From: "smithhilary1947" <[EMAIL PROTECTED]> >The Hankscraft motor is rated for 3 volts >and supposedly draws less than 10 mA; I am >bringing 12-14 volts. So >I need a resistor
OK so far. Let's see about using Ohm's Law which states E=IR where E is the voltage applied to a circuit, R is the resistance in ohms, and I is the current in amperes. In this situation, E=13 (halfway between 12 and 14 volts), I=.010 amperes (10mA), and R is the unknown. Actually, E really is not 13, but is 10 volts since the motor itself will "consume" 3 volts leaving the unknown resistor to "consume" the remaining 10 volts. The objective here is to have the resistor utilize 10 volts while the motor uses up the other 3 volts. Forget about the diode temporarily. Thus: E=10=.010 x R is the same formula as R=10/.010 which results in R=1,000 ohms. In theory, this should work fine and the motor should have 3 volts across it's leads. So why might you be measuring 5.5 volts? Possibilities: bad meter, bad use of complex meter, applying more than 13 volts, motor specs are incorrect, etc. All of these are things that should be checked out so that the problem could be understood better. Another thing to check is to see if the motor actually draws .010A when 3 volts is applied. Hopefully, you have an ammeter. The motor specs you quoted might be incorrect. As a general rule, the Hankscraft motors made for Switchcraft years ago take about 4-5 seconds to rotate from one position to the other when attached to the switch points (needs a load). This would be somewhat less than 180 degrees for moving the points from one extreme to the other. If the motor takes about this much time, you are in the correct ballpark. I would suggest checking out the above factors and seeing what you can determine before going on to changing the resistance and/or installing a diode in the circuit. With the diode in the circuit, the motor will work in only one direction, but not the other. Try reversing the polarity of the applied 13 volts and see what happens. Good luck....Ed Loizeaux The poll results are in....... To REPLY to the list, use REPLY ALL, to reply to the sender, use REPLY. I do NOT know if this works on all e-mail software, but it works on some of the most common ones. For those of you on DIGEST mode, all REPLY messages go to the list. Change your membership, change your message settings, use our CALENDAR, view shared files or photos, view the list archives, GO TO http://groups.yahoo.com/group/S-Scale/ Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/S-Scale/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
