Coil Gun Help

[mneary]

You need to know more about your circuit, before choosing an output transistor. What does your transformer look like? Your primary supply voltage? How much power will you be operating at? Will it self-oscillate or will you have an oscillator/driver?

 

[Krumlink]

I have been overloading the little FET, SO this time I worked on it and I built TEH BEAST!

I am going to improve the coil on it

C1
Power: 30 Joules (going to improve it soon)
Voltage: 150VDC

 

[Krumlink]

I still can't get the darn thing to fire! Is 30 Joules enough Power?

 

[jpanhalt]

QUOTE=Krumlink]I have been overloading the little FET, SO this time I worked on it and I built TEH BEAST!

I am going to improve the coil on it

C1
Power: 30 Joules (going to improve it soon)
Voltage: 150VDC[/QUOTE]

Trying to help you here, but it is unclear to me at what stage you are. That is, what is working and what is not? Please correct any of the following assumptions that are wrong.

As we left the story on the previous page, you had obtained a flash unit from a disposable camera, removed the PCB and determined that you could get the capacitor to charge to 250 V in 2 sec. Then, you gave the part number for a transistor on that board (?) and later a link to a datasheet for it. The transistor appears to be a medium power NPN with a max collector current of 5A and hfe of 350. Somehow, the discussion then switched to MOSFETS and now FETs.

Are you calling that transistor a FET? Have you substituted a FET into the circuit and got it to run? What sort of voltage are you seeing and what size capacitor are you using?

Last, when you say that you cannot get it to "fire," do you mean that you cannot get the capacitor to discharge or that you can't get your coil gun to shoot? How are you trying to discharge the capacitor and do you know that your coil gun circuit would work even if given enough power?

John

 

[Krumlink]

No I wasnt sure what it was, so I called it a FET, sorry for the confusion.

I can get the Cap's Charged up to 200V (2160uf) and the circuit waiting to fire the coil, except the coil won't launch the Copper BB. Everything works fine but that. I have built it correctly, but I still don't think the Coil is Correct for some reason. How many ft roughly do you think that I will need of winding? I have probably been using around 20feet of copper wire.

 

[jpanhalt]

What are you using to switch the capacitor to the coil or switch the coil to the capacitor ground (those are equivalent actions)?

I have never built a coil gun like yours. Presumably you are following an example. What does that example use for length of wire and AWG? Do you have a link to that source? Can you feel any magnetic field at all (using a piece of steel) in the coil when it fires?

John

 

[audioguru]

A copper BB is not magnetic. If it is steel with a copper plating then it is magnetic and should work in a coil gun.

 

[Krumlink]

God I am so stupid! I would keep telling myself to use a ferromagnetic projectile, when a Copper BB isnt! Thank you so much audioguru, I will try a bolt when I get home (especially with my 50ft Coil )

JP, I have seen a few coilgun's using a camera flash board, but I have been going solo for a while. I have found out my problem, and it should work now

I was using 22 AWG enamel magnet wire.

 

[jpanhalt]

With the price of copper, I assumed the BB was just copper plated. John

 

[Krumlink]

Thanks I got it working. With 40.5 Joules, I got a inch long screw to shoot across my basement (about 20 feet very roughly). I then tried to push the circuit to 250V, but then a capacitor exploded, so it no longer works

I was going to pick up some Cameras from Rite Aid, the ones that they dump away, then put them all in parallel, with a massive + and - power bus, and then the capacitor bus too. How should I trigger the coil? I know a SCR works great, but is there any other method? I have just been connecting the lines directly to the coil, but after melting about an inch off after each shot, I don't want do do that anymore (not to mention the molten copper balls that would result from the explosion )

 

[Salgat]

Hey Krum, I noticed you're in Michigan. What area? This project sounds pretty cool.

 

[Krumlink]

I live in the Flint/Grand Blanc Area. You?

 

[Krumlink]

Anyways, do you know of the legendary Nebraksa Power Cube (SCR Cube) is called and where I can get it?

 

[jpanhalt]

Go to DigiKey and search on SCR. Then go through the selection filters. Here are two examples applying 200A or more and 400 V:
https://www.electro-tech-online.com/custompdfs/2007/12/st223s.pdf
**broken link removed**
They are a bit expensive, though. John

 

[chemelec]

Go to DigiKey and search on SCR. Then go through the selection filters. Here are two examples applying 200A or more and 400 V:
https://www.electro-tech-online.com/custompdfs/2007/12/st223s-1.pdf
**broken link removed**
They are a bit expensive, though. John

You don't even need such High Current SCR's for your application. The Current ratings on SCR's is based on Continuous Current draw. In your application it is Just a Short Pulse of current.
A 25 amp SCR will probably handle greater than 200 amps for a "short period of time", as is the situation in these Coil guns.

But make sure your SCR Voltage rating is Much Greater than the Applied Voltage.
"Inductive Voltage Kick back is a Problem".
** Diode Protection is Also Recommended to help protect the SCR from these voltages.

 

[Krumlink]

I will look around for SCR's at low Power. I think Jameco has some that I am looking for.

Anyways, I am trying to get a bunch of people together to help sponsor a massive Coil Gun Project. Roughly 3kJ, at 200VDC, controlled by a beefy SCR: https://www.newark.com/jsp/search/productdetail.jsp?sku=09F5071

It is going to cost roughly 480$ plus shipping.

 

[audioguru]

You won't have such a high current in your coil. Its resistance, its inductive reactance and the resistance of your wires will limit the current.

 

[chemelec]

I will look around for SCR's at low Power. I think Jameco has some that I am looking for.

Anyways, I am trying to get a bunch of people together to help sponsor a massive Coil Gun Project. Roughly 3kJ, at 200VDC, controlled by a beefy SCR: https://www.newark.com/jsp/search/productdetail.jsp?sku=09F5071

It is going to cost roughly 480$ plus shipping.

It isn't just how many Kg you have that really matters.

Its Magnetic Coupling and Multi Stage coils, that will get you the Best Distance.

And your point in Doing this is ??????????????????????????

 

[audioguru]

And your point in Doing this is ??????????????????????????

Hi Gary,
Welcome back.
He is an American. Unlike us Canadians they are obsessed with guns and violence.

 

[Krumlink]

Hi Gary,
Welcome back.
He is an American. Unlike us Canadians they are obsessed with guns and violence.

Yeah that sounds about right