Blower rating from amps/impeller size?

[Scott M Perry]

Hi, all -

It dawned on me today that, in cold storage (read: bin in the snow outside) is the blower we used to use with our long-gone bounce house. It's not your garden variety bounce house blower - it's substantial, and moves a whole lot of air.

http://farm4.staticflickr.com/3687/12226792126_053b6f05aa.jpg (http://www.flickr.com/photos/scott--/12226792126/)
P1010938 (http://www.flickr.com/photos/scott--/12226792126/) by Scott -- (http://www.flickr.com/people/scott--/), on Flickr

http://farm4.staticflickr.com/3821/12226200905_2719bfa37f.jpg (http://www.flickr.com/photos/scott--/12226200905/)
P1010939 (http://www.flickr.com/photos/scott--/12226200905/) by Scott -- (http://www.flickr.com/people/scott--/), on Flickr

As you can see, there's no HP or CFM rating on the tag. I'd like to put this into use as the basis of a home-spun DC; is there any way of backing out the CFM based on the above motor info and the impeller size (14")?

Thanks,
Scott

[Jim Neeley]

Scott,

This is a WAG from an electrical engineer. It's a WAG because predicting motor size based on amp draw is highly dependant upon motor efficientcy. That said, my old Jet 1100CFM dust collector has a 1.5hp motor and it's nameplate is 15amps.

Your motor info reports it as 10A so I'd expect it to be about one HP. A CFM guess gets even wilder since it's dependent upon the shape of the fan blades and many other things. I'd *guess* it to be on the order of two thirds the capacity of the 1100.

The larger uncertainty is that a bounce house fan is designed to have no pressure drop on suction, instead providing pressure. Many DC's on the other hand have a warning not to run the unit without some kind of pressure drop on the suction as it will overload the motor. Based on that I'd guess your motor will draw well under 10A in DC service, generating less than 1hp of output and moving less air than predicted above. How much is unknown.

This is just my thought process and $0.02.. YMMV.

Jim

[Dennis McDonaugh]

What's a bounce house?

[Scott M Perry]

Scott,

This is a WAG from an electrical engineer. It's a WAG because predicting motor size based on amp draw is highly dependant upon motor efficientcy. That said, my old Jet 1100CFM dust collector has a 1.5hp motor and it's nameplate is 15amps.

Your motor info reports it as 10A so I'd expect it to be about one HP. A CFM guess gets even wilder since it's dependent upon the shape of the fan blades and many other things. I'd *guess* it to be on the order of two thirds the capacity of the 1100.

The larger uncertainty is that a bounce house fan is designed to have no pressure drop on suction, instead providing pressure. Many DC's on the other hand have a warning not to run the unit without some kind of pressure drop on the suction as it will overload the motor. Based on that I'd guess your motor will draw well under 10A in DC service, generating less than 1hp of output and moving less air than predicted above. How much is unknown.

This is just my thought process and $0.02.. YMMV.

Jim

Thanks, Jim, for the thoughtful response. I'd kind of figured about 1 HP, given optimistic efficiency, so that kind of agrees with your observation.

On the pressure drop across the impeller: I'm planning on venting this through a bag (3 micron or less), and I'm guessing that it will produce an effect similar (though likely reduced) to the fan blowing against the bounce house fabric. Maybe? Regardless, I'm not planning a duct network or anything elaborate: I'm envisioning mounting the blower (somehow - it's very heavy) on a roller stand, inlet connected to a rudimentary cyclone, the exhaust hosed to a bag filter. I'd be rolling this thing around to machines, which will likely only include the bandsaw, tablesaw, jointer, and planer. Hopefully the blower is up to it.

Scott

[Scott M Perry]

What's a bounce house?
http://5starbounce.com/wp-content/uploads/2013/02/BounceHouse.jpg

This is pretty similar to what we had. It was very heavy-duty, but a mouse got to it a few winters ago...

[David Kumm]

Oull off the front and look at the impeller. Diameter, straight or curved blades, and depth of fins. A 1 hp motor won't pull many cfm and I'm surprised if a 1 hp motor would be big enough to handle the impeller at 3500 rpm. If it runs at 1750 you won't get nearly enough flow under pressure to work as a DC. Put a 2-3 hp 3450 motor on it and you may have something workable depending on the impeller. Dave

[Judson Green]

Here's a watts to HP converter.

http://www.rapidtables.com/convert/power/watt-to-hp.htm

The watts of your motor is 1150. Volts * amps = watts.

In your case 115 volts * 10 amps = 1150 watts.

1 HP = ~745 watts

So your motor is ~ 1.5 HP.

You should have a look at the impeller, it may not be able to handle getting debris run though it.

[Dennis McDonaugh]

a bouncey!

[Scott M Perry]

Thanks, Judson! I'm hoping a baffled cyclone in front of the blower will keep the debris to a small volume and size. FWIW, I dropped a handful of planer chips onto the inlet and it blew through fine. I know that's not exactly analogous to a planer under full load, but it makes me feel a little more confident.

[John Lanciani]

Here's a watts to HP converter.

http://www.rapidtables.com/convert/power/watt-to-hp.htm

The watts of your motor is 1150. Volts * amps = watts.

In your case 115 volts * 10 amps = 1150 watts.

1 HP = ~745 watts

So your motor is ~ 1.5 HP.



Not quite. 746 watts is the equivalent of one horsepower but it takes more than 746 watts of input to a motor to produce one horsepower of output. The actual formula is volts(measured, not nominal) x amps x power factor (assume .80 for an inexpensive motor) x efficiency (again, .80 is a safe number here. This is a function of the design and construction of the motor) / 746 so that gets the op's 10 amp motor almost exactly to 1 hp output.

[Judson Green]

Dough! Sorry for the mis- info. Just going off that website.

Good idea to have a clycone in front of the impeller.

[Michael W. Clark]

The housing looks narrow compared to my Jet 1.5HP blower. I'm guessing this fan is made more for lower volumes and higher pressures. You need good pressure (2-3 psig?) on the boucy house so it is bouncy. A DC fan will top out at less than a psig at no flow.

The fan doesn't care if it has anything on the suction side or not. It needs some resistance on one side or the other, else it could overamp the motor unless the motor is sized to handle it. If you had a way of checking the flow and pressure capability, sounds like a neet project.

[Scott M Perry]

Well, I asked around at work this morning, and it turns out we *do* have a couple CFM meters around for checking the blowers here. So, I'll be able to gain some empirical data on flows, at least under no load. It's a baseline.

[Scott M Perry]

As this is turning more into a DC thread than a tool thread, should/could this be moved to the "Workshops" forum? Probably should've put it there in the first place...

[Joe Hillmann]

You could measure it by building a simple pitot tube out of a piece of clear tubing and lots of math and charts.

http://www.engineeringtoolbox.com/pitot-tubes-d_612.html

[Scott M Perry]

Geez, Joe - there was a time when I had the Bernoulli equation memorized. I've forgotten 99% of the engineering I ever knew at this point. Out of the game far too long...

[Scott M Perry]

Comes in right at 900 CFM, no load. I'll play with it some more this weekend, but I'm thinking it should be good for a mobile unit, first pass...

[Judson Green]

Comes in right at 900 CFM, no load. I'll play with it some more this weekend, but I'm thinking it should be good for a mobile unit, first pass...


What do you mean by no load? If you aren't restricting the airflow somehow (baffles, air filters, piping) then your fan is at full load. Think of when you put your hand over the vacuum cleaner intake... the motor speeds up... less load cause its got no or little resistance.

If ya wanted to have some fun you could also hook up a amp meter (mulit meter set to amp) and your CFM meter. Put a little piping on the intake and then play around with different baffles.