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

[Christian Fandt]

At 05:43 27-05-98 -1000, you 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."?)

Full Load Amps
>
>One question - how do I apply 3-phase 240vac to a single-phase
>motor?

Easy. Just hang the single-phase load across two of the three legs of your
three-phase supply. The load could be a moter, heater coil, lights, whatever.

Now, I'm wondering if you have this a bit backwards. You say it followed
you home. Our homes in the USA and CDN most usually have 240VAC
*single-phase* supplies, not three-phase.

If the siren is three-phase and your house supply is single, things get a
bit more complex. You would need some sort of single-to-three-phase
converter. They are available but I don't have a source at hand. Some very
small machines shops have three-phase machine tools running under some sort
of converter.  They may also simply buy a single-phase motor if it's less
than 2 H.P. or have their three-phase units rewound to single (which to me
is not economically practical.)

European homes, at least those in Germany which I personally know, do
indeed have three-phase supplies (380VAC, 50Hz three-phase, 240VAC across
two legs). I assume Nevada conforms to the North American standard? <big grin>

10 HP....  That's a heap o' power that would be drawn. It will also draw a
whole heap of annoyance from your neighbors if you ever light that thing up
;-)   Live way out in the desert?

>
>73 from Nevada,
>Jeff KH2PZ/7
>
Have fun,  Chris
-- --
Christian Fandt,         Electronic/Electrical Historian
Jamestown, NY  USA
Member of Antique Wireless Association
        URL: http://www.ggw.org/freenet/a/awa/

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