Leaf blower help

[stretch5881]

I'm helping a buddy build a leaf blower to use on the parish grounds. This is the smaller of the two. We are having trouble figuring out what RPM is the most efficient for the fan, and what size electric motor to use. The fan is a 30" centrifugal type. We have tried a 5 horse motor with 3 different pulley sizes and the motor won't kick into high speed. We figured that the fan was only turning around 600 rpm. We can fabricate stuff, but algebra is beyond us. Any fan gurus out there?

 

[WhoWhatNow]

Why not use the tractor PTO to run the fan? Should be plenty of power there.

The PTO should turn at either 540 or 2000rpm. Use a pulley calculator to figure out what size pulley you need to turn the fan shat at whatever speed you are looking for.

First one I pulled up:

http://www.blocklayer.com/Pulley-BeltEng.aspx

 

[stretch5881]

I'm not sure how that would work, the blower is on a lazysusan and can be turned 90 degrees both directions using a remote switch.

 

[zkling]

One thing you are fighting is the extreme sudden choke on the output. Is the wheel 30" in diameter?
That type of blower isn't exactly what you want for what you are doing.
Edit, also is it spinning on plain or ball bearings?

 

[theoldwizard1]

What is the pulley diameter on the fan ?
What size pulleys have you tried on the motor ?
Do you have any specs on either the motor or blower RPM ?

 

[Bdgjr215]

Why not just get a little wonder blower and build a frame that mounts to the
Front of the tractor you could raise or lower it with the tractors hydraulics
Google search or you tube the subject .some guys mount them on zero turns
And it works well .its very similiar to what golf courses use

 

[stretch5881]

I'll be over there today, working on a wood furnace. I'll get the specs on everything and post them later.
I do know that it is a forward curve fan. The wheel is 30".
The reason for using a fan of this type, is they are donated. The bigger setup has two fans, larger than this one, rigid mounted, pto powered with a 60 horse tractor.

 

[bczygan]

I feel so inadequate!

 

[theoldwizard1]

The bigger setup has two fans, larger than this one, rigid mounted, pto powered with a 60 horse tractor.

Sounds like you need to fix that one !

 

[zkling]

I'll be over there today, working on a wood furnace. I'll get the specs on everything and post them later.
I do know that it is a forward curve fan. The wheel is 30".
The reason for using a fan of this type, is they are donated. The bigger setup has two fans, larger than this one, rigid mounted, pto powered with a 60 horse tractor.

Yes, but those types of blowers don't do well with restrictions as they are very poor for pressure. You really should be using a radial impeller type blower. Remove the nozzle restriction and see if it comes up to speed.

 

[Dozerhand]

I hate to be disagreeable with another member but restriction is what you need more of. That blower needs a damper to let it start. Construct a plate with a shaft thru it and install it in the discharge. (think carburetor butterfly) Build a turnbuckle or something similar on one side where you can adjust it. I'd shoot for about 1750 rpm. Have it cracked no more than about 1/4 inch and start the blower. After it comes up to speed slowly open your damper while checking amps on the motor. If you can get it all the way open without getting to rated amps on the motor that means you can turn it faster. You can achieve the same result by rubeing a plate on with c clamps, but obviously there are some dangers to that approach. On the other hand you might just be wasting your time. I spent 20 years at asphalt plants working with a lot of blowers about that size. Most were powered by anywhere from 25 to 100 hp motors. but hey you never know till you try........ Good luck

 

[stretch5881]

My mistake, it is an 18" forward curve fan donated by Greenheck. It is ball bearing with a 12" pulley. That's all we know about the blower.
The motor is a 5hp Leeson 1740 rpm 220v single phase. We have tried 4", 6" and 8" pulleys on the motor. No matter what, the motor does not ramp up enough to pull in the second capacitor. So we can't even guess what the wheel rpm is.
Zkling, We have tried a radial. It didn't do well. We are looking for volume more than pressure.
Dozerhand, We never thought about a damper. We will be discussing it further tomorrow. I am guessing, if air isn't moving through it, there should be very little back pressure?
Thanks to everyone for your suggestions. It's really making us use our thinker.

 

[stretch5881]

By the way, the big tractor with dual fans works great for the open areas. The church grounds is 10 acres, with 2 acres being cemetery. That's a lot of stones to blow around.
There are many big pines on the main grounds, and big hardwoods around the cemetery. In some spots, the leaves are up to 18" deep.

 

[taumac]

I can be mistaken here but if the fan has a 12" pullie then to achieve 1725 rpm on the fan wouldn't you just need a 12" pullie on the motor? Can the pullie on the fan be changed?

 

[stretch5881]

Yes, the pulley can be changed on the fan.

 

[Regnar]

Have you tried plugging into a wall outlet and seeing if the fan spins up then? Just thinking maybe the Generator isn't big enough for a 5hp motor.

 

[1950mercury]

Can u ditch the electric motor and put a 5hp side shaft gasoline engine with pullys. Seems like it would be way better than dragging a cord around

 

[stretch5881]

Generator output was tested by an industrial electrician.

 

[G_P]

Have you tried plugging into a wall outlet and seeing if the fan spins up then? Just thinking maybe the Generator isn't big enough for a 5hp motor.

Was going to post the same thing. The generator may be struggling with the starting current of a true 5hp motor.

 

[stretch5881]

A 5 horse motor puts out 100% of it's rated horsepower. The same rated gas engine does not.

 

[zkling]

I hate to be disagreeable with another member but restriction is what you need more of. That blower needs a damper to let it start. Construct a plate with a shaft thru it and install it in the discharge. (think carburetor butterfly) Build a turnbuckle or something similar on one side where you can adjust it. I'd shoot for about 1750 rpm. Have it cracked no more than about 1/4 inch and start the blower. After it comes up to speed slowly open your damper while checking amps on the motor. If you can get it all the way open without getting to rated amps on the motor that means you can turn it faster. You can achieve the same result by rubeing a plate on with c clamps, but obviously there are some dangers to that approach. On the other hand you might just be wasting your time. I spent 20 years at asphalt plants working with a lot of blowers about that size. Most were powered by anywhere from 25 to 100 hp motors. but hey you never know till you try........ Good luck

What you are describing is typical of a choke on the inlet to allow the machine to come up to speed. Common example is if you put your hand over the intake of a shop vac. It gains in speed as there is less mass being flowed against the wheel. A restriction on the output is different, especially when starting as the motor is fighting not only the inertia of the wheel, but also the stall slip condition as the mass is trapped inside the blower cage.

 

[Regnar]

Generator output was tested by an industrial electrician.

With the load attached? Just like someone else mentioned you might not have enough there for the starting load (3.5 x 5 times the continuous amperage). Im guessing your closer to the 5 times rule with the big *** fan attached. Also something else to consider is your Hz. With a larger load on the generator the gas motor may not be able to produce enough horse power to keep the generator up to speed so your Hz will be lower in which case your motor speed will be lower as well even. Hz is usually adjustable on the generator by RPM.

 

[redmondjp]

What size generator is being used to attempt to start the motor? I'm thinking that this application really needs a gas-powered motor (less power loss, and lighter than a 5HP electric motor and a generator large enough to start it).

I'd say that, given the size of that blower, you're looking at a 8HP gas engine minimum, and 12-16HP would give more margin and allow for a higher airflow.

 

[stretch5881]

Alrighty then, looks like we have some work to do. First and easiest, we will try it plugged into the welding outlet and see what happens.
If the blower outlet is too restricted for startup, we will have to enlarge the spout and add a damper that we can close down after rampup.
We would like to stay with the electric motor. Being that it's used only a week or two in the fall. Less maintenance.
The weather will change fast here and it's time to get his 4 wheeler fixed for deer hunting, so we'll get back at it in December.
We thank everyone for the help, it's very much appreciated.

 

[Mooky]

You need the fan model number to research the performance curve. From that the speed/power/flow/pressure can be determined.

That blower was almost certainly removed from an air handler. That size would be much higher than 5 HP. Do a quick search for "HVAC blower performance" Wikipedia will give a straightforward explanation.

See if there is an HVAC contractor in the parish. They will be familiar with the equipment.

 

[stretch5881]

No model number. It was donated directly from Greenheck 15 miles away. Brand new even.

 

[Dozerhand]

I'm not an engineer and can't tell you why more outlet restriction makes fans easier to start but it does. The restriction needs to be there to let the motor get up to speed. As you remove restriction it increases motor load. To try to start the fan first and then increase restriction won't get you anywhere. Neither will increasing the size of the discharge. That will just make it harder to start.
Restricting all but about 1/2 inch lengthwise on the discharge will let that motor start that fan. As far as rpm 1750 would be good but just go with whatever you have until you find out if that motor is going to have any chance of running it. Trust me

 

[stretch5881]

We'll give that some thought too. Stranger things have happened. Thanks Dozer.