Coil Gun Help

[Krumlink]

I was in the process of designing a coil gun and stuff, but I needed a 200V compact power supply. I have seen them before, but I don't know where to start (not even Google).

So basically I need design help on:
200V tiny Power supply (run off 3-12V)
Barrel Design help (I have a few ideas)
Single Stage or Multistage

I have done the math, and I want to use 4 8200uf Cap's at 200VDC, so:

E=0.5*200^2*0.032800 (32,800uf)
E= 656 Joules of energy

Any suggestions to the Power supply?

Thanks

 

[jpanhalt]

Try a CCFL or electric fly swatter transformer or scavage a model CDI ignition. If you look here: https://www.rcuniverse.com/forum/m_4344316/tm.htm
you will find a design to charge a capacitor to 400V (you can use a half wave rectifier to reduce that). The capacitors you plan to use will charge more slowly because of their size, but then you don't plan to fire it 10,000 per minute either. John

 

[Krumlink]

That is more complex than what I am looking for. Is there any easier way to do this? I have a tiny Inverter transformer, but I don't know how to run it, only the pinout I know of:
https://www.goldmine-elec-products.com/prodinfo.asp?number=G13599

If I knew how to power this little thing, I could get a good 200VAC out of it, then I would only have to rectify it.

Thanks

 

[mneary]

You could have taken your math one step further.

That little transformer will give you maybe a hundred milliwatts. Your 656 joules will take 6560 seconds to produce; you'll be able to fire your coil gun once every two hours.

 

[jpanhalt]

Here are some schematics for different ignitions. One includes a voltage doubler (Chinese); one is an American version without the doubler; and the last is a comparison of the oscillator side of the circuit. The circuits are all pretty similar. One difference between these circuits and the one I linked you to is the use of NPN instead of PNP oscillator transistors. Of course, you can use whatever you want ot rectify the AC and charge the capacitors. John

Edit: The names didn't come through. The Chinese ignition is the center image.

 

[Krumlink]

I think I am just going to use a Camera flash board instead of trying to build my own, just so I know it will work. I will have to repick the Caps, but thanks for giving me those circuits

 

[Krumlink]

Couldn't I just modify**broken link removed** this circuit and remove some of the Diode Capacitor pairs?

 

[Krumlink]

Instead of 120VAC at 60hz, Could I feed in 12V PWM? He said it took 2 Seconds to charge up 2.5kJoules, so at 1/10 of the voltage, it would have take 20 seconds, but at 1/3 it would take roughly 7 seconds to charge, correct?

 

[gramo]

* Alarm Bells *

Another victim of the Rail Gun project

Don't hurt your self with these high power & voltage devices hehe

 

[Krumlink]

Oh don't worry I have experience with High Voltage, so I know what to touch and what not to touch. ALso not to look down the barrel of the coil gun

What about my question though?

 

[Krumlink]

In a camera flash circuit, it has a dinky little Transistor that can blow easily, so I was wondering could I replace it with a beefy MOSFET or build a whole new system to 300V (yeah I changed it, now it will run at 300V, I don't think that the cap's will mind too badly)?

 

[Krumlink]

Look here I found the exact thing I wanted!

**broken link removed**

Where can I get the Xformer? I think that Camera's have a 5 pin Xformer like this?

 

[audioguru]

The 2N3904 transistor has a max allowed current of only 200mA and performs poorly above only 100mA.

Go to a camera shop that develops film from disposable cameras and ask for the camera that is thrown away. It has a very low amount of power for its flash.

 

[jpanhalt]

Isn't that circuit essentially the same as the American CDI design posted above (ignore the SCR firing mechanism)? From what I have seen, they are all about the same with a single transistor oscillator. Differences are mainly on whether to use NPN or PNP.

For the transformer, you can make it yourself (see: prior link), try to use a CCFL transformar (main drawback is low current capacity), scavage one from a CDI, or buy from CH Ignition (https://www.ch-ignitions.com/#cat). For just the transformer, you need to call CH. CH also has complete HV boards with transformer but minus the ignition coil for $30 (item #68). Some people use the 3055, TIP31, or MJE521 or equivalent for more current capacity. The 3904 as AG points out will get real hot at any reasonable current for charging your capacitor bank. John

Edit: Since size and weight are not such big issues as they are with models, you might consider using a 110-volt step-down transformer with a center tap on the secondary wired with the intended seconndary (LV side) as the primary.

 

[Krumlink]

Good News!

I went out and bought a couple disposable cameras and opened them up. After doing some testing, I can get 250V in about 2 seconds across the Camera's Capacitor. I know that If I hook this up as it is now, the Little MOSFET would blow on it. The Part# is D2687. There is also a quick PIC of the modified Circuit (removed the Trigger Coil, Switches, Flash tube and added a few other things). Can I replace the MOSFET with a stronger FET?

EDIT: Picture was upside down

 

[Krumlink]

Found the Datasheet:
**broken link removed**

It is a low frequency amplifier? What can I replace that with?

 

[audioguru]

Select a Mosfet with a voltage rating higher that you have and a current rating high enough for your load.

 

[Krumlink]

Ok, thanks I will have to look around then.

Well it is going to be working in short circuit mode (aka coil)

What channel should I pick? N-Channel?

 

[Krumlink]

What MOSFET should I pick? I was going to order some parts later today.

 

[jpanhalt]

Why do you want a mosfet? John