My first 'real 'coilgun / Electromagnetic Projectile Accelerators / Forums

Forums

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

« Previous topic | Next topic »

My first 'real 'coilgun

previous 1 2 3 4

Move Thread

LAN_403

Maxwell

Mon Mar 04 2013, 11:41PM

Registered Member #8497 Joined: Tue Dec 04 2012, 06:24PM
Location:
Posts: 74

__=|(:3)-|--{__ wrote ...

Im somewhat worried about the metal on the barrel and the eddy currents reducing the efficiency, i would have used Acrylic or PVC

No way - External iron in low-power (which yours does fall into this category) CG's is a good thing. Internal Iron between coil and armature, including barrel material is very bad. You could take laminated transformer cores and 'shield' your coil for an extra .1% probably.

I have not experimented much with external iron, only with end-plate iron. Before I destroyed my CG earlier this winter, I saw at least .3% efficiency rise with thick external iron plates compared to thin end washers.

Yandersen

Tue Mar 05 2013, 12:46AM

Registered Member #6944 Joined: Fri Sept 28 2012, 04:54PM
Location: Canada
Posts: 340

Keep it like you did, Hanzie - good work. Unless you want to reshape your coil and projectile to more efficient dimensions. I would recommend 1:1.5 diameter to length ratio for projectile and the same length for wound coil part while washers at the ends add additional length to coil. To maximize washers efficiency their thickness should be at least 1/4 of internal hole diameter (so before saturation all flux from central hole with projectile can escape completely through the washers).
BTW, don't you want to try recuperational tech? It will take two double-C electrolythics instead of one and two protection diode instead of one. Wanna circuit diagam?

Hanzie

Tue Mar 05 2013, 02:29PM

Registered Member #6534 Joined: Sat Sept 08 2012, 12:22PM
Location: The Netherlands
Posts: 32

Alright, I'll just leave it there then. There's no iron between the coil and the barrel, only those washers on the ends and the bolts keeping stuff together.

Yandersen, sure I'd like to see your idea! This is mainly a proof of concept, but I could try other techniques in future versions. I'm sure this won't be the last one I'll build.

I'm gonna start working on the outside. ^-^

Yandersen

Tue Mar 05 2013, 09:11PM

Registered Member #6944 Joined: Fri Sept 28 2012, 04:54PM
Location: Canada
Posts: 340

Here is recuperational tech for electrolythics:

So C2 should have 0V before the shot - only C1 is charged. After the shot C1 will have 0V while C2 will hold the leftover energy. You can slowly damp it by bleeding resistor in parallel with C2 or you can use this recuperated energy to feed the second stage.
Diodes required in case capacitances are not exactly equal - if so, one of the cap will be repolarized if not protected. Ideally, two caps should have the same capacitance and voltage rating, but you can play with those values.
The original recuperational tech require single non-polar cap (which I have), but in case of electrolythics it can be equivalently substituted with two of doubled capacitance to simulate the same capacitance. Taking into account that my non-polars are 800Vx60uF, I would need 2pc of 400Vx240uF to keep energy the same as polars are 450V rated at most. Take into account low ESR and higher peak currents of non-polars. But still, you can try recuperational tech, see if it is beneficial, and maybe it will stimulate you to buy non-polar caps?..

Hanzie

Thu Mar 07 2013, 02:00PM

Registered Member #6534 Joined: Sat Sept 08 2012, 12:22PM
Location: The Netherlands
Posts: 32

AH, thanks. I'll try that on my next one. ^^
Managed to blow up one of the leads of my SCR. I accidentally bent it a little trying to fit it in there, so I think that was enough to make the pin too thin to survive the current pulses. Already found a new one. Turns out I actually had a 50ria40 laying around which should be able survive much more. Not sure if it still works though, have to test that first. We'll see.

Hanzie

Mon Mar 18 2013, 08:01PM

Registered Member #6534 Joined: Sat Sept 08 2012, 12:22PM
Location: The Netherlands
Posts: 32

Well, it seems to be still alive, but I might have to take a break from the project for a while. Final exams are coming up, so I don't really have any time left to spend on the gun.
I'll get back here once the exams are over.

h3X

Sat Jun 08 2013, 02:48PM

Registered Member #3306 Joined: Mon Oct 11 2010, 12:37PM
Location: Abelstua, UiO, Oslo, Norway
Posts: 3

How is the project going? I've been lurking this thread with some curiosity. :) Hoping to build my first cg soon too, so it's great to read your journey.

Hanzie

Thu Jul 11 2013, 09:05PM

Registered Member #6534 Joined: Sat Sept 08 2012, 12:22PM
Location: The Netherlands
Posts: 32

Wups, sorry for the late reply!

Haven't done much yet. Passed my exams and blew up the charging circuit so I'll have to build a new one of those. At the same time however I'm also building a gaming rig and a pneumatic cannon, and I'm terrorizing the neighborhood from above with an RC-drone I'm putting together. AND as I'm starting a study electrical engineering in September, I'll also have to find a place to live as I now live 2.5 hours away from the university. Ugh, I'm doing way too much at once again... xP

previous 1 2 3 4

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