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Registered Member #1805
Joined: Sat Nov 08 2008, 06:29AM
Location:
Posts: 67
Hi,
I have built numerous single stage Coil Guns from used disposable camera's and I want to try and build a multistage one. I found a schematic for a photo interrupter circuit that activates a relay, but it runs on 12v and I would like to use 9v.
Will this circuit work for what I'm wanting to do? Do I have to change any resisters or anything to make it work at 9v?
Registered Member #571
Joined: Thu Mar 08 2007, 12:48AM
Location:
Posts: 1
To be honest, you may want to avoid any circuit that involves a relay as your switch. It's slow, and won't allow enough current to flow through to make a worthwhile accelerator.
Registered Member #1643
Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039
I use SCR. As long as they are rated for the power you will be using they are good. This way a 9V battery triggers it one time, and it lets all current flow until its under X volts. mines like a 500V 50A surge rating, and rated for 800V 50Amps. I got 2 so I can do a multi stage :D
Registered Member #1262
Joined: Fri Jan 25 2008, 05:22AM
Location: Maryland, USA
Posts: 451
Switching methods really depend on bank energy.
Under 100J you can always get by with a mechanical switch, although relays are slow to close if your attempting to time the current flow. Relays should always take around the same time to close though, so you can build the delay into the design and placement of the interrupter.
Banks up to around 1kJ can be switched with spring loaded contacts or an SCR, an SCR is the only option past about 1kJ. Unless your talking about several kJ, in which case you'll need a trigatron.
Registered Member #1805
Joined: Sat Nov 08 2008, 06:29AM
Location:
Posts: 67
Thanks for all the help.
I think Ive worked out my problem about the 12v. I'll just hook together 2 AA or AAA and a 9v battery to get the 12v. Will this work though? I tried it and tested with my multimeter and it worked but will it do anything over time?
For the relay issue I'm only working with disposable camera caps and chargers so I think a relay will work, its worked so far.
I did look at SCR's but I didn't really understand how they worked it seemed to me that they only work with a set voltage but I want to be able to try more or less capacitors.
Any more opinions or help will still be very much appreciated.
Registered Member #1262
Joined: Fri Jan 25 2008, 05:22AM
Location: Maryland, USA
Posts: 451
Do not try using disposable camera caps in series. They will die young, and potentially explode. Getting 12V from a 9V battery and two AAAs can work, although its not ideal.
How to trigger an SCR
You can use an SCR at whatever voltage you like, up to its rating.
We can tell you a bit more about deign if you give us a rough idea of how many flash caps you intend to use.
Registered Member #1107
Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792
Backyard Skunkworks wrote ...
Do not try using disposable camera caps in series. They will die young, and potentially explode.
Not really. I have a photoflash cap bank with 8 strings of 6 capacitors and i charge it up to around 1.8kv and i have yet to have one die on me. Maybe that is because i am using proper balance resistors and a protection diode?
Registered Member #1262
Joined: Fri Jan 25 2008, 05:22AM
Location: Maryland, USA
Posts: 451
teslacoolguy wrote ...
Backyard Skunkworks wrote ...
Do not try using disposable camera caps in series. They will die young, and potentially explode.
Not really. I have a photoflash cap bank with 8 strings of 6 capacitors and i charge it up to around 1.8kv and i have yet to have one die on me. Maybe that is because i am using proper balance resistors and a protection diode?
Registered Member #1805
Joined: Sat Nov 08 2008, 06:29AM
Location:
Posts: 67
I'm not sure on how many caps or chargers I'm going to use and to what voltage the caps will be charged to. That's why I like relays because they just work at any voltage (until they weld together but I haven't had that happen yet), but SCR's look like voltage and capacitance need to be set.
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Photo Interrupters
