OVERSPEED an ST-12?

[SHIPCHIEF]

I was wondering if I could run up the governor on my 25/2, which is de-rated to 735 RPM. Suppose I run it at 850? The voltage and cycles would be higher, then when I mow the lawn with my Black & Decker electric mower, the higher voltage would give more power? I suppose it's a universal motor and won't care what the frequency is? 

[mobile_bob]

my st7.5  is direct driven for 1800, and i have taken it to 2200 without issues
of course i didn't have anything plugged in to it though

bob g

[Doug]

Rim speed issues that aply to flywheel also aply to wound rotors.

Spin it too fast and you will regrete it.

[SHIPCHIEF]

I guess I was thinking about voltage, frequency and current issues, rather than centrifugal force, on account that the alternator rotating section is a fairly small diameter compared to the flywheels on the engine. The engine is rated 1000 PM, so I'm well into the safe zone there.
The Alternator (I suppose, now that you made me think of it) has a design speed of 1800 RPM with an overspeed tolerance of X% (?) ....So it would experience some increase in stress and wear even if it did not fail outright or something? 

[jzeeff]

If you are talking about a little boost to make up for some voltage drop, I think it would be fine for everything other than synchronous motors.   Or would the voltage regulator just bring the voltage back down?  If you want to double the voltage to get a "turbo mower", I would expect major problems.

[mobile_bob]

i suspect a 10% overspeed is probably safe enough,, but 20% or so that i did once
was probably getting close to the manufacture of vast quantities of copper kitchen pot scrubbers!
but i am not sure,, and not really interested to find out how fast a typical st head can be spun up
without spinning itself all over the place.

that would be a really bad day indeed

bob g

[Doug]

Hard to say what the Chinese figuere is safe for 50 hz. Since they designed these for 50 hz and we are already running them 20% over speed and know thats safe then who knows whats next

[SHIPCHIEF]

True enough;
I was thinking that my long extension cord has a pretty severe voltage drop. Low voltage=high current=heat.
A little more voltage would get me back up to "rated" at the mower.

[jzeeff]

A variac will allow you to dial-in a voltage.

[SHIPCHIEF]

So should I carry the variac on the mower deck? I've got a couple of them, but I think they are good for warming up tube radios, maybe 1-1/2 amps? 

[mobile_bob]

awe heck Scott

just take that 25/2 and build yourself a "man's" riding lawnmower!!!

(arrrrgggg, as tim the toolman would say)



bob g

[jzeeff]

I suppose you could.  Probably more fun (ie, sparks and flames) than buying a 30 amp model and putting it at the other end.

[cujet]

So, you have a diesel powered push mower!

[SHIPCHIEF]

That's right.
I've used my 25/2 to mow the lawn.