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My new dilemma is how to trigger the Marx generator with my camera flash circuit. It's easy enough with an SCR but the Marx generator is not so easy to control. Any help would be appreciated [have to rush to work now] Thanks :)
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714
You could let the Marx generator fire on its own schedule, while camera waits with shutter open in a dark room. Or contrive a to make one of the small spark gaps be a triggered spark gap.
Registered Member #56316
Joined: Sat Aug 08 2015, 05:24AM
Location:
Posts: 13
klugesmith wrote ...
You could let the Marx generator fire on its own schedule, while camera waits with shutter open in a dark room. Or contrive a to make one of the small spark gaps be a triggered spark gap.
Thanks, my intention is not so much to photograph that spark but to involve it in a bigger photographic project - my invention involves high speed photography in sunlight triggered by the act of taking a photograph. I can trigger a spark from an ignition coil by soldering it in series with flash capacitor and generating a 20000 volt as I take a picture - all the way to 1/4000th sec. I really want to be able to trigger the Marx generator at 1/4000th sec. otherwise perhaps a large coil of some sort - I could dump a 3300uf 450 volt cap through a winding with my SCR perhaps but I do want a BIG spark.
Registered Member #46264
Joined: Sun May 11 2014, 05:27PM
Location: Tucson, Arizona USA
Posts: 61
You could use a phototransistor slave trigger on the Marx. The light from the camera flash would trigger the phototransistor which in turn could trigger the Marx.
Registered Member #56316
Joined: Sat Aug 08 2015, 05:24AM
Location:
Posts: 13
Russ Edmonds wrote ...
You could use a phototransistor slave trigger on the Marx. The light from the camera flash would trigger the phototransistor which in turn could trigger the Marx.
Would it be able to trigger the first spark gap? If it's only going to trigger the power supply that will have too much delay for it to charge up. The Marx generator needs to be fully charged when it is switched which would mean a 30kv photo transistor if they exist.
Registered Member #46264
Joined: Sun May 11 2014, 05:27PM
Location: Tucson, Arizona USA
Posts: 61
The phototransisitor would trigger a HV pulse generating circuit. This HV pulse would then trigger the fully charged Marx via a bottom triggered spark gap in the Marx.
Registered Member #56316
Joined: Sat Aug 08 2015, 05:24AM
Location:
Posts: 13
Russ Edmonds wrote ...
The phototransisitor would trigger a HV pulse generating circuit. This HV pulse would then trigger the fully charged Marx via a bottom triggered spark gap in the Marx.
I built a trigatron last year, blew a 40 amp fuse with 400 volts before blowing the tips off and haven't had much success since. How easy will this spark gap be to make? I did put the flash tube in series with the gap so that the flash circuit could ionize the gap and trigger it - but the spark kept jumping through the tube like it was already ionized - unless the high voltage was doing that itself but it was a big gap on either side as well.
This was one of my first attempts at using a camera flash to fire a 20 000 volt spark across the spark gap. I think the Marx generator was perhaps jumping through the ignition coil or something because it didn't work.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
In that schematic, the iggy coil is directly across the first gap, so will be short-circuiting the charge process.
There are at least 3 well-known methods of doing this.
a) If you have a bright enough spark from your coil, then the cleanest way of getting the marx to trigger from it will be to illuminate the first gap with the UV from the spark. The UV ionises the gap and triggers breakdown. This may however require careful setting of the first gap, too much excess gap and it won't trigger.
b) The next way is a bit more intrusive, make the first gap into a classic 3 electrode triggered gap, and connect the coil to the trigger electrode. The ionisation caused directly by the spark is drawn into the main gap by the main field, making it much easier to trigger than b y UV light alone.
c) The next more intrusive way of doing it is the RF arc starter circuit for welders.
Registered Member #56316
Joined: Sat Aug 08 2015, 05:24AM
Location:
Posts: 13
Dr. Slack wrote ...
In that schematic, the iggy coil is directly across the first gap, so will be short-circuiting the charge process.
There are at least 3 well-known methods of doing this.
a) If you have a bright enough spark from your coil, then the cleanest way of getting the marx to trigger from it will be to illuminate the first gap with the UV from the spark. The UV ionises the gap and triggers breakdown. This may however require careful setting of the first gap, too much excess gap and it won't trigger.
b) The next way is a bit more intrusive, make the first gap into a classic 3 electrode triggered gap, and connect the coil to the trigger electrode. The ionisation caused directly by the spark is drawn into the main gap by the main field, making it much easier to trigger than b y UV light alone.
c) The next more intrusive way of doing it is the RF arc starter circuit for welders.
Thanks very much - this is all very helpful! I suppose I am looking for the easiest[balanced with cheapest] way of doing this. I have a feeling the 3 way spark gap will be the solution. This is the flash I currently use to charge my 3300uf capacitor but before it was wired up like this to fire a spark when I take a picture. I now have a smaller flash doing the job but it gives me a reasonable spark,
This is the type of spark I get from it - I can trigger, and photograph at the same time, a spark up to 1/4000th sec.
I have an article on my blog of my attempts at a spark gap switch/trigatron as well The Trigatron But I still have several questions on that:
For ionization to occur there has to actually be a spark as a result - true? I mean I couldn't simply set up my circuit and have the HT lead from the coil in the middle without also having the earth of the spark system on the other side[?] or connected to the rest of the Marx generator circuit. ALSO: Could I limit the voltage of my Marx generator to prevent it jumping around resistors to fire for example, by having a jacobs ladder at the beginning of the circuit and adjusting the gap at the base to control the voltage that charges the system?
So here's my new drawing. Where to place the earth wire of the spark trigger circuit? If it is across from the main HT lead will the ionization be too narrow for the system? One more thought before I head off to get some sleep [night time in New Zealand] will it be safe to suberge the resistors in transformer oil to help insulate them?
Registered Member #46264
Joined: Sun May 11 2014, 05:27PM
Location: Tucson, Arizona USA
Posts: 61
With the schematic you have It looks like the ignition coil trigger circuit will have to be isolated and be able to withstand 30KV. Once the trigger gap fires the low side of the ignition coil will raise by 30KV relative to the Marx power supply low side. Assuming the bottom of the Marx power supply is low.
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Triggering a Marx generator with my camera.
