Capacitor voltage multiplier with caps paralleled

Thread Starter

RogueRose

Joined Oct 10, 2014
375
Let's say I have qty 40 400v 1000uf caps and I want to run at 2kv and I want to have the highest capacitance possible. To get to 2kv would I need 5 or 10 caps (or how many stages - how many caps total to get 2kv)? To get the higher capacitance, would I run equal # of caps at each stage to get a higher total capacitance?

Also, is it possible to run 5 voltage multipliers in parallel (5 identical setups) to get 5x capacitance? I know it is similar to running the caps in parallel in each stage, but can be utilized differently.
 

Alec_t

Joined Sep 17, 2013
10,728
The number of stages would depend on what each stage consists of and what the input voltage to the first stage is. If you post your schematic we may be able to help you better.
 

Thread Starter

RogueRose

Joined Oct 10, 2014
375
I looked closer at voltage multipliers and it looks like each stage adds the value of the cap.? Looking at wiki it looked like it might have been 2 caps for each stage.

So if that is the case, to get my 2kv with the above caps, could I run 5 stages and put 8 caps in parallel in each stage to get a total of 2kv @ 8000uF?

BTW, I tried to edit my OP but there is no edit button. Is that normal?

Hello,

For a voltage multiplier you will need an AC voltage to get it working:
http://www.allaboutcircuits.com/textbook/semiconductors/chpt-3/voltage-multipliers/

Why do you need 2 kV at high energy?
The energy stored in the stack of capacitors can be lethal.

Bertus

I just picked numbers that were easy to visualize - I could say qty 40 caps, 10v 100uF with a desired voltage of 100v @ 400uF.

The number of stages would depend on what each stage consists of and what the input voltage to the first stage is. If you post your schematic we may be able to help you better.
THat is good to know. As I said, this is more of a theoretical exercise to figure out how to get to X from Z..

Let's say that input voltage is 360vac (1:3 transformer from 120VAC).

But what would happen if 480vac were applied to the multiplier?

I guess one thing I am trying to figure out is if there is a difference (and how much) in energy/joules if the 40 caps from the OP were run in parallel

40 caps in parallel
400v 40,000uF = .5 * 40,000 * 400^2 = 3,200 joules

Voltage multiplier - 5 stage - 8 caps parallel in each stage
2kv 8,000uF = .5 * 8,000 * 2,000^2 = 16,000 joules

I know these calculations are correct but I'm not sure if the electrical aspect is correct, meaning will the voltage multiplier act as I described?

Now I look at it the joules is 5x for the 2kv stage. Do I need to divide by the number of stages when figuring out energy for this or is the 16kj correct?
 
Last edited by a moderator:

bertus

Joined Apr 5, 2008
20,230
Hello,

The peak voltage of AC is √2 times the RMS voltage for a sine.
So if the AC voltage is 480 Vac, the peak voltage will be 538 Volts.
The 400 Volts caps in your OP post will not survive.

Bertus
 

Alec_t

Joined Sep 17, 2013
10,728
But what would happen if 480vac were applied to the multiplier?
There would most likely be a loud bang, capacitor guts spewed everywhere and a lot of acrid smoke :eek:.
If you are planning on discharging the caps at high current they would need to be rated accordingly.
 

Thread Starter

RogueRose

Joined Oct 10, 2014
375
When the caps are put into a setup like a voltage multiplier, does this effect the speed of discharge for them. Is this what the ESR value indicates? Is the ESR value of the multiplier the sum total of the ESR values for each stage?

I guess what I am trying to figure out is how exactly these multipliers can work.

The following is a hypothetical as I can correlate this to other examples..
If I need a cap of something around 240v with as much capacitance as possible but I am restricted to using 25v or 50v capacitors. I'm going to be using pulsed DC current of 49-50v. The energy requirement is to release as much power as quickly as possibly with these caps at roughly 240-250vdc.

Similar to the above voltage multiplier, there are qty 100 - 50v 3300uf caps available. If a 5 stage multiplier is used to get 250v and running 20 parallel caps on each stage (49-50vdc pulsed input) does this circuit act as a single higher voltage/larger capacity capacitor (250v 66,000uf)? Meaning does this circuit store energy for quick discharge or does it simply act like a transformer allowing for higher voltage while not being able to discharge in a single pulse.

I'm sorry if I haven't been able to make this very clear but I am a little confused as to the potential of this circuit.
 
Last edited by a moderator:

Alec_t

Joined Sep 17, 2013
10,728
I suggest you download LTspice (free, from Linear Tecnology), then you can simulate all sorts of scenarios/configurations and see what happens.
 

Thread Starter

RogueRose

Joined Oct 10, 2014
375
Well, think about the advantages of full wave rectification over half wave, then apply that reasoning to your multiplier :)
Thanks. I looked up the differences and it I saw something about peak ripple and some other things I have to look more closely at. After reading it I was leaning towards full wave rectification.


So, I still am not certain as to whether this voltage multiplier will act like a higher voltage capacitor or if I will be limited to the amount of energy the power supply can deliver in one "pulse".

So, 100 caps of 50v 3300uf -- if all paralleled - 50v 330,000 uF = 413 joule potential

5 stage, 20 caps paralleled per stage -- 250v 66,000 uF = 2016 joules (if it were a cap rated at those values - IDK if I divide by 5 as it is 5 tiers and 5x the energy of the 100 caps paralleled). So if the power supply charges the caps to capacity would I get the 2016 joules from it if discharged at once or does it not work that way when arrainged as a voltage multiplier?
 

recklessrog

Joined May 23, 2013
985
I think I know what you want to use it for and cannot in all good conscience advise you further except to say that the energy levels and voltages proposed take no prisoners and will happily KILL YOU in an instant with NO SECOND CHANCE!
I worked on the design and development very high voltage @ high current equipment and the degree of training and safety precautions were of the highest order, hence my survival to become an O.A.P!!
I don't warn you lightly, and hope you really consider the potential dangers that can cause your death or serious injury in view of level of your expertise.
This is not in any way meant as "put down" or insult, Just genuine concern for the direction in which you may be heading.
Please re-read this and think about it!
Take care :)
 

Thread Starter

RogueRose

Joined Oct 10, 2014
375
I think I know what you want to use it for and cannot in all good conscience advise you further except to say that the energy levels and voltages proposed take no prisoners and will happily KILL YOU in an instant with NO SECOND CHANCE!
I worked on the design and development very high voltage @ high current equipment and the degree of training and safety precautions were of the highest order, hence my survival to become an O.A.P!!
I don't warn you lightly, and hope you really consider the potential dangers that can cause your death or serious injury in view of level of your expertise.
This is not in any way meant as "put down" or insult, Just genuine concern for the direction in which you may be heading.
Please re-read this and think about it!
Take care :)

Well I guess it's the good old guess & test method then!

Ok, would it be better if I changed the cap voltage to 6.3v and 10uf. If I had 100 caps, 5 stages, 20 parallel per stage.... That would be 31.5v 200uf. IDK if that can kill. I just picked some numbers that seemed easy to work with. This is a question of theory, I'm not saying those caps will be used. I just wanted to know if the multiplier works like a cap or more like a wired transformer
 

Thread Starter

RogueRose

Joined Oct 10, 2014
375
I think I know what you want to use it for and cannot in all good conscience advise you further except to say that the energy levels and voltages proposed take no prisoners and will happily KILL YOU in an instant with NO SECOND CHANCE!
I worked on the design and development very high voltage @ high current equipment and the degree of training and safety precautions were of the highest order, hence my survival to become an O.A.P!!
I don't warn you lightly, and hope you really consider the potential dangers that can cause your death or serious injury in view of level of your expertise.
This is not in any way meant as "put down" or insult, Just genuine concern for the direction in which you may be heading.
Please re-read this and think about it!
Take care :)

I just re-read your post. IDK what you have in mind, but I understand the hesitation if the numbers I posted are correct. I don't plan on building that. Thank you for making it clear that it is potentially lethal.

On another note, is a 50v 3300uf cap deadly at 4 joules?
 

Thread Starter

RogueRose

Joined Oct 10, 2014
375
Recklessrog - will you answer me as to whether the question I was asking made sense, as in did you understand it? I really just want to know the "theory" behind this. The reason I'm researching this is because all the posts/pages/sites I read about various mid to high voltage projects usually say somewhere on the page "a high voltage cap would cost a fortune" while they have like $4-5,000 in parts + time + manufacturing costs invested in the project. So I started running some numbers, comparing what they said to the #'s, and yeah, it is expensive but it seems that their approach to building the cap banks is similar to installing 8 single cylinder 2-stroke engines in a Charger (dodge/plymouth/whatever) instead of a single V-8...

This question is the culmination of fact checking some research on sites, comparing claims of companies selling various "high tech" "future tech" things - most of which require a good deal of energy - thus the research into this. I'm trying to see is the $30,000 asking price for some "toys" is because cost of parts, or due to intellectual property (knowing how to build XYZ)..
 

BR-549

Joined Sep 22, 2013
4,938
I don't have a clue what you are building. Don't really care.

But very concerned that you do not have the knowledge, nor skill to build such a device.

That much charge under that kind of pressure is jumpy and lethal.

Usually an innocent person gets hurt.

I recommend much more study.

This is not a put down or insult.
 
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