Electronic controls.

I’ve been rebuilding my electronic control assembly. I need two current sources, one for the core and one for the coil. In addition, I need to monitor both the input and output. I’m relying on two oscilloscopes to detect any change.The idea is simple but changes will be difficult to detect. As I’ve not included any cooling system in this prototype, my intention is to discover if iron’s Curie Point can be changed by applying electrical stress in those few degrees before the core becomes completely non-magnetic.

Most probably, this should be noticeable by a change in the current used to energize the coil. When the core is below its Curie Point, it behaves as an iron-core inductor. When it is close to its Curie Point, it acts more like an air-core inductor and draws additional current. (After compensating for the increased resistance of the copper wire at those higher temperatures.)

If all works out like I hope, when the core’s temperature is around 690-750°C sending a bias current through the core will have the effect of increasing the coil’s inductance and be noticeable by a drop in the current draw.  When the bias current stops, the current should once again increase.

This is not an especially elegant test of the theory. I’m simply hoping to get enough positive data to make more intense studies worthwhile. Working with mild steel’s lower permittivity and over-high Curie Point has proved to be next to impossible. But without some indication the Curie Point can be changed by electrical stress, the research necessary to produce a high permittivity, low Curie Point core metal just isn’t going to happen.

Here is the main control table:

Control table

I’m running the coil at 120V 60Hz AC from the wall outlet. The core can be energized by either 24V or 13V AC transformers. There’s a reversing switch to invert the phasing.  The meters and oscilloscopes should tell me what the current is doing.

Here is a closer look:

The table

The back of the control table looks rather confusing, but it’s all wired point-to-point so if I didn’t make any errors, it’s good to go.

Back of controls

As the core resistance will change significantly once it’s up to temperature, I need to use ballast resistors for testing and making the initial measurements. At room temperature the core has a resistance of 0.4 ohms, so these resistors are necessary to keep the current under control. They might get hot, so I’m using that cooling-fan tower I made previously to keep them cool.

Balast resistors

The generator unit isn’t connected at this time. (I still have to apply its final insulation.) But this is its connection point plus a monitoring panel for observing the output of a secondary winding. The yellow and black input wires are for energizing the core and coil respectively. The two plug and switch boxes are for the heaters. There are two 120V heaters and one 240V heater down the center of the core.

This is as far as I can go until the insulation around the core unit is finished.

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