[GreenKeys] Teletype 50HZ and 60Hz motors

[Jerry Murphy]

The motor which is most often found in M28 and M35 machines is the LMU3.
The LMU3 runs on 120VAC and 60HZ current.  It turns at 3600RPM and puts
out 1/20th HP.  Its 50HZ cousin is the LMU38.  It runs on 120VAC and 
turns at 3000RPM and puts out 1/20th HP.  The ONLY difference between
the LMU3 and the LMU38 is the thermostatic protection switch.  The LMU3
consumes 1.85 amps when running while the LMU38 consumes 2.4 amps.  If
you wanted to run an LMU3 on 50HZ current, you might want to short out 
the thermostatic protection switch and put a time-delay fuse in the motor 
power leads.  The capacitor, starting relay, rotor and stator are the same 
on both motors.  Find more information on M28 and M35 motors here: 

http://navy-radio.com/manuals/tty/jh/bsps/bsp/570series/570-220-100TC-Iss4.pdf

The 1/12th HP motor that is found on M28 ASR sets is the LMU12.  It turns
at 3600RPM when fed with 120VAC of 60Hz current.  It should NOT be used
on 50Hz current.  Teletype made a special motor for powering M28 ASR sets
on 50Hz current.  The motor is the LMU50.  A quick look will reveal that 
the LMU50 is about 1.25 inches longer than the LMU12.  The rotor and stator
are bigger and contain more iron.  The capacitor and starting relay are
also different from the LMU12.  There is an ebay seller who has an LMU50
for sale at this time.  Here is the link:

    www.ebay.com/itm/254172915159

The seller does not refer to it as an LMU50 but that is what it is.

Go to the M28 motor parts manual and look at the 304538 motor mounting
cradle to get an ideal of how much longer the LMU50 motor is.  Here is
the link:  

    http://navy-radio.com/manuals/tty/570-220-800TC-6701.pdf

Teletype did make a 1/20th HP motor for use on 50Hz current and 230VAC.
that motor was the LMU55.  Of course, it would also work on 60Hz current
at 230VAC.

Regarding the unusual device that is attached to the motor fan on Ed
Groenenberg's M35 KSR, it appears to be a centrifugal device that 
operates a switch to let some device know that the Teletype machine is
running.  There are several of these switches shown in the Teletype
motor parts list.  Look on pages 24 and 26 of the motor parts manual.
Here is the link:

  http://navy-radio.com/manuals/tty/570-220-800TC-6701.pdf

Jerry Murphy