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[moved] Very High Voltage Coil Gun

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LAN_403

Quantum Singularity

Sat Apr 26 2008, 06:16PM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

There is always a chance of failure, diode or not. Are your HV caps polarized? I'd think they were not, as it would be difficult/costly to get big enough diodes. I've seen some much bigger Maxwell caps that had blown up internally, but didnt rupture the steel housing (but made a huge dent in it). One thing I heard years ago, never confirmed it though, was that on the big Maxwells you need to charge them quickly and discharge them quickly, as a small amount of internal leakage current can overheat them if left charged for a while and cause a failure. Not sure if this would apply to yours or not, if someone knows please do speak up, as I too am curious is this is something that needs to be paid attention to. I havent played with the Maxwells in many years but when I did I tried to keep the charge cycle at around a minute or less, and discharge them within a minute of that.

Travlax1

Mon Apr 28 2008, 08:27PM

Registered Member #1388 Joined: Wed Mar 12 2008, 04:42PM
Location:
Posts: 23

Ok that makes sense. Im a few days from testing out the launcher for the first time with the big caps. My teacher and I are trying to figure out how to monitor the charge and havent found an inexpensive voltmeter that goes above 1000 V. any ideas or do you guys just charge blindly and fire?

Also, from the power source to the Cap, can I just use alligator clips and then right after its done charging, yank them off and then fire, so as not to cause any damage to the power source?

FastMHz

Wed Apr 30 2008, 05:39PM

Registered Member #179 Joined: Thu Feb 16 2006, 02:08AM
Location: Hagerstown, Maryland - Close to Prime Outlets
Posts: 287

Solid wire will be more efficient...but use what you can get!!

Travlax1

Wed May 07 2008, 02:36AM

Registered Member #1388 Joined: Wed Mar 12 2008, 04:42PM
Location:
Posts: 23

Ok, so I'm launching day after tomorrow and just want to confirm a few things.

I just got a high voltage probe (one of the long sword looking things with an analog readout at the base of it. Im thinking of attaching that straight to the capacitor in order with a long connection cord so I can monitor the charge from a distance. However, I'm wondering if I would need to disconnect it before I launch or would it not cause any problems to keep it connected to one side of the cap.

Also, I'm not in the classroom right now, but the power source we're using looks fairly basic. I believe it goes up to 5000 volts but its just a 18"X8"x4" box that plugs straight into the wall outlet. Our calculations showed that this thing would charge the cap in less than a minute but that doesnt seem right. Does that make sense (without any numbers for you guys) that a small power source like that connected to just the wall outlet could charge the 4000v 375uF cap in less than a minute?

...

Wed May 07 2008, 03:16AM

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

3KJ isn't much energy in the grand scheme of things, you should have no problem charging them off a normal wall outlet...

You should be able to keep the probe away from the cap bank, but make sure that you use wire rated for 5kv, and make sure that all of the connections are well insulated. If you end up with the lead to the probe (either the hv lead from the bank, or the ground lead from the probe) connected to you, you will die.

Just be extremely careful, as that 3kj still is enough energy to do serious damage should anything come in contact with it.

That idea of using alligator clips and yanking them off sounds like a sure way to kill someone...

Travlax1

Wed May 07 2008, 05:08AM

Registered Member #1388 Joined: Wed Mar 12 2008, 04:42PM
Location:
Posts: 23

What do you mean by "If you end up with the lead to the probe (either the hv lead from the bank, or the ground lead from the probe) connected to you, you will die."

I agree about the alligator clips, but how else would you recommend being able to remove the wires from the power source to the cap from a safe distance? I was thinking of having about 10 feet of wire from the power source to the cap and then pulling the two wires from the cap after charging so that there was no way there could be any damage to the power source.

Andyman

Wed May 07 2008, 05:25AM

Registered Member #1083 Joined: Mon Oct 29 2007, 06:16PM
Location: Upland, California
Posts: 256

I think he means, if any part of you comes into contact with any part of the charged circuit, you will die. That kind of energy will stop your heart without any trouble.
Try using a large relay or contactor. The 12-24 volt activating circuit will be much safer. Plus, you can have the switch far away from the rest of the setup.

Travlax1

Thu May 08 2008, 09:49PM

Registered Member #1388 Joined: Wed Mar 12 2008, 04:42PM
Location:
Posts: 23

Ok i'll look into that. How bout for power source? I have a pasco model 9586 kV power supply that goes up to 6kV and just plugs into a wall outlet. I think pasco is just a distributor so they must have just slapped their name on it. What do you think about it? and what do you guys all use?

Quantum Singularity

Fri May 09 2008, 01:00AM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

I've done something similar to the 'yank the alligator clips off' method before, as long as the charger is off and there is no caps in it (so there is no stored charge on the charger side). And make sure there is no chance of anything shorting out if the clips go were they shouldnâ€™t, basically had everything insulated with plastic (like thick cutting board plastic) with a small port for the alligator clips to pass through, and the wires wrapped around a long pvc tube. It is safer and easier too to use a proper relay/contactor. Another option is a large resistor on each leg of the charger. That is what I ended up doing mostly, as I needed some current limiting in the charger anyhow. With a 500K huge power resistors inline I never had any problems leaving the charger hooked up (but off of course).

Travlax1

Wed May 14 2008, 01:50AM

Registered Member #1388 Joined: Wed Mar 12 2008, 04:42PM
Location:
Posts: 23

Ok, and what are you guys all using for your power sources. We have one that goes up to 6000V but its not designed for this type of application and I think it could take days to reach full power.

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