2. What is a coil gun?
•A coil gun is a device that uses a magnetic field
to launch a Ferromagnetic projectile.
•In our coil gun, we store high levels of charge
within capacitors
•We discharge it through a coil
•We build up the charge with a 36 volt source
•We control the circuit with a DPDT switch and
SCR.
4. Power source
•4 nine volt batteries
•Possibly 10 volts fresh
•Jury-rigged equivalent
for testing purposes
5. Power Source
•The source is 36V when the
capacitors are charging, and 9V
across the SCR gate when in
the firing stage
•36 volts is more than the
capacitors are rated at 35
Volts, batteries sometimes say
9 volts but actually are
sometimes 10 volts giving a
range of 36 to 40 volts.
•Resistor not sufficient to drop
6. Zener Voltage regulator
•Zener diode a better
solution to the voltage
problem
•Creates opposing
voltage regardless of
capacitor bank charge
•Drops voltage to a safe
31 to 35 volts.
7. Current Branches
•Current moved
through two branches
and into the capacitor
bank to charge it.
•First branch just
general load
•Second branch
controls indicator
•Indicator is on when
8. Capacitor Bank
•Capacitors are used to
obtain high charge
•8 X 4700uF capacitors with
total capacitance of 37.6 mF
•At 31 volts the charge
stored is 1.1656 Coulombs
(Q=CV)
•total energy stored in
capacitor bank is 18 Joules
(W=C*V^2)
Multisim Analysis of Capacitor charge,
9. SCR Thyristor
•The thyristor is a 4 layer semiconductor which can be logically represented
with 2 BJT transistors.
•When the NPN bjt portion is in saturation, it forces the PNP bjt portion into
saturation as well.
•Thyristors are used because they provide a high surge current rating. A
normal switch would break.
10. SCR Thyristor
•When the voltage difference between
the gate and cathode is high enough, the
diode will turn on.
•When one diode is on/off, the other
diode is in the same state. So if gate-
cathode voltage isn’t high enough to turn
on the diode, then current won’t flow
from anode to cathode.
•Once the SCR is switched on, it stays on
even if the trigger voltage is removed.
The SCR will only switch off once the
anode-cathode current reaches 0 A.
11. Switch
•The switch has three modes:
–The capacitors are charging, and the SCR is off
–The capacitors are not charging, and the SCR is off
–The capacitor are discharging, and the SCR is on.
12. Coil Operation
•There will be a spike in impedance as the current spike goes through our coil.
•The current spikes for a moment as voltage drops sharply because v(t) =
L(di(t)/dt), so a sharp change in voltage creates a sharp increase in current.
13. Coil Operation
•A changing current induces a magnetic current.
•F = (B2A)/(2u0), where u0 is a constant value for
the permeability of air.
