Barry's Coilguns

Protective Diode

A "protection diode" is intended to protect the electrolytic capacitor from inductive kickback, and from reverse charge and damage.

Protective Diode

Schematic of coil when switch opens We choose… none! The “protection diode” is intended to allow the current to circulate in the coil, protecting the electrolytic capacitor from damage.

However, the diode will extend the current time, which then decays at the L/R time constant. This is very slow compared to the LC time, and vastly increases the dreaded suck-back effect.

Instead, we will use a series damping resistor which is carefully chosen to make the LCR circuit critically damped.

The V-Switch Alternative

One good alternative would be to use a V-switch circuit, which dumps another smaller capacitor into the coil to quench the current. Read about it on the excellent Pskov 1100 Gauss gun web site. This idea was not used here because it adds a great deal of complexity due to the position-detector required to fire the additional capacitor.

The simplified schematic below illustrates the V-switch concept.

Coilgun v-swirtch illustration


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