Brook Motors 3 phase synchronous motor.

TedinNorfolk · Oct 31, 2020

I was at my neighbour cross the road and saw a 1hp motor with other scrap. He had cut the shaft off flush cos he wanted the pulley off it. Long story short he gave it me,and I plugged it in and runs well. It's 1500 rpm ie synchronous. What would a 1hp sync motor be used for? A very large electric clock? Pleased I saved it,anyway.

Phil in Montana · Oct 31, 2020

Look at the tag real close, does it say synchronous or asynchronous? The first has to have a dc wound rotor, the latter will have 4 flats ground into a standard rotor. I have never seen a real 1 hp synchronous motor, the cost to build is quite high, asynchronous motor is used where you need a sync speed motor and are not common but shay are out there...Phil

L Vanice · Oct 31, 2020

One use for a 3PH motor with the shaft cut off is to make a phase converter.

"Very large electric clock" can be a tower clock that the owner got tired of winding or repairing and had converted to electric drive direct to the hands. Yes, it has been done. A gentler solution is to devise an electric drive to periodically raise the weights and leave the original works alone. The picture shows part of a collection in Illinois. These are three small to medium tower clocks that obviously no longer reside in their original towers, whether church, court house or factory.

Big Ben - Wikipedia Note that this famous clock has a non-original electric motor backup.

Larry

TedinNorfolk · Nov 2, 2020

Looked at tag again today-the actual wording is Synch speed 1500rpm. Larry-I love those old turret clocks,with the Chippendale legs!

Limy Sami · Nov 2, 2020

A thought Ted

Bearing in mind electric motors are ''not my bag man'' I think I read something like (????) ..... that although at 50 Hz the true synchronous speed is 1500 RPM ''normal'' motors are ''derated'' (or something like) to 1425 RPM to allow for manufacturing tolerances, variation in voltage etc etc

So I'm wondering if the plate is stating the synchronous speed, leaving it to the user to work out the exact speed (if necessary) from the available supply.

Thought #2, is the motor very old??

(Okay I know, Sami crawls back under his stone

)

L Vanice · Nov 2, 2020

From a 1939 engineering textbook:

Synchronous speed of an induction motor is the speed of the rotating magnetic field, and is determined solely by the frequency and the number of poles. An induction motor might run at synchronous speed if it has zero friction and zero load, but that is just theory. In actual use. the rotor will be slowed by friction and load. It is usual practice to state the rated power at a certain nominal lower speed, like 1425 RPM in the case of a 50 HZ 4 pole motor.

Larry

Limy Sami · Nov 2, 2020

Thank you Larry

.like I said electric motors aren't my thing, but I was sure I'd seen something, .nice to know there's a few braincells left

TedinNorfolk · Nov 3, 2020

"The plate reads 1500-ergo it's a synchronous motor" that was yrs truly,s train of thought! It was explained to us at Tech that there has to be a natural Lag for a motor to be practical-hence the speed usually given as 1425 or near. When I split it,to do something about the sawn off shaft,I will see whether it has the usual squirrel cage rotor or something else. Sami-it's all sandcast iron with fins,about 1940s I'd say. I've always had a soft spot for old motors and dynamos-I have an open frame Siemens 3phase motor with ring oilers still working.

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