The most unusual 'anchor that's ever followed me home

[Mike Dinolfo]

Jeffrey Herman wrote:
>
> This should be an interesting thread - I encourage everyone to
> contribute!
>
> Yesterday, a Federal Signal Corp. "air-raid" siren somehow ended
> up in my garage - all 400 pounds of it. Model SD-10, 10 hp 240
> VAC single phase motor driving an aluminum rotor. The rotor has two rows
> of opennings - 12 opennings in one row, 9 in the other, which produce
> 2 tones, in a freq'y ratio of 4-to-3 (for example, 400 and 300 Hz
> tones). The stationary portion (the "stator") also has the same number
> of opennings which align exactly with those of the rotor. The rapid
> openning and closing of these matching ports is how the tones are
> created.
>
> The spec plate says the motor shaft spins at 3300 rpm, or 55 rps.
> Hence, at top speed, one hears 660 and 495 Hz tones (plus all
> the harmonics generated - this is what gives these sirens their
> distinctive sound).
>
> The plate also says "F.L. Amps 54." (What is "F.L."?)

"F.L. amps" is "full load amps", i.e, the running amps after the motor
comes up to speed.  It appears that you have a full-voltage starting
motor.  This motor will probably draw from five to seven times the full
load amps at startup; you will need to provide a suitable full voltage
starter to run the motor (at least, if you want to do so according to
the current National Electric Code).  In addition, you will want to
provide overcurrent protection (fuse or circuit breaker) at not more
than about 2.5 times the full load amps (a 125 amp 2 pole breaker should
be about right).

A 240 volt single phase motor can be energized by obtaining power from
any two phases of a 240 volt three phase system (not to be confused with
a 208 volt 3 phase system; the 208 volt rating for a three phase system
is much more common in the USA, but connecting a motor which is 240 volt
rated, but not 208 volt rated, on a 208 volt system will lead to
overheating of the motor.  Unlike what we are used to when working with
radio components, running a motor at a voltage less than its nominal
rating will lead to premature motor failure.)

To run this motor, you will need access to a system of moderate power,
and one which is not very forgiving of mistakes.  I strongly encourage
you to get a licensed electrician involved (and maybe a professional
engineer) before you try to energize the beast.  Personally, I'd use the
siren as a "real" boat anchor (if only I had the boat to go with it!)
>
> One question - how do I apply 3-phase 240vac to a single-phase
> motor?
>
> 73 from Nevada,
> Jeff KH2PZ/7
>
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