# OT - I need some engineering help

• posted on July 5, 2016, 10:11 pm
Got a 30 yr old large squirrel cage fan (fan turbine about 15" diam) with a 10" pulley on its axle. The motor has a 2" pulley. I understand motor/pulley is engineered to match the fan specs, so that the motor doesn't burn up.
I'd like to change the motor's pulley to a 2.5" or 3", for the fan to blow more volume of air.... and/or blow it faster.
I suppose I don't need specific math specs/calculations for an answer.... just a good common sense guess at it.
What's the likelyhood of burning the motor, if I enlarge its pulley to a 2.5" or 3"?
I have several salvaged motors, so I may have an appropriate replacement motor, if need be. With a 3" pulley, might I need a motor with more HP and/or less/same RPMs, as the present motor?
I don't have the motor in front of me, to give its HP or RPM specs. Would this info help?
Thanks. Sonny
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• posted on July 5, 2016, 10:24 pm
On 7/5/2016 5:11 PM, Sonny wrote:

Everything you need to know:
http://web.fscj.edu/Mark.Bowman/handouts/BLOWER%20AND%20MOTOR%20CALCULATIONS.pdf
--
eWoodShop: www.eWoodShop.com
Wood Shop: www.e-WoodShop.net
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<%-name%>
• posted on July 6, 2016, 12:35 am
On 7/5/2016 6:11 PM, Sonny wrote:

The faster you turn the blades the more power you need. If you have 1/4 hp go to at least 1/3 or even 1/2.
You also have restrictions that have nothing to do with fan speed. You have an inlet and an outlet that also limits the volume of air that can pass.
Then you get into blade design, angles, pitch, turbulence,
Worst case, try it and see what happens. Maybe the motor or bearings will seize, maybe you get the air you want.
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• posted on July 6, 2016, 2:19 am
wrote:

It's hard to know - too many variables. But I might try it and see what happens. If you're wondering about the increased power and whether it'll burn out the motor, monitor the power used by the motor with something like a Kill-A-Watt or PowerAngel. Measure before and after. At least you'll get some idea of what's going on.
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• posted on July 6, 2016, 10:52 am
On Tuesday, July 5, 2016 at 9:19:39 PM UTC-5, snipped-for-privacy@attt.bizz wrote:

With Karl's info and calculating CFM, I should be able to make a good guess. The motor plate may have additonal info about the blower, also.
Thanks All. Sonny
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<%-name%>
• posted on July 6, 2016, 3:53 pm
On 7/6/2016 6:52 AM, Sonny wrote:

No, it won't. If, however, it is a Dayton motor you may be able to find the same or similar setup in the Grainger catalog.
You probably already know that 48 frame motor takes a 1/2" pulley, a 56 frame takes 5/8"
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• posted on July 6, 2016, 3:59 pm
On Tuesday, July 5, 2016 at 6:11:37 PM UTC-4, Sonny wrote:

If you increase the size of the pulley, won't you have a belt length issue to deal with?
Won't you need a longer belt or need to move the motor closer to the squirrel cage. Is the motor position adjustable?
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<%-name%>
• posted on July 6, 2016, 8:02 pm
On Wednesday, July 6, 2016 at 10:59:38 AM UTC-5, DerbyDad03 wrote:

This salvaged fan is stand alone, no ducts, etc., and the housing is open o n both sides of the blade cylinder. The cage is mounted on 1/2" ply, with casters underneath. It works fine with its present pulleys and blows quit e a bit of air.
I just wanted more or faster air flow, to cool off some small dogs, housed in a large room with no AC.... but that's a lie. We bought a Walmart 5000B TU unit and placed it on the floor, for the dogs, but that doesn't seem ade quate. The 48" fan, in there, is too noisy. The motor shaft is 1/2". The motor's position is adjustable. The fan's ax le is 1" dia., mounted with roller bearings, each with grease zerks. The fan is quiet running.
I do need to clean the fan blades. The dirt dobber nests fell out on their own.
I'll go, this evening, and further inspect the motor specs, etal.
Sonny
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<%-name%>
• posted on July 6, 2016, 8:19 pm
On 7/6/2016 4:02 PM, Sonny wrote:

well w/o putting the compressor side outside, you are creating more heat than you are removing. So it's going to get hotter.
put them in a smaller room with the A/C mounted in the window and it will get cool enough.
The fan won't solve the problem of the compressor side, And the evaporator is not going to cool more than the compressors heat puts out
--
Jeff

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<%-name%>
• posted on July 6, 2016, 9:50 pm
On 7/6/2016 4:02 PM, Sonny wrote:

You put the AC on the floor? Where is it vented? It is vented to the outside I hope, or you are just making more heat.
What do you want the fan to do? If the room is enclosed it is not going to cool it any more, just move air.
How bif is the room? A 5,000 BTU AC is enough for a small bedroom. Mine is a medium sized room and we use a 6,000 BTU.
How many dogs? People give off about 350 btu at rest and a medium dog is probably not far off. A few active dogs will give off half the heat the AC can rrmove. http://www.tombling.com/cooling/heat-load-calculations.htm
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<%-name%>
• posted on July 6, 2016, 10:31 pm
On Wednesday, July 6, 2016 at 4:50:51 PM UTC-5, Ed Pawlowski wrote:

LOL. Yeah. I'm still laughing. I can imagine what you're thinking.

LOL. 5 dogs. My sister is visiting and she brought her puppies. Mom doe sn't want the dogs in the house, all the time.
The room is about 50'X 50'. We call this area the pool room, use to have a swimming pool in there, but we filled it in & concrete over it. The ceili ng is not insulated, so it gets hot in there, despite the louver windows be ing open. We recently pulled up the old outdoor carpet and cleaned the co ncrete floor, walls, etc.
We put the AC in front of the dogs' beds, so it was mainly for just that im mediate area. Our thinking, to have an AC, was somewhat short sighted, as it's not as efficient as we had hoped.
Pics of the area. These should help explain a few things: 1st pic is fro m January 2 yrs ago. Lots of stuff was just stashed in there. At the time , we were cleaning/prepping for Mom's 90 BD, hence the heater is on. The o ther 2 pics were recent, carpet removal. Lately, it's been in the high 90 s with heat index 105-108. We need any kind of volume air movement in the pool room. https://www.flickr.com/photos/43836144@N04/with/28033834012/
Sonny
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<%-name%>
• posted on July 7, 2016, 12:59 am
On 7/6/2016 6:31 PM, Sonny wrote:

Tough area to cool. It would not be so bad if you could partition off a 10 x 10 x 8 space quickly and cheaply, then the AC would help.
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<%-name%>
• posted on July 7, 2016, 2:24 pm
The squirrel cage motor is 1/8 HP, 3450 RPM, 1.6 AMPs. I have a 1/2HP motor in the shop. I'll do some calculations to make sure a 3" pulley is not a risk for the 1/2 HP motor. I had initially guessed 10" for the fan pulley size, but it's 12".
Sonny
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<%-name%>
• posted on July 7, 2016, 7:43 pm
On 7/7/2016 10:24 AM, Sonny wrote:

I'd guess the motor can handle it at 4X the power. Assuming it is also 3450.
At any rate, it will move more air, now you have to figure how to remove the heat. Given the volume of the room I doubt you will see much difference.
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<%-name%>
• posted on July 8, 2016, 12:17 am

He will be pumping in a maximum of 500 watts of heat - more likely closer to300 watts. Moving the air will not cool the air - but it willgelp with evapoative cooling of people (and to a lesser extent dogs) in the room. A breeze will make it FEEL cooler. Properly placed it will also evacuate some of the air heated by the sun on the roof, allowing cooler outside air to take it's place, effectively cooling the room somewhat.
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<%-name%>
• posted on July 8, 2016, 10:42 pm
On 7/7/2016 8:17 PM, snipped-for-privacy@snyder.on.ca wrote:

Iffy at best. Given the size of the room you will barely notice the breeze if you are 50 feet away from it. Nah, you won't feel anything.
The room is about 25,000 cubic feet. Any blower with 1/8 hp is pathetically under powered to do much even if you double the output.
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<%-name%>
• posted on July 8, 2016, 12:13 am
wrote:

As long as they are both 3450 RPM the half horse should do just fine.with the 3 inch pulley. 2-12 = 6:1, - so the rpm is 575, the 3" pulley will be 4:1 and 862 RPM. You are increasing the speed by 50% and increasing the horsepower by 4 X.. Definitely enough power.
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<%-name%>
• posted on July 6, 2016, 8:37 pm
On Wed, 6 Jul 2016 08:59:35 -0700 (PDT), DerbyDad03

Being a furnace blower the motor mount will be adjustable. It is likely just on a rocker. Many blowers had "adjustable sheaves" so you could fine tune the blower speed.
A 10% speed increase will require something over 10% increase in power. If you had 1 1/6HP motor you will likely need to use a 1/4. If you had a 1/4 you may need a 1/3 and if you had a 1/3 you may need a 1/2.
You were running a 5:1 reduction - the new setup will be 3.3 to 1 with a 3 inch, and 4:1 with a 2.5".
With a 1750RPM motor the original setup ran the blower at 350 RPM, the 2.5" will run it at about 437, and the 3 inch will run it at 530 RPM. This means the fan would run 1.5 times as fast with the 3 inch pully as it does with the 2 inch pulley - so I'm guessing a larger motor WILL be required unless (a) it was grossly over-powered to start with or (b) the blower starts to stall at the higher speed, moving less air
(plug the intake to your vacuum cleaner (or the outlet if it is available) and notice the motor speeds up - meaning less load - because the "blower" is moving less air.)
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