The Situation:
Example of a Little Giant trip hammer, motor belting problem:
Tom asks:
I have recently aquired a 25# little giant and am finding a 1 hp motor too small to run it even though it's the recomended size motor as far as i can tell.
The hammer seems to run smoothly and freely. Any thoughts?
The Answer, back to Tom:
Basic questions that I ask:
1. Does the motor have trouble starting up, or does it bog down when hammering?
Is the motor a capacitor start model or not? Since it needs to start under load, you need a motor of this type.
2. What speed is the motor and what is the speed of the Little Giant crankshaft?
I assume you have a 1725 rpm motor. If you have geared it to run the crankshaft at more than about 375 rpms, then the
1 hp may not be enough.
Some people use a bigger motor (1 1/2 hp or so) if they are in a cold building and if the hammer is stiff.
3. Is it possible that there is something wrong with the motor?
-Bad start switch
-Bad start capacitor(s)
Tom's reply:
The motor bogs down while hammering. It is indeed a 1725 rpm motor and capacitor start. However the drive pulley that
came with the hammer is 5" rather than the recommended 3" so the shaft speed is faster than called for.
I have a 3" pulley on the way to try. I believe the motor is okay; freshly rebuilt. I did find that I have some
voltage drop on the circut the motor runs on so I will trouble shoot that. It may well be that those two
things are it. I will know shortly.
Thx
My reply to the above comments:
I'd say that the 5" pulley IS the problem.
Goal: 375 crankshaft rpms max.
Motor ClutchRatio MtrRPM ShaftRPM
5 12
2.4 1725 718.75
3 12
4 1725 431.25
You can see from the above, that, assuming a 12 inch diameter clutch pulley (if the clutch pulley is smaller than that,
the problem is even worse).
You only have about half the torque available that you should have from a 1HP motor in that application.
Even with the 3" pulley, you are still somewhat overspeed.
2.5 12
4.8 1725 359.375
With a 2 1/2"pulley, you'd be well within spec.
The saving grace with the 3" pulley is that you may experience as much as 5% slip, so:
431.25
X 0.95
409.6875
Which is still a little high, but Sid at Little Giant does that, I think.
As a reminder, though, if your clutch pulley is smaller or larger than 12", you should rethink the ratios.
A 2 1/2" pulley may be mandatory, to get enough power.