

• Fronzbot
In summary, the individual was trying to make a simple negative ion generator. They used a reference website and calculated the values correctly, but when they tried to make the circuit work, they ran into problems. They are hoping someone can help them out.
Fronzbot
Hey everyone.

So I like to have electronics projects going on to keep me on my toes during the academic year and my project I chose for fall ended up being a Cockroft Walton Generator. Basically, I was just looking to make a simple negative ion generator from it. I finally got the parts in today but am having SEVERE problems getting it to work properly or even figuring out what the hell is going on. This is my first HV project, so I'm pretty unfamiliar with this territory. I'm hoping someone out there can help me figure this stuff out.

First, the calculations. I used http://www.blazelabs.com/e-exp15.asp" as a reference.

I wanted an output of -40kV at a current of 0.845mA. I chose 20nF as my capacitance and, as per the suggestion on the site, I made C1 & C2 = nC, C3 & C4 = (n-1)C etc... To save on cost (since I'm a poor college student) I chose 5 stages and was just going to use the input from my Function Generator which has a peak of about 5V and the frequency I settled on was 100Hz.

$$V_{out} = 2n * V_{peak} - (I_{load}/(6fC) * (4n^{3} + 3n^{2} - n))$$
$$V_{out}= 2(5) * 5 - 0.000845/(6*100*20 \times 10^{-9}) * (4(5)^{3} + 3(5)^{2} - 5)$$
$$V_{out} = 50 - 70.4166667 \times 570$$
$$V_{out} = -40087.5V$$

$$V_{ripple} = I_{load}/fC = 0.000845/(100 \times 20 \times 10^{-9}) = 422.5V$$

So those values were perfectly fine for me. When I attached it up, though, it was only outputting -47VDC. Problem. I tried increasing the frequency and the max output I could get was -101VDC at an 8.3kHz Square Wave. I then added 5 more stages in (Stages 1 and 2 with 100nF, 3 and 4 with 80nF, 5 and 6 with 60nF, 7 and 8 with 40nF and 9 and 10 with 20nF) This time I got it up to -205VDC with an 83.2kHz Square wave.

I'm confused.

I've concluded that my output problem likely lies with the fact that I have such a small input voltage and if the circuit was attached to a more beefy supply, such as mains*, the output would be much greater. I've also concluded that these equations don't make any sense. I see no flaw with my arithmetic and so there are, as I see it, only two possibilities:
1) The equations are wrong
2) I have assumed something I shouldn't (such as Load Current, capacitance, etc)

Number 2 is the more likely case.

So anybody out there that can help me out?

*I should mention that that was just an example. I'm not going to connect this to mains for a few reasons, one of them being I don't have an isolation transformer on hand and another is I don't want to mess around with the mains, especially in my apartment.

Last edited by a moderator:
By coincidence, another post today has a circuit that might suit you.

See the excellent simulation by Bob S in this thread, :

This appears to run at about 150 Hz, but this could be increased by decreasing the value of the 0.39uF capacitors.

You would attach your CW circuitry at the bottom of the diagram, on the secondary of the transformer.

## 1. How does a Cockroft Walton Voltage Multiplier work?

A Cockroft Walton Voltage Multiplier is a circuit that uses multiple stages of capacitors and diodes to increase the voltage of an input signal. Each stage doubles the voltage, resulting in a high output voltage.

## 2. What is the maximum voltage that can be achieved with a Cockroft Walton Voltage Multiplier?

The maximum voltage that can be achieved with a Cockroft Walton Voltage Multiplier is dependent on the number of stages in the circuit. Each stage doubles the voltage, so the maximum voltage will be 2^n, where n is the number of stages.

## 3. What are some common problems faced when building a Cockroft Walton Voltage Multiplier?

Some common problems when building a Cockroft Walton Voltage Multiplier include capacitor leakage, diode failures, and voltage breakdown due to insufficient insulation. Additionally, the output voltage may be lower than expected due to losses in the circuit.

## 4. How can I test the functionality of a Cockroft Walton Voltage Multiplier?

The functionality of a Cockroft Walton Voltage Multiplier can be tested by using a multimeter to measure the output voltage. It is also important to check for any shorts or open circuits in the circuitry.

## 5. Can a Cockroft Walton Voltage Multiplier be used for high power applications?

No, Cockroft Walton Voltage Multipliers are not suitable for high power applications. They are typically used for low current, high voltage applications such as in electronic devices or laboratory experiments.

• Electrical Engineering
Replies
22
Views
3K
• Electrical Engineering
Replies
17
Views
2K
• Electrical Engineering
Replies
1
Views
1K
• Engineering and Comp Sci Homework Help
Replies
0
Views
817
• Electrical Engineering
Replies
9
Views
3K
• Electrical Engineering
Replies
1
Views
2K
• Electrical Engineering
Replies
3
Views
3K
• Introductory Physics Homework Help
Replies
1
Views
558
• Electrical Engineering
Replies
5
Views
3K
• Engineering and Comp Sci Homework Help
Replies
5
Views
865