[Amps] Here's a new one for me that I'd like to share

Paul Baldock paul at paulbaldock.com
Tue Dec 5 15:45:49 EST 2017

It seems counter intuitive, bit what Jim say's is true, block the 
blower  and it does not have to move the air so is doing "less work". 
You can demonstrate this by monitoring the current on the vacuum 
cleaner which will DECREASE when you block the input or output.

- Paul
- KW7Y

At 10:07 AM 12/5/2017, Jim W7RY wrote:
>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.
>Jim W7RY
>-----Original Message----- From: w2cqm at juno.com
>Sent: Tuesday, December 05, 2017 11:48 AM
>To: amps at contesting.com
>Cc: goodguyham at 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 at contesting.com
>Amps mailing list
>Amps at contesting.com

More information about the Amps mailing list