"First" Coilgun / Electromagnetic Projectile Accelerators / Forums

Forums

4hv.org :: Forums :: Electromagnetic Projectile Accelerators

« Previous topic | Next topic »

"First" Coilgun

previous 1 2 3 next

Move Thread

LAN_403

Michael Witt

Mon Mar 06 2006, 02:18PM

Registered Member #282 Joined: Sat Mar 04 2006, 11:45PM
Location: North Chicago, US
Posts: 28

Ok, I'll get an SCR. But what is a "Pulse Generator"?

And how do I make/buy a voltage tripler/quadrupler?

...

Mon Mar 06 2006, 03:05PM

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

a pulse generator is a device that puts out a short pulse when you push the button instead of just being on. You could use a simple 555 or whatever, but it requires decent electrical knowledge, and it is just one more thing to go wrong... If you aren't looking for efficiency I would stay away from IGBT (for now). Because most of the efficiency gain from using a igbt/half bridge is that you don't fully drains the caps, so they can say they only used 82j, instead of the full 100; but the projectile speed isn't really all that much higher for a given cap.

Here are the schematics for a doubler/tripler/quadrupler. Use normal 1n4007 or whatever diodes, and caps in the 100uf range rated for 200v. I could sell you one for $20...

Good luck!

Michael Witt

Mon Mar 06 2006, 09:47PM

Registered Member #282 Joined: Sat Mar 04 2006, 11:45PM
Location: North Chicago, US
Posts: 28

I wasn't planning on making a pulse generator, I just wanted to know what it was, in case I saw it in the near future.

Simon

Tue Mar 07 2006, 12:54AM

Registered Member #32 Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549

I once used a single PhFC to throw a sawn off nail (of a few grams) across a room at just over 10m/s. Experimenting with that taught me a lot about cg efficiency and was pretty fun.

As to switching, going from mechanical, touching-leads-together switching to an SCR improved efficiency by something like .5%, IIRC. That's significant when the whole cg is only a few percent efficient, and the benefit is probably much better with higher power models.

Thought you might like some actual numbers.

rupidust

Tue Mar 07 2006, 02:20AM

Banned
Registered Member #110 Joined: Fri Feb 10 2006, 12:23AM
Location: Banned City
Posts: 85

You present manual method of switching will still work with an SCR upgrade. But instead of the noise, heat, and light you are now manually triggering a small current in the 100mA range to the SCR gate. Further upgrading to pulse control is nothing but electronics. When the electronics know how is present, such an upgrade is routine.

Regardless of SCR or IGBT, the coil geometery and projectile position is the key foundation. You can get 4% efficiency on a first stage even with SCRs by using < 50J (low joule cg) for the first stage. Second stage at < 50 will up that even more. Low Joule CGs have good efficency levels. 10 layers, 30 turns, 8mm inner diameter 20 awg mag wire and 10 gram steel slug 30 mm long will surprise you.

Michael Witt

Tue Mar 07 2006, 10:45PM

Registered Member #282 Joined: Sat Mar 04 2006, 11:45PM
Location: North Chicago, US
Posts: 28

Still a few questions.

Could I use the transformer from a microwave to put out the voltage necessary to charge a large cap? (is the amperage too low?)
Could I use multiple SCRs to pass a larger current (in parallel)?
and, what is a PhFC?

Self Defenestrate

Tue Mar 07 2006, 11:53PM

Registered Member #87 Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191

The microwave transformer has to be rectifyed to DC, and that would probably be too high a voltage anyways. Bear in mind they output ~2kv at ~.5A, so play carefully. Multiple SCR's are good, as well as cheap and easy if you go for TO-220 package devices. Lastly, a "PhFC" is a photo flash capacitor, like on out of a camera flash circuit out of a disposable camera.

Michael Witt

Tue Mar 07 2006, 11:58PM

Registered Member #282 Joined: Sat Mar 04 2006, 11:45PM
Location: North Chicago, US
Posts: 28

Thanks.
For the transformer, I was thinking that I could use a resistor (or two) or a voltage divider to get the required power, either way, I want to be making as little as possible from scratch ('cause I have evil gremlins in my fingers).

Simon

Wed Mar 08 2006, 01:36AM

Registered Member #32 Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549

A better idea than a voltage divider would be to run the MOT (Microwave Oven Transformer

) from a lower voltage. Even better would to build one of the many cap charging circuits around.

The best thing would be if you can get hold of a professional flash unit cheaply. Then you have a nice capacitor with its own (very nice) charger. I've found ones with dented/cracked cases here in Australian tip shops for $5.

Michael Witt

Wed Mar 08 2006, 04:09AM

Registered Member #282 Joined: Sat Mar 04 2006, 11:45PM
Location: North Chicago, US
Posts: 28

I'm a photographer in my other life, I probably have one lying around somewhere

. My PhFC currently is one from a $4.99 walgreens disposable camera. I didn't want to spend that musvh money upfront (if it didn't so much as move the nail, I gurantee I would have given up).

I would LOVE to be able to build one of the cap charging circuits I saw on one of the older fourms, but if I don't have explicit part numbers for everything (and a PCB layout doesn't hurt), then my gremlins go to work.

previous 1 2 3 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob