Induction Motors

[f350ca]

That would be too simple Vinny. The place had a couple of vents but I closed them in when I put the Veranda around 3 sides of the house. The veranda has a full cement footing to shed the melt water in the spring. It came down the hill and into the crawl space before the dam was built. Got to love old houses, I should have renovated it with a match and saved a lot of head aches.

[Roadracer_Al]

Ha. A Cat D9 Make-Over. When I worked for a contractor in college, that was our standard joke about doing work in POS homes.

Don't make it more complicated. Try an ordinary consumer grade window fan in one of the vents.

[f350ca]

That would be far too easy Al. But a great idea. They make those booster fans that fit in a duct.

[starlight_tools]

(05-13-2015, 10:46 PM)f350ca Wrote: Dug out an small squirrel cage blower I recycled from the dump, need to ventilate the crawl space under the house.
Made up a widow maker connection to an extension cord to see if the motor worked, ran fine and filled the shop with dust and leaves that blew out of the blower, it obviously works. It has a rather large driving pulley so the fan is running close to motor speed 1740 rpm. I don't need a lot of air movement so thought about putting a smaller pulley on the motor to reduce load and make it cheaper to operate. To make this scientific I thought I'd measure the current so clipped the AC amp meter on a line and it read 6 amps, hum, thats 660 watts, this isn't going to be cheap to operate. Check the plate and its 1/3 hp rated at 5.8 amp.Hum again 1/3 hp is 250 watts, is this thing that inefficient. So I slip the belt off, still draws 6 amp or there about on my analog meter. Hum again. So out to the storage facility and check another motor out of inventory, (pull from the junk pile). Another widow maker and we have it running. This one is 1/4 hp rated at 5 amp, 550 watts. Guess what, thats what my meter says it draws with no load. If I hold a piece of wood against the pull, (proper dynamometer testing) the current goes up well above the rated 5 amp, like 10 or 15 amp. So is my meter not reading correctly? Thought the plate rating was at full load.

Greg

The motor with the Squirrel cage blower on it is "loaded", it is amazing how much energy is required to move air.  Your readings are what I would expect to see when testing a unit like that, and I have a special power supply that I can read the amps draw of a motor as it starts and runs.

Walter

[f350ca]

Its a belt driven one Walter, the motor draws within an amp of full rated current with no load,
Checked on the inline duct fans, the performance isn't too impressive. Found one site that listed losses with runs of ducting. Think I move more air when I break wind than they would through 30 or 40 feet of pipe.
So back to the original plan and go with the blower. Made up a couple of transitions (don't laugh at my feeble attempt at sheet metal work) to go to 6 inch duct, which I found at the dump.
 Used the plasma table to cut them out. Need to tune the motors I guess. With a 40 amp nozzle it wanted 320 inches per minute cut speed. Rounded the corners quite a bit, probably added a 1/4 inch radius as it tried to accelerate. Didn't take long to cut though.

[starlight_tools]

Lookin' good so far.

If the current is within spec with the motor driving the fan, you should be fine.

Walter