[ Dave Krall wrote in 130911 MMDigest:
> It heated up to the point where it was too hot to keep my hand
> on it for more than about five seconds. ... My question is, is it
> normal for this style QS15 Holtzer-Cabot motor to run this hot?
Hi All, In the absence of real numbers, can we have a meaningful
discussion about the temperature of anything? What constitutes "hot
to the touch?" For some people, it might be 105 degrees F. To others,
it might be 125 F. Still to others it might be only 100 F.
How long are we touching the device? And are we touching it with the
tip of our finger? Or the palm of our hand?
I ran some tests using the Electric Specialty Co. motor that I've used
as a grinder motor in the shop for well over 30 years. The motor has
never (and I mean 'never') been serviced, and it has seen hours of
continuous use on any number of occasions (while polishing a set of
ivory keys, for example). I ran the test in 10-minute increments and
checked the case temperature with a racing tire infrared thermometer.
After the first 10 minutes, the case was 87 degrees (F), and it felt
warm when I place my open palm on the case. After 20 minutes, the
temperature has risen to 104 degrees and I held my palm on the case
for about 40 seconds before deciding I could probably hold it there for
a few minutes.
After 30 minutes, the temperature was up to 117 degrees, and I had to
remove my hand after only 7 seconds. After 40 minutes, the temperature
of the center section (what I would call the 'core') was 124 degrees,
the rear bearing was 116 degrees, and the front bearing was 118 degrees.
After 50 minutes, the core was 137 degrees, and the bearings were 123
degrees. At 60 minutes, I detected the faint odor of oil and the core
was 142 degrees. I could touch it with the tip of my index finger for
2 or 3 seconds, but I removed my palm the moment after it made contact
with the metal (I'm not a masochist!).
After stopping the motor, I measured the temperature of the rotor and
the stator. The rotor measured 127 degrees at the center and 148
degrees at the outer edge. The stators measured a consistent 125 all
the way around. The rear bearing was 127 degrees -- which makes sense
considering the temperature of the center of the rotor, but the front
bearing was 10 degrees cooler.
Over the next 5 minutes, the temperature of the shaft (at the bearing)
had fallen to 92 degrees. I owe this drop to the length of the metal
shaft, which is 5-1/2 inches long and exposed to the free air. (The
room temperature is 80 degrees).
I don't know if any of this really helps anyone, but I found it
interesting that I could only hold my open palm on a surface that
was 117 degrees for 6 seconds. At 137 degrees, I lasted for about
three seconds, but I might have been counting fast seconds at that
John A Tuttle
Brick, New Jersey, USA
[ An interesting article about measuring tire temperature is at
[ MMD discussion threads related to motor temperature are indexed
[ at http://www.mmdigest.com/Archives/KWIC/O/overheating.html
[ and http://www.mmdigest.com/Archives/KWIC/M/motor.html and
[ -- Robbie