Some seven years ago I rescued this 50+ year old old blower/motor out of a skip at work. The blower had been part of a chemistry lab fume hood ventilation system so was covered in sticky chemically smelling muck and corroded in parts. The squirrel cage impeller was also bent and unbalanced.

The original motor was a 0.3HP, 6 Pole, 415V hard wire Y connected motor so I converted it internally to run on 240V 3Phase and attached a used VFD to it.
After washing it down I took the whole thing apart, straightened everything up, statically rebalanced the impeller, and repainted the fan housing and motor.
I did notice some light greenish looking corrosion on the internal coils which I brushed off and revarnished.

The 6 pole motor ran at ~920 RPM at 50 Hz pulling 1350 CFM and I ran it up to 60Hz which was about 1600 cfm - very quiet and low power (0.5A) was all it drew to get this flow.
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This fan was my general shed ventilation fan, located up close to the ceiling above my TS and main WW work bench. It expelled air out of a vent in the central gable and it has been very useful at clearing the shed of any escaped dust.

The motor/fan ran fine up until about a month when would not go any faster above 30Hz and the VFD would just stop teh motort. I was surprised it even ran at all because most VFDs will prevent the motor from running due to a phase current imbalanced. I opened it up and sure enough more corrosion and one of the motor coils lost continuity (open circuit) - not worth messing about with so I started to look for a replacement. Small 6 pole motors are difficult to find and also expensive so I opted for a 4pole motor and but because I would need to run it at lower frequency than the original motor, I decide to get a higher power rating and settled on a 0.5HP motor from Conons.

Of course old motor replacements are rarely straight forward. The first thing was the new motor was physically smaller so the mounting bolt holes in the fan frame were too low and just a few mm away from those of the new motor. To get around this I made up an adapter plate out of some 3mm steel plate that raised the new motor up 11mm and accounted for the different bolt positions - that was the easy bit.

The next thing was the old motor had a 5/8" shaft but the new one was 14mm. To get around this I turned a new up a new adapter from a piece of 25mm diameter steel.


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Re-assembeled the whole thing and took the opportunity to tidy up the electrical cables a bit.
Terrible colour clash but it's above my head so out of sight unless you look upwards.

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Now I had to determine what max speed I could operate this fan/motor combo.
I did some air flow and current measurements and below is a summary of the results.

The black dots irepresentss the air flow - use LHS axis while the red dots are current - refer to RHS axis.
The blue dot (A) is the air flow for the old 6 pole motor air flow at 50Hz
The red arrow is the nominal continuous max current draw of the new motor (1.8A).
This means I should not run the motor continuously at more than about 35Hz - that still about 1500 CFM which is more than enough for ventilation purposes

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I can of course run the fan a bit faster for short bursts but at about 45Hz the fan starts to vibrate the housing and at 50Hz it's making an audible rattle. This is probably because was not that careful when I first balanced the impeller and it probably need redoing.

Anyway - I'm back in business.