Later inspection revealed less then fantasic electrical conductance between the ground cable and the aluminum chassis.
Wired up the SCR and polywell coils:
For the triggering circuit I improvised with available parts. I settled on this circuit:
Looks like this:
I tested it out and it works!
When the SCR discharges you can see the coils flex and hear a sound from the SCR… and the voltage across the capacitors drops sharply. I took it up to 400V with 5 caps.
Pretty major step forward for the coil power supply.
Nest steps include:
Making a front panel with master power switch, AC indicator, capacitor bleed switch, high voltage LED indicator.
On the back panel: IEC C14 AC connector, screw down terminals for coils power out, and D-sub interface for computer control (via DAQ). I want to computer control the AC power, bleed resistor and SCR triggering.
Stuart made a keen observation about a relay on the DC side: Relays have a much lower voltage rating for DC vs. AC. So a relay rated at 240VAC may only be rated at 30VDC. This is because DC sparks are harder to quench- they don’t naturally drop to 0V like AC does. So long story short – I’m going to put the relay on the AC side of the transformer.
I also want to fuse the AC and DC sides.