Subject: Re: Rewiring FORGE MOTOR (& PB-50 warning)

From: "David C. Hufford" <[email-masked]>
Date: Mon, 26 Aug 1996 15:01:04 -0400 (EDT)

As an extension of the forge blower discussion, I would like to ask if 
there is any reasonable way to rig a 3500 rpm induction motor (such as 
is on the PB-50 blower) to run at half speed, or 1750 rpm?  I mean, 
other than the use of an expensive AC motor speed controller?  If the 
PB-50 blower motor is run at half speed and an air gate used to control 
the blast, it's a very workable blower.  I run the blower at half speed 
now using the stupid fan control supplied by Centaur Forge, but you get 
that obnoxious drone noise (which can't be good for the motor).  Any of 
the electrical engineers out there have any suggestions?

D.C. Hufford

---

From: "Steven O. Smith" <[email-masked]>
Date: Mon, 26 Aug 96 13:38:17 MDT

> is on the PB-50 blower) to run at half speed, or 1750 rpm?  

Nope. Induction motors run (almost) synchronous with line frequency.
If you have a 50/60 Hz motor, it will have different rpm's for 50 and
60 Hz. 3500 vs 1750 is achieved by putting a different number of poles
in the windings inside the motor. No way to change this.

A great way to speed control an induction motor is to supply it with
110VAC and vary the frequency. This is not a trivial thing to do. 

Replace the motor. Get a used one from a furnace repair shop. Go armed
with the outside dimensions of the motor and mount plate. Try for a
motor with the same HP rating. You should be able to find one for
$15-20 used. You can also look in the local junkyards (excuse me,
recycling centers). Bring a line cord, and try the motor out. If it
works, the price will probably go up, but then you get a good motor!

Your replacement motor may need to be reversed to run the other
direction. This is pretty easy on most motors--write me if you need to
do this.

--
Steven O. Smith
[email-masked]