Spinning up the Spark Gap Motor

Finished the last bit of wiring on the synchronous motor and the step down transformer supplying it. Annoyingly the little ceramic 3 pole terminal block cracked when re-mounting it, on closer inspection it really is a horribly made piece of crap from B+Q. I have ordered a similar looking unit from eBay tonight, hopefully it's better quality and will fit the mount holes already drilled, if not I may create my own from a block of perspex. Anyway time to plug in the the spark gap module. Fingers crossed.

Well that went pretty well. The spark gap disc seems to be well balanced and the motor is very quiet, not that that will make any difference once the gaps are firing. The motor took more than 40 seconds to come to a complete rest after unplugging. There is a fair bit of weight involved in the spark gap disc but I still think this is a good indication to the quality of the bearings in this little motor.

Hers's a close-up of the cracked terminal block. I had to remove it when I was wiring in the cable in the pic as I had trouble tightening the cable clamp screws. When I checked the screw heads non of the slots were formed correctly. I used the 2 best formed clamp screws to secure the new wiring and refitted the block, this is when it cracked. Two steps forward, one step back.


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230V to 110V for Synchronous Motor

Did a little more wiring today. It consisted of connecting one of the female IEC socket in the front panel to the step down transformer on the second level of the tesla coil. I used a length of standard 3A 2 core round black flex. The synchronous motor is rated at 7.5W at 110V so by the equation

                  Power (Watts) = Current (Amps) X Voltage (Volts)

            so   Current (Amps) = Power (Watts)
                                                ------------------
                                                Voltage (Volts)

                                             = 7.5
                                                ----
                                                110

                                             = 0.068 Amps

So, as you can see it draws very little current and even the lightweight 3A cable is a bit of an overkill.

The top IEC socket will supply 240V to the step down transformer which in turn will supply 110V to the synchronous motor. The transformer was sourced from Newlec and came in panel form (uncased) but mounted on a pressed steel bracket. I removed the bracket so I could mount the transformer on a perspex base. This meant that I had to remove the connection strip. This task was undertaken several months back and I thought it would be wise to check that the connections were correct and the transformer is doing what's expected, also a good reason to play with my Xmas present.

The transformer has inputs for 230V and 240V with an output of 110V. I decided to supply a 50Hz AC voltage across the 230V inputs and measure the output of the terminals marked as 110V. I used the function generator built into my oscilloscope to supply this signal to the transformer at a very safe amplitude of about 3 volts. The same signal was feed into channel 2 on the oscilloscope.

The oscilloscope probe was plugged into channel 1 and then connected across the 110V output terminals. With the same volts per division set on both channels and the scope set to dual I could view the input and output waves at the same time. I did take a pic to show you the result but my camera only got an image of a few dots on the oscilloscope screen due to the high speed of the trace. So I took a quick video with my Sony Bloggie.

As you can see, the terminal connection are correct and the transformer is stepping down the voltage by  a factor of about 2 so 230V would be output at about 110V.

I can now finish the wiring to the transformer with confidence. Very pleasing to see actual inputs and outputs on the oscilloscope screen also interesting to see how the 2 signals stay in phase.