Control Cabinet

Here is the inside of the control cabinet. It contains the 140V variac for the power supply, the vacuum control (lower right, under the variac), the triggered spark gap control (lower left), a cooling fan (upper left, back wall), a relay assembly (upper left), and a warning beeper (to the right of the fan).

Here is the cooling fan at the back of the control cabinet. Sitting next to it is a warning beeper that sounds an intermittent tone for 15 seconds when power is first turned on.

This is the relay assembly that keeps power routed in the correct order. A main power switch activates the cooling fan, the beeper, and this relay assembly. The relay assembly controls three main stages, which can only be turned on in order: (1) triggered gap vacuum, (2) triggered spark gap, and (3) the power supply. A main kill switch disconnects all power.

Here is the gap vacuum controller. This is just a beefed-up fan controller. The stacked line filters (one on the input side of the controller; the other on the output side of the controller) look like overkill but early tests indicated they were necessary (though this size is not---you take what get when you shop the surplus market). An initial test of the spark gap resulted in erratic performance of the vacuum controller--undoubtedly the result of voltage spikes getting back to the controller triac. The line filters solved that problem.

A little closer look at the heart of the controller. The jumpers to the control adjustment were used for testing only. Sturdier connections were made in the finished control cabinet.

Here is the controller assembly for the triggered spark gap. This one deviated a bit from that used by most coilers. It is based on plans I found in an application note for using triacs to control inductive loads.

A little closer look at the heart of this controller. It uses two triacs instead of the one usually found in a fan controller. Two line filters are used here as well to keep those triacs isolated from voltage spikes.

Front view of the assembled control cabinet. The meters on the top display the voltage and current for the vacuum, triggered gap, and NST stages. Each stage is controlled by a switch and each has an adjusting knob to control fan speed, firing phase, and voltage respectively. A kill switch in the middle, bottom of the panel cuts all power immediately. Above each set of meters are neon indicator lights. Red indicates that the stage has no power and cannot be given power even if its switch is thrown. Yellow indicates that it is not currently powered but is the next available stage that can be powered. Green indicates the stage has power. The relay assembly controls the indicator lights. A key switch is wired in and key activation is necessary before power can be applied to any stage. The cabinet also has an hour meter to log the total run time. A main fuse (15A) is wired to the input of the cabinet. Each individual component is also fused.

This is the back of the control panel, showing the vent for the cooling fan and the outlets for the different stages. One last safety feature--the main power inlet (lower left corner) is a standard receptacle so that a standard power cord with a female end will not work. Instead, a double-male-ended connector is used to bridge a standard power cord and the receptacle. That connector and the key are kept well away from the control panel when I'm not around.