05-13-2015, 10:46 PM
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.
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.
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Greg
Greg