SCR Test Fire

18 04 2010

I successfully fired the coil power supply’s SCR today. Here’s how: I started by grounding the chassis:

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.

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