A vacuum cleaner motor also speeds up when you plug the suction or the
discharge.
That's the nature of a blower. Remove the load (moving air) and it speeds
up.
73
Jim W7RY
-----Original Message-----
From: w2cqm@juno.com
Sent: Tuesday, December 05, 2017 11:48 AM
To: amps@contesting.com
Cc: goodguyham@aol.com
Subject: [Amps] Here's a new one for me that I'd like to share
After some preliminary tests, I decided that a dual 8877 hombrew amplifier
project would not be cooled adequately with a previously installed low
RPM tandem blower. Checked the "junk box" for another candidate with higher
speed and more volume and thanks to a long forgotten hamfest purchase,
from yesteryear(s), I found a suitable replacement. The squirrel cage
blower was larger and the manufacturer's label indicated TWO speeds.
Imprinted on the motor were specifications including a 115VAC operating
voltage and a schematic showing the three wire hookup sequence. Two color
coded wires indicated line voltage input and the third wire (black)
depicted the installation of an AC starting capacitor wired from that
lead across to one of the color coded AC leads. NO VALUE WAS GIVEN TO
THE CAPACITOR. I initially utilized a 1uFd cap for testing. I was
disappointed since there were no other wires that could be used for speed
selection. To test for suitabili
ty, I nevertheless increased the opening for the larger blower mounting
flange and installed it on the rear of the amp enclosure. It started to
work; but nowhere near that potentially higher value of rotation stenciled
on the motor body. I was a bit stymied at that point! Not certain what
possessed me, but I decided to reach in and placed my hand over the blower
output to restrict flow. Mysteriously, the fan substantially increased its
speed. Removed the back pressure restriction caused by my hand and it
slowed down. Not certain if I can explain the phenomenon , but I did
experiment with much higher AC capacitors values and found the fan speed
increasing but that resulted in the buildup of abnormal heat around
the motor. That was unacceptable. I settled on the one and only low
value 1 uFd capacitor I had since the amplifier cooling system was now
operating well with adequate cooling volume. After replacing the tubes in
the sockets and sealin
g off the pressurized lower cabinet, the fan increased under the two tube
cooling requirement restrictions and the blower motor heat build up is no
longer an issue. Obviously, the automatic speed control has something to
do with the value of the starting capacitor, the normal back pressure of
cooling, and to some extent the resultant additional current draw. It's
safe to assume that it's not a ghost nor is there an air flow control.
within the fan body! Hopefully, someone can explain what's happening and
share it with me and the other AMPS subscribers? Thanks, Ron W2CQM/3
Note! you can view some early digitals of this project with annotations on
my QRZ site. Click on SHUTTERFLY at the bottom of the page.
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|