Why won't people use dpdt switches in their coilguns?

I know that switches are not so efficient because the contacts spark.
But i will start my coil-gunning with switches.

Comments

[iceng]

As Steve said even if you find a very good C&H switch with silver contacts.

When your switch closes to send CAP bank to the coil...

Even the silver contacts will weld the switch always closed for ever.

Why ?

The initial current surge will be Hundreds of amps heating the contact points to the melting point silver causing the contacts to weld each other into a single mass of metal...

The way to avoid welding contact is to use a fast power SCR,
see the pic.

A

[jukees]

And that foot-thingy-above the switch(?), what is that?
You're using the correct drawings for the SCR, resistors, triac, and for the diode, why wouldn't you use them for the switch(?) and for the batteries?
And that moc3023 is a microcontroller?

also, ICENG?

Sorry if this is offensive.

[iceng]

1. That is a foot-switch.
2. A switch that is activated be a foot pressure.
3. What is correct ?
4. If you can tell its a battery and a switch, I have succeeded :-)
5. What voltage am I suggesting ?
6. MOC3023 is an optical isolating 6pin IC ( Integrated Circuit )
7. MOC3023 uses LED light to in effect close a switch from pin4 to pin6 when the foot presses the red button down.
8. I used to design Integrated Circuits as an engineer ( IC eng )
9. I'm smiling and Not at all offended..

A

[jukees]

yup, i'm buying the SCR, as soon as i have money.
but my coilgun is going to be small-scale.
And the main reason i'm asking this question as i see lots of coilgun instructables with separate trigger and capacitor loading switches.
and im wondering that if it can be done with one single switch.

[steveastrouk]

Flashover ? Contact welding ? There's two major reasons.

[jukees]

I know that switches do weld, and are not suitable for coilguns, but i intend to use it in my first model.
which has like 500 µf at 450 volts.
And i do know that switches weld, fixed one switch today that had contacts welded. it was pointless because we had a new switch coming through the mail.

[kelseymh]

Let the poor newbie try it! There's no better way to learn something than throwing your effort and money down a hole. And when it's over, Ol' Scarhand Jukees will probably have a better design for his second coilgun :-/

[jukees]

I'm only newbie in instructables, not in electronics.
As soon as i have money/ordering huge stack of parts, i'm buying the SCR.

[Jayefuu]

"There's no better way to learn something than throwing your effort and money down a hole."

You saying I shouldn't have stopped The Ideanator from trying to wire a 240V relay with uninsulated copper wire? It's okay though, he was going to isolate it by holding it away from the metal frame with an insulated pair of pliers.

[kelseymh]

Well, did he pay for the relay, or did somebody else?

[steveastrouk]

I did.

[kelseymh]

In that case, learning by destruction isn't the best choice :-)

[cwleveck]

Depends on whether or not we get to see it happen. I'm guessing this ones going to be a Wile E Coyote kind of a moment more than a Green Mile event. I say let the kid experiment. Its not a hobby if you dont singe the hair off of something now and again. Just because some of us are more advanced in our tinkering, I burned a hole in my wifes countertop with a laser yesterday (don't tell her, k?), doesn't mean we don't make the same mistakes on a different scale than we did in the beggining. My advice, ALWAYS assume you are going to set SOMETHING on fire. And realize that it won't be the thing you thought could even catch on fire, and also realize that its more likely to set ablaze before or AFTER your experiment. I find the time to be most suspicious is right after you "THROW THE SWITCH!" and nothing happens. Nothing happened YET. Your experiment is NEVER over until the power source is in a different room from whatever you had it connected to a minute ago.
OH! And follow your instinct but follow your sense of smell closer. If you can smell it, you can stop it.

[kelseymh]

My reply to Steve was made in the context of "who paid for it." I completely agree with your philosophy (in fact that was the point of my original comment :-).

However, if you're dealing with something relatively expensive, and it was purchased on somebody else's dime, then you really don't have the right to mess around with it when there are known and researchable precautions you can take.

[cwleveck]

Im not sure I understand how who paid for it plays into this? Not trying to be argumentative, but shouldn't that be his concern? I don't know that it matters as long as it belongs to him when he decides to do something that may destroy it. Plus, who are we to say when something is relatively expensive? I know that his expensive might be different than mine. In fact, my expensive changes all the time. That's why they call it relative I guess. which is what you said. I think if we are going to comment and try to help give a young or new inventor some practical advice about his projects we should concentrate on what he needs to know about what he's doing and leave the life lesson stuff up to his father like mine did me. Sort of .
And, btw, I agree with you philosophically, so don't think Im giving you crap, its a good message your trying to put out there.