Couple squirrel cage blower questions...

R

razorhunter

Joined
Jan 27, 2002
Messages
470
Guys,
I'm about to make a home made air filter with a squirrel cage blower. I'm thinking of some type of box made of wood? to surround it. I assume this blower I have just intakes air on the SIDE holes, as there is no other intake really. I was thinking of putting HVAC filters on either side of the blower, to filter the air as it comes in, and then put a filter on the output, for even more filtration. Is this what you guys have done?
I have an old belt drive unit, which will need a motor. I could use some suggestions on HP and RPM? It is a fairly big blower unit. The pulley on it for the belt, is about 6" - 8" in diameter. I was thinking a 1HP 1725 RPM motor would be good for it. What do you think? (I thought 3450rpm would be too fast, and might overheat the motor) Also, I'm not really wanting to spend top dollar on a motor. Probably pick up one off ebay or something locally.
Also, I have several electric compressor motors, (actually my buddy has them) and they all state the "rpm" rating clearly, but they all say "SPL" next to HP. How can I tell the HP rating???? In fact, every compressor motor I've seen says "SPL" next to the HP mark, and I don't know what this means.
Thanks for any other tips.
 
The SPL rating is useless. It's a deceptive rating used on things like those air compressors that claim to be 5 HP but run off a 120V circuit. :mad:

The motor should be marked with an amperage rating, typically labelled "FLA" (full load amps). You can back-calculate peak HP from this.

I'd stick with a 1750 RPM motor for that application just for noise considerations. You could also slow down a 3450 with a small pulley on the motor.

I would *guess* that a 1 HP motor would run a blower just fine, unless it's just HUGE. If you're into experimenting you could hook up one of your motors and measure how many amps it's pulling driving the blower, and compare that to the rated FLA.

I'm contemplating a similar project, so keep us all posted on your progress!

Hope this helps a bit.
Dave
 
This is a project that woodworkers will occasionally undertake for their shops. You could ask this question on some of the woodworking forums or bulletin boards on the web. Below is a link to a description on how one guy made his air cleaner.
http://no-wood-unturned.com/images/air_cleaner/air_cleaner.html

Depending on the size/weight of what you are trying to remove from the air, prefiltering can be a way to reduce the frequency of filter replacement. FWIW pantyhose material works well as a pre-filter material for larger particles. Pantyhose can be gotten cheap at dollar stores or sometimes at inventory disposal stores. If you're married, I recommend against simply stealing some from your wife's sock drawer. ;) :D
 
Thanks fellas.
Dave,
I will post the FLA and other info from one of the motors to see if you can tell me what HP it would be. It is my buddies motor, so I'll have to call him to check. Thanks fellas, and I will keep you guys posted.
 
Hey Abrasive,
I just checked over at my buddies and his motor is an Emerson compressor motor.
It says:
FLA 15.0
PH 1 (single phase)
HP SPL
SF 1.0
230 volt

Can you tell what true HP rating this thing has from the info? I can get any other info needed. Thanks bud.
Also, the squirrel cage blower I've got is rather big. It has an 8" pulley on it, and was wondering what size pulley I would need for a 3450 rpm motor?
How about if I can come up with a 1725rpm motor? What size pulley then? Would the squirrel cage blower turn at the same RPM as the motor, IF I use the SAME size pulley on the motor, that is currently on the blower? I would think so.
However, I would think that it would be wise to use a smaller pulley, to slow the blower down a little. Just not sure what size pulley. Maybe 3"? Thanks bud.
 
RokJok,
That's almost the same as the one I built, only I put legs on it, ad use it as a table in the shop.
I use furnace prefilters and electrostatic filters on it. Clean air...
I couldn't get it high enough off the floor by hanging it, and still not whack my head on it.
 
OK, plug 15A and 230V into the conversion page here:

(I just found this when I was double-checking my numbers. Pretty slick.)

http://www.onlineconversion.com/motor_horsepower.htm

and you end up with a 3 HP motor. That should be PLENTY big enough.

Yes, if your pullies are the same size, the fan and the motor will run the same RPM's. The ratio between the pulley sizes will tell you your speed. An 8" pulley on the fan will spin 3/8 as fast as a 3" pulley on the motor. (The motor revolves once, moving the belt PI*3", which only moves the fan pulley 3/8 of its PI*8" circumference, if that makes sense. The PI's cancel out and can be ignored.)

So, at 1725 on the motor you get 647 RPM on the fan. At 3450, it's 1294 RPM on the fan.

I would NOT spin a big pulley that I didn't know the history of at 3450. That's pretty fast. If it has a hidden crack or defect or if it's unbalanced it could fly apart. Bad news. :eek: The bigger the pulley, the more stress at the outside edge. I wouldn't put more than a 3" or 4" on a 3450. Any bigger than that and you are spinning the fan at a ridiculous speed anyway. I'll bet a 3" would really move some air for you. Plus you get a mechanical advantage by dropping the RPM's on the fan.

Does the fan have any markings? CFM at X RPM or anything? Or max RPM? You don't want to build a wind tunnel - just move some air through a filter. :D

You might try to rig something up to test airflow before building the whole unit. Just mount the motor and the fan to a board with the pullies you are thinking about using and fire it up. See if you end up blowing all the belts off your bench or something like that...

Hope this helps,
Dave
 
Hey thanks Abrasive,
That conversion forumula is sweet. I've got it now. Yes, I figured 3450 was way too fast. The other formula (3/8 speed) is awesome to know as well.
Yes, I plan on doing a little "mock up" of the system before I commit. Just needed a little help in choosing a pulley size mainly.
Thanks so much for your helpful info!
 
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