# Simple Spark Gap Circuit

Discussion in 'The Projects Forum' started by kevin1337, Apr 25, 2015.

1. ### kevin1337 Thread Starter New Member

Apr 25, 2015
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Hi,

I'm working on a simple project and have run across a problem. Been a long time since I've done circuits and cant seem to get this problem solved.

I need a simple circuit that when a switch is flipped it will produce a spark over a 3mm gap. Does anyone have an idea on how to do this? I've tried creating a simple/modified marx generator to create the spark but still no luck.

Been using:
1 Mohm resistors
4kV 102 pF Capacitors
9V Battery

Thank you,
kevin

2. ### Papabravo Expert

Feb 24, 2006
11,084
2,159
Given the voltage and the capacitance, the energy stored in the capacitor is 40 nano-Joules. I'm sure it is not enough to jump the gap. The dielectric strength of Air is 3 MV/m or about 9000 Volts for the 3 mm gap. I think you are a ways away from that level.

3. ### kevin1337 Thread Starter New Member

Apr 25, 2015
8
0
Thank you for the advice. How might I go about changing the circuit? I've tried putting multiple capacitors in series... up to four (4) of the 4K capacitors but still no spark. Is my charging voltage too low?

4. ### kubeek AAC Fanatic!

Sep 20, 2005
4,851
859
How is a capacitor supposed to create any spark? It will never make more voltage than the 9V you are putting in. You need a transformer or inductor to create any sparks.

5. ### kevin1337 Thread Starter New Member

Apr 25, 2015
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Thank you kubeek.... I think that is what I am missing.

Sep 22, 2013
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Try this.

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Apr 25, 2015
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8. ### blocco a spirale AAC Fanatic!

Jun 18, 2008
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408
I had to google the Marx generator as I had never heard of a passive DC voltage multiplier; It relies on the input voltage being high enough to reliably produce an arc so a 9V input is a non-starter.

If the TS just needs big sparks;

http://www.ebay.co.uk/itm/Boost-Hig...225?pt=LH_DefaultDomain_3&hash=item5d578158e9

Apr 25, 2015
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10. ### DerStrom8 Well-Known Member

Feb 20, 2011
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1,333
Marx generators work by charging capacitors in parallel and discharging them in series. This is how you get a higher voltage out than what you put in.

In order to use a 9v battery to charge the capacitors, you'll need a driver circuit along with the transformer. You cannot run a transformer on DC.

Sep 20, 2005
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12. ### kevin1337 Thread Starter New Member

Apr 25, 2015
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Blocco's idea of the Boost Step-up Pulse Power Module High-voltage Generator is exactly what I need. I was over complicating a simple solution. Didn't know this device existed.

13. ### #12 Expert

Nov 30, 2010
17,842
9,178
I di
I didn't know it existed, either, but it looks scary to me! 40KV on some tiny little hook-up wires? The diameter of the winding wires must be microscopic. Treat it gently. I don't think it will survive much abuse.

14. ### kevin1337 Thread Starter New Member

Apr 25, 2015
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So #12 gives me another noob question....

If I want a spark to last something like 0.1 seconds (or just a small amount of time really) then stop for like 1.0 second then make another 0.1 sec spark... then repeat over and over until a switch is hit. Is there an easy way of doing that?

15. ### blocco a spirale AAC Fanatic!

Jun 18, 2008
1,541
408
I have a couple of these modules and I can confirm that they are terrifying, but I haven't manage to destroy one yet.

Lower voltage modules are also available:

http://www.ebay.co.uk/itm/New-DC-3V-to-7KV-Boost-Step-up-Power-Module-High-voltage-Generator-1PCS/251541077786?_trksid=p2045573.c100033.m2042&_trkparms=aid=111001&algo=REC.SEED&ao=1&asc=29479&meid=9c8ffe9335154039a5f41c08e0cf390f&pid=100033&rk=4&rkt=4&sd=251875437450

Last edited: Apr 25, 2015
16. ### #12 Expert

Nov 30, 2010
17,842
9,178
It's called an astable oscillator. Easily done with an LM555 timer chip. You will need to add a current carrying transistor to provide the 2 amps your module needs and you have to let it cool off enough. It is rated to run for 5 seconds before overheating but no mention of cooling time required. I don't think a 10% duty cycle would work. Too much heat.

17. ### kevin1337 Thread Starter New Member

Apr 25, 2015
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Thank you, reading up on it now. Looks like this might work.