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Registered Member #2848
Joined: Tue May 04 2010, 05:19AM
Location:
Posts: 44
I've been a lurker on this board for many months now and I've posted a few questions regarding my coil gun I'm working on. I've learned a lot and wish to thank everyone who has helped me. I'm sorry if I've been a little non responsive in the past.
Anyhow, my coil gun is working amazingly right now. I've added a second capacitor bank, got the scr switching working marvelously, improved the charging circuits, and put shielding around my coil.
My coil is made of 65 meters of 25 gauge speaker wire, with 1300 turns or so. The coils resistance was 7ohms which was way, way too much. So I decided to cut my wire in half, solder the two halves in series, and rewind my coil.
I did this because I wanted to reduce the resistance while keeping the same number of turns. It worked. My coil resistance is now 1.8 ohms instead of 7 ohms. I am receiving much more velocity from my projectiles as well.
I was wondering if there was any downside to what I did, and if it would be worth my trouble to double up the wire again to reduce the resistance even more. This would result in basically 4 coils wired in series all in the same space.
Registered Member #1208
Joined: Thu Jan 03 2008, 05:30PM
Location: Chesterland, OH
Posts: 154
aarpcard wrote ...
solder the two halves in series, and rewind my coil.
You mean parallel. You were correct in the thread title.
Doing this actually halves the number of turns, while quartering the resistance and halving the inductance. If we ignore inductance, you theoretically quadruple current, and thus double the peak field strength, while quartering the duration. This is just like using larger wire. Depending on your exact setup, cutting again could either increase or decrease performance. In the worst case, it could damage your SCR.
Registered Member #2848
Joined: Tue May 04 2010, 05:19AM
Location:
Posts: 44
Ok thanks for the reply. I'm thinking about adding a dual coil setup triggered by an i/r sensor. Can anyone recommend me a good sensor circuit that would get the job done?
aarp, I've played around with some SCR switching configurations triggered with IR sensors. I was wondering if you could share how your SCR works. For my current model I've sidelined the SCR switch with high current mechanical relays with are more straight forward.
The IR sensors are working perfectly with the mechanical relays and in bench testing it appears that the relays handle the 1200+V just fine, but I know they will wear out eventually and I really want to use SCRs eventually.
Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
Coils in parallel will raise the current. This will be harder on your SCR. They will also shorten the pulse length.
You'll have to find the "sweet spot" for your design. If you think your device is "working amazingly" then maybe you should stick with what you have now.
What is the pulse rating of your SCR? What is the voltage of your capacitor bank? You should aim for a coil resistance equal to the voltage of your bank divided by the pulsed current rating of your SCRs.
If you did the paralleling thing again, you would end up with slightly under .5 ohms, which is around the value most coil guns I've seen use. That's not to say it's best, though.
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Coil Design - Multiple Coils In Parallel.
