Electronics > Projects, Designs, and Technical Stuff
Convert blower motor for ductless ops
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zz28zz:
Thx for all the replies. I knew blocking the inlet would decrease the load but assumed blocking the outlet would increase it but the more I think about it, I think you guys are right. Looks like I'll be keeping the restriction plate on the outlet for now.

My original thought was to mount the blower above my boat to help dry it out after an outing. That's why I wanted it unrestricted, so it would blow air over a wider area. With the restriction plate, the airflow is somewhat concentrated. I may play with various grills and see what I come up with. Humm, wonder if I could accomplish the same thing by partially restricting the inlets? That way I could keep the wide air distribution pattern.

My understanding of A/C induction motors is that the speed is determined by number of connected poles inside the motor and the frequency of the line voltage. Different speeds are determined by which wire is connected since the different wires are connected to different number of poles. The motor I'm using has 4 different speeds so I have 3 wires left un-connected.
 
james_s:
That is interesting, I had a niggling feeling in the back of my mind that blocking the output may in fact reduce the load but it's non-intuitive and I wasn't certain enough to mention it. It makes sense though when you think about the air just swirling around in a blower.

Does the same apply to a centrifugal water pump? What about a centrifugal compressor like that of a turbocharger?
ejeffrey:
For a normal blower, the static pressure is so tiny compared to absolute pressure that it doesn't make a difference which side you block.

For a centrifugal water pump you always want to restrict the outlet never the inlet otherwise the static pressure can drop low enough to cause cavitation.  Keep in mind that many pumps are cooled by the working fluid.  Even if blocking the flow causes the overall power consumption to decrease the rotor might still overheat.

Centrifugal compressors only work properly with flow, otherwise they can oscillate.  That is why turbochargers have bypass valves.
Simon:
if you block the outlet you will have more turbolence than if you block the inlet.
james_s:
I wasn't suggesting blocking a water pump or turbo compressor as a practical application, only questioning the effect of doing so on the mechanical source.

Older turbochargers lack a compressor bypass valve. The one in my '84 Volvo is like this and you can hear the odd pulsing flutter if you suddenly close the throttle while under high boost. Adding a bypass valve is something I've been meaning to do for years.
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