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Everything wrong with amateur railguns and how to make them better

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Honda Rider 271:
At the moment the main problem is figuring how I will get 10e5-10e6 currents for 1ms or greater.

Options:

0) Really huge lithium battery bank. This would appear doable for a few thousand based on the ACIR 13.2 mohm and max charge voltage of cells like the Samsung 25R. Used Tesla modules appear to be initially less expensive but may have inferior resistive losses at pulse current due to the fused interconnects. Not sure about practicality of either option. Over 1000 high discharge 18650s would be required in parallel. This option would almost certainly preclude a plasma armature due to the inherently low voltage without an impractically large bank size.

0.5) Supercaps? I don't know anything about supercaps.

1) Homopolar generator. I would have to design and build a really big spinning wheel and brushes that carry the foregoing amps which is not trivial. Or buy a used one from a physics lab.

2) Inductor. How do I charge a really big inductor? Probably from one of the previous two options, so it might be more practical to just use one of them. Any suggestions are welcome.

3) Pulse alternator. This option looks impractical from an engineering standpoint since it is even more complicated than option 1. On the other hand, compensated pulse alternators or compulsators are apparently a very attractive means of compact pulse power supply and also entirely unknown outside of research.

4) Cap bank. Already ruled impractically expensive, unless I can find a physics lab throwing out their old particle accelerator.


--- Quote from: 13 on December 29, 2019, 02:40:08 am ---\There are quite a few "cheap" SCRs on Ebay that are sold as NOS because the seller can't find the data sheet.

--- End quote ---

The whole point of pneumatic injection was to avoid the problem of putting in a switch somewhere else. But it looks like pneumatic injection may be undesirable anyway.

I've been looking for SCRs on ebay and it's not immediately clear which ones will do ludicrous current. They all look kind of small. At least I would have to parallel a handful of SCRs, which is fine.

T3sl4co1l:
Not sure what you're thinking with the inductor.  You're charging an inductor with an inductor, so how do you charge the inductor?  Only makes things worse...

I think you are missing some idea of just how much power is involved here.  It's not just amperes, it's volts too.  Typical figures are in the hundreds to low kV.

Supercaps are useless, they have a far longer time constant (seconds) than the regular kind.  Batteries have an even longer time constant (minutes-hours).

Tim

Marco:
You could have an inductor with a lot of opening switches which switch the inductor from series to parallel. An aircore inductor for 10+ kJ with RL times in excess of 10 msec seems doable.

I suspect that an aircore inductor with such a massive amount of energy will be troublesome to handle from the stray magnetic field effects even if build as a toroid though.

Marco:
Lets do a bit of an order of magnitude calculations here using the formulas from here.

To get 10 grams up to mach 1 over a meter will take around 600 Joule and also 600 Newton, which will take around 60 kA and cause an acceleration of 60k N/m taking 6 ms to accelerate the projectile. Lets say the system resistance is 1 mOhm then you want your inductive energy storage to have on the range of 6 uH to not drop current too much, which will require it to store around 10 kJoule, so 6% efficiency. Lots of 6's there ...

This shows a problem with one big inductor to store energy, you are losing most energy because you want to keep acceleration constant high, leaving lots of energy behind in the inductor which you can't use.

mzzj:

--- Quote from: Marco on December 29, 2019, 06:39:33 am ---You could have an inductor with a lot of opening switches which switch the inductor from series to parallel. An aircore inductor for 10+ kJ with RL times in excess of 10 msec seems doable.

I suspect that an aircore inductor with such a massive amount of energy will be troublesome to handle from the stray magnetic field effects even if build as a toroid though.

--- End quote ---
1MJ flyback transformer  >:D

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