Shop Fox 1.5hp Dust Collector Replacement Motor

[conscience]

As you can tell by the 1 on the post counter this is my first post here. I'm amazed by the amount of knowledge on these forums. Once I owned a small cabinet shop and I had a pretty sophisticated dust collection system.

Now, several years later I am putting a shop together again, mainly for personal use since I switched careers. I'm very concerned by dust collection. A friend of mine has a fairly new Shop Fox but the motor is pretty much shot (those things should really be plugged into a dedicated outlet and not on a 100' 16 ga cord but that is another story.)

Anyway he will basically give it to me if I want it. My question is what happens if I replace the motor with a 2 or 3 hp Baldor motor that turns at 3450 rpm? Part of me says it will increase the cfm but part of me says it won't.

The impeller on the 1.5 and 2 hp models is the same size, both spin at 3450 and the units seem to be exactly alike other than motor hp and static pressure. The 2hp produces another 300 cfm.

I'd like to increase the cfm from the listed 1280 for the 1.5hp as much as possible since I'd like to run 6" hard pipe to all my machines with only a bare minimum of 6" flex.

Rated cfm is usually tested with no ducting or filters so in reality that 1280 is going to be substantially lower and I am concerned with catching as much of the fine dust at the point of contact as possible. This is where the 4" pipe in conjunction with the lower cfm ratings fail. They do great with chips and shavings but don't pull all of the fines in. As I get older I am getting more sensitive to fine wood dust in the air.

Sorry if this has been covered before. I did a search but couldn't find anything.

Jeremy

[LCHIEN]

Induction motors for Dust collectors act differently from what you'd expect. The way a DC works is that the motor draws maximum current and produces maximum power when the DC is essentially unrestricted - maximum CFMs - e.g. no inlet piping and either no filter bags/filter canister or a very new clean one. Adding restriction -e.g. as the bags clog and you have piping on the inlet the motor current will drop. Blocking off the inlet duct completely will draw the lowest current - essentially what it takes to spin the motor in fixed air but no thru flow. This sounds the loudest so its counterintuitive but that's the fact. Basically the power consumed is proportional to the air moved and given a fixed speed, and no restriction, the motor cannot move any more air even when the motor HP is increased beyond the design size (unless the motor was undersized to begin with).

Running a undersized motor with the minimum of static pressure loss can burn the motor out, which is why some DCs that are designed close to the edge recommend not running them with no ducting and no bags.

Running an oversized motor of the same RPM will just waste the extra capacity of the motor with no CFM increase.

What you may have when they have two DCs with apparently the same impeller diameter but two different HP and CFM ratings is not the extra HP driving the same impeller but probably a extra HP driving the same size impeller but not the same impeller design, perhaps one with more or different shaped fins or curved fins (both more expensive but moving more air or leaking less air per revolution) which makes it more efficient in terms of air movement for the same diameter and RPM.

[conscience]

Yeah that is kind of what I was thinking. Just hoped to get a DC for free after I put on an old compressor motor I've got laying around. Some much for being cheap. Thanks for the reply. Now I either have to buy a good one (expensive) or make my own.

[dbhost]

Are the field windings damaged? It's possible that the thing just needs brushes...

[LCHIEN]

sorry dave, no brushes in an induction motor.
I don't mean to say Conscience that putting in a larger motor is bad. You won't get a boost in CFM but you won't use more power either nor is it dangerous. You'll just have an oversize motor working at less than 100% power capability. Just like your table saw motor, most of the time.

[conscience]

I may still throw the 3hp Baldor in the thing and maybe look at getting a different impeller but I really want a higher cfm at the point of use. I was looking at the Wynn website and they had a link to a guy that has devised a DIY cyclone complete with home made blower. I may give that a try. Or just build a stronger blower with a bigger impeller and put the filter outside.

Thanks again for the help Loring (and Dave).

[AlanWS]

It's possible that they use a smaller motor in a DC of similar design simply by restricting the air inlet to keep the motor from burning out. If that's the case, you could safely let more air get to the blower if you had a bigger motor. It's quite possible that this was the case, and the previous owner removed restrictions, which did improve the performance -- until the motor burned out.

But it is unlikely you could increase the airflow above the nameplate value because that is likely an exaggerated value measured without any duct, and possibly without even connecting the blower to a DC. In actual use, I suspect few DCs pull as much as half the advertised flow.

[Mr__Bill]

Or just build a stronger blower with a bigger impeller and put the filter outside.

Don't forget that if the filter is outside then you will need to bring the equivalent amount of air back into the shop. Air that is perhaps not as conditioned as the air already in the shop.


Bill

[BobSch]

I'm siding with Loring on this one. Unless there's some other loading factor involved, a 3450 rpm motor is a 3450 rpm motor.