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Forum topic by rockindavan posted 02-22-2014 12:28 AM 3623 views 0 times favorited 11 replies Add to Favorites Watch
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rockindavan

299 posts in 2097 days


02-22-2014 12:28 AM

Last night I picked up a blower that I plan on using for my dust collection system. It was hard to tell from the craigslist pictures, but he said it was “commercial grade”, whatever that means. After a quick look when I got there I realized it was a home made unit, but most of it was relatively robustly made, just lacking on the engineering side of things. The motor is a 1 1/2 hp powermatic, which I think came from a contractors saw.

The impeller on it is massive at 16” by 5” deep made out of 1/4” aluminum. I immediately realized after taking off the cover that this could be problematic. There is no way that motor will last without long runs to keep resistance high enough to let the impeller spool up.

My thoughts are to either cut down the impeller to a more manageable 12-14” so I don’t overload the motor, which would be a pain to do without completely ruining it. It is relatively balanced, although it could use a little work. The other option is to play around with pulley size to slow the impeller rotation and provide more motor torque. I’m a bit worried it could affect the amount of airflow, but the bigger impeller might make up for it.

Anyone have any suggestions or am I on the right track with reducing the speed? I don’t have any ducting yet so I can’t run it to measure air speed and amp draw yet. It blew the 20 amp circuit in about 5 seconds running without hose, so I don’t plan on trying any more free air tests.

I am planning to hook it up to the SDD and run 5” lines. The inlet/outlet are both 6” on the blower, but i’m not sure I could get sufficient airspeed with 6” lines. I do plan on upgrading to a nice 5hp cyclone once I can get 220V in a few years (I’m renting now and can only get 110V) but I would like to have something until then. Before anyone comments on the dangers of homemade impellers, I am aware, and the blower case is pretty thick steel, and I will likely build a secondary enclosure around it.


11 replies so far

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bigblockyeti

3667 posts in 1182 days


#1 posted 02-22-2014 12:36 AM

Don’t try to cut down the impeller. First get ahold of an ammeter and see how much of the name plate current the motor is pulling. Ideally it would be very close to the maximum after it’s completely up to speed. As you add duct work and your filter plugs, this current draw will only go down. If it’s over then start with getting a larger driven pulley for the impeller shaft to reduce the speed and thus the load. I wouldn’t worry too much about the homemade impeller, I’ve been in close proximity to three that have blown apart and given the steel housing and much lighter impeller, it’s very unlikely you’d have a problem even in the event of a failure. I can tell you that running dust and chips through the impeller are much more likely to damage it than steel. It would be a good idea to set up your system with either a cyclone or baffle to greatly reduce the abrasive action of the debris across the impeller blades.

View The Box Whisperer's profile

The Box Whisperer

678 posts in 1531 days


#2 posted 02-22-2014 12:39 AM

I am far from the authority on such things but I would say that while that is a nice motor it is underpowered for a massive 16” impeller. I also agree with bigblockyeti that a separator would be in due order.

-- "despite you best efforts and your confidence that your smarter and faster than a saw blade at 10k rpm…. your not …." - Charles Neil

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rockindavan

299 posts in 2097 days


#3 posted 02-22-2014 12:44 AM

I am planning on getting the oneida super dust deputy, just haven’t picked it up yet. I need to get a ammeter to check the current draw, does anyone know if the hf one is any good? I have a $1500 wife approved tool budget so the less I spend on making this blower work, the more I can spend on other things. Would a 10’ section of flexible hose provide enough drag to find the correct pulley to keep the amp draw in the sweet spot?

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The Box Whisperer

678 posts in 1531 days


#4 posted 02-22-2014 12:48 AM

You are in over my head, but good luck bro! I have a feeling this thing will be epic when its done. You are wise to save where you can. I assume you already have the proper safety equipment!

-- "despite you best efforts and your confidence that your smarter and faster than a saw blade at 10k rpm…. your not …." - Charles Neil

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bigblockyeti

3667 posts in 1182 days


#5 posted 02-22-2014 04:08 AM

The super dust deputy should be something you can hang onto for a while even after upgrading. Not sure about the hf ammeter, if it’s a dud you can always take it back. I would start by capping off the intake, fire it up and check the current draw at full speed with zero air flow. Remove whatever you have blocking the intake (watch your fingers!) and check it against the rated name plate amps. Too many variables to even be able to calculate if a 10’ section of flex hose would do the trick if you’re over on amps, but it certainly will cut down on the air flow slightly and thus the amp draw as well. Keep us posted with your progress.

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rockindavan

299 posts in 2097 days


#6 posted 02-23-2014 10:58 PM

Has anyone measured their factory DC at full load (no hoses) so I can get sense of what the amps should be in relation to the plate specs?

View crank49's profile

crank49

3980 posts in 2432 days


#7 posted 02-23-2014 11:26 PM

Fan manufacturers regularly adjust one of two things to get the most out of a motor or fan.

They either adjust the RPM with belt driven fans, or, if they have a direct drive situation and a fixed fan diameter they will adjust the width of the impeller.

Motor horsepower is directly proportional to the volume of the air being moved. So, If your fan motor is pulling 50% more power than the motor is rated for, reducing the impeller width by 50% will bring it in line.
With a 16” diameter impeller and a 1 1/2 hp motor what you will wind up with is a system with relatively low CFM and high pressure capability if you cut the width of the impeller down..

On the other hand by slowing the fan down with a belt drive the volume (CFM) will change directly proportional to the RPM in this case., but since the power required to run the fan varies as the cube of the pressure you will wind up with a better volume to pressure balance by reducing the RPM I believe.

-- Michael: Hillary has a long list of accomplishments, though most DAs would refer to them as felonies.

View dogmir's profile

dogmir

25 posts in 1433 days


#8 posted 02-24-2014 01:14 AM

Are you in WI I swear I saw that on craigslist.

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rockindavan

299 posts in 2097 days


#9 posted 02-24-2014 01:50 AM

Yes, it was in Portage.

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woodchuckerNJ

1153 posts in 1095 days


#10 posted 02-24-2014 02:39 AM

nice find, I hope it was a good price.
Looks like it’s already reduced.
Like everyone else said, ammeter, then change the ratio if necessary.
A big impeller will move lots of air even if you lower the rpm.

In model airplanes, when the electrics hit the scene they used gearing to launch big planes, low rpm but big propellers, it moved lots of air to move big heavy planes, I think the gearing here will do the same and you will be happy. It is a flat impeller, so not sure how well it is going to work, but it should do ok.. let us know..

-- Jeff NJ

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dogmir

25 posts in 1433 days


#11 posted 02-24-2014 02:52 AM

rockindavan wow I guess I should have looked at your profile. I am in Madison too. Small world.

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