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A new coilgun Idea, will it work?

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LAN_403

rp181

Thu Oct 16 2008, 08:52PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

So i was bored in spanish today, and came up with this:

It works like this:

SCR 1 is triggered, dumping power into the coil.When a detector senses the projectile in the middle of the coil, it activates SCR 2. This would Take all the leftover charge from capacitor one, connect in series with capacitor 2, and power coil 2. This repeats with the other coil. If this design works, it would allow you to cut the pulse, causing no suckback, and recycle the remaining energy into coil 2. In a cascade fashion, coil 2 would have more power than 1, and 3 more than 2.

This would allow close placing of the coils, and increased effeciancy.

BTW, the + and - are wrong on the coils. Anode of the capacitor is connected to te anode of the SCR.

...

Thu Oct 16 2008, 11:20PM

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

i have a feeling you are going to run into problems with there still being a coil connected to the other capacitor and causing things like caps getting reverse charges, but its worth a try!

rp181

Thu Oct 16 2008, 11:52PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

I was thinking that since the current would be cut, the inductive kickback would stabalize with existing charge in acpacitors, just dropping the charge. A diode across the cap should get rid of reverse charge.

I was thinking about this more, and the EM fields would probably work like this:

Since the Second coil triggereing is instantly after detection, coils would be close together. When fired, current would ramp up in coil 1. When current is cut, then the second coil would ramp up, but current would still go through the 1st coil, causing a level of neutralness, but the second coils field will be stronger. The current staying in the 1st coil shouldn't be a problem if the coils are long enough, otherwise it would be a normal version with early triggering.

In my original thinking, the load on the second coil would be enough to cause SCR to go open, but that wouldn't happen. Is there anyway i could cause the current though SCR 1 to drop to zero at the triggering of the second SCR?

OZZY

Fri Oct 17 2008, 12:11PM

Registered Member #511 Joined: Sat Feb 10 2007, 11:36AM
Location: Somerset UK
Posts: 55

Hi rp181

As I see it triggering SCR2 will not cause SCR1 to stop conducting. SCR1 will stay on as long as current is still flowing in coil1, you cannot cut the current.

If you tuned the RLC circuit formed by C1 and coil1 so that C1 is empty when SCR2 fires, then C1 would be reverse charged by current flowing in coil2. This negative voltage would cause current in coil1 to ramp down faster which may be beneficial, BUT you are using energy from C2 to switch off coil1 and the reverse charge may damage C1.

On the other hand if the circuit formed by C1 and coil1 is overdamped then there will still be some charge left in C1 and triggering SCR2 will quickly drain it. A diode accross C1 will protect it from reverse charge. This approach will help to reduce suck back, BUT overdamped circuits are inefficient anyway because of high resistive losses. Try simulating this circuit in spice and see what happens.

Ozzy

rp181

Fri Oct 17 2008, 01:25PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

I was having doubts about that, but wouldnt coil 2 draw all the current from coil 1 so current would have stopped to that SCR? If not, im not going to risk trying it.

i downloaded spice, but when i try to create a new simulation profile, i get an invalid profile name error.

OZZY

Fri Oct 17 2008, 05:02PM

Registered Member #511 Joined: Sat Feb 10 2007, 11:36AM
Location: Somerset UK
Posts: 55

Hi rp181

If the coils are short and fat and there is no gap between them then they will have a useful amount of mutual inductance or coupling. The rise in current in coil 2 will cause a fall in current in coil 1, this means there is a transfer of energy from stage 1 to stage 2 (very useful). BUT if SCR 1 does not turn off then when the current in coil 2 starts to fall the current in coil 1 will ramp back up and energy is transfered from stage 2 back to stage 1 (not very useful).

SCRs take a long time to turn off, by my reckoning it would work for the first stage but after that all the SCRs would stay on. However the idea of using the magnetic field of one stage to shut down the previous stage should work if you can open the switch in the very short time that the current is zero.

Ozzy

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