I remember some discussion here about using a standard household florescent shining onto the moving flywheel to determine RPM's. The concept was to 'mark' the flywheel with a piece of white tape and then shine the light on it while varying the rpm's. Supposedly, you'd see two 'marks', (180-degrees opposed), at 1800 rpm and four marks, (@ 90-degrees), at 3600 rpms.... I tried this with a florescent shop light to no avail from low-R's to high-R's.... Has anybody got this to work? Not having a tach causes me to wonder if I am passing the critical revs too fast...or what.
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Hans
The Fluorescent Strobe Myth
Well, here is how it is supposed to work (fair warning: contains basic math and logic reasoning, and therefore maybe harmful to your health): North American AC comes at 60 cycles or Hz, which means the electric current changes its polarity 120 times per sec. (a full cycle consists of periods of both polarities). Any light on AC (fluorescent, incandescent) will shine its brightest at the maximum current for each polarity, i.e. the light will “flicker” at a constant rate of 120 times per sec. Fluorescent lights are known to do a better job at “flickering”, i.e. the differences between brighter (on) and less bright (off) are more striking than in incandescent lights – that is why fluorescents are used in our experiment. Now, if you have a white mark on the circumference of the flywheel, and this flywheel makes exactly one full revolution between two “on” occurrences, the mark would appear “frozen” in place if the flicker were instantaneous (as in a true strobe light).In our context, this would require 120 revolutions per second or 120x60=7,200 RPM – a bit too much for our Diesel engine. Now, at half that RPM (i.e. 3,600 RPM); your white mark would only manage one half revolution, and would therefore appear “duplicated” at exactly opposite locations on the flywheel, and it would also be much less clear, as each 2nd of your “light on” episodes would shine on no mark, blurring “mark” and “no mark” events would together. While 3,600 RPM maybe manageable by your engine, you need to appreciate that several factors are against you: the flicker of a regular fluorescent is not very pronounced, the “on” episodes are not instantaneous and therefore will blur the white mark across a significant sector of the flywheel, while at the same time the “each 2nd on” effect described above will make it even harder to see. Add any truly continuous background illumination, and the already weak “signal” will be fully contaminated. You could improve your chances by marking up the crankshaft pulley instead (if you have one): this rotates at twice the crankshaft RPMs and you are back at perceiving only one “frozen” mark at 3600 RPMs Conclusion: while theoretically workable, I have never heard of any real person who has successfully used this method in any practical context. You might want to look into acquiring one of the cheapo bicycle speedometers, stick the little magnet on the flywheel, rig the sensor for pickup and do the simple math to convert: at a setting of 20” for wheel diameter and at 1,000 RPM, the speedometer should read approx 60 mph (make sure the speedometer reads up that high!) Good luck, Hans
Well, here is how it is supposed to work (fair warning: contains basic math and logic reasoning, and therefore maybe harmful to your health): North American AC comes at 60 cycles or Hz, which means the electric current changes its polarity 120 times per sec. (a full cycle consists of periods of both polarities). Any light on AC (fluorescent, incandescent) will shine its brightest at the maximum current for each polarity, i.e. the light will “flicker” at a constant rate of 120 times per sec. Fluorescent lights are known to do a better job at “flickering”, i.e. the differences between brighter (on) and less bright (off) are more striking than in incandescent lights – that is why fluorescents are used in our experiment. Now, if you have a white mark on the circumference of the flywheel, and this flywheel makes exactly one full revolution between two “on” occurrences, the mark would appear “frozen” in place if the flicker were instantaneous (as in a true strobe light).In our context, this would require 120 revolutions per second or 120x60=7,200 RPM – a bit too much for our Diesel engine. Now, at half that RPM (i.e. 3,600 RPM); your white mark would only manage one half revolution, and would therefore appear “duplicated” at exactly opposite locations on the flywheel, and it would also be much less clear, as each 2nd of your “light on” episodes would shine on no mark, blurring “mark” and “no mark” events would together. While 3,600 RPM maybe manageable by your engine, you need to appreciate that several factors are against you: the flicker of a regular fluorescent is not very pronounced, the “on” episodes are not instantaneous and therefore will blur the white mark across a significant sector of the flywheel, while at the same time the “each 2nd on” effect described above will make it even harder to see. Add any truly continuous background illumination, and the already weak “signal” will be fully contaminated. You could improve your chances by marking up the crankshaft pulley instead (if you have one): this rotates at twice the crankshaft RPMs and you are back at perceiving only one “frozen” mark at 3600 RPMs Conclusion: while theoretically workable, I have never heard of any real person who has successfully used this method in any practical context. You might want to look into acquiring one of the cheapo bicycle speedometers, stick the little magnet on the flywheel, rig the sensor for pickup and do the simple math to convert: at a setting of 20” for wheel diameter and at 1,000 RPM, the speedometer should read approx 60 mph (make sure the speedometer reads up that high!) Good luck, Hans
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Jack
4 Marks at 1800 RPM
The line frequency is 60 cycles per second or 3600 cycles per minute. The light flashes 2 times per cycle. Therefore, 1800 RPM is 4 marks on your engine pulley. You need it really dark to see the marks as any outside light swamps out the florescent flashes.
The line frequency is 60 cycles per second or 3600 cycles per minute. The light flashes 2 times per cycle. Therefore, 1800 RPM is 4 marks on your engine pulley. You need it really dark to see the marks as any outside light swamps out the florescent flashes.
R
Rick Webb
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J. Tesoriero
Hey, it works!
This realy works! Some older folks may remember the faint light from the DC timing light we used to use to time the points on our old cars. You have to use an alternating power (AC) fluorescent light held within a reasonable (and safe) distance from the engine pulley and have a relatively dark work area around the engine. At 1,800 RPM, there are four relatively steady white marks at 90 degrees from one another. You can use plain old 1 inch white tape. Some of the reflective kind may work better but is expensive.
This realy works! Some older folks may remember the faint light from the DC timing light we used to use to time the points on our old cars. You have to use an alternating power (AC) fluorescent light held within a reasonable (and safe) distance from the engine pulley and have a relatively dark work area around the engine. At 1,800 RPM, there are four relatively steady white marks at 90 degrees from one another. You can use plain old 1 inch white tape. Some of the reflective kind may work better but is expensive.
D
Don
J
J. Tesoriero
Terminology
I have been reading the original and subsequent posts on this topic. There seems to be some problem with the terminology as to when to observe the timing marks. The AC Fuorescent light strobe method only works when you shine it on the pulley on the front of the engine, the one that is mounted on the crankshaft! You have to be able to see the entire face of the pulley in order to see the marks. Hans mentions this in his post. Putting white marks or tape on your flywheel won't work. You can't see much of the flywheel anyway without an inspection or timing port.
I have been reading the original and subsequent posts on this topic. There seems to be some problem with the terminology as to when to observe the timing marks. The AC Fuorescent light strobe method only works when you shine it on the pulley on the front of the engine, the one that is mounted on the crankshaft! You have to be able to see the entire face of the pulley in order to see the marks. Hans mentions this in his post. Putting white marks or tape on your flywheel won't work. You can't see much of the flywheel anyway without an inspection or timing port.
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