Impeller/motor sizing . . .

[Kevin]

I realize this question has been asked a lot, but I have a size I can find no history for. I am upgrading the DC in my woodshop, and I operate a sawmill so I have quite a bit of machinery and equipment. Some if it excess such as a 20" impeller and housing. It was built by a machinist and ran for 20 years sucking the debris out from the below the pit of a 56" saw, so I have no doubt it can handle whatever my woodshop can throw at it without coming apart.

Ideally I would not use it sipmly because it won't be very efficient to run. But since I don't run the DC but a couple hours a day max I figured I'd see what the guesstimate would be on a properly sized motor. I do have a 3 phase convertor I use to power some of my equipment but the slave motor is only 10HP so with my 5 HP table saw running that leaves 5HP I could use for the DC motor. I don't really like the idea of running a full 10HP load on the cheap Chinese slave motor but I doubt a single phase 5 HP would pull a impeler of that size and weight would it?

I will be venting everything outside into a bin  with no chip separator.

[jdon]

Okay, first some disclaimers: I'm not any sort of qualified engineer, nor have I had any personal experience with such a monstrous blower, so don't say I didn't warn you!

You might want to check out Cincinnati Fan http://www.cincinnatifan.com/index.htm Their catalog section (and maybe elsewhere) has tables of impeller type, size, cfm, hp, etc., to give you some idea of what routine motor hp requirements would be.

Since your impeller is such overkill for the needs of most any woodworker (except maybe Bill Pentz  ;) ), one thing to consider is to run at a lower rpm by using a small pulley on your motor, with a v-belt driving a larger pulley on the impeller shaft.

According to fan laws (who knew?) ftp://www.nyb.com/Letters/EL-03.pdf cfm is directly related to rpm. Static pressure is proportional to rpm squared, and hp is proportional to rpm cubed.

So, if I am not mistaken, if you reduce impeller rpm by half, cfm would be one half, static pressure would be one fourth, and hp requirement would be one eighth. It seems that you ought to be able to use your 5 hp motor, and still get acceptable performance for your needs.

[Kevin]

That sounds like good advice Don. Pulley sizing was briefly captured by my filter but it didn't stick around long for some reason - I guess I was too focused on motor sizing. You refocused my train of thought in what is probably the only realistic place where an answer could be found to use this impeller. Thanks for that link also - that's handy.

I did see where PSI sells the exact blower unit I want but they are asking $900 before shipping. I haven't found a single source that sells a 3HP+ unit with a 15" (or even a 14") steel  impeller that doesn't discourage buying them by price. otherwise I'd just go that route. Thanks for the info. Kevin.

here's the link to the PSI unit just for grins.