DIYbanter - multiple speed furnace blower

Australopithecus scobis wrote:
Greetings,
Just got a new furnace for the house. ouch. Snagged the squirrel
cage fan from the old unit. (Eyed the burners, but let them go.)
This fan has five electric connections; one for common and four to
select the fan speed. Heat used one speed, A/C used another.

It's not little like this one, right?

http://www.panix.com/~alvinj/burner.htm

I'm picturing a big blower like the one in my furnace that also has
four speeds and the motor is inside the squirrel cage.

I've pulled a few of little-blowers out of furnaces at the scrap
yard (and abandoned ones out in the desert) only one so far was
~120V instead of the usual 240V. YMMV, don't know nuthin about
your electric service there.

Checked out the Google archives for this group. I don't trust the
dimmer switch idea for this fan. A bank of light switches on the
yet-to-be-built case could select fan speed. The deadman switch
idea is one I hadn't considered, but will add one to the common
when I do the case.

Oh man, the light dimmer idea sucks for these types of motors.

Sloppy as hell. :/

The baffle idea works like a champ, instant, precise changes can be
had with a baffle. If the motor is inside the squirrel cage blower
then the air will need to come into that side and go over the motor,
otherwise the motor (like in the one pictured) will see a much lower
"load" with the air cut off.

I've been using that one all the way closed since I reduced the
burners to 1/2" bushings. Almost all the air it gets comes through
the motor.

My question: Any body here played with this sort of fan? I want to
know if I'd fry it if two of the speed circuits were live at the
same time. The 120V rotary switches I've found on the web seem all
to be make-before-break.

I see lots of arcing on the switch points in your future? ;)
(but don't know for sure). :/

I say, forget the various speeds and first try the baffle idea. :)

Alvin in AZ
ps-
http://www.panix.com/~alvinj/drills.jpg
Now that's what a light dimmer is good for... single speed,
double reduction ~1000rpm power-drills... works great! :)
pps- yeah, I have a Milwaukee VSR and it's nice but not as
good for pocket knife work as either of those two drills
with the light dimmer, IME
ppps- ceiling fan speed controllers are the same thing except they
come on full blast and slow down as you "twist it" farther,
also they have a speed adjustment which I needed to change
on the two I have for drill use