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Registered Member #2906
Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727
..well SCRs still, however without a freewheeling diode,so the caps could repolarize. thus getting energy back from the coil. this left energy is then used to feed the next coil. He is actually using the full positive sine-wave current, instead of only the quater waveform. this has inherently much much higher efficiency (not wasting half the energy, and having less suckback) as said: real advancements are only possible by creativity. building the same circuit again and again wont improve things. the limit has been reached.
e.g. Signification has his big Puck-SCR... and big plans in mind - not realizing, that bigger means only deeper into saturation thus less efficiency and at the end: is another crappy design with <5%. Getting a decent energy out of it will require even more input capacitance.. it will only grow impractical.
Yes this is crying and raging... but my complaints are on topic: I am complaining right now that most fo the CG-Community is a bunch of kids that found CGs on youtube and want to impress their friends. the minority are advanced hobbyist and even less are educated engineers. the problem is that the advanced hobbyist are really good at explaining things to otheres but most of the explainations are wriong in the fine details. Thats in no way a basis for "large coil gun"s. Which actually need to be engineered by maths - where every minor error would offset the results.
CGs are a good school project, but most people here who claim to make more out of it wasting only time and money on a concept that simply cant be scaled up. Or more comprehensive: if you increase your output power you are likely to decrease your technical worthyness. ...and noone gets it
Registered Member #54278
Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367
DerAlbi, I do NOT have 'big plans in mind' for some super coilgun with some monster puck SCR. I would have to be insane to throw together a coil and power it with 10's of kJ with a 56kA SCR. This is the impression you give the readers!
FYI: I asked about the use of other (than electrolytic) types of capacitor in coilguns such as energy / pulse caps, with the latter stages of a multi-stage coilgun in mind. As the projectile is then moving very fast and perhaps needed the energizing best applied by a fast discharge capacitor. The point was leading up to whether there becomes a stage where increased efficiency requires a faster type capacitor that could dump a greater percentage of it's energy (thus increased efficiency) into accelerating the projectile. My thought was that at this point an electrolytic cap would barely discharge (crippling efficiency). your harsh words discourage my continuing...
You seem experienced and your words seem wise, why don't you use them in a more positive manner instead of using this jump-the-gun to a (self-described) "raging and crying" style. Nobody gains from that.
Registered Member #2906
Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727
I cant use my knowledge here in a much positive way because i did research and experiments that can describe optimization of a CG.. but i cant tell anyone "this must be so, and this should be like this etc". Who here actually could do some advanced FEM or even knows what the cross correlation of Coilcurrent and potential coil force means physically. Its just hard to teach, when the most basic caluclations are avoided because they are too hard. Even more, if you can only write about it
But dont be discuraged - at least not much. Its ok, if you take a step back and notice "there is a guy raging about SCR users - could he be right; what can i do?" Answer: Math. You worry about stuff thats way ahead of you. May i ask for reasons? I mean: who needs low ESL (what impact would it have - this can be calculated), The same is with the ESR. You just talk about the "later stages" Even at 100m/s and "only" 2cm Projectile length the time scale is still 200us. You know how fucking long that actually is for the order of magnitude where parasitic effects are? The ESR of the Cap: do you know how low 10..50mOhm actually are in comparision to your coil or the differential resistance of a SCR?
Your worries are good - you NEED to know what CAN go wrong. But the consequences are not be best: you immediately look out for material... but what is actually good enough? That what others say? No. From your design goal comes directly a specification what will be good enough. This IS the hard part of the project.
Dont take it as an offense I started out exactly the same. Now i am heading for 35-40% eff and my highes current is only 700A... kind of crazy, issnt it? Parasitics? Yes, extremely important! But only where they are actually at work and causing issues.
I concluded from your way of acting in the forum, that you are enthousiastic like hell. Having a thought everywhere - reviving dead threads because thoughts just jump around making it impossible to actually watch for Threads-Dates... and it shows that you are willing to study - because you use the forum search to dig out these threads and you actually read them! Thats GOOOD! If i have taken a little peak of your motivation then i am glad to help, you are now much more productive state - you are able to focus on the important stuff and determine if you really have a goal or just the mood to build a CG
Really: i am offering my help by questioning your fears. First show me a basic calculation that shows the relevance and thats it. For basic ball park figures its often enough to know Resistance R = U/I; Inductance I = U*dt/L Capacitance: U = I*dt/C
If you determine that your ESR has only 10-20% impact? who cares. If you determine that your ESL reduces voltage by 100V? Who cares? Back EMF reduces your voltage by U = F*v/I (What is F_orce? -> FEM, v is your planed velocity, and I is your peak current) are thes 100V still important? Until you dont know the answers... you know what i mean?
Registered Member #11591
Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556
DerAlbi wrote ...
I cant use my knowledge here in a much positive way because i did research and experiments that can describe optimization of a CG.. but i cant tell anyone "this must be so, and this should be like this etc". Who here actually could do some advanced FEM or even knows what the cross correlation of Coilcurrent and potential coil force means physically. Its just hard to teach, when the most basic caluclations are avoided because they are too hard. Even more, if you can only write about it
But dont be discuraged - at least not much. Its ok, if you take a step back and notice "there is a guy raging about SCR users - could he be right; what can i do?" Answer: Math. You worry about stuff thats way ahead of you. May i ask for reasons? I mean: who needs low ESL (what impact would it have - this can be calculated), The same is with the ESR. You just talk about the "later stages" Even at 100m/s and "only" 2cm Projectile length the time scale is still 200us. You know how fucking long that actually is for the order of magnitude where parasitic effects are? The ESR of the Cap: do you know how low 10..50mOhm actually are in comparision to your coil or the differential resistance of a SCR?
Your worries are good - you NEED to know what CAN go wrong. But the consequences are not be best: you immediately look out for material... but what is actually good enough? That what others say? No. From your design goal comes directly a specification what will be good enough. This IS the hard part of the project.
Dont take it as an offense I started out exactly the same. Now i am heading for 35-40% eff and my highes current is only 700A... kind of crazy, issnt it? Parasitics? Yes, extremely important! But only where they are actually at work and causing issues.
I concluded from your way of acting in the forum, that you are enthousiastic like hell. Having a thought everywhere - reviving dead threads because thoughts just jump around making it impossible to actually watch for Threads-Dates... and it shows that you are willing to study - because you use the forum search to dig out these threads and you actually read them! Thats GOOOD! If i have taken a little peak of your motivation then i am glad to help, you are now much more productive state - you are able to focus on the important stuff and determine if you really have a goal or just the mood to build a CG
Really: i am offering my help by questioning your fears. First show me a basic calculation that shows the relevance and thats it. For basic ball park figures its often enough to know Resistance R = U/I; Inductance I = U*dt/L Capacitance: U = I*dt/C
If you determine that your ESR has only 10-20% impact? who cares. If you determine that your ESL reduces voltage by 100V? Who cares? Back EMF reduces your voltage by U = F*v/I (What is F_orce? -> FEM, v is your planed velocity, and I is your peak current) are thes 100V still important? Until you dont know the answers... you know what i mean?
You are right. But, you could be less condescending! Maybe he just wants to make a coil-gun. Maybe his goal was not to make the highest efficiency one ever. Maybe, like I, he would love to spend some time going through the math(s) and design and make a really highly efficient coil-gun but has other stuff to be getting on with.
Registered Member #54278
Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367
First: you grossly misjudge me... and it seems what you are saying is, 'this is not the place to learn', and since you view yourself as *advanced*, you don't have to help anyone. Your logic makes no sense. Instead of all the criticism, why don't you just offer that help or say nothing?
Registered Member #2906
Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727
Right. maybe its just my cry and my frustration that i have basically noone to work with above a certain level. I understand, its a nice fun project but it can become art. And i often get the feeling that most people see it as art whatever they do. i seem to be easily offended by this
@ Sig: of course i may misjudge.. its the internet. i can only watch for signs and interpret them in my way. "this is not the place to learn". no no, its not the place to teach. its just not possible with people who avoid basic equations. (that does not implie you, its more general) As a fun project most people do not want the uncool stuff. Cant you understand this hopeless situation everyone is in who is actually educated in electronics? If you cant even relie on basic knowledge of Ohms Law.. where to start? And people tend to want to fly to the moon with their designs... basically you need to give others a perfect solution . if not, you are a bad person hard to do that.
For my part i would really be interested in your calculations and double check them - no problem. Then lets discuss the parasitics and what you can expect and idendify the problems that actually exist. It first starts with a specification: what do you want to achieve.
Registered Member #11591
Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556
DerAlbi wrote ...
... "this is not the place to learn". no no, its not the place to teach. its just not possible with people who avoid basic equations. ...
Bollocks. I, for one, enjoy equations. You seem to be assuming nobody wants to learn on this forum. You may misjudge, but if you think there is a possibility of misjudgement you should refrain from comments like that.
Registered Member #54278
Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367
hen918, exactly! I love equations --and more so, learning their meaning deeply enough to apply them practically (I think this is obvious through my posts). My degree is in physics, BUT if I even made a 'B' on any math test, I considered it somewhat a failure since there was something I was not getting. Above all: I want to understand why something works -or fails-
I am new here, but will adjust to any rules--I NEVER saw a problem until DerAlbi apparently got me thinking maybe I am on the wrong forum (with every single reply to me!). I came here to learn as much as teach--and enjoy. I will *very carefully* re-read the rules and in the meantime post a bit less frequently.
Registered Member #2906
Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727
hen918: You are obviously here to contibute, not to ask Thats not what most Threadstarters in the EM-Accel.-Forum do...
Just listing the topics: 72MJ escape velocity, storage for 5 hours on mains: wishfull thinking. 2.4Kj to play with....: first ordered parts then searched a project for the Caps. Beginner. Brooks coil: its an ok thought. Coils - contract or expand?: holy... "GAUSS CONTROL": if current measurement is expensive, its done wrong. Parallel coil-layers?: "bored guy", but not willing to search how inductance behaves in coupled inductors? Induction launcher experiments: belong in the project section. Coilgun - 1 long 1 layer coil as long as the barrel? Good, Bad?: Has not done basic reading about the topic. flat copper coil...?: asks basically, if he should do an experiment to learn something. ?? Circular railgun?: good one. Its BigBad. Hes great. action integtal: good start but no information why its considered... Pulse D optimizations: asks for complex optimization. Just a quote: "What im trying to workout is, with more volts more amps are produced from a cap, but the joules increase by power." What? Capacitor charger for multi stage coilgun: again a ZVS deriviation. And it will just blow up. Low Voltage Capacitor ETG: Hasnt read the basics of what he want to do. He googled not longer for 10min. Infrared trigger circuit: has problems with rebuilding a given design.
Shall i continue? Its nice that YOU are good.. But YOU are then not the person my posts relate to. Pick a topic that gives you hard reasons to be discussed. You notice that you will need to be picky.
Sig: then show the stuff you think about in math language! I am interested - really!
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large coil gun
I started out exactly the same. Now i am heading for 35-40% eff and my highes current is only 700A... kind of crazy, issnt it? Parasitics? Yes, extremely important! But only where they are actually at work and causing issues.