EM Gun - New PSU Ideas

[Karl Williams]

Hey Guys,

Ya, there are huge energy losses in the conversion of magnetic to kinetic energy with coil guns. If you dump the same amount of energy from the capacitor bank into a thin wire contained in a more traditional breech -> exploding wire -> projectile -> barrel system then you get much higher velocities (closer to a .22 LR with my circuit) but obviously we're trying to get away from the exploding part with these devices. Electronic detonator systems use exploding wire or thin metallic film in the same way. There are three awesome books on exploding wire from the late 50's to early 60's titled "Exploding Wires, Volumes 1-3: Proceedings of the Conference on the Exploding Wire Phenomenon". I scanned the chapter about a hyper velocity rifle using exploding wire and will post the PDF.

Sorry for getting way Off Topic here...

Take care, Karl

[MrAl]

Greetings Mrai,

If you would like to stick with discrete parts that's ok too, i was just
trying to simplify the design a little so the board layout is easier and
it's not too complex to build up. It's up to you what you prefer though.

To SPICE the design before building a prototype
requires either a descrete circuit or macro-models
of any complex functions. Linear Tech has models
for many (if not all) of their IC products. Third
party SPICE models are available for common
functions (555 timer, for example).

A simple model runs much faster, so adding a
complex sub-circuit or macro-model is better
avoided.

Modeling is much faster than, say, winding new
transformers, for each iteration, even if the
models are off slightly.

A soft-start converter would take care of the high
in-rush current of the cold capacitor. The flyback
converter topology does this automatically, as
described earlier.

The resistor-capacitor concept was presented to
demonstrate the challenges in an efficient design.
Start with zero volts at one amp,
end with one kilovolt at "no" amps.

Comments Welcome!

Hello again,

To 'spice' the IC's im talking about isnt all that hard to do. It's the
same as when you do the discrete parts. All you have to do extra
is to look at the internal diagram of the chip and draw each part on
the sim schematic. Not all chips are this simple, but many are simply
error amplifiers, logic (like FF's), and a couple transistors...same as
the discrete design. The oscillator can be simulated as a pulse generator,
and the appropriate cap/resistor value chosen from the data sheet for
the final design.
One of the other neat things about chips like this is that you can
double bang the output, having energy transferred on both halves
of the oscillator cycle, by using a center tapped transformer primary.

[Bigglez]

Greetings Mrai,

To 'spice' the IC's im talking about isnt all that hard to do. It's the same as when you do the discrete parts. All you have to do extra
is to look at the internal diagram of the chip and draw each part on
the sim schematic. Not all chips are this simple, but many are simply
error amplifiers, logic (like FF's), and a couple transistors...same as
the discrete design. The oscillator can be simulated as a pulse generator,
and the appropriate cap/resistor value chosen from the data sheet for
the final design.

Great! Do you have the SPICE models for the parts you
were suggesting (TL494 and SG35, IIRC)?

One of the other neat things about chips like this is that you can
double bang the output, having energy transferred on both halves
of the oscillator cycle, by using a center tapped transformer primary.

Actually, you can't do that with a flyback design.

Comments Welcome!

[MrAl]

Greetings Mrai,

To 'spice' the IC's im talking about isnt all that hard to do. It's the same as when you do the discrete parts. All you have to do extra
is to look at the internal diagram of the chip and draw each part on
the sim schematic. Not all chips are this simple, but many are simply
error amplifiers, logic (like FF's), and a couple transistors...same as
the discrete design. The oscillator can be simulated as a pulse generator,
and the appropriate cap/resistor value chosen from the data sheet for
the final design.

Great! Do you have the SPICE models for the parts you
were suggesting (TL494 and SG35, IIRC)?

One of the other neat things about chips like this is that you can
double bang the output, having energy transferred on both halves
of the oscillator cycle, by using a center tapped transformer primary.

Actually, you can't do that with a flyback design.

Comments Welcome!

Hi again Peter,

SPICE model...
Well since you started the thread i thought you would be willing to do
all the homework...ie, do the spice model. All it takes it so look at the
data sheet for the TL594 and i think you will find it surprisingly simple
to draw out in your simulator. BTW another chip is the TL598 with
totem pole outputs.

FLYBACK design...
Who here said we *have* to use a flyback?

Oh yeah, BTW...

Code: Select all

It's "MR. AL", not "MR. AI" .

[Karl Williams]

I just put the exploding wire hypervelocity gun pdf up:

http://www.thinkbotics.com/exploding_wire.pdf

They were getting 4000 ft/sec from 2000 joules all the way up to
49,000 ft/sec from 3,500 joules with a lighter projectile.

[Bigglez]

Greetings mrai,

One of the other neat things about chips like this is that you can
double bang the output, having energy transferred on both halves
of the oscillator cycle, by using a center tapped transformer primary.

Actually, you can't do that with a flyback design.

FLYBACK design...
Who here said we *have* to use a flyback?

Please reread the quote above. A flyback
design will not allow the diode arrangement you
proposed.

It will be interesting to benchmark your PSU
design against the original one.

BTW, I'm working on a flyback design by choice,
may be it won't fly (back...)

Comments Welcome!

[MrAl]

Code: Select all

It's MR AL, not MR AI.

Get it now?