John Popelish suggested this repost.
The self-excited induction generator (SEIG) I am designing is a model of an SEIG that would provide all the electrical needs of an infantry solider. Currently resupply of batteries to infantry occupies a problematic proportion of supply resources. Land Warrior proposes a networked solider. Objective Force Warrior proposes a "mule" to carry these supply loads. I believe a bicycle with energy capture ability is a possible solution to the problems of supplying the Land Warror without the limited mobility of Objective Force Warrior.
With Daqarta, I can produce a Bode plot of SEIG response or Q, but only a plot of driven SEIG ouput as a function of parallel capacitance can provide the actual response of the system. However, a Bode plot of SEIG response would assist development efforts.
Producing a Bode plot is easy with Daqarta. A sound card output is applied across the terminals of the motor with parallel capacitor and the response is measured with the line input or the microphone input. Predicting the response of the SEIG from a Bode plot is difficult as the internal losses cannot be measured with this rig.
Driving one SEIG with its corresponding identical motor produces a certain output at near synchronous speeds if the load is low or nearly null, such as the oscilloscope and DMM voltmeter load on my SEIG, a Burden's Surplus Center 10-1134 motor connected to its mate with an 1/8 inch pipe nipple and a threaded rod coaxial with the shaft.
A standard capacitance substitution box, GC Electronics 20-102, range
0.001 - 11.111 ufd, is not quite adequate for the task. It costs the right amount, about the same as one or two motors, yet offers too little capacitance (C)) to approach SEIG resonance. It does provide a fine increment of C for measuring SEIG output with constant drive frequency.An extended sub box is on my bench, in construction. It will provide
10-50 ufd and this should be enough, as a trial with 30 ufd produced 1 VAC ouput and with 50 ufd, 0.9 VAC output, indicating operation on the capacitive/capacitative side of the resonance, while the GC box operates on the inductive (low frequency side). Six additional 50 ufd caps are available but may not be needed.The oscilloscope provides a rather crude frequency measurement but additional intution as to waveform purity. One more relatively inexpensive DMM would provide a clear measure of output frequency. I believe I will find on examination of SEIG output with changing C that the frequency, while not exactly known, changes less than the uncertainty of its measurement. We shall see....
Stepping capcitance in 1 ufd increments will produce 50 measurements of SEIG output as a function of frequency. I don't propose to fit a curve, only to plot one.
Then the fun begins. Each output data point is a point on a Bode plot, but they are all the same frequency so a Bode plot of total impedance versus frequency would just show fifty different positions on a vertical line. That won't say much.
However, since the shape of the curve is symmetrical when plotted with log frequency I believe it will be possible to recomposite the data to produce a true Bode plot without phase data, with frequency (f) on the X axis and something like z or Q on the Y axis, for the one capacitor value producing maximum output. That would say a lot; more than a Bode plot produced with Daqarta would say.
Such a plot would aid a rewinder in choosing a wire size for a stator rewind. The wire would have to be coarse enough to substantially reduce the series resistance (R). By reducing the ratio R/sqrt(L) generator operation *might* be increased from at least 1 VAC currently, at a likely non-resonant capacitance, to at least 80 VAC, the design goal.
The model design load is a white LED signal lamp produced by Dialight, and will function as a headlight on the test vehicle, a Lightning Cycle Dynamics Thunderbolt recumbent bicycle.
Four years have gone into this project. Just about the only thing that has *not* been tried is a car alternator. A backup battery provides self-excitation for an alternator. However, the remanant flux in an SEIG is more reliable than any battery. All the other design loads are computer style power supplies that go off line at 80 VAC and lower, protecting the remnant flux in the generator.
The SEIG has been mounted to the front derailer post on the test vehicle and pedaled chain drive debugged and tested for at least 100 miles. The advantage of pedal drive over wheel drive is that pedal drive has a smaller long term range than wheel drive. I admit wheel drive has a smaller short term range than pedal drive, and have explored wheel drive with a DC generator of hundreds of watts capacity, but the ability of the test vehicle to park and pedal the SEIG satisfies the requirement above. Also rear chain drive has a much longer throw than pedal drive and chain derailment has been a problem; large bumps derail the wheel drive chain and usually destroy the DC generator mount.
"All I am asking" :) is how to invert the capacitance based graph to produce a Bode plot of Q or Z or output as a function of variable f. Daqarta won't do it; it will only produce a graph of Q or Z, not a graph of actual output. It's a complicated system!
Yours,
Doug Goncz Replikon Research Falls Church, VA 22044-0394