Quote:
Originally Posted by footfootfoot
It's got a 300° rotation, in practice if I pot it down more than 1/10 of a turn the fan stops spinning.
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Reread those previously posted numbers. Your resistor must vary by maybe 30 ohms. You are using a resistor that is 10,000 ohms. You cannot possibly adjust a 10K resistor between 1, 5, 10, and 30 ohms. And if you did, the 10K resistor must burn.
Trying to do this stuff without a layman tool is frustration. A multimeter that any layman should have for anything electrical (even a car battery) sells even in WalMart for maybe $12. So required for simple problems that a meter sells in almost every store that also sells something more expensive - hammers. Using that meter would have made that problem obvious. Also make numbers in my previous post just as obvious. Even explain 6 volt and 12 volt behavior.
You also have another complication to consider. Electric motors require a high startup torque. Just another reason why the 555 solution can be so useful. And again, another reason why that digital multimeter is needed.