The properties of a simple coil of wire transformed this planet from tying notes to Homing Pigeons, to galactic door knocking. The discovery of magnetism and especially the electromagnet, in this authors opinion, were the greatest technological discoveries in history and, once again, a simple coil of wire may hold the answer to a problem that I have scoured the web in search of: a high current test load. Experimenting with large amounts of current posed a problem right from the start. What kind of load can I use to get a satisfactory reading without incinerating it? One that would hold the current steady enough to get an accurate reading. Nothing has survived the procedure. However, I have found a means of limiting or controlling high current.
The device is called a "Saturable Core Reactor" and it is basically a large, adjustable, Iron cored inductor with a DC control winding to vary the inductive reactance of the windings and drive the core to saturate. I built a welder with better than average amperage, 85 amps, with no current control. I decided to build this reactor I found on the Web just to check the theory. I stripped down a MOT and left the primary as the DC control winding. I put the same number of turns on the reactor as I put on the welding trannies as a starting point, 20 turns on each outer leg. I ran the 85 amp current through the reactor and took a reading, it reduced the amperage to 42 amps, more than 50%.
The next step was to test the DC control. I found a cube transformer rated at 6 VDC and 700 milliamps. I ran this through a 50k ohm Pot. From zero to the full 700 milliamps DC, the AC through the reactor changed from 42 to 45 amps. Granted, this is a relatively small amount of DC current but, the ratio of change is impressive. The obvious question here is " How much control is possible with a larger amount of DC through the control winding?" Regretably, I can't answer that question until I advance the experiment. My next project is to build a DC power supply to test the full range of this homebuilt reactor.
The project began with stripping the MOT to the primary winding. I used a hammer and a screwdriver to remove the magnetic shunts, I just tapped them out. Care was taken not to gouge into the primary winding, or it will short.
I wound the outside legs of the reactor ( just like the diagram ) with the same size wire as the circuit I was trying to control. I started with a few turns and checked the amperage. Also, I checked for voltage in the DC ( primary ) winding, there should be zero volts. If turned correctly, no flux will flow in the center leg, no voltage induced. I kept adding turns, evenly to both legs, until I reduced the amperage to the range I wanted to use. Adding turns will reduce amperage, applying DC current to the control winding will increase amperage.