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2.4Kj to play with....

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LAN_403

Thomas W

Fri Jun 28 2013, 11:12AM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

Hey guys,
ive recently ordered 2x 450v @ 12000uf capacitors for an amazing price.
together its about 2.4Kj availble, the capacitors are made by Cornell D.

Im deciding between 2 things:
Coilgun:
in series:

in parallel:

or a Electrothermal gun:

or just a old railgun but im not to sure about it
because i think i need more capacitors to do that.

Wizzup

Fri Jun 28 2013, 11:34AM

Registered Member #3302 Joined: Sun Oct 10 2010, 02:21PM
Location: Finland
Posts: 42

I suggest an ETG if you have never built one because it is completely different than coilguns and also maybe easier to design as there is no need to worry about suckback etc that is a problem with coilguns. Also with an ETG the projectile doesnt need to be ferromagnetic so you can shoot anything you can fit in the barrel.

For an ETG it is good if the caps have low ESR because in an ETG the caps are pretty much shorted out so the ESR affects a lot.

Also use kJ instead of Kj, it annoys me lol

Signification

Thu Feb 12 2015, 10:11AM

Registered Member #54278 Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367

Wizzup, you wrote:

"Also use kJ instead of Kj, it annoys me lol"

Kj would REALLY annoy me, I -do- use kJ, (capital J because it is someone's name) somewhere I read, in spite of this, that when expressing units ALL letters should be lowercase. ie kj. I just can't seem to stop the kJ format. ...just thought I would add my two cents to what most would think of as a trivial subject--but not so in writing technical papers for highly respected publishers.

Shrad

Thu Feb 12 2015, 10:45AM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

I'd be curious if one was to try using molecules which release big quantities of gas, like KMnO4 or other compounds which release a big quantity of gases when burning or being decomposed...

DÃ©dÃ©!

Fri Feb 13 2015, 03:00PM

Registered Member #4932 Joined: Thu May 17 2012, 01:42PM
Location:
Posts: 59

Or an azide like sodium azide (the gas producing chemical in airbags). It is however very very toxic.

klugesmith

Fri Feb 13 2015, 03:48PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Permanganate? Azide? Why not black powder, or regular smokeless powder, or match heads?

I thought we were talking about electrothermal guns.

Signification, it's easy to find consistent references for proper use of SI units. For example,

A common mistake is to confuse the rules for unit names, symbols, and abbreviations. kj and kiloJoule and KJ are wrong; kilojoule and kJ are right. The symbol for second is s, not sec. I think forum readers have no problem excusing "u" instead of lowercase Greek mu, or omitting the degree symbol in temperature values, because the right way is much harder to type. There's no easy answer for the ohm symbol, but I can't fault the style borrowed from European schematics: 220R, 4K7, 0R15. Better than datasheets where the capital omega is misrendered as W.

Signification

Sun Feb 15 2015, 02:54PM

Registered Member #54278 Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367

Another little 'peeve' I have with these things concerns charge (Q) and current (A). Charge has units of Columbus. Derivable from Coulomb's law F=kqQ/(r^2) using SI units of unity. For example, one Q = 6.24EE18 "electrons". Now, the Ampere is the time rate of flow of charge or one Amp is the flow of one Coulomb through a cross sectional area of wire per second--or in more mathematical terms A=dQ/dt. BUT you see, and hear, EVERYWHERE, amperage expressed as the "FLOW OF CURRENT" i.e. "how much current is FLOWING through the circuit". This is properly expressed as "how much CHARGE is flowing through the circuit". Mathematically current is dQ/dt NOT dA/dt = (d^2) Q / (dt)^2. In the latter expression this generates the question "How much charge is ACCELERATING through the circuit".

There are actually cases of flowing current (dA/dt). This would be called "charge JERK" as the third time derivative is refereed to as "JERK". i.e. successive time derivatives: 'velocity', 'acceleration, 'jerk'

One actual example involving dA/dt that comes to mind is found in the units of inductance--the Henry: 1 H = 1 Volt per (Amp PER second) = V/(A/s) = V/(charge JERK). (to be rigorously correct mathematically, the equation would require two differentials).

NOW, to fill in this "blank": Charge (Q), current (A), "BLANK" (?): what should we call the rate of change of current (dA/dt)??

DerAlbi

Sun Feb 15 2015, 03:42PM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

Dude, this thread is from Jun 2013. Do you really think your Information is in any kind still relevant to Thomas W ?
And at LEAST if you revive the dead thread with useless information about your way of writing kj, Kj, _kJ_... then stay with an "I" if you describe Currents. Your "A" stands for Amps, not current. Thats as if you use "H" for inductance "L". One thing is the Unit the other issnt........

To sumarize: you throw useless information in a dead thread which has no relevance to anyone anymore just to make this kind of mistake that itched you in the first place. Great work

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