series/parallel capacitor bank

[Tigrathi]

Yep I am just an old fashioned mad scientist.
Well what about on a smaller scale?

 

[Sceadwian]

Out of my field =) I've never played around with high voltage stuff.

 

[Tigrathi]

You should give it a try; lightning is fun when done safely.

 

[tcmtech]

Ive done a similar setup with smaller capacitors running off of a 600 volt AC source but instead of spark gaps I use HV diodes. Simple diode and capacitor voltage multiplier circuit.

If you intend to use it for a spark gap the first diode one the bottom of the voltage multiplier is always the one that goes dead short after a few good HV snaps.
Triple it up and then double the next set in the multiplier and and the problem seems to go away.

Being the input is alternating current using motor run/power factor correction type capacitors works very well for a current limiter on the input side. They will give you current inrush limiting during charging and also current limiting during short circuits.

 

[Sceadwian]

Never liked marx generators even though they can generate incredible voltages, but only in short pulses. One day I'll get my hands on a neon sign transformer to play with. I've played around with a few 280volt flash capacitors and those have me wary already. My common nickname is Jake so I've always wanted to make a Jacobs ladder =) I've always wondered if it would be possible to make a DC jacobs ladder, I want one that doesn't have that AC hum associated with it.

 

[Tigrathi]

I don't suppose you have a schematic with notes so I can add it to my idea doodle book?

 

[tcmtech]

I keep my notes in my head! Its harder to loose or get stolen that way.

Just look for the multistage voltage multiplier circuit diagrams. Do like your doing and make one positive referenced and the other negative referenced. I think I used something like 50 positive and 50 negative stages on my experiment.
Mine would blow a nice fine cone shaped coronal discharge off of the HV leads when it was all charged up and could jump a 5 inch gap every few seconds.
If you put a home made Leyden jar or glass plate capacitor together and use the multiplyer circuits to charge it up you could get some serious discharge power that is pure DC at very high voltage!

Guaranteed heart stopper!

 

[Tigrathi]

Oh yea I forgot that one can make your own capacitors. Wish I remembered that before I purchased expensive HV Caps.

 

[tcmtech]

Ah... If I only had a nickle for every dollar I wasted due to poor planning or research.
That would still be a lot of dollars!

If you go the voltage multiplier method it works better if your starting voltage is higher. I used a small 480:120 step down transformer set up as a 120:600 step up auto transformer. That way the common line on the transformer was also my center tap and earth ground all in one.

Plus this way each step was multiplying the 848 volt peak from the 600 volts and not a the 170 volt peak from the 120 volt line.
50 x 848 = 42400 volts
50 x 170 = 8500 volts

 

[Tigrathi]

I wonder would it be wrong to make a lightning gun?
*giggling maniacally as I rub my hands*

 

[Sceadwian]

Control isn't so great on those things =) And it's just as likely to kill the shooter as it is the target =)

 

[tcmtech]

A fake shotgun like device with a load of sparks at the barrel end is enough to scare the crap out of most people.
Irrational fear is often far more effective than actual device usage.

A buddy of mine is former special forces military. He says he has been trained to not be afraid or Guns, Knives, or just plain crazy people.
But my high voltage toys scare him!

He said the only military strategy that he ever knew of for dealing with someone like me is to just back away and call in an air strike and hope I dont have a PGRMUD!

(Plane or Guided Rocket Messer Upper Device) Military technical term I guess.

 

[Tigrathi]

Well I could always connect it to an EMP generator with a microwave carrier beam.

 

[MikeMl]

if i had 20 1000uF 100V capacitors and wanted to make a bank of them...

If you are still monitoring this thread, the way you choose the "bleeder" resistors is usually by power dissipation in the resistors, and how long it takes for the capacitor to bleed down after turning off the supply.

If you are using 1000uF capacitors charged to 100V, the resistor would dissipate E^2/R. If you are starting with a 5W resistor, then R=100*100/5= 2000Ω or higher. The time it would take to discharge the 100uF cap to a save level is about one time constant τ=R*C = 2000*1000E-6 = 2sec.

1meg or 10meg resistors would be useless as bleeders. τ = 1E6*1000E-6 = 1000 sec, or about one third of an hour to bleed down.