Quote:
Originally Posted by Aaron
Hi Shamus,
For the pots, you can put one in line with a resistor. Hook a scope to it. When you slowly start turning your wheel you might see 4 spikes per pulse...when up to speed you only want to see 1 spike per pulse...turn the pot until you only get 1, measure the total resistance, then replace with fixed resistor of the closest value to the tuned resistance. If you don't have a scope, you can use a radio or something else to hear or see the spikes..
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My setup has a 100 ohm and 1k rheostat in the base, NE-2 (EC), 1N914 (EB), 1N4005 on the output from collector (when second battery is connected).
Coil probably has around 450 winds 26/24AWG with usual 1/16" copper coated rods (R45 not R60 though it shouldn't matter, that quality only applies to welding application)
In the source battery I use 8x1.2V NiMh 2300mAh or a 12V 1.2 Ah gel battery.
I guess you've just answered one of my questions above, I have been seeing more than one trigger per cycle which sort of baffled me? I know JB is talking about the "h" waveform and I have seen it on my scope from time to time, but it is always preceded by couple of more spikes. Most I could get it is one or two spikes and an "h".
What bugs me even more is that I get quite different waveforms depending on the batteries I use. I'm attaching some examples...
First scope photo shows just a motor setup (no second battery) while the second one has a second battery in (don't mind the noise in the waveform, comes from the AC adapter scope is hooked up to).
When I wind the rheostat to what I think is over 1k resistance, I eventually reach self-oscillation point, but the waveform changes as well and becomes more uniform, with consistent spikes, sometimes as large as 200V.
I think my disc/magnet assembly needs to be reworked, I did not have bearing assemblies or an axle, so I used bearings from a broken CD-ROM unit and as a result the disc with magnets is suspended above the coil, held by the aluminium bar across.