--- On Thu, 7/30/09, Horace Heffner <[email protected]> wrote: > Say, thanks for the response! There's nothing like > robust equipment, eh!
Heh. I've got some nasty stuff here I've acquired from various times and places. Having a good friend who we here affectionately refer to as "The Scrounger" (apologies to James Garner's character from 'The Great Escape') also helps get interesting stuff. > If I can get my dual motors to work in series, which I > doubt, I expect the stainless steel bearings to simply wind > down to a stop. I expect the stainless ones to wind > down to a stop also when stand alone, but if they run alone > it will be easier to just turn off the power right before it > freezes (hopefully). The stainless ones may run down > before the ordinary ones get up to speed, especially if the > current makes them "sticky". I suppose I could make a > run using one stainless and one regular bearing on one motor > to demonstrate that both bearings conduct enough. What are you using as a power supply? I believe you said it was a 12V battery, but do you know the peak amps of it? A jump-starter is a good choice in my opinion, because it is built to do this and survive. I've killed regular batteries before with these kinds of experiments. I don't know if you have a Harbor Freight tools nearby, but they sell these battery booster packs for about $75. Hmmm... AC is supposed to work. What if we sawed off the secondary of an old microwave oven transformer, wound our own secondary (few turns of HEAVY wire) and used that? I've gotten what must be a kiloamp or so out of something like this. Be more robust than a battery, it seems. If I find some time, I might try this. > Did you ever take a look at your actual current? The > lowest resistance I've been able to measure is 0.2 ohms per > bearing, which is 0.4 ohms for the system. The resistance of > the rest is about 0.1 ohms for me, but I don't know what the > resistance of your shafts and power leads are. My shafts are > 1/2 diameter aluminum rod. In any case, using 0.4 ohms > for the system, just the bearing resistance, that is a max > of 30 amps for continuous conduction, and way less I expect > due to the highly intermittent nature of the conduction. Have not measure it directly, but it must be more than 30A. Battery drains rapidly when powering the motor, and everything gets HOT. Even the heavy lead wires from the jumper box. The insulation on them softens. > I added a 0.3 ohm nichrome resistor to my circuit as a > current sense resistor for my scope, and as a means to try > to keep the current down initially. That gives me a > 0.8 ohm resistance overall, or a max continuous current of > 15 amps to start out. I can probably increase the effective > amps greatly, if necessary, by placing a large capacitor > around the motor, in parallel to it. Doubt 15A will run it. How big are your bearings? But hey, give it a shot. If it doesn't, it's trivial to remove the resistor. I wonder if the inital resistance is higher than the dynamic (spinning) resistance when current is applied. If the arc starts, does it spread out and cause the gap resistance to be lowered dramatically, letting an avalanche of current through? Might the initial resistance be 0.2 ohms, but then it drops? Plus once everything heats, are things pressed together? I do have some old conical automobile wheel bearings from my old Monte Carlo sitting here. Reckon I should try those? They are roller type, not spherical bearings. I wonder if they would do anything? > It is probably the case that I don't have any problem at > all, except the desire to demonstrate the two motors running > in series, which looks to me impractical at this > point. I could run them in parallel, but that would > not prove much visually. I wanted to post a single > continuous short video on youtube demonstrating that > magnetic material is required to get the effect. I'll just > have to do it in parts. If 12V won't cut it for series, try two batteries in series for 24V? Keep us posted as to your results. Very interesting, to me at least. --Kyle
