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need assistance on my first coil gun

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williamn

Tue Mar 14 2006, 04:28AM

Registered Member #55 Joined: Thu Feb 09 2006, 04:56AM
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Posts: 149

You can do alot with that 555! Use it in monostable mode to generate an adjustable pulse, I have used them in counltess coilguns with accurate timing down to 10usec. IGBTs are definately something to aim for in your future research. You can use the 555 in astable to drive a simple boost converter, see the archives for a thread I started ages ago about this topic. Find or build a chronograph. This will really help you figure out what you are doing. You will actually be able to tell when something you do makes a difference in performance. All that theory is great to know, but I always learned more when I get my hands dirty. Wind some coils and start experimenting. Also search some of the older threads for actuall coilgun construction, I know there is one thread in there somewhere I addressed a bunch of new commer questions. Coilguns are great fun, I too have been rebitten by the switched reluctance bug again!

Yohan

Tue Mar 14 2006, 07:17PM

Registered Member #194 Joined: Fri Feb 17 2006, 07:52PM
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Posts: 19

I have seen archives. Lots of typing and no proof. Ditto on the contributions.

Rupidust, are you suggesting that we haven't proven our design? Alternately, are you suggesting that our data is just typing and makes no contribution?

Surely you're not. You wouldn't be that naive. I'm certain you lost your way when writing that statement. Because if you had read the archive as mentioned, you would've seen the most efficient SRLA on this forum to be ours; employing the quite successful TTF system along multiple stages with several supporting photographs and video. I've also made numerous configuration details available and welcomed any and all to verify our results.

Read again, Chief.

I'd be more than happy to field your questions.

Quantum Singularity

Tue Mar 14 2006, 10:04PM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

Hey lets offer good ideas here without having to cut down on others ideas, thats uncalled for and rude, not to mention possibly against the rules. I think some basic info for those who arent an expert is great for a newb. Breaking into a new field typicaly has a learning curve, and its often more fun, entertaining, and useful to start off with a good simple working design, then experiment from that point. I built my first TC when I was 18 and didnt understand it. I went off a design someone emailed me. It wasnt even that good of design, but it worked, and if I had to learn every aspect and design it from scratch I probably wouyld never have built it. If I had to re-invent the wheel on every project I started I probably would have a lot less projects under my belt. When I build a CG it willmost likely use SCR's because I have some. If I can get some IGBT's for cheap that can pulse the kind of current I'll be using then maybe I'll consider that after I have a working design. I have alot of elect. eng. skills and I even find some of the IGBT circuits quite daunting to understand - definatly not beginner stuff unless your familiar with them. IGBT's appear to be the best solution for switching, but SCR's can be just fine - just need to tune pulse length with other things like cap size and # of turns and layers in your coil.

phil

Wed Mar 15 2006, 04:32AM

Registered Member #314 Joined: Mon Mar 13 2006, 03:12AM
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Posts: 52

How do I go about charging a capacitor. do i hook up the positive side to the positive side of the battery, and the negative to the negative side? or do i just hook up the positive side? sorry to sound like a noob but normally i only use capacitors for timeing applications, not voltage storage

...

Wed Mar 15 2006, 04:56AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

I am kind of reluctant to give information here for fear that Yohan might deem it inappropriate, but to charge a capacitor you need to connect both terminals to a dc source. Because for most coil guns you need several hundred volts batteries get expensive/bulkley, so most people turn to different charging methods. For a beginner coilgun I recommend taking to small 120v->12v transformers and hooking the 12v sides of the first one to the 12v side of the other one, then plugging the first one in so you get a relatively low current 120vac on the output. From there you can full wave rectify it to give about 170v, add a doubler to get 330v, or a tripler to get a little over 500v. Do not think of plugging a cap strait into a wall outlet.
Just be safe about it.

Bjørn

Wed Mar 15 2006, 06:14AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

do i hook up the positive side to the positive side of the battery, and the negative to the negative side?

Yes and it is good that you ask even if it is simple because doing it wrongly and blowing the capacitor up in your face is not very clever.

I am kind of reluctant to give information here for fear that Yohan might deem it inappropriate

Only the moderators are allowed to do that job. If someone sees something that breaks the rules they should report it and not mention it in the thread. If they disagree with the rules they have to use the Suggestion Box to request a rule change.

The only thing that is on topic here is phils quest for a working coil gun so everyone keep that in mind.

Yohan

Wed Mar 15 2006, 01:14PM

Registered Member #194 Joined: Fri Feb 17 2006, 07:52PM
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Posts: 19

Phil - In a circuit, an uncharged capacitor is considered to be a short at the instant it is connected. Although people do it all the time, it is never a good idea to hook a cap directly to a battery without a current limiting resistor.

I pulled some 450 volt capacitors off a circuit board, so i'll probably use one of those.

uF?

... - What you said was not inappropriate but I feel that you should leave something for phil to figure out on his own. Don't give the roadmap; make him dig a little. That's the only way he'll truly learn. It's ok to nudge people in the right direction. But, a tutorial on voltage triplers and coilguns will do nothing for him if he doesn't understand electricity fundamentals.

I believe you said KISS...so just rectify the AC off the wall. Bridge, resistor, filter cap, done! Probably about $2 worth of components for a 170vdc power supply that'll take him 3 minutes to put together.

phil

Wed Mar 15 2006, 04:05PM

Registered Member #314 Joined: Mon Mar 13 2006, 03:12AM
Location:
Posts: 52

Thanks alot for all the help. And i would prefer that noone gives me a roadmap becuase i like to learn by myself. But i was just asking so i dont blow up a capacitor in my face

.

EDIT:
I tried to make a test coil/circuit today. i'm not going to experiment with the 555 timer yet. I already burned out 2 25 volt capacitors

. But i have another question. whenever i put power to the capacitor it cahges to the voltage of the battery, do i need a transformer to step up the voltage?

Yohan

Wed Mar 15 2006, 10:07PM

Registered Member #194 Joined: Fri Feb 17 2006, 07:52PM
Location:
Posts: 19

whenever i put power to the capacitor it cahges to the voltage of the battery, do i need a transformer to step up the voltage

If ever there was an opportune time to break out the water tower analogy...this would be it.

Anyone feel up to the explanation?

phil

Wed Mar 15 2006, 10:09PM

Registered Member #314 Joined: Mon Mar 13 2006, 03:12AM
Location:
Posts: 52

What your basicly saying is that i need a higher electrical potential. right? If so then i'll have to get a transformer

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