# Newbie high voltage question

Discussion in 'The Projects Forum' started by grunge, Feb 2, 2009.

1. ### grunge Thread Starter New Member

Feb 2, 2009
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0
Hello all,

I am new to this forum. I am also new to electronic circuits. I am building a high voltage DC circuit for an experimentation project. I have a capacitor bank containing five 400v 470uf capacitors wired in series to give me a 2000 vdc pulse about ten times per second. What I don't know is what size power supply I need for charging the capacitor bank to do what I want it to do. Do I just need a 400 vdc power supply or do I need a 2000 vdc power supply? Any help would be appreciated.

2. ### Tesla00010010 Member

Jun 20, 2008
21
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If you need 2000vdc pulses then you need a 2000vdc power supply,unless you are using a transformer or an ignition coil
If the capacitors receive pulses of 2000vdc when their breakdown voltage is 400,it probably wont destroy the dielectric but it will shorten capacitor s life and it can cause it to fail in the long term

3. ### Bernard AAC Fanatic!

Aug 7, 2008
4,248
424
Ball park figures : First , keep one hand in your pocket ; be extra carefull ; 5 caps @ 400V @ 470μF = 94μF @ 2000V; Q=CE = .000094 X 2000 = .188 = IT , I= .188A/.1sec. = 1.88A. Need 2000V power supply @ about 2A. Two A probably much to high, depends much on power supply internal Z.

4. ### triggernum5 Active Member

May 4, 2008
216
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Is your intention to build a voltage multiplier like this?
http://en.wikipedia.org/wiki/Voltage_multiplier
Do be careful though.. Make sure you know where all possible shorts to ground are in your work area, and glove one hand, but still keep that hand behind your back.. I've gotten bit more than a couple times by leaning into ground contact when I focused too much on what my hands are doing, so definately know your work area..
HV, capacitors, and newbie are terms that make me really nervous when used in the same sentence..

5. ### Bernard AAC Fanatic!

Aug 7, 2008
4,248
424
I forgot: best to connect a 100kΩ, 2W resistor across each cap. to equalise strain.

6. ### grunge Thread Starter New Member

Feb 2, 2009
3
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Thank you one and all for your input and concern. I will be careful. I was thinking I would need a 2000 vdc power supply. What brought the doubt was, I was thinking about it (first mistake) and wondered why I would even need a capacitor bank if I have a steady flow of 2000 vdc from a 2000 vdc power supply? That is why I asked.

Thanks all,
grunge

7. ### triggernum5 Active Member

May 4, 2008
216
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Alot of HV sources are safer than you'd expect because their instantaneous current capability is so low.. If you use that to charge a capacitor though, the cap will pose a signifigant threat because it stores the energy provided over x amount of time at supply voltage, and can dump it all in one chunk..
The circuit I showed is capable of charging a large cap to lethal levels, hooked up to 120VAC or lower (Its a voltage multiplier).. The danger of that circuit by itself would depend on the capacitor sizes used in the circuit itself..
You can make an HV supply analogous to a VandeGraff generator with not much more than a piece of cloth, wire, and some pvc pipe.. Its essentially a static electricity generator, harmless by itself, but could charge a big cap to lethal levels with enough time..
Flybacks from CRT devices are one of my favorite HV sources.. They themselves usually teeter the line between harmless, and 'umm, it might not be totally harmless'.. They typically output up to 25000V, and are pretty versatile.. Harvesting them from an old tv/monitor can pose risks though.. If you decide to look into them, read up on safe crt handling first.. The sticker on the back of the tv doesn't lie.. Its possible for them to kill even when unplugged..

8. ### ifixit Distinguished Member

Nov 20, 2008
639
110
If I read your first post correctly you said you wanted to completely (5 TCs) charge and discharge 94uF @ 2000V 10 times in 1 second. Assuming your charge and discharge times are equal then it's 50mS (T5=RxCx5=100ohms x 94uF x 5 = 47mS. Max current from 2000V supply at start is 2000V / 100ohms = 20Amps. That's 40KWs.