User talk:Jcmaco

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--Jcmaco | Talk 16:16, Jul 16, 2004 (UTC)

[edit] Knots

Hey! Thanks a ton for helping to improve the knots listed on wikipedia. sik0fewl and I were doing a bit of talking on IRC about trying to really organize the knots better. He made a good start for a template on Talk:Alpine_butterfly_knot. I'd love if you'd go take a look and give your input. I was thinking about maybe starting a wikipedia project for knots, but I haven't done a lot of research on it. kmccoy (talk) 18:17, 16 Jul 2004 (UTC)

[edit] MOSFET

Hi,

I've reverted your latest addition to MOSFET. While I understand that it is correct, you must understand that all MOSFET manufacturers have given a fancy name to their technology, although most of them use a DMOS structure. I don't think this is of interrest in the MOSFET page (as far as I know, Fairchild's contribution to the MOSFET history is not much more than that of the others...). If you really want to put it, why not add it to Power MOSFET under a new section (e.g "trade names")? CyrilB 21:22, 29 May 2006 (UTC)

[edit] Battery tests

I used a D cell Duracell, and I was surprised to find that the used cell kept putting out 1.3 to 1.4 amps for 4 minutes and held the voltage to 1.0 volts. It showed no signs of pooping out after 4 minutes. In fact, I gave it a 4 minute rest, then it gave 1.4 amps for another 3 minutes whithout collapsing. I expect that it could supply more current for several minutes, but remember that the load resistance has to be extremely small for that to happen. What is the iresistance of your circuit? My test circuit just happened to have enough resistance that it could not draw more. At a specified internal resistance of 0.2 ohms, a D alkaline should be able to put out 7.5 amps into a short circuit initially. I did not want to connect my digital multimeter directly across the cell because the 10 amp fuse is expensive and I was afraid of an initial current surge. You said you are restricted to AA cells as energy sources. My theory is that whatever is not explicitly prohibited in such an assignment is pretty much allowed, and if you want to boost the initial current, or to allow bursts of high current, you badly need a husky electrolytic capacitor connected across the battery. The energy draw will vary as the motor load varies, and a cap will reduce the chance of stalling. The draw will probably not be a constant 20 watts. A capacitor, initially discharged, cannot properly be called a source of energy. You could put a large resistance (megohm) across the cap to ensure it is initially discharged. You did not specify how long you need to draw the 20 watts from the battery. Nor did you note the efficiency of the DC-DC converter. Perhaps you could use a low burden DC-DC converter or a lower burden 3 terminal LM3xx regulator to supply your microcontroller (do they make them to run on around 1 volt?) with raw DC from the battery to the motor. Motors do not need highly conditioned power. A motor controller using pulse width modulation might be more efficient if more total Joules are needed, or just a simple switching circuit that uses the full energy from the battery, or a tiny relay. Figure out how long the little machine has to run. Figure out series (preferred) or parallel connection. Series will give the electronics more voltage to work with, and avoid discharge from one cell to the other. I have found that Energizer alkalines tolerate high discharge better than Duracell. For your project you will want to use a fresh cell, of course. 20 watts from 3 volts is 6.66 amps, and I doubt that an alkaline AA can put out that much, so redesign to reduce the power requirement, or use a cap to store up energy for the bursts of power when the motor has to release a rubber band or some such. To current test your AA alkaline, you can use a length of wire as a resistor. 3 amps from 1.5 volts requires .5 ohms, which would be 31 feet of #22 wire, reduced by the meter resistance. Rather than a rheostat, you can put clip leads at fractions of the total wire or solder coils of wire to a rotary switch and just short out segments of the wire to maintain the current if the voltage declines, or just slide a clip lead along the length of bare wire to maintain current. Any cheap digital VM is pretty accurate with DC voltage. A wire table such as[1] will let you guesstimate what length of wire to use based on bare wire you find at a hardware store. Edison 15:44, 18 January 2007 (UTC)

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