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Old 04-03-2020, 07:15 PM
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Default Box fan project

I've got a old fan I want to turn into a box fan to use in my shop. Before we know it it'll be 90+ outside and ill still be working in here finishing things up.

It has no motor. What size should I use?

It's a 36" fan and the drive pulley is 9" across.
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  #2  
Old 04-03-2020, 07:28 PM
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The old chicken house one I have only has a 1/3 horse 1740 rpm on it . 1940's 1/3 horse . You don't want it turning that fast ,my bearings are sleeves with oilers .
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Old 04-03-2020, 07:49 PM
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Yep,slow and steady,it will be quieter that way too.I bet if you looked on Graingers at the fans they will tell you how big a motor you need.
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Old 04-03-2020, 10:54 PM
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Our 48" barn fan uses the motor below, with a 36 inch I think a 1/3 Hp will be
fine. The barn fan uses a 5 or 6 to 1 reduction with a V-belt. I moves A LOT
of air.



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Old 04-04-2020, 12:14 PM
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Since it's a belt drive I'd start with a 1/3-1/2 horse motor and a 2" drive pulley--that should put you in the ballpark. The nice thing about the belt drive is that you can change the ration later if you feel that the fan is either too fast or two slow...
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Old 04-04-2020, 01:48 PM
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Quote:
Originally Posted by LKeithR View Post
Since it's a belt drive I'd start with a 1/3-1/2 horse motor and a 2" drive pulley--that should put you in the ballpark. The nice thing about the belt drive is that you can change the ration later if you feel that the fan is either too fast or two slow...
Do you have formula for to figure the ration
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Old 04-04-2020, 02:09 PM
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Quote:
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Do you have formula for to figure the ration
About 2000-2500 calories per day...
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Old 04-04-2020, 06:41 PM
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Quote:
Originally Posted by digr View Post
Do you have formula for to figure the ration
With belts it's dead simple. Divide the diameter of the large pulley by the diameter of the small pulley. The answer is the ratio between the two pulleys. If the large (driven) pulley is 9" and the small (driver) pulley is 2" then the ratio is 4.5:1. If your motor RPM is 1725 then the fan will run at (1725/4.5) 383 RPM...
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Old 04-04-2020, 07:17 PM
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:d
Quote:
Originally Posted by lkeithr View Post
with belts it's dead simple. Divide the diameter of the large pulley by the diameter of the small pulley. The answer is the ratio between the two pulleys. If the large (driven) pulley is 9" and the small (driver) pulley is 2" then the ratio is 4.5:1. If your motor rpm is 1725 then the fan will run at (1725/4.5) 383 rpm...
lol I know how to figure ratio, it's ration that I have a problem with.
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Old 04-04-2020, 07:29 PM
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All the 36s we built were 1/2 hp. Being a belt drive, and looking at the number of blades, I'm going to throw a guess of 600-650 RPM. Put a pulley on the motor, and do a quick clamp on ammeter check to see if you're where you need to be. Ideally you'll have a specific speed for a blade at a certain static pressure to give you the best efficiency. As a box fan moving air, static pressure is a moot point. Don't spin it too fast (whatever the real rated speed is) as the blades can fatigue crack and exit spectacularly. Any markings on the fan to id make and model?

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Last edited by chumly2071; 04-04-2020 at 11:09 PM.
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