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phil

Tue Sept 11 2007, 02:23AM

Registered Member #314 Joined: Mon Mar 13 2006, 03:12AM
Location:
Posts: 52

Hello again everyone. I recently began college and came to be the owner of 64 160V 3300uF capacitors. Which instantly started the gears in my head again and sucked me back to when i had tinkered with coilguns. However this time i did a lot more reading on the subject(primarily in MEC104, the most boring class known to man). I plan on using a 555 timer to oscillate a MOSFET with an inductor to create a boost converter to boost 12V up to 120V. I know this is low voltage for a rail gun but it's a start. However at the moment i'm planning on turning some 24 gauge insulated wire around a random ferrite core from a PC power supply transformer for the inductor. Is this an acceptable option? if not should i shop around for one? also I'm planning on using the projectile to complete the circuit between the rails, essentially the switch. I understand that this will inevitably cause erosion to the rails due to arcing, has anyone used this method before? and if you have how much damage will this cause to the rails? Thanks in advance.

Steve Conner

Tue Sept 11 2007, 09:12AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Try the large yellow donut shaped core, it's an iron powder toroid

It will trash the rails

That's not how you spell "opportunity" :P

phil

Tue Sept 11 2007, 04:19PM

Registered Member #314 Joined: Mon Mar 13 2006, 03:12AM
Location:
Posts: 52

ok I'll give that a shot

then what other form of triggering should i use?

EDIT: I was looking around and it looks like a good bet would be to inject the projectile using compressed air and then having a laser/detector to make sure the projectile is in the rails before triggering the SCR banks. correct?

Steve Conner

Thu Sept 13 2007, 10:49AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Forget all that fancy laser detector and compressed air stuff, I suggest you just load the projectile by hand and then slam-dunk it with a big SCR. Thomas Rapp used an ignitron, but I'm sure one of those big hockey puck SCRs will do fine.

Rapp also invented a clever projectile made from a chunk of plexiglass with a hole through it stuffed with copper wire strands, that can be fired from a standstill without welding itself to the rails. So if you decide not to use an injector, I suggest you use a projectile like his too, it should increase the odds of success.

It's too bad his site's in German.

phil

Fri Sept 14 2007, 02:31AM

Registered Member #314 Joined: Mon Mar 13 2006, 03:12AM
Location:
Posts: 52

Thats an interesting idea, i might experiment with a projectile like that. I made a boost converter today, however it's not working properly. The voltage i'm getting as an output is .4 volts lower then the input. I think my problem is i'm not switching fast enough. My skills with mr.555 arent that great so thats probably my problem.

Dalus

Fri Sept 14 2007, 07:58AM

Registered Member #639 Joined: Wed Apr 11 2007, 09:09PM
Location: The Netherlands, Herkenbosch
Posts: 512

What core are you using as a inductor. Those yellow core's from old computer psu are suitable. But it's better to make your own transformer by rewinding old atx transformer for a higher voltage. You can use a 555 flyback driver to drive it. At least that's what i always do.

Steve Conner

Fri Sept 14 2007, 10:55AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

An ATX transformer doesn't even need rewound to get 120V. If you drive the 5V windings with a ZVS running off 12V, you can get 150V with a plain rectifier or 300V with a voltage doubler on the output. I did this on one of the old 4hv forums years ago.

Note I got my transformer from a supply that was switchable 120 or 240V. A 120V only supply might only give half the voltages.

Ken M.

Fri Sept 14 2007, 02:06PM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

I'm pretty sure most atx power supplies are switchable now a days so, I doubt he'll have trouble finding one.

phil

Fri Sept 14 2007, 05:49PM

Registered Member #314 Joined: Mon Mar 13 2006, 03:12AM
Location:
Posts: 52

I yanked one of the toroidal cores with the copper wire wound around it for use as my inductor. But before i get into that part of the boost converter i first need to figure out how to get the 555 timer to work. The fact that i don't have an oscilloscope doesn't help the matter. The output of the 555 timer is showing voltage which means its working, however i can't tell exactly what frequency it's outputting.

Zum Beispiel

Sat Sept 15 2007, 08:09AM

Registered Member #514 Joined: Sun Feb 11 2007, 12:27AM
Location: Somewhere in Pirkanmaa, Finland
Posts: 295

phil wrote ...

I yanked one of the toroidal cores with the copper wire wound around it for use as my inductor. But before i get into that part of the boost converter i first need to figure out how to get the 555 timer to work. The fact that i don't have an oscilloscope doesn't help the matter. The output of the 555 timer is showing voltage which means its working, however i can't tell exactly what frequency it's outputting.

You can get DMMs with frequency/duty-cycle range for pretty cheap (20 bucks). I strongly recommend you find one, as it is very helpfull with these kind of measurments.

Or failing that, you could just "probe" the 555 pin 3 with a small speaker. You can make a rough (very rough!) estimate of the frequency by the sound it makes.

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