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DC Tesla Coil

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New Member
I'm making a small DC tesla coil with a rotating spark gap. The motor controlling the RSG draws about 3.8 amps of current at full load, and the 555 control circuit and amp draws about 4 amps. Would it be best to run the motor and 555 circuit parallel from the +12v or in series? If it's in series would the motor current draw cause an excess of current through my 555 or am I looking at it wrong?


New Member

Sorry for the non-conventional elements of the schematic. The dotted lines represent the elements of the circuit I'm questioning. A and B are the same thing, obviously. They both represent the motor connected in parallel to the signal circuit, but C (without the ground to the left of it) would be the motor connected in series to the main circuit.

After posting this thread I realized it was probably a stupid question and I should just connect the motor in parallel, but I was wondering: would connecting the motor in series would cause more current to be drawn to the coil?

Incidentally, I just put b. in there for my own reference, in terms of layout on the PCB. :)
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Active Member
Niether of those will work. Config C wont spin at all, config B will just spin at full speed.

You'll probably need a seperate 555 to drive it.
I found this schematic:

Simple DC motor PWM speed control
this guy used it for a tesla coil too.

Here's my coil:


Well-Known Member
The motor won't run if it's in series. The 555 will limit the current to a few milliamps.


New Member
Makes sense, and thanks. I have a lot of 2n3055's laying around; would that work well for Q1 or is the IRF540 substantially better for the job?


New Member
If you use a 2N3055 with a 100 ohm base resistor, you'll get about 100 mA of base current. This would be enough for the 2N3055 to comfortably support a 1A load. Any greater load and the 2N3055 will begin to come out of saturation and get pretty warm.

The IRF540 should work until the load is heavy enough to heat its Rdson of 0.044 ohms, at over 4A (with no heat sink).
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