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First Marx Gen

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LAN_403

Reaching

Sat Feb 18 2006, 07:04PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

Yeah, now i have all parts together to build my first "real" Marx Generator.

i have 12 stages , each with a 30kv 590pF ceramic Doorknob capacitor. the whole thing is only 37cm tall, so when it works properly it could make discharges in its size. for the spark gaps i want to use M4 Brass Head Nuts, all sparkgaps are adjustable.

heres a pic from what ive finished today

i have a bunsh of 1M resistors lying around. iÂ´ll test if they can withstand the voltage but i dont think so.
i want to drive the marx with two Obits, rectified and wired in series to get around 28kV DC.

Marko

Sat Feb 18 2006, 07:32PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I wouldnt push so much voltage, rather use one obt and spare capacitors...
28kV seems too close to dielectric breech...
Lots of people want to push marx capacitors to and sometimes over rated limit, this is very bad practice, rather leave couple of kilovolts and be sure... (my opinion)

That marx seems good work for now, gaps are from other side

?

1M resistors seem small for so high voltage, you will have 15ma flowing trough each (peak) I dont know how good would they be...

Resistors are really cheap, maybe its best to use some ''original'' high-voltage resistors and forget about them...

Hazmatt_(The Underdog)

Sat Feb 18 2006, 07:59PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Very nice!

You could always use corona dope on the hardware to prevent breakouts, course it looks like hell if you do that, but it will fix most of the problem.

Reaching

Sat Feb 18 2006, 08:05PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

yeah, i have to look for some resistors, i testesd my 2,2m(yeah not 1M) resistors on a 10 kv obit and they broke down. i have to find some others, maybe 4,7 or 10M

HV Enthusiast

Sat Feb 18 2006, 09:36PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Reaching wrote ...

yeah, i have to look for some resistors, i testesd my 2,2m(yeah not 1M) resistors on a 10 kv obit and they broke down. i have to find some others, maybe 4,7 or 10M

Depending on the type of resistors, 1M is fine. I use 1M, 3W carbon resistors for my marx generators (charged 40kV per stage) with no problems.

Putting a resistor across an OBIT and in a marx generator are two completely different applications. Remember, that the voltage across each resistor drops as you charge. When the marx generator is charged completely, there is zero voltage across each resistor (except leakge of course)

Marko

Sat Feb 18 2006, 10:02PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Depending on the type of resistors, 1M is fine. I use 1M, 3W carbon resistors for my marx generators (charged 40kV per stage) with no problems.

Yep obt and max are completly different but it seems that 1M is low and repetition rate will be high, and resistors have to be high power, but lets say its OK...

Just dont overrate capacitors, keep them safely few kv under rated voltage

Reaching

Sun Feb 19 2006, 01:12AM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

yeah, i know that are two different things. i only wanted to make a stand up voltage test. i dont have 3 watt+ resistors in this size, only 0,5 watt and they are relatively small so i have to wire 2 or 3 in series to be sure they dont arc over. but i think i will go up to 4,7M ohm or so, 0,5 watt is not much and i dont want to stress the resistors too much at the charging period.

do you think i can use this double obit powersupply or do you think its too much voltage?. i have 2 10kv 20mA obits. i want to rectify each obit and then wire them in series. 10x1,4=14 kV each, so 28kV dc for 30kV rated capacitors.

and to answer the question how i make my sparkgaps, heres a pic

Update

Got it to work but my setup seems to compact to give the output it could have
the capacitors are to close together, so when i apply more voltage, they arc over to the other wiring.
heres a pic of a spark with ca 16cm lenght,

to make it work properly i have to make it less compact, more space between components i think. i found some reliable resistors ith 4,7m ohm 2 in series , it works fine, no arcovers even at 28kV

Update

I made a less compact version and it works much better now. i use a flyback driven by a zvs as my powersupply. measured at the output, each stage goes up to ca 22kV. sparklenght is now around 25 to 27cm, not too bad for my first marx generator
the pic shows the marx in action, 10 seconds exposure, discharge ca every 1 second. i changed the charge resistors to 4,4M ohm, (2x 2,2m ohm in series)the first charge resistor is 40m ohm (4x10 in series)

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