Saturday, June 11, 2011
Here I have a 208/220V; 440V, 5 horsepower 3-phase motor that I am experimenting with converting to an inductive generator, powered by my Changfa S195 Chinese 12 hp diesel engine. I'm learning here; I have never done this before. In both clips, the motor is wired for low (208/220) voltage. That means it is wired Wye-Wye (two sets of windings paralleled), whereas it would need to be wired Wye (both sets in series) for 440V. Does this mean I could produce 440 volts with this setup? Undoubtedly. Rectify that to DC and power the plate circuit of a tube linear amplifier without the big transformer normally required. Add a small transformer for the low voltage stuff, and this would make a good power supply for a legal-limit ham radio station.
So anyway, in the first clip I am using only one capacitor, and it is the only capacitor I could find in the microFarad range that was rated for high voltage AC. It has nowhere near enough capacitance; I think it was 0.75 uF or something like that. As you can see, it didn't work.
Digging around in cyberspace, I found reference to C-2C wiring for this specific purpose. Unfortunately the guy who was describing it didn't have a firm grasp of what he was describing, having simply followed someone else's directions. Thus, although it would seem that "2C" would imply double the capacitance of "C", the narrative did not leave me with a feeling of confidence that that was what he meant. Not disrespecting the guy or anything, just telling it like it is.
So I searched further and ascertained that, indeed, 2C means 2C and not merely C2. I found other stuff about it too, which gave me the confidence to actually spend a bit of money.
Basically, it works like this: imagine a delta-wound, 3-phase motor. There are of course 3 legs to which the power connects; L1, L2 and L3. L1 and L2 will be the output. C, the first capacitor, connects in parallel across L1-L2. 2C connects in parallel across L2-L3. Nothing connects across L3-L1.
2C can be either a single capacitor of double the value of C or, as you see here, two caps of the same value as C, connected in parallel.
So I went to everybody's least favorite online auction site and bought three identical, new, 55 uF 440V motor run capacitors. As you can see, this works; at least as far as producing voltage. Stay tuned, because next I plan to load it with some heating elements to see what it can do.
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