Coaxial LC design for pulse compression using a moving short / Electromagnetic Projectile Accelerators / Forums

Forums

4hv.org :: Forums :: Electromagnetic Projectile Accelerators

« Previous topic | Next topic »

Coaxial LC design for pulse compression using a moving short

first previous 2 3 4 5 next last

Move Thread

LAN_403

Shrad

Fri Mar 06 2015, 01:50PM

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

I have realized that the time constant of a RC circuit having ten times the capacity and the same equivalent resistance would be under the picosecond discharge time, so you are totally right by saying my idea is impractical

do you see any mean of changing that time constant to a more practical value while still being able to transfer a decent amount of energy to the coil?

DerAlbi

Fri Mar 06 2015, 09:30PM

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

Sry, i lost the context.
RC-Constant in a LC-Circuit? Increased Capacitance, but decreased discharge time? Nothing here fits together.
Attach your simulation file.

To the moving short: what can i say. a traveling magnetic field is allready a known concept prooven working in the transrapid train. Of course thats a good thing, but there are many ways to realize this.

If you have only so short time to spare to think about stuff and do things, maybe you should resort to stuff that are practical for you and will source real projects.. this was a global was of time for everyone who was forced to react to get this content clean. there is a backside to sharing irrelevant ideas. imho.

Andy

Sat Mar 07 2015, 12:43AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Sorry bad day :(

Shrad

Mon Mar 09 2015, 09:08AM

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

Doesn't the RC constant of the capacitor and path to the inductor account for the discharge of the capacitor into the coil?

I would at least appreciate to be explained... or if this is such a waste of time for you to discuss on a conversation that you encouraged (developing my idea and confront it to your knowledge) then so be it, I won't cry you know... anyway, don't take offense but I was at least expecting you to educate my reasoning to a point of understanding my errors, which seemed to be a claim of yours

DerAlbi

Mon Mar 09 2015, 11:27AM

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

I do everything i can :)
I understand now what you mean by RC-Constant. You describe your Capacitor modely only and its ESR*C is ~10e-12s. Are you sure you used R TIMES C and not R over C ?

But i dont see why this concludes the setup as impractical. The circuit alone would still work. just assume practical values for R, L and C..

There are others things here that make it impractucal. Only if you would specify a projectile and then do the calculations you can know it. If there values emerge so that you need a RLC-Circuit with unrealistic quality factor you know for sure its bogus.

Shrad

Mon Mar 09 2015, 12:26PM

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

then assume an iron projectile of 3mm diameter for 2.5cm of length

I assume that if the projectile acts as a switch, current will flow only during the time it is shorting the circuit

my questions is then how to design the circuit so that the projectile launch occurs only in the positive part of the first period of oscillation of the RLC equivalent, to take advantage of having only one direction of a magnetic flux

I'm almost sure you know what I mean, but I just have no clue where to start regarding practical values for coilguns so I won't be able to deliver correct ballparks

DerAlbi

Mon Mar 09 2015, 02:39PM

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

"correct ballparks"

Oxymoron again.
What equations are your considering and where is your exact problem? I cant come up with values if you dont say what you need.

Using the projectile as a switch wont work. As long as there is any current flowing it will arc as hell. But if you wish to use the whole positiv halfwave of the current, replace the switch with an SCR.

Shrad

Mon Mar 09 2015, 03:32PM

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

I don't really care about arcing, but I wouldn't use an SCR

I can reduce arcing later on and want to keep with a pure LCR design like I explained

to start on values I'd say 10ÂµH for the inductor and 10nF for the capacitor are what I would consider practical if I was to build simple components

what is the achieved speed for a usual coilgun projectile? you'll say that depends and I must give values

I want to slow down the discharge into L so that its duration is low enough that a projectile would be able to travel a distance of 20cm or 30cm during the whole positive halfwave of the first period of the current, while keeping enough of that current so that the magnetic flux is strong enough to project the unpractical projectile in a practical way

is this practically practical?

joke apart, my simulation shows a current of 640 amps at max with a 50 ohm current limitation resistor... that makes a discharge of 1.6Âµs

I'd be curious about your advise, without arguing about the unfeasability of the thing ;)

DerAlbi

Mon Mar 09 2015, 05:50PM

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

Use

to get an overview what people achieve. You can estimate Speed and Efficiency of the common designs there.
What you try to do is called critical dampened oscillation. Thats done before. See

for theoretical background. I suggest you read the whole site at least twice.
The question is: do you really want to proceed from this point? You struggle with the most basic things.
Basically you ask how you could increase the resonant frequency of an LC-Oscillator with a fixed C... soo.. increase the L ? Why do you come up with 10uH anyways.. What pulls the projectile is Amp*Turns. Having low inductance brings nothing but a short pulse and high current..
I really dont understand why you consider this as practical when you allready see that your discharge time is in the mirosecond range.

Sry, i can not make the research for you. I am not paid for this and its going nowhere anyways. This whole situation is not the most promising situation for something "new" that actually works even after one does the math.
And i am getting bored to discurage you and beeing the ass for it just because people stuggle to accept their limitations. Sry again.

Signification

Tue Mar 10 2015, 05:05AM

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

There are actually four RLC system configurations of a series RLC circuit (each configuration is determined by the RLC values. The series circuit remains the same). I have found that each can have their place for particular needs of projectile accelerators. They are: un-damped, under-damped, critically-damped, and over-damped. Each is described by a differential equation. The oscillatory systems (un- and under-damped) occur when the characteristic equation involves complex roots (but cancellation leaves only real solutions). The 'over-damped' systems occur when the equations yield only real numbers in the solutions. The interesting, critically-damped, system occurs in the transition from the under-damped (where R=0) to the un-damped system. I am in the final stages of working out in detail, application-friendly versions specifically for coilguns. It would be inconvenient to try to write the equations with corresponding solutions here.

On another note: it is incorrect to write "dampened"--the word is "damped". The former always makes me think "inexperienced" user. To increase the frequency of an LC circuit, DECREASE L and/or C.

Shrad: those are some excellent-looking current and voltage waveforms--no ringing! I really need to look into obtaining that "LTspice"? simulator.

first previous 2 3 4 5 next last

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob