The Difference HP Makes

[Rheems1]

So a question I have always had and never wanted to ask for fear of sounding dumb is, what difference does HP make in a siren and why? If you have a 12 port siren with a motor rpm of 3,400... would a 10 hp motor make the siren louder/carry further than say the same siren with a 7.5hp motor? The STH-10 has been discussed as orignally having a 10hp motor which was changed to a 7.5hp motor later on in it's run, this is what made this question come to my mind.

[Jim Z]

The hp rating of a motor depends on it running at a given speed with a specific load on it. An induction motor running by itself (no load) will be running @ about 3500-3550 rpm but only produce a fraction of it's rated hp. When you put a load on it- say, a siren chopper- which drags it down to its nameplate rpm, it'll be producing it's rated hp.

Now, the thing to keep in mind is the chopper of the siren is little more than a centrifugal blower. The faster you want to spin the thing,the more power you need. If you have a certain chopper/stator combo which can reach the motor's rated speed with a 7.5 hp motor, then all you'll get with a 10 hp motor is faster spin-up. Also, the 10 hp motor may last longer as it might not be as thermally stressed.

Going the other way, if you have a chopper/stator combo which can reach the motor's rated speed with a 10 hp motor, a 7.5 hp motor might not be able to get to rated speed and will spin up a lot slower. And may fail prematurely.

[Rheems1]

Thank you Jim, that is exactly what I wanted to know and your answer makes perfect sense!