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Registered Member #1525
Joined: Mon Jun 09 2008, 12:16AM
Location: America
Posts: 294
Hey, I have a few questions about building a coilgun.
I am very new to this, and have only theoretical knowledge from physics and EE classes. The only hands on experience I have thus far with electronics is soldering a few batteries together and making a weak camera flash coil gun, so please bear with me.
My question is on the power supply. I would like my coilgun to be portable, so it has to be powered by a battery. I plan on having a capacitor bank at ~800V, and I am having trouble finding a power supply that can take DC input and put out 800 plus volts.
I realize that I could use a voltage inverter to convert DC from the battery to AC for the transformer, but all the transformers I can find take at least 120V input, not 1.5V that would come from a battery.
Any suggestions? What are some methods that others have applied to power high voltage coilguns with batteries?
Also, do you have any safety tips? I don't want to electrocute myself.
Registered Member #1083
Joined: Mon Oct 29 2007, 06:16PM
Location: Upland, California
Posts: 256
Try a simple power inverter. A 1.5 volt battery is WAY too small. Go with a 12 volt battery. An important safety tip that I learned the hard way: ALWAYS discharge any caps before touching them with your bare hand.
Registered Member #1525
Joined: Mon Jun 09 2008, 12:16AM
Location: America
Posts: 294
Ah, thank you very much. I will look into this.
Also, what would you think about using something like this? It seems kind of like cheating, not assembling your own circuits and all, but it looks like it would work well.
I'm looking at the 4th one down.
Again, thank you for your help. It is very appreciated!
Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
That uses a voltage multiplier, that means that the output would be really low current, which means long charge times. Then thers also the issue of overcharging.
Registered Member #1525
Joined: Mon Jun 09 2008, 12:16AM
Location: America
Posts: 294
About that, it seems like I'm going to need to manually switch off the charging circuit because every power supply I can find is severe overkill (>1kV). Is there a way to get the circuit to shut off automatically once your caps reach your target voltage? I'm going for 680V on an 800V capacitor bank (15% safety factor, at least for now).
Registered Member #1464
Joined: Sat May 03 2008, 10:56AM
Location:
Posts: 9
Designing and constructing coilguns are very difficult tasks, because you must build everything by yourself. You can buy only parts, not whole function blocks.
DC/AC converter and transformer aren't best solution for portable (especially handheld) coilgun - it is too big and heavy. Voltage booster with some loopback (i.e. comparator with hysteresis) is perfect.
(my booster can charge 15J per 2seconds, and take 12A from 2/3 AAA NiMH batteries - special bateries for high current of course )
Registered Member #1525
Joined: Mon Jun 09 2008, 12:16AM
Location: America
Posts: 294
Ok, I have another question.
If I had an inverter take 9VDC --> 120 VAC and fed that into a voltage tripler or quadrupler, would the current be too low to charge a cap bank of appx. 900J in a reasonable amount of time? If there is a way to calculate the exact output current please let me know.
Thank you all for your suggestions, you have been very helpful!
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040
that depends on the values of the caps (assuming the tripler is a cockcroft-walton, like mine) also, for safety's sake, I would recommend a high value high wattage resistor over the cap, due the capacitance memory (even if you "discharge it" it can retain a charge, I watched my friend get shocked by a homemade cap he had "discharged"... luckily these were not made for performance, but just as a demo in a class)... the resistor keeps the cap from retaining a charge when not in use, but if you use a high enough value, charging time wont be affected too much it may add time, but better safe than sorry.
also, if 680 to 800V is your target, that charger is way overkill (the one referenced, unless I misread, is 10Kv)... their minimax2 seems like a better option, but is at 1Kv
Registered Member #1525
Joined: Mon Jun 09 2008, 12:16AM
Location: America
Posts: 294
DaJJHman wrote ...
that depends on the values of the caps (assuming the tripler is a cockcroft-walton, like mine) also, for safety's sake, I would recommend a high value high wattage resistor over the cap, due the capacitance memory (even if you "discharge it" it can retain a charge, I watched my friend get shocked by a homemade cap he had "discharged"... luckily these were not made for performance, but just as a demo in a class)... the resistor keeps the cap from retaining a charge when not in use, but if you use a high enough value, charging time wont be affected too much it may add time, but better safe than sorry.
also, if 680 to 800V is your target, that charger is way overkill (the one referenced, unless I misread, is 10Kv)... their minimax2 seems like a better option, but is at 1Kv
Good thinking. So is that one resistor in series with each capacitor? We're talking about the caps on the CW right? Also, how do I chose the capacitance and diode values when designing the CW multiplier? I have searched quite extensively and I am still not sure. Thanks!
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Beginning Coilgun Project
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