The Fence Charger went Tango Uniform

The twenty-year-old, low impedance fence charger stopped working.

I popped it open to see if there was anything obvious.

All connections were tight.  None of the capacitors had obvious shorts.  Oh well, it was worth a try and it is always interesting to see what is "under the hood".

The main capacitor is the energy heart of the device.  At full charge this capacitor can hold about 12 Joules.  This fence is rated as a five Joule energizer and low impedance fence chargers have an open circuit voltage of about 8000V so this must be driving an inductance which is then shunted to the fence line at mid-pulse.  That would be one way to convert 12 Joules of 900V to 5 Joules of 8000V.

Hmmm!  Three more capacitors on the left side of the photo.

Four Silicon Control Rectifiers.  Silicon Control Rectifiers (SCRs) are switches that are normally closed but open when "gated", that is, a voltage is applied to the switch leg of the chip.  The other quirk about SCRs is that they only allow current to flow in one direction.  Think of them as being like the trap-door beneath the hangman's gallows.  SCRs are very robust and (larger ones) are used in industrial spot welding equipment where they undergo millions of cycles.

I wonder if there are any circuit diagrams for similar devices on the Internet?

A circuit for a "Coil Gun"

And a four minute video of a coil gun.

This is a 1250 Joule device, 100 times the energy that can be stored in the fence charger's main capacitor

To my way of thinking, a fence charger is a coil gun that pumps a run of fence wire instead of a solenoid coil.

When the government outlaws capacitors, only outlaws will have capacitors.