Repulsion start induction motors in sirens

[NCAsirens11]

Just out of curiosity, what sirens use a repulsion induction motor? The only one I know of is some kinds of the Denver siren that use a Century motor. Are there any more?

[cooldomino]

Correct me if I’m wrong, I believe the 1 ph motor on the older 6m thunderbolt is one.

[NCAsirens11]

You are correct! The Civil Defence Museum website mentions that the older A-series single-phase blowers use a repulsion-induction motor.

Link (scroll down to the Thunderbolt Siren Blowers section)
http://www.civildefensemuseum.com/sirens/tboltinfo.html

[Hacksaw]

I think the SD-10 uses one.

[cooldomino]

Those are brushes motors. Like a model 2. The one I’m thinking about is that kind with a flat commentator that helps it get started.

[29 ALF]

I am no expert, but I just read that they can cause radio interference on startup, so perhaps that's a reason why they're scarce for sirens?

[NCAsirens11]

With a quick google search, this is true! It can definitely be a factor that they aren’t used in many sirens. RSIR motors output EMI (electromagnetic interference) which can affect the signals.

[SamtheSirenMan(531)]

As far as I know all of Federal Signal’s large single phase sirens(5B, xT22B, STH/STL-10B etc) used repulsion motors which are distinct from repulsion-start induction-run motors. The repulsion motors used by Federal had fixed brushes which were not powered, and served as a shorting bar across two points on the wound rotor through the commutator. Repulsion-start induction-run motors have a brush assembly that can be moved out of the way and replaced with a shorting bar once the motor is up to speed, and they are veeery old. Not sure if any siren has ever used them as I have only seen small ones where the shorting bar is manually actuated by a lever.

[cooldomino]

I believe the motors in the older 1 ph thunderbolt blowers are these.

https://youtu.be/1Gc2WyfhIlM?si=M5P04itT97j5-MT7

[Greenrid]

This 4M 3-phase blower uses one:

The blower

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