[AT] Old shop lathe motor-- motor questions for you "experts"

[John Wilkens]

Greg, this old motor of mine says it is an "SCA type."    Any idea what 
that means?  (Wonder if that's related to the "service factor' you 
mentioned.   John



At 08:59 PM 01/20/2006, you wrote:
>List traffic is a little slow, so I thought I'd put out a few comments on 
>this subject.  What I am going to say is based on both experience and 
>things I have read.
>
>In the past I had both beef cattle and hogs.  My feeding setup for cattle 
>required 10 motors ranging from 1/4-hp to a couple of 5-hp on the silo 
>unloaders.  My grinding setup for hogs used 9 different motors ranging 
>from 1/4-hp to 5-hp in various sizes.  I believe it is true that the old 
>big motors were that way because they were American-built and were true 
>horsepower/horsepower.  On one auger conveyor I installed a 1-hp motor 
>that my dad had purchased for a different use some 50 years 
>ago.  Unfortunately, about 15 years ago the shaft spun in the ball bearing 
>race and ruined the motor shaft beyond repair.  I replaced it with a 1-hp 
>Dayton motor.  However, if the conveyor became heavily loaded it would 
>stop, whereas the old motor had carried it through.  After enough 
>aggravation I started studying the problem and found on the nameplate two 
>letters.......S.F.    I found that that means "service factor", or the 
>percentage of the motor's rated horsepower that it could put out 
>continuously without overheating.  I found the new motor had a service 
>factor of 1.0, and the old motor (which I still had lying around) had a 
>service factor of 1.35, which meant the old motor had a lot of reserve 
>power that the old one didn't.  I talked to a local dairy equipment dealer 
>who said he had run into the same problem on milking machine pumps.  He 
>would replace a bad motor with one of equivalent hp, only to have it keep 
>overheating and stopping.  Then he'd have to go back a week later and 
>replace it with the next bigger hp.  I then had to buy a 1-1/2 hp motor 
>for the conveyor and it ran almost as well as the old 1-hp.
>
>As a side job, I also repair appliances and found about 10 years ago that 
>the newer motors would start smoking right away when overloaded, whereas 
>30 years ago when I first started in the business they would hum but not 
>smoke.  I could not figure out the difference until a neighbor (who takes 
>motors apart to sell for scrap) showed me the difference.  It turns out 
>95% of the appliance motors in the last 15 years have aluminum windings, 
>not copper, and cannot tolerate being run hot.  We have three of those 
>Baldor motors that someone was commenting on - two 5-hp on silo unloaders, 
>and a 2-hp on a gutter cleaner.   Although we no longer use them, they are 
>still good and after years of use were never repaired.  They could be 
>slowed down to where they were barely moving but they would never stop, 
>and would always slide the belt but not trip the circuit breaker.  It 
>maybe true that they are no longer available, but a few years ago when 
>they still were made an electrical contractor told me that a new 5-hp was 
>around $2000.
>
>I was in Tractor Supply the other day and noticed that Ingersoll Rand 
>compressors are now listing 2-hp on the tank.  For example, it will say 
>"running 5-hp, peak 11.5-hp."  HINT: If the nameplate on a motor does not 
>list the HP, or after HP says "spl" (meaning special duty),  you can be 
>assured the actual motor hp is nowhere near the hp listed on the tank of 
>the compressor.
>
>Just a few random thoughts for the evening.
>
>Greg Hass
>Bad Axe
>from Michigan's snowy and getting snowier Thumb
>
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