Msg: 2121 *Conference*
03-24-92 09:33:54
From: DREW BLANCHAR
To : CORY HAWKINS
Subj: ELECTRONIC WIZ
Cory, You didn't say how smoothly you wanted to dim your battery operated light nor how much money and room you want to invest. If the lamp is flurescent, forget about dimming.... trust me, you don't want to spend that much time & money. If the lamp is incandescent, then you just have to add some resistance in line between the batteries or from battery to lamp. The old rule of thumb says you need 5 times the resistance of the lamp (v^2/watts) to dim it out enough to call it black. If you just want a half-bightness stage, just add a resistor equal to the lamp resistance (v^2/w) and add a switch that will short out the resistor for full bightness. You can see that you could add a multiple contact switch and put in or take out any number of resistors to dim the lamp. The trouble with using a rheostat or potentiometer is the power the pot has to disipate when you're at very low resistance (near full brightness). Since the current will be near that of the lamp alone, you might be putting 1 amp (assuming the lamp draws 1 amp) across a winding or carbon area of 1 ohm thus heating it to 1 watt power which is too much for the very small area to handle without vaporizing. If your lamps are higher power and you're using 12 volts, you might look into the dash board light dimmer for Toyotas or Datsuns at your local auto wrecking yard. I know some model railroad owners who use these for their train speed control units. Beyond the above, we're talking some fun electronics and a schematic via land mail. Hope to read you again soon and good luck. -dB