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A question for @gunrunnerjohn and the other electronics gurus: 

I'm rigging this Pullman panel: 

Panel 01

to run a 6 volt fan for a friend.   My question is:  At high, the fan would get 6v, medium 4v and low 2v.  What value resistors should I use to get the desired results? 

Thanks!

Mitch

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In that case current draw is likely small, still to use resistors you need to know current draw when running. Diodes will drop the voltage by approximately 1.5 volts. So instead of 4v one diode would give 4.5v and two diodes in series 3v. 3 diodes of course would give 1.5 volts. I guess it depends how close you want to be or just see the effect of slowing the the fan.

Pete

Last edited by Norton

Mitch, not trying to be difficult. Just saying how it works. You have to know the current draw of the load, not the source. I bet if you shorted out one AAA battery it could supply over 1 amp (same for 4 in series BTW). If you have a meter with a 10 amp current range you could do this yourself. Simply put the probes across the battery. Your fan likely draws less than 200 ma.

Pete

Last edited by Norton

I'd use diodes for 200ma, that way you don't actually have to know what the precise current draw is, and you'll still get consistent operation.  Also, it's not carved in stone that the voltage increments of 2,4, and 6, are going to be the ideal speed settings, so you may want to do a small experiment with a variable supply to see where you'd actually like the set points to be.

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