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jaysun92

Wed Apr 21 2010, 08:04PM

Registered Member #2114 Joined: Fri May 08 2009, 11:58AM
Location: London, Ontario
Posts: 36

Well now i finished making the updated schematic with the changes that were recommended. Here it is.

GhostNull

Thu Apr 22 2010, 11:08AM

Registered Member #2648 Joined: Sun Jan 24 2010, 12:45PM
Location: Australia
Posts: 291

Looks good, hope everything works out and you post your finished coilgun soon

jaysun92

Thu May 06 2010, 01:07AM

Registered Member #2114 Joined: Fri May 08 2009, 11:58AM
Location: London, Ontario
Posts: 36

Ok, I have it all hooked up now but it wont charge to more than 30V. I checked the FAQ on Uzzor's website and I tried different batteries, so I don't think that is it. Does anyone know what might cause the problem?

Thanks to anyone who can help!

Turkey9

Thu May 06 2010, 03:45AM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

I'd double check your comparator circuit. Read the voltage at the divider output from your cap bank and see if it matches your reference when the caps are charged to 30v. If it does, there's your problem and you have to change your resistors.

You might also need to play around with your inductor. If it's not large enough (in terms of inductance) then I don't think it will charge as much. I may be wrong here; I don't have any hard proof, it just seems right.

I built one of these a while ago and it worked great! The inductor was the main limiting factor of voltage if memory serves me right. Frequency also has an effect, so you may want to play with that too.

jaysun92

Thu May 06 2010, 07:41PM

Registered Member #2114 Joined: Fri May 08 2009, 11:58AM
Location: London, Ontario
Posts: 36

Ok, i checked when the capacitors are charged to 30V and the reference voltage is 4.40V and the divider output is only 0.37V. On Uzzor's website it says that any inductor from 100-200uH will work, so I don't think it is that. Is there anything else that it could be?

Thanks for the help!

Turkey9

Thu May 06 2010, 10:15PM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

So we know that the problem is somewhere between your 555 and the cap bank. I'd bet it's one of three things: The signal ( frequency and duty cycle), the switch, or the inductor.

Are you using a commercial inductor or a homemade one? If it's homemade you should make sure it's in that inductance range. If it's commercial then I bet that's not the problem.

If you have an oscilloscope you should check the frequency and duty cycle on your 555. I think you need at least a 50% duty cycle to have good results. Not sure about the frequency but it should probably be between 10kHz and 50kHz. Most fair quality digital multi meters have a frequency and duty cycle setting that will help you out a lot. Just because the values are right on the components doesn't mean what's supposed to happen is what's going on.

jaysun92

Thu May 06 2010, 11:02PM

Registered Member #2114 Joined: Fri May 08 2009, 11:58AM
Location: London, Ontario
Posts: 36

Thanks for the help. I'm using a commercial 120uH inductor. I don't have an oscilloscope and my multimeter doesn't have frequency or duty cycle setting

. Is there any other way to figure out how to make it work?

Turkey9

Thu May 06 2010, 11:15PM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

hmmm.... Other than putting a couple pots as the resistors on the 555 and playing until it works, you could hook a small speaker up to the 555 output (before the power MOSFET) as listen to the tone. With your values the frequency should be around 5kHz so the tone would be pretty high pitched and loud but not make-your-head-explode high pitched.

I'm not too clear on saturation of your inductor but depending on the material that might be your problem. You could get a toroid and wind on it till it's all filled up and try that. I've always had great results with that type of inductor.

GhostNull

Fri May 07 2010, 09:05AM

Registered Member #2648 Joined: Sun Jan 24 2010, 12:45PM
Location: Australia
Posts: 291

Turkey9 wrote ...

you could hook a small speaker up to the 555 output (before the power MOSFET) as listen to the tone.

It might be a better idea to use a pizeo element instead, since the mosfet gate high impendance will mean there may not be enough current to drive the speaker.

jaysun92

Fri May 07 2010, 12:02PM

Registered Member #2114 Joined: Fri May 08 2009, 11:58AM
Location: London, Ontario
Posts: 36

So you are saying that i should listen to the frequency and then play around with the timing until it works?

Thanks for the help.

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