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Camera flash circuit with no ignition coil

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Unread postAuthor: microman171 » Tue Oct 21, 2008 1:06 pm

You could put them in oil? That would be similar to the ignition coils. IIRC you can just use regular cooking oil.
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Unread postAuthor: ramses » Tue Oct 21, 2008 2:38 pm

jimmy101 wrote: Only problem is coming up with a switch that can handle the ~6J in the big-ass cap. Most switches will fry their contacts pretty quickly carrying that much power. Lets see, 6J discharged in say 1mS would be 6 kilowatts. A typical 120VAC wall switch is a pretty sturdy switch rated for 120 VAC at 15 AMPS (or so) and will handle about 1.8 kilowatts, roughly 1/3th the power the photo cap will supply. A typical pushbutton switch handles much less power and will cook its contacts pretty fast in this kind of setup.


yes, but one could possibly just put the low side of the step down transformer in series with the tube. there is the possibility of it not working, but if that happens, run leads to the chamber, put them in series with the tube, and stick some steel wool in there. if your mix is remotely flammable, it WILL ignite, and fast!


just be careful not to shock yourself, it hurts :D :twisted:
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slightly more energy(486j) between copper pennies. steel wool is MUCH more exciting, even with 6.5j
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Unread postAuthor: Hotwired » Tue Oct 21, 2008 3:50 pm

The very fine steel wool I have tends to ignite if you short a flash capacitor into it :)
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Unread postAuthor: DYI » Tue Oct 21, 2008 4:45 pm

Only problem is coming up with a switch that can handle the ~6J in the big-ass cap


Problem? Hardly. A short look on eBay will bring up several SCRs capable of handling at least a hundred times that. Then, just put together one of these:

Image

When you get bored of trying to figure out what went wrong in that rat's nest of wires and easily ruined circuits, and when your $50 SCR randomly stops working after only 10 uses at less than 1/10th its rated current surge, build a simple switch that uses two large copper or stainless steel plates as contacts, something a bit like this*:

Image


*The olde fashioned plunger detonator aesthetic is completely optional.
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Unread postAuthor: rp181 » Tue Oct 21, 2008 5:19 pm

speaking of SCR's....
I will most likley be getting a donation of 7 SCR's, 3 of them can handle 10.9kA surge for 10ms at 3.6kv, and the other 4 can handle a peak of 100kA at 3kV for 1ms. Can someone say railgun :wink:

you dont need an SCR. Capacitors charged and ballasted (i used a 200ohm 1500W resistor bank, way overpowered) and the capacitors will arc if you touch electrodes together and pull them apart. That would be easy to rig up, and electrodes last awhile (i used brass screws). Here's a pic:
(keep in mind the pic is 1.5kJ at 300v, a smaller cap will have the same affect, but for a shorter time. Also, the spark in the pic was initiated with a HV pulse.)

Image


DYI, your wiring looks just like mine... (quality wise (crappy and prone to spark))
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Unread postAuthor: ramses » Tue Oct 21, 2008 5:25 pm

yes, DYI: that is why I use a penny switch (pic)


microman171 wrote:You could put them in oil? That would be similar to the ignition coils. IIRC you can just use regular cooking oil.


Cooking oil goes rancid, smells much better to use mineral oil.
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I put 3kj at 1800v through these things. needless to say, they get rather warm afterward:D
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Unread postAuthor: rp181 » Tue Oct 21, 2008 5:30 pm

wow, and you wonder why theres talk about discontnuing the production of pennies :wink:
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Unread postAuthor: ramses » Tue Oct 21, 2008 5:33 pm

rp181 wrote:wow, and you wonder why theres talk about discontnuing the production of pennies :wink:


sounds like it's time to invest :D :D
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Unread postAuthor: LikimysCrotchus5 » Tue Oct 21, 2008 5:37 pm

Hm, So what is this a transformer, (the black cylindrical thingy in the video)

[youtube]http://www.youtube.com/watch?v=0bMF3MPE5FE[/youtube]

And if it is, could i use that to make a good enough spark that will allow me to have 3 spar gaps?
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Unread postAuthor: ramses » Tue Oct 21, 2008 5:43 pm

I think it is a capacitor, but I can't be sure. I doubt you could use it for 3 gaps with any reliability.
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Unread postAuthor: jimmy101 » Wed Oct 22, 2008 11:31 am

DYI wrote:
Only problem is coming up with a switch that can handle the ~6J in the big-ass cap


Problem? Hardly. A short look on eBay will bring up several SCRs capable of handling at least a hundred times that. Then, just put together one of these: (custom parts, assemblies etc removed for brevity)


See, like I said, the problem is coming up with a suitable switch :roll:

I didn't say it was impossibe, or even all that difficult, you just can't use a generic switch you might have laying around in the garage. Even a 120V 15A wall switch (which is actually a pretty beefy switch) wont take the current for very long.
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Unread postAuthor: Hotwired » Wed Oct 22, 2008 12:58 pm

I've been switching a 10 flash capacitor (parallel wired @ 3-400V) coilgun using a cheap toggle switch probably rated to 10A @ 240V.

Very little notable damage is being done to the contacts, probably no more than it would receive in normal switching.
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Unread postAuthor: microman171 » Wed Oct 22, 2008 1:06 pm

I once used micro switches to switch that kinda current. After about 10 pushed the contacts would weld together.

I fixed this by simply pulling them apart.
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Unread postAuthor: TurboSuper » Wed Oct 22, 2008 4:04 pm

For my old coilgun, which used 3 photocaps wired in parallel, I used a small PBST switch- and it worked perfectly fine till the charging circuit broke. Keep in mind that these switches are rated for continuous use, and the current you can force through them in a fraction of a second is much higher.
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Unread postAuthor: rp181 » Wed Oct 22, 2008 5:22 pm

but after each shot, the contact gets worse and worse, getting less effeciant every time, until theres so little surface area, it welds.
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