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4hv.org :: Forums :: Electromagnetic Projectile Accelerators
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Project Log- Coilgun testing

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Karmaslap
Fri Jan 15 2016, 02:30AM Print
Karmaslap Registered Member #58215 Joined: Wed Dec 30 2015, 11:27AM
Location: Boise, Idaho
Posts: 65
I am currently working on putting together a small coilgun. The goals of the project aren't big- I just want to see how well simulations and theory can line up with reality when building a coilgun, and create a small change-friendly prototyping platform. Progress will be slow, as I put school first and I really like to think things through and simulate them before testing. I will also likely stop along the way for other little projects. The purpose of this thread is to serve as a log for me for what I've accomplished, as well as to ask questions and provide some incentive for me to keep moving.

Goals:
-Create small coilgun with available materials
-Have an "acceptable" correspondence to the theoretical values with regards to efficiency and projectile energy.
-Learn for future coilgun projects
-Stay under 50$ budget

Materials:
-16 camera photoflash capacitors totalling ~2250 uF. Some of them do not have their capacitances labeled and I guessed based on their size and shape, but this should be a respectable amount of energy at 330V (~120J)
-8mm diameter x whatever length I want steel projectiles. No idea on the carbon content of them, but they were pretty easy to cut with a belt saw. I initially cut them to 40mm length for a 5x length to diameter ratio- what should be the upper limit for projectile stability in the event I decide to try to spin them (which I will eventually try with a high-rpm hard drive disk motor).
-Assorted resistor values, and some small diodes. Most electrical components which can be found at a University.
- Arduino for timing if I decide to go with a controller (hopefully I can do this with logic gates)
- a few power supplies from cameras to charge the capacitors- 4 if they all work
-Assorted wires, connectors, switches, gates, misc items that might prove useful

Needed Materials:
-IGBTs- per Deralbi trumpeting the benefits these have in a half-bridge configuration over SCRs, I'll be ordering some offline when it comes time to use them over a normal mechanical switch.
-Photogates/phototransistors for multistage- My college didn't have any in any of our components bins, but I can order offline.
-Barrel for the 8mm projectiles- I can 3d print things about 1/2mm thick but don't want a 3d printed barrel if I can find something better. The printer will help with other things such as coil forms, though.
-Components for a better power supply/control circuitry for the halfbridge etc.
- Magnet wire for the coils! If I had some, I would be winding up a prototype now instead of posting on the forum. I need to do some basic optimization work for the projectile size and capacitors I have to determine the size of the inductor I want, and what wire I can use for it to get a low resistance. I am thinking 18AWG wire just from what I've seen, it shouldn't be burning up.
-Various miscellaneous materials (some copper rails for the capacitors, epoxy for coils, whatever else I need when I run into it).

Initial Plans:
-Run brief simulations and determine necessary materials to order
-Begin single stage gun, and log data.
-Expand to 2 and then 3 stages (3 being the max I plan for this project)
-Test various coil timing, projectile, loading mechanisms, power supplies, and control architecture to learn what works for a later larger scale project

I am lucky enough to be on a college campus with access to their eelctronics lab, machine shop, 3d printer, and underclassmen willing to press the button to fire the coilgun with exposed wiring.

Some Pictures
Projectiles and the bar (from a printer) they were cut from:
Jh9zynhm


Badly taken shot of the lab I get to work in: Pretty much whatever tools I need, scopes, power supplies, whatever. I'd like to get started on the project before I graduate and have to buy all this stuff for myself.
8MPgwNWm

Capacitors and charger circuits, soldered into random formats from the small gun I built last year with some friends, and some caps I found that a graduated senior left after trying to make a taser...
CYlKuugm

As this thread is mainly for me to record my own progress, I will be editing updates onto the first post so that it isn't bumped to the top and so that I don't run into any trouble for double posting.

Edit 1/16-
Found two coils that my friends and I made when we originally got all the camera capacitors. Hooked one up to a single 80uF cap charged to 360V and found a small projectile to fit into the pen we used as a barrel, and it shot pretty well (4-5% efficiency) a 5 gram projectile or so. Was fun lauching it across the lab.

Naturally, I hooked up ALL the capacitors. It takes a long time to charge with one photoflash circuit. Fired, but didn't work- the projectile appears to be getting stuck where the coil is wrapped around the barrel. It seems the coil is crushing the plastic pen barrel enough to stop the projectile. Did a quick simulation and seems like the pulse is twice as long now (or more as I don't know how to get LTSPICE to show/simulate the current rising through the inductor, it just magically starts at the peak when I set up an RLC circuit)

I didn't expect it to work all that well, and I'm using REALLY thin wire. I'm rethinking that I wanted to get 18AWG wire- of course I'll look at the resistance increase, but I'll check that vs the number of turns that can fit in a coil and how the inductance increase of more turns +more resistance changes the waveform more closely.

If anyone has an opinion on the diameter of wire I should use, I'd be interested.

Most importantly, I'd like to order IGBTs for the gun (I would like to get enough of the size I pick for a single half-bridge, or to fire two stages with a single LGBT. I don't mind putting them in parallel either, which it seems others have, but I'm not sure that paralleling them is very helpful? With two, if each has a small internal resistance, then in parallel their equivalent resistance is 1/2 of what a single one is, meaning that there is the same current traveling through two in parallel as there would be through one alone, but I've seen people here say that it helps?

I am looking at a ~450A peak which should, of course, be very brief (maybe 2 ms above 100A). I'm not entirely sure what IGBT to pick for this as mouser and digikey list their specs for continuous current, and I have no experience with them (or ordering any electrical parts offline, which I plan to remedy). I could order some and try them, but that could get expensive fast and there are others with experience to ask.



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Karmaslap
Sat Jan 16 2016, 11:59PM
Karmaslap Registered Member #58215 Joined: Wed Dec 30 2015, 11:27AM
Location: Boise, Idaho
Posts: 65
[QUESTION]
How does the "Continuous Collector Current" correspond to the peak current I can put through? Is that what I should be looking at? Can I get a 100A IGBT, or two in parallel? ($6.00 cost) or do I need a much higher rating? (400A- 20$ or so) being safe, 550A+ peak is only 5$ more than the 400A ones, but if it isn't necessary and the lower one is perfectly safe I'll go cheaper of course.

Looking at datasheets I am guessing that "I_CM" is the max peak collector voltage as it has a time next to it. In this case I could use
<http://www.mouser.com/ProductDetail/IXYS/ IXGX120N60A3/? qs=sGAEpiMZZMv4z0HnGdrLji290Jq8RNevx% 252bS3kPRRMvw%3d>
This IGBT and would have enough to buy 4 of them along with whatever wire I need. Does this look acceptable?
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Blackcurrant
Mon Jan 18 2016, 02:19AM
Blackcurrant Registered Member #2989 Joined: Sun Jul 11 2010, 12:01AM
Location: UK
Posts: 94
if you have 450A at 2ms then that igbt may be able to handle it as the data sheet for it says 600A at 1ms

A lot of the manufacturers have application notes and how to use them (Ti ST microchip ixys etc)
look for something to explain all the device data sheet parameters
a few other things to think about wound be

The drive circuits required for the igbt
mounting the igbts (some have isolated mounting tabs that make things easier ie isoplus247)
IGBT protection (like snubber circuits)

When buying parts see if you can buy direct from manufacturer or look around as sometimes they are far cheaper on other sites, also the college may get a discount from somewhere. You also maybe able to get free samples from manufactures.

Build a simple and reliable discharge circuit.
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Karmaslap
Mon Jan 18 2016, 03:11AM
Karmaslap Registered Member #58215 Joined: Wed Dec 30 2015, 11:27AM
Location: Boise, Idaho
Posts: 65
Thanks for the reply and advice. I won't order the IGBTs until I'm done modeling what wire size/coil turns and geometry to use.

I was under the impression that I could make a drive circuit fairly easily for them, though I have yet to look into how. I think making a driver circuit for a MOSFET is covered in one of my electronics labs this semester.

Thanks for the tip, I will look for those to help me read datasheets. Most of it is sensibly marked, at least.

I didnt think IGBTs needed such protection? I think by snubber you mean a diode antiparallel to the capacitor for when the current is shut off. I plan on hooking the IGBTs up in a half-bridge and getting rid of the need to do such a thing.

My discharge circuit right now is just the coil itself for safety discharges, I should probably up the level of safety for the whole project.

Update 1/17/16
Tried doing some LTSPICE simulations regarding what wire guage to use for the coils. Tested 10 AWG, 18AWG, and 24AWG with various coil geometries (inside diameter fixed for the projectile). 18AWG looks the closest to what I want so far: with a 40mm long 25mm diameter coil with 9mm wide opening (1/2mm barrel width if I could do that somehow, maybe rolled and epoxy hardened paper) and my cap bank, I can get to a 4ms wide pulse. The problem would be that it is very underdamped, but adding in a resistor to help that lowers the peak current by a large amount. Am hoping the IGBTs will nicely switch to cut off the current and maybe recharge the capacitors. If anyone has an opinion on wire diameter go ahead and share, otherwise I think I will do more simulations to see what the "optimal" diameter is, and then use it for now until I can order more wire and actually test.

All I have tried for is a low pulse time with high peak current, I haven't looked at the number of turns and how this will affect fhe magnetic field strength yet but best to get a feel for how one changes before worrying about the field strength.
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DerAlbi
Mon Jan 18 2016, 09:44AM
DerAlbi Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727
and it shot pretty well (4-5% efficiency) a 5 gram projectile or so
Beeing the ass, i say: unlikely smile On a SCR-based (or just mechanical switch?) design this is possible but achieving it on the first try? Lucky.. or systematic error.
1) Check your capacitors, if their capacitance value is actually as stated. These things can have -20%, and this is most likely cheesey (i feel like they produce +/-2%, and design the caps to -82% of their rated capacity, just to shit on the customers head cheesey )
2) Double check your speed measurement.
3) Make sure you measure way beyond the coil. (at least one projectile length). You should currently suffer from suckback. if you measure too close to the coil, then you might get false readings.
4) Depending on your measurement use 2 sensors to verify the speed. You may simply shoot the projectile through an other (unconnected) coil. Just hook up your oscilloscope to the open ends... the remanent magnetized projectile will induce a voltage in the shape of x*exp[abs(x)^3]. The time between maximum and minimum of that waveform divided by your projectile length will be the speed i guess. If not... its interesting too! cheesey
I didnt think IGBTs needed such protection? I think by snubber you mean a diode antiparallel to the capacitor for when the current is shut off. I plan on hooking the IGBTs up in a half-bridge and getting rid of the need to do such a thing.
IGBTs need to be protected against the stray inductance and ESL of your cap bank. Please look at "active clamping" circuits. Snubbers wont do it. Without protection your IGBTs are dead after the first test.
I can get to a 4ms wide pulse. The problem would be that it is very underdamped
Wow. What time constant does your coil have? (L/R)

Am hoping the IGBTs will nicely switch to cut off the current and maybe recharge the capacitors. If anyone has an opinion on wire diameter go ahead and share
Wire diameter can only be too thin for a certain speed, but not really too thick. <- This is only true for an IGBT-Design. But its way too dependend on coil and projectile geometry to make an educated guess. Just remember: the thicker, the higher the current. Respect your switches. wink

I am looking at a ~450A peak which should, of course, be very brief (maybe 2 ms above 100A). I'm not entirely sure what IGBT to pick for this as mouser and digikey list their specs for continuous current, and I have no experience with them
Your head is stuck to the SCR-design. Half-bridges work different... you will need much less current. I think you are safe with anything above 150A with maybe 300-400A. 1m-Pulse current. What is way more important than current capability is security for your IGBTs: i have a dedicated microcontroller sensing the switching of the IGBTs. The dedicated µC does have the power to completely shut down everything. So if my main controller crashes or i am halted in a debug breakpoint, nothing explodes. I see this as mandatory. No way around it.

With two, if each has a small internal resistance, then in parallel their equivalent resistance is 1/2 of what a single one is, meaning that there is the same current traveling through two in parallel as there would be through one alone, but I've seen people here say that it helps?
Do not start paralleling IGBTs. Been there.... rolleyes . They do also not have an "internal resistance" like Mosfets. They are infact like a bad PNP-Transistor from emitter to collector. They have a saturation voltage.

4x IXGX120N60A3
Acceptable.. yes. They will do the job just fine. I think for a 320V design they might be a little overkill. Maybe you find 400V IGBTs for the same price with more current. On the other hand: if you are fine with a little uglyness then: i have IXGX320N60A3 (the bigger bother) just laying around here. They do not have any legs anymore (the are cut directly where the legs become thin). For the price of those 4 IGBTs i could just give you 10. I have no need for them.. i need 650V rated stuff at least. The missing legs are really only a mechanical problem. Thick legs of a diode soldered onto them and they will fit into any PCB again.
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Karmaslap
Mon Jan 18 2016, 08:09PM
Karmaslap Registered Member #58215 Joined: Wed Dec 30 2015, 11:27AM
Location: Boise, Idaho
Posts: 65
Your reply is very informative as always smile

i say: unlikely smile On a SCR-based (or just mechanical switch?) design this is possible but achieving it on the first try? Lucky.. or systematic error.
just a mechanical switch, and with a (fairly) well-wrapped coil of some small diameter wire, with a projectile only slightly shorter than the length of the coil and one that fits the barrel to a fifth of a millimeter ish to take advantage of all the flux. Not to mention, using only one little capacitor. Not the whole bank.

Depending on your measurement use 2 sensors to verify the speed. You may simply shoot the projectile through an other (unconnected) coil. Just hook up your oscilloscope to the open ends... the remanent magnetized projectile will induce a voltage in the shape of x*exp[abs(x)^3]. The time between maximum and minimum of that waveform divided by your projectile length will be the speed i guess. If not... its interesting too! cheesey
I measured by hitting a wall some distance (15 feet or so) away and calculating the projectile drop time to solve for speed. Not the most accurate way but one of my friends was in the lab and it was the quickest way to find speed.

A sense coil! What you are using for yours. I will give it a shot, if it works well I could skip photogates completely.
IGBTs need to be protected against the stray inductance and ESL of your cap bank. Please look at "active clamping" circuits. Snubbers wont do it. Without protection your IGBTs are dead after the first test.
Wow. What time constant does your coil have? (L/R)
Will do. Don't want to break anything expensive or have a danger I could eliminate.

It was a coil I was simulating, not a real one I tested. Have to order wire before testing. I'll edit in those vslues when I go back to the lab and see what it was.

Wire diameter can only be too thin for a certain speed, but not really too thick. <- This is only true for an IGBT-Design. But its way too dependend on coil and projectile geometry to make an educated guess. Just remember: the thicker, the higher the current. Respect your switches. wink
Thanks for the advice smile
Your head is stuck to the SCR-design. Half-bridges work different... you will need much less current. I think you are safe with anything above 150A with maybe 300-400A. 1m-Pulse current. What is way more important than current capability is security for your IGBTs: i have a dedicated microcontroller sensing the switching of the IGBTs. The dedicated µC does have the power to completely shut down everything. So if my main controller crashes or i am halted in a debug breakpoint, nothing explodes. I see this as mandatory. No way around it.
More current through the coil and a faster pulse time =more force on the projectile as it passes through, half bridge design or not?

I'll keep the microcontroller thought as I design but I am still figuring what parts to get. Was hoping to not use any microcontrollers, yet. If I need to, I have an arduino on hand.

Acceptable.. yes. They will do the job just fine. I think for a 320V design they might be a little overkill. Maybe you find 400V IGBTs for the same price with more current. On the other hand: if you are fine with a little uglyness then: i have IXGX320N60A3 (the bigger bother) just laying around here. They do not have any legs anymore (the are cut directly where the legs become thin). For the price of those 4 IGBTs i could just give you 10. I have no need for them.. i need 650V rated stuff at least. The missing legs are really only a mechanical problem. Thick legs of a diode soldered onto them and they will fit into any PCB again.
Thanks, I'll be more comfortable ordering now.

Wow! How much would shipping be from germany to idaho, though? I haven't analyzed yet but it seems that doubling the voltage and halving capacitance (series combination) had a nice effect on the waveform.

I will not be able to work on this for a few days while I stay ahead on school but will try creating a sensing coil and finalizing thought-work for what coil wire to get so I can order everything by next weekend. I hope to print a test coil form and get some epoxy to make coils next weekend, if I can avoid getting stuck on simulating what would be best and get it done. I already ran into problems with my coil crushing the barrel and causing the projectile to get stuck when I hook up the whole capacitor bank to the small wire coil I was using for fun, so I know I need to prevent the coil from moving.
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DerAlbi
Tue Jan 19 2016, 02:39AM
DerAlbi Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727
Not to mention, using only one little capacitor. Not the whole bank.
That could imply that you are below saturation. maybe thats the key. I still dont trust such high eff wink

A sense coil! What you are using for yours. I will give it a shot, if it works well I could skip photogates completely.
I use a whole different concept.. has nothing to do with induced voltages. What i proposed is nothing that works in a compact design. You need to make sure that the voltage is only induced by the still magnetized projectile and not by the field of the coil. So you need some distance to the acceleration coils. You cant really sense the projectile with that. Its just a short test, to verify your speed measurement. I used a coil that was left. Photogates are the way to go in the long run.
Your current measurement doesnt sound so bad actually.. but it really depends on the starting angle... too many unknows for a precice result. Specially considering the kick-back. it will likely lift the muzzle up.

More current through the coil and a faster pulse time =more force on the projectile as it passes through, half bridge design or not?
In an SCR-Design (whats what you currently have even if you dont usw SCR) a thicker wire makes a shorter pulse with higher current. The overall energy in the coil stays the same (ignoring capacitor ESR). The timing can be good or bad.. the pulse form should correspondent to the projectile speed.
In a Halfbridge: you do not allways want a fast current rise, as you put current through the coil while its relative pullforce is low compared to its maximum pull force (based on projectile position, basically the same reason as for the SCR-design). But you can simulate a higher inductance by using PWM on the haldbridge. This is only feasable for the first some stages. As soon as the current becomes higher, you cant handle the switching loss anymore.
This is most relevant for the first stage. Any other stage can easier compensated by a later turn on. The efficiency will rise, but it will not have the optimal energy transfer (because you only use a small portion of the pull force curve).

I'll keep the microcontroller thought as I design but I am still figuring what parts to get. Was hoping to not use any microcontrollers, yet. If I need to, I have an arduino on hand.
SCR-Design do not demand µC... so its fine for the beginning. As soon as you go to Half-bridge, then there is no way around it if you want to use the full flexibility. And as soon as you use one µC you need to use two for redundancy. So 2 Arduinos will do. Sry, buts thats the minimum.. wink

Wow! How much would shipping be from germany to idaho, though?
I think its about 3.70€... so maybe 4$? 10 suckers are about 100gramms. I would have allready included that in my offer.. no worries. The parts are basically worthless to me... but if i give them away for free, i know you will just destroy them carelessly cheesey You will destroy them anyway (thats why i offer 10 instead of 4) but you know what i mean. I am also greedy as hell. cheesey No, i actually worked 2 weeks to get 50 of them wink But its so long ago.. it basically feels like the dept has been paid. Anyway.. thats what you are going for...

1453170840 2906 FT174839 Livingtorso
As said... no legs. But cleaned and working.

I haven't analyzed yet but it seems that doubling the voltage and halving capacitance (series combination) had a nice effect on the waveform.
Well.. you end up with double the energy. And double ESR (more damping, "dampening?") Its not only the electronics that change its also the acceleration behavior. It accumulates.
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Karmaslap
Tue Jan 19 2016, 04:17AM
Karmaslap Registered Member #58215 Joined: Wed Dec 30 2015, 11:27AM
Location: Boise, Idaho
Posts: 65
I am undoubtedly below saturation but probably close. I trust the basic math to be close enough to accurate and I'm not worried and don't care if it's off a bit. I have the barrel being held by 2 sets of helping hands to stabilize it from kicking, and I used a level to make sure it had a flat shooting angle. It's close enough until I get above 10 m/s with the larger projectile, then I have to set up a backstop instead of firing across the lab full of expensive equipment.
Darn. I was thinking that sounded like your sense coils.

My mechanical switch stays on until the current drops to 0 essentially, because I can't switch it on and off so fast, so I see why you call it an SCR design. I hadn't even heard of a PWM controller until you just brought it up. Pulse width modulation, I have yet to see how it will help as you describe over trying to get the shortest possible pulse and careful initial placement (better, I plan on "kicking" the projectile into the coil to trigger the first shot in the final 3-stage design). I will find out later. It seems there are other advantages to the half-bridge than the ability to switch the current on and off quickly and use the inductor kick-back to recharge the caps. I suppose an arduino could even measure the waveform if I got fancy enough with it. Another arduino is cheap compared to destroying a bunch of electronics! Thought I might want to get a Raspberry Pi instead so I have one of each.

I will PM you regarding the IGBTs- I'm sure I'll blow things up while I learn. I always have safety glasses on :)

Hooking capacitors up in series doubles the max voltage, halves the capacitance if they are identical, but you end up with the same amount of energy. And double ESR but it doesn't seem like the ESR matters a whole lot compared to the resistance of the circuit (or it does, and I should be factoring it in...)
Doubling the voltage and halving capacitance in simulations is giving me a waveform 2/3 as wide with a +1/3 current peak. I like that. I think I will go with 650V instead of 330.


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DerAlbi
Tue Jan 19 2016, 04:50AM
DerAlbi Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727
ooking capacitors up in series doubles the max voltage, halves the capacitance if they are identical, but you end up with the same amount of energy.
Pls check that again. Double voltage quadruples energy. Halving Capacitance halves the energy. ..so still factor 2 remains. Or put it this way: why should the energy density of one capacitor halve just because you use 2 of them?
Voltage only matters in an SCR-Design for pulse shaping. In a halfbridge you dont care much.. the higher the voltage the less current. Basically the power remains constant. But in a Halfbridge you cant go above 500..550V with 600V IGBTs.

Thought I might want to get a Raspberry Pi instead so I have one of each.
I would be against that. You dont want to run linux in a real time sensitive application. I figure programming the ARM standalone (without operating system) is way above your head. Use 2 Arduinos. They will do fine. But no, you do not want program complexity - the more you have the more goes wrong. You only want the flexibility.

Doubling the voltage and halving capacitance in simulations is giving me a waveform 2/3 as wide with a +1/3 current peak.
You achieve the same with double capacity (double energy), and a lower inductance (higher peak, shorter current rise. Think about it how everything goes together. (This is not a suggestion, just a side node.. there are many ways to skin a.. coilgun.)

I hadn't even heard of a PWM controller until you just brought it up.
Just to clarify: its not about a PWM-controller, its about the PWM-Signal <- that will be generated by an Arduino. Its not a pure PWM.. A halfbridge has more than 2 switching states. You need High/Low-Side load sharing and stuff. Buts thats for later when it comes to it... thats why i urge you to use a controller. And a second one if stuff goes wrong wink

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The output of the Main µC is connected over 470 Ohm. The Guard-µC senses the lines and if a fault is detected (wrong switching order, too long on-time) the guard just switches its sensing inputs to outputs and actively pulls all Gate-signals to GND overruling the 470 Ohm. This is the default startup behavior. In order to enable the Gate-outputs the Main-µC needs to communicate to the guard that stuff will happen.
The guard is programed once with a known-to-be-working program. Then software development of the Main-µC is without danger.
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Karmaslap
Tue Jan 19 2016, 06:17AM
Karmaslap Registered Member #58215 Joined: Wed Dec 30 2015, 11:27AM
Location: Boise, Idaho
Posts: 65
DerAlbi wrote ...

Voltage only matters in an SCR-Design for pulse shaping. In a halfbridge you dont care much.. the higher the voltage the less current. Basically the power remains constant. But in a Halfbridge you cant go above 500..550V with 600V IGBT.

Use 2 Arduinos.

You achieve the same with double capacity (double energy), and a lower inductance (higher peak, shorter current rise. Think about it how everything goes together. (This is not a suggestion, just a side node.. there are many ways to skin a.. coilgun.)

Actually did the math, redid, checked, don't know why I thought differently. Turned to google. I used this site for theory and read all through it. Let's play: find the math error <http://coilgun.info/theorycapacitors/ capacitors2.htm> Says something for doing the work yourself instead of using someone elses, I suppose. He uses 2C and C/2 instead of C and one or the other.

How would higher voltage be less current in a half-bridge? Why would it act differently? That makes no sense to me. You want the highest possible current because that gives you the highest magnetic field. To get the highest possible current, you need more voltage.

Ok. I'm sure I could use the Raspberry pi but it's just a matter of which is easier to use. I'll cross that bridge when I get to it, though.

I'm trying to think of how it all fits together. I'm simulating different shapes of coils- long and skinny, short and fat, in between. Trying to optimize peak current, minimize inductance and resistance, and maximize the energy imparted as the projectile travels. Combining FEMM sims and LTSPICE sims.

I will ask about using microcontrollers and the PWM and such later when it is relevant for me to be thinking about it. The safety program ensures it all won't break, then you have your constraints for the main controller. Of course that is the smart way to design.

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