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Halfbridge? The idea of it is the best solution possible. But the realization is shitty. See, he implemented dynamic current control: he pumps the coil when current depletes to the certain level and then discharges it back to the cap when current gets high again. It is not optimal to jerk switches so often. The coil should only be periodically pumped during the on-period, and when the current reaches the required level, only one of the switches should be closed. This way the pumped energy will stay circulating in the coil-switch loop without returning back to the cap. This will eliminate unnecessary switching losses. The overall efficiency is way too low for halfbridge. Can't tell the reason for sure. As usually I will state that projectile is too long, or energy in the coils is not optimal... Well, at least the copper barrel is surely a bad solution as it is made from conductive metal (brass, as I was told). He used the varnish for coil's soaking. Maybe it was the reason the coils were not solid enough so the old barrel was squeezed. I stick to epoxy because it dries solid due to 2-component consistency eliminating the need to evaporate gases during drying. My paper-made epoxy-soaked barrels are not as hard as brass, but not conductive and thinner.
The proximity of the small-current electronics to the coils causes glitches. Not sure if he understood that it is an issue...
The coil's wire is too thin and the operating current is too small for the last stages, imho.
I thought that halfbridge could do over 20% of efficiency at such speeds. Seems strange to me that it didn't, even taking the design flaws into account.
I've did some comparison search on the prices of the IGBT which can be used for halfbridge designs. Seems like the time for powerfull coilguns implementing halfbridge for each stage did not come yet - hundred bucks per stage or so comparing to the non-polar cap design with a single SCR of 40TPS80 kind which costs under $5. Anyway, finally the world has a high-voltage halfbridge, and it is russian! :D
Registered Member #1513
Joined: Sat May 31 2008, 12:08PM
Location: Russia Klin
Posts: 48
well, this halfbridge design is pretty old. prototype can be found here 18 August 2008
next step in halfbridge circuit design can be found here 22 June 2011
it part of bigger project basic idea this design,energy recuperation is achieved in not only using electrical circuits, but also through mutual inductance adjacent coils. but DANTIST use magnetic core around the coils it closes the magnetic flux within the coil so there's just a matrix switch efficiency of the system is quite high for such a small caliber in its class, this system is unique
Use a brass barrel is not such a bad idea losses in such thin metal minimal
if you carefully examine the circuitry is perfectly able to see that the system is protected from switching surges
I made a mistake this technology presented in patent US 5763812 in 1998
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