Can a three-phase tornado siren motor continue spinning the siren's rotor on single-phase?

[Robert Gift]

Under our garage workbench we have a 15? hp 240V three-phase motornado siren.
If I use a drill to get the siren rotor spinning and apply 240 VAC, could it continue turning on single-phase?


On New Year's Eve I move a 2hp 120/240VAC single-phase siren outo the sidewalk.
28 amps @ 120V, so it is connected to 240V so the 20-amp garage subpanel circuit breaker will handle the 14-amp load.

It is sounded precisely at 07:00:00 GMT. (Midnight Mountain Standard Time.)
It quickly gets up to speed.
But when coasting down, it reaches a speed at which it slows faster!
What causes that coasting speedrop? Can I defeathat slowing by disconnecting the starter capacitor? (I would install a switch.)

Thank you

 

[Reach4]

A 3-phase motor does not have a start capacitor.

So you may have a single phase 240 volt motor with a start capacitor or a run-start capacitor.

Are you trying to make that motor decelerate faster?

 

[Sponsor]

 

[Robert Gift]

A 3-phase motor does not have a start capacitor.
So you may have a single phase 240 volt motor with a start capacitor or a run-start capacitor.
Are you trying to make that motor decelerate faster?

Thank you.
The two-tone siren has a 15-hp three-phase motor. That siren is too heavy to move outside by myself.
Would be fun to get it to sound by turning the rotor faster than my spinning its rotor using a wood dowel.
Its rotor has two rows of ports, producing a perfect 4th* musical interval. (*Difficulto discern a such low frequencies.)

The single-phase 2-hp siren is one tone. Fortunately I can manage to lift ito the sidewalk 8 feet at a time.
I wanthe siren to naturally wind down (decelerate). But during coast-down, as it descends to a certain speed, it slows faster and therefore the tone drops faster. Presumably its two-horsepower motor has a starter capacitor.

 

[Reach4]

So you want the 2-hp siren to sustain the sound longer when you drop power. Other than making sure it is lubricated, I don't know how you would do that.

 

[Robert Gift]

So you want the 2-hp siren to sustain the sound longer when you drop power. Other than making sure it is lubricated, I don't know how you would do that.

Yes. The rotor RPM descends naturally, then suddenly drops faster at a certain point.
Was wondering if the starter capacitor wasomehow causing the quicker descent through a reverse EMF.
Turning the rotor with a wood dowel, it feels very free with little resistance.

My Federal Signal 2t22A 10hp three-phase sirenaturally descends from peak 1,350? RPM to Stop in over two minutes!
When near the siren at lower frequencies I can feel the sound pressure waves in my lungs!

 

[Reach4]

If the start capacitor was still in the circuit, I would think that would decelerate the motor vs having an open circuit for both run and start windings. It would be interesting to add a switch to open that start winding path if the centrifugal switch is re-making the path. I think you may be on to something.

 

[Robert Gift]

Can the motor be hand-started (using wood dowel spinning the rotor) without the start capacitor?
If so, I would just leave the capacitor disconnected and just hand start.
Shall try inside the garage.

Poor neighbors. But many set off fireworks at midnight New Year's Eve, so the siren is not that annoying.

 

[Reach4]

I don't know. Wiring in a second pole of the switch in series with the start cap would be more sure I think.

 

[Fitter30]

The only capacitor a three phase motor could have would be three caps not for starting not for running but to correct the power factor. Single phase won't run a spinning 3 phase motor. Sure there isn't a damper that closes for spin up and spin down?

 

[Robert Gift]

The only capacitor a three phase motor could have would be three caps not for starting not for running but to correct the power factor. Single phase won't run a spinning 3 phase motor. Sure there isn't a damper that closes for spin up and spin down?

No dampers. Both sirens are open to air being sucked in and pumped out by centrifugal force through the rotor's ports.
As the rotor's ports align with the stator's openings, (both the same size), the air bursts out, creating the sound pressure wave.

 

[Robert Gift]

Disconnected the 2-hp single-phase motor's capacitor.
Turned the rotor fast with a wooden dowel.
Turned on the 240 VAC.
The motor did not speed up. Then the 20-amp circuit breaker tripped.

Siren is out on the sidewalk ready to sound precisely at 00:00:00 MST January 1st, 2025

When winding down, I shall disconnect the capacitor to see if the wind down continues normally
without suddenly slowing more.

 

[Robert Gift]

After turning off the 20-amp circuit breaker, I was not able to geto the siren out on the sidewalk before it hit the speed at which it slows faster.

 

[Fitter30]

The Siren Board - Forums

www.airraidsirens.net

 

[Robert Gift]

The Siren Board - Forums

www.airraidsirens.net

Thank you.
Member for manyears. Buthey do not know motors.
I do not know the 120/240 VAC motor winding. Assume the start capacitor is causing the motor to slow faster when its descending RPM gets to a certain speed. Centrifugal switch?

 

[Fitter30]

Thank you.
Member for manyears. Buthey do not know motors.
I do not know the 120/240 VAC motor winding. Assume the start capacitor is causing the motor to slow faster when its descending RPM gets to a certain speed. Centrifugal switch?

Happen to have brand of siren and pic of motor name plate.

 

[Robert Gift]

Happen to have brand of siren and pic of motor name plate.

Shall get it. Thank you.