I don't know if the attachment will come through, but maybe someone
can link it somehow?
After reading the recent threads about syncing a rotor gap I thought
that there must be a better way to do this than just trial and error.
The attached schematic I just made up and it seems to work, but your
mileage my vary.
The idea is to use LEDs to flash at the peak of the AC waveform. To
do this I used a simple Opto-Isolator (4N37 but many types would
probably work fine). The 120VAC is dropped down through a 150k
resistor, then through a blocking diode into the input of the 4N37. A
5k potentiometer is across the 4N37 input LED for something of a
gain/sensitivity adjustment (an additional Variac on the input could
do the same thing.)
On the output of the 4N37 are two NPN transistors, these are used to
invert the signal and provide current gain for the LEDs (a single PNP
could probably work as well.) The LEDs I used was from a cheap LED
flashlight. It already had the LEDs in series and was setup for 6V
input, but since we're flashing the LEDs pretty quickly the 9V input
shouldn't hurt anything. You'll want some bright LEDs because they're
only ON for a moment at 60Hz.
I setup a standard 1725RPM 1/4HP motor with a pulley and made a single
line with magic marker. With the motor running and the 5k pot
adjusted I could see two distinct lines on the pulley at 180 degrees
apart. Since this isn't a synchronous motor the marks slowly rotate
at the slip factor. So it took about 10 seconds for my marks to
rotate through a revolution. With your sync motors the marks should
not move at all. Then proper phasing of the disk to shaft can be done
very quickly and safely since you don't need the gap actually running.
You could also add a bridge rectifier to the input and get 4 strobes
per rotation.
Hope this is useful to someone, it was an interesting exercise for me.
CP8071
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