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Registered Member #1808
Joined: Tue Nov 11 2008, 06:43PM
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Posts: 3
I can´t solve this problem myself, so I have to ask. I have capacitor bank ~1400uF, and I use 400V.
I got three new 470uF 400V Siemens capacitors, and when I connect them with my old capacitor bank, they charge as they should, but when I shoot with my coilgun, the power is MUCH weaker than without these new ones!
But if I use only those three new ones, it shoots well. I can´t understand how this is possible.
Registered Member #1808
Joined: Tue Nov 11 2008, 06:43PM
Location:
Posts: 3
Ok. Can you give some information about the coil witch I should do, If I use 2500uf 400V ? How big wire (AWG)? How many layers? How long? Optimal resistance?
Pipe´s diameter is about 6mm (the projectile is about 5,9mm :) )
And how long the projectile should be to compared to coil?
Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
14-20AWG should be fine, dont use many layers, no more than 3. Barry ran some FEMM simulations, and it showed the optimal coil length is 25% more than the projectile length.
Registered Member #1808
Joined: Tue Nov 11 2008, 06:43PM
Location:
Posts: 3
This question drives my crazy:
As I sayed before, with 400V 1400uF, and using my about 25mm long coil with 15-30 (maybe) layers, I have got pretty good results (thru two sodacans ) ). So when I use same coil with 2800uF and 400V, there comes the saturation, it shoot about one meter. So I have to make a new coil, with less turns. They say to use 3-5 layers. If more turns (layers) means more powerful magnet wield, and therefore higher speed to projectile, I should get with this 4 layer coil about 1/10 magnet field combared to my older 20-30 layers! Ofcourse resistanse is lower with new one (old 1ohm, new 0.3), and it makes more higher current, but that not raise up the magnet field even close the older one.
And what I have now tried, I have maybe got the projectile go about 1/5 from the speed what it was
But with more energy, we MUST use less turns because of inductance and saturation.
So are there some kind of contradiction? I mean, do I have to get like 5 times more energy thru my new coil to get even the same results what I have whit my old coil?
Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
With a smaller coil, you have a higher peak current, so there will be a bigger magnetic field. You can use much bigger coils, but you are going to have to look into alternate projectiles that don't saturate as easy. Silicon steel works well in my coilgun (shot at 955J), much better than steel.
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Interesting capacitor problem
) ).