Motor conversion - Where do I start?

[BobL]

This is getting up to a dozen 3P Y to ∆ motor conversions but might be the trickiest.

It's a Crompton Parkinson (CP) 1/4HP, Y connected, 960 RPM motor from a sturdy Squirrel cage fume hood exhaust fan I rescued from the skip at work.

Interestingly the motor body, fan and bearings are identical to a 1P CP 3/4 HP motor I did up last week.
The 3/4HP motor was from a Tough DP I posted about here (http://www.woodworkforums.com/showthread.php?t=182060&p=1813845#post1813845).

The 1/4HP motor has been under the patio table for about 4 months but it still Meggered OK and ran sort of OK on a VFD (but half power of course) but the bearings do need attention.
After opening it up I checked it out for spiders and sure enough there was a red back in there.

The only motor that I have opened up that had anywhere near this many junctions was a relatively modern two speed ABB motor that I was easily able to follow the wiring on.
Any suggestions as to where I should start?

http://www.woodworkforums.com/attachment.php?attachmentid=328363&stc=1

[jhovel]

This is an 6-pole motor of course and therefore has 50% more connections as a 4-pole one....
I'd start at the 8 O'clock position in the photo and work towards 6 O'clock.... that's just my perspective of pattern recognition in the position of the sleeves though....

[BobL]

Top marks for the recommended location Joe.

I started at 8 o'clock and found the common point fairly quickly around the 7 o'clock mark by probing with a hypodermic needle attached to one of the leads of a DMM set on resistance.

The varnish was layered on pretty thick which made it difficult getting the individual wires connected to the common point out so I could attach leads to them. As I was levering them out and as the wires were fairly thing (1/4 HP motor) two of them snapped within a cm of the coils but there was enough there to connect to.

I've got the flying leads on and the HT silicone is on so lets see how it goes.
The end caps are pretty rusty so they will get a but of a tidy up.

[Anorak Bob]

As I was levering them out and as the wires were fairly thing (1/4 HP motor) two of them snapped within a cm of the coils but there was enough there to connect to.............



Phew! :)

[BobL]

Phew! :)

Of course I was thinking of you when this happened.

[BobL]

Finally got round to assembling the motor and putting it back onto the fume hood blower.

Of course there was a fair bit of work to do before it all came together.

This motor and attached squirrel cage fan are more than 40 years old and were originally used as a fume hood fan. They were rescued from of a skip at work during a bout of lab refurbishments about 2 years ago. There more than half a dozen of these motor/fans in the skip. I could only get at one on the top of the pile as the rest were covered in building rubble and concrete.

Getting the cage out of the fan was a bit of a PITA as the housing was bent and the grub screws that held the cage onto the motor shaft were rusted in. I ended up drilling out the grub screws but it still took a bit of biffo to drive the motor shaft out of the cage so things got even more "bent" in the process, In the end it was touch and go whether it was worth persisting with it.

The cage blades were caked in brown/black crud which mostly came off with a hose - a pressure wash would have been better - might have to get myself one of those sometime.
Underneath the crud was some rust so a coat of phosphoric went onto that and then I just sprayed some matt black on it to tidy it up a bit.

The cage housing was galvanised so it was not as rusty as the motor or cage. All I did with that was beat it back into shape, modify the motor support so that it will fit onto a bracket up near the shed roof, and wire brushed the loose paint off (there were 3 distinct colours - original hammer green, red and white) and then put a coat of green hammer finish green on it. There were already so many paint dribbles and lumps and bumps from the beating it got during the disassembly process so the final finish is far from fancy - it's really there just to keep the rust a bay from the areas which have lost their galv.

The motor end caps and outside of the main body of the motor were quite rust y so I cleaned that off with a wire wheel and then it got coats of H3PO4 and metallic blue - my standard motor colour - yes I know it clashes horribly with the hammer green.

http://www.woodworkforums.com/attachment.php?attachmentid=329029&stc=1
The motor is only a 0.25HP and is powered by a used 1HP HT VFD. It's a strange place to put a VFD but the motor support frame will be on a platform suspended from the roof frame and I should just allow me to able to reach the VFD controls. If it proves too awkward I will detach the control box and locate it a bit more conveniently.

Here is a side view. - that opening will be located hard up against a window that runs along the roof line in the middle of the shed. I might have to add a bit of a sheet metal duct to help the air through the opening in the window.
http://www.woodworkforums.com/attachment.php?attachmentid=329030&stc=1

After all the belting/bashing/scraping etc the squirrel cage had been through I was not surprised that it was a tad wobbly while it rotated.
In fact the whole thing vibrated quite badly especially at higher RPMs and at 50 Hz the entire unit was humming its way nicely across the bench
Some of this was probably due to different amounts of paint and rust getting added and subtracted from the cage.
The motor bearings were still good so letting the cage spin down by itself after turning the motor off I could see that it always came to rest at the same rotational position.
Then rotating the cage by hand by 180º and letting it go resulted in the cage moving back to the same position.
By clipping some small piece of thin galv sheeting onto the fan blades (see pic below) I was eventually able to better balance the cage.
Now the cage spins nicely up to 60Hz with only a very small amount of vibe.

http://www.woodworkforums.com/attachment.php?attachmentid=329028&stc=1

The air inlet is 8" (0.35 ft2) and the outlet is 0.32 ft2
By measuring the air speeds across a grid on the outlet I was able to determine the air flow rates.
At 40 Hz the flow rate is 920 CFM, @50 Hz its 1150 CFM and @ 60 its 1400 CFM

http://www.woodworkforums.com/attachment.php?attachmentid=329031&stc=1

Oh yeah - what's it all for? It's to help vent my shed when I use my gas powered forge which turns my shed into an oven. I already have a 1600 CFM fan in my welding bay at one end of the end of the shed near the forge. Unfortunately that fume hood is at the low end of the roof so not all the hot air and exhaust from the forge rises is grabbed by that fan and it then gets trapped under the higher roof line area of the shed. Hopefully this fan will clear this hot air away from this end of the shed.

[BobL]

Got the blower in place - still have to create an opening in the window.

It sits just above the table saw so I can use it to clear fine dust while that is running as well

http://www.woodworkforums.com/attachment.php?attachmentid=329146&stc=1

I can reach the GPO and Switch panel easily enough provided there is not too much crap on the floor underneath.
http://www.woodworkforums.com/attachment.php?attachmentid=329144&stc=1

It's hanging out in the breeze a bit on the angle iron base but it runs smoothly so it should be O but might add a brace WIGRTI,
Yes I know I have to tup that power cord entry point with a better gland arrangement.
http://www.woodworkforums.com/attachment.php?attachmentid=329145&stc=1