Halo Style 2 stage COILGUN

So I spliced my strongest 1st stage coil to a 2 stage barrel. I put an 8mm ID epoxy tubing sleeve over the 2 barrel pieces which were glued together. Looking down the bore its smooth after sliding my .25 inch steel rod a few passes. Then I just tested as a single stage and *WHAM*. It strongly pierces both sides of the can. So I'll work on the 2nd stage to try and get moar power.

Edit:With my 1st stage cap bank, the strongest coil has always been 21AWG and 6 layers as well as .75 inches. So I'm trying out different 2nd stage coils to find what's best there.

Sounds good so far.
Epoxy tubing is great for barrels. Easy to work with...cheap.

Did you have to change the design?

So far the design is the same, but while both stages have charged properly, the SCR didn't discharge. So I'm back to the problem of getting the SCR to trigger. That is the "only" problem I have left, which is to get the gate to fire for the SCR. I am not "in love" with SCR's :/ used in this fashion. I have another "new" SCR to try tomorrow.

OT: Germany has just shut down it's nuclear reactors while one or two of Japans nuclear reactors melt down like Chernobyl. We need to be taking iodine tablets for thyroid protection, as the radioactive cloud starts getting into the atmosphere. It may be a world-wide catastrophe.

Nuclear energy...like riding rockets to the moon. You start a reaction you cant stop....stupid...and sad. Glad Mrs. Merkel starts thinking these days. This incident will change a lot of things.

Your SCRs wont fire huh? Contacts are working? That was the first big error on my gun.

Ok, so I removed the old SCR and replaced it with the 800v, 650A max SCR. So this time both circuits charged and the coilgun fired 3 times without failure. The last 2 firings had a fireball leave the barrel. The 4th firing did not discharge the 2nd stage. I looked down the barrel and it looks like one spring contact blew off. I will check again tomorrow. This is the most success so far, if the SCR isn't damaged. I"m suspecting a blown-up spring contact in the barrel though. There was incredible force with the last 2 shots. :eg:

Edit: made sure the contacts were there inside the barrel and fired one more time. The second stage did not discharge. Maybe the SCR couldn't take it.

Thats why I like to use stacked SCRs actually they can handle 15-20 times the rated current for a ms.

But why the hell do you have plasma inside your barrel? Thats not normal.
The SCR gate is connected to the charged caps of stage 2 and a 270 Ohm resistor right?

The flash was so quick that it could have been the capacitor bank flashing, but it sure looked like it came from the barrel. I think my mistake was to use 280R resistance, because I think the SCR's gate might be fried. I'll test it later with an LED attached to the cathode or anode. Maybe I should have used a higher value resistor like 420R? I think this would have better protected the SCR. Or the 650A peak was not a high enough rating for the circuit? If I could get the SCR part of the equation right, I would be in business. ^^ Thanks for your help once again AFZ.

"Maybe" I will finally get to a solution, but my luck hasn't been as good as I thought it would. ;-) It reminds me of when I went through several cheap violet laser diodes during my learning phase a couple of years ago.

A cheap "trick" would be to put a fuse in series with the contacts without an SCR and just allow the projectile to short the cap bank. Then you just replace the fuse with each shot. xD J/K

As soon as I get the 2nd stage to work, I can start creating my projectiles that are modeled like a "dart". Sharp steel point inserted into an axial drilled hole then epoxied. Then a lighter wooden stick inserted into the other end with a thin plastic "feathered" flight for stability. I can't wait to build that! ^^ Then I will fire at a sporting "dart board". xD

Yay...I had the same idea: Stabilized projectiles

280 or 420 should both be enough.
Guess the SCRs were to weak.

You did simulate the new coils on Barry's site did you? Will give you the estimated peak current.

Yeah, projected 1000A peak for the circuit with only 650A peak on the 400V SCR. I found an SCR on E-bay that would certainly work all by it's self. It's specified at 1200V 235A and 10,000A peak, but of course it's $99.00.

Stick with the SCRs from digikey. I use them as well. Easier to stack as many as you need and maybe one more

Yeah I'll purchase 6 of these that you recommend and stack them........


IT(RMS) RMS on-state current (180° conduction angle) Tc = 95°C 40 A
IT(AV) Average on-state current (180° conduction angle) Tc = 95°C 25 A
ITSM Non repetitive surge peak on-state
currenttp = 8.3 msTj = 25°C 480A
tp = 10 ms 460A
I²t I²t Value for fusing Tj = 25°C 1060 A2S
dI/dt
Critical rate of rise of on-state current
IG = 2 x IGT , tr £ 100 ns F = 60 Hz Tj = 125°C 50 A/μs
IGM Peak gate current tp = 20 μs Tj = 125°C 4 A
Edit: if I stack 6 of these what "peak" current will that handle?

Then onto the dart construction(just a "little" potassium cyanide on the tips or curare.)(Bond .... James Bond) J/K
I also thought of a way to make the barrel screw together in stages/modules for each coil. But that will have to wait for another build.

I would try to use a one-piece-barrel...way easier. COULD be a reason for jamming or other errors. You never know.

Regarding the SCR: 5 of those should do it as well. 6 for sure.
420R on the gate. Has to work.

millirad said:

...(just a "little" potassium cyanide on the tips or curare.)(Bond .... James Bond)

Click to expand...

win


about the stacked peak current
I readed someday that when you stack SCRS, the peak current should be 20% or 10% lower..

1 scr peak = 400A
2 stacked peak = 640A or 720A

dunno really, just my 0.02 Brazillian cents







I'll be off a time dudes.. need to take care of my real life etc.. cya in a month, maybe less.

CU around soon Leo.