2 HP versus 3 HP DC Input Needed

[Mike Chalmers]

I currently have a 2 HP DC, a CX400 from Busy Bee with canister filter. Same machine as the Grizzly (http://www.grizzly.com/products/2HP-Canister-Dust-Collector-with-Aluminum-Impeller-Polar-Bear-Series/G0548ZP)G0548ZP (http://www.grizzly.com/products/2HP-Canister-Dust-Collector-with-Aluminum-Impeller-Polar-Bear-Series/G0548ZP). I have a short 6" ducted run (12') which reduces to 4" at my machines, except for the planer which reduces to 5". It all goes through a Super Dust Deputy before the DC.

Machines are
Table Saw, 8" Jointer and 20" planer with spiral cutterheads, bandsaw, 6 X 89" edge sander, miter saw, full size spindle sander.

Am contemplating moving to the 3 HP variant, CX402 (Grizzly (http://(http://www.grizzly.com/products/3HP-Double-Canister-Dust-Collector-with-Aluminum-Impeller-Polar-Bear-Series/G0562ZP)G0562ZP (http://(http://www.grizzly.com/products/3HP-Double-Canister-Dust-Collector-with-Aluminum-Impeller-Polar-Bear-Series/G0562ZP))

My issue is that both units have the same size impeller (12 3/4"). I also read a post on the Canadian Woodworking site which seemed to tell me that I would not really see any improvement following this course of action. I have cut and pasted the relevant section below.

"The impellers are exactly the same diameter with same number of curved vanes. The 3HP unit is cast, the 2HP fabricated.


They drew exactly the same amount of water on test. About 5" on my rig or a total SP of 10".


Why then does one have a 3HP motor and the other a 2HP? I have suspected for some time that these units had the same blowers, but because the larger one has two filters instead of one, there is way more surface area and 1/2 as much back pressure, therefore more airflow. More flow requires more HP. Could explain why the impeller is cast as the additional flow puts more stress on the vanes.


Therefore I can expect minimal performance improvement with my current setup."

Looking for input about the position stated above.

[Art Mann]

The whole story is more complex than what the forum you were reading indicates. Each of the referenced machines will have a performance curve associated with it that plots mass air flow (CFM) as a function of resistance (SP). I expect you will find that as the static pressure gets higher, the 3 HP machine will sustain a larger air flow. If both machines are operated in the unloaded state, they may indeed have the same flow rate but that doesn't mean anything. That is why CFM specs for dust collectors don't mean much. I would expect the cast blower fan will work better than the fabricated one because all the vanes are smoothly contoured with no fasteners protruding.

[David Kumm]

You are on the right track in your analysis. With additional filter area, the cfm will generally be higher due to lower pressure. The problem is that you may not see any significant increase in your application other than the additional flow created due to the reduction in static pressure. If you have a cfm curve for your 2 hp collector, you can just look at the numbers corresponding to 1-2" less SP and get how the new one will compare. The 3 hp will only exceed the 2 hp at low pressure, not high. With your sized machines, I'd look for a collector with more cfm than either of the two you are talking about. The upgrade won't have enough bang for the buck. Dave

[Dan Friedrichs]

I expect you will find that as the static pressure gets higher, the 3 HP machine will sustain a larger air flow.

I don't think this is true, if the impeller is really the same.

An induction motor runs at the same speed, regardless of load. The blower, ductwork, filters, etc, all contribute in some way to the load presented to the motor. More filters reduce the static pressure, increasing the CFM, and increasing the load. A bigger impeller increases the load. Larger diameter ductwork increases the load. Etc. If the total load presented to the motor is <2HP, then the 2HP motor is fine, but if it's larger, then you'd require a larger motor. A motor that was undersized would exceed its current rating (and hopefully trip an integral overcurrent protection device), but if your system was presenting a load requiring <2HP, you would notice no difference in performance between a 2HP and 3HP motor on the same blower.

If you aren't tripping an overcurrent protection device on the 2HP motor, switching to the 3HP motor will provide ZERO improvement. If it's the same impeller spinning at the same speed, it must be performing the same. Now, the increased filter area might improve performance, but that's a completely separate issue from the motor size.

I would bet that your present system doesn't come anywhere close to needing the full 2HP, and you can check this by measuring the current drawn from the motor and comparing it to the nameplate current rating on the motor. If you find that you're well below the full load ampacity of the motor, you could make various changes to the system to improve performance, such as reducing static pressure losses in the system (increasing duct size all the way to the machines without necking down, increasing filter size, eliminating sharp bends in ductwork, etc)

[Chris Padilla]

I'm with Dan. I've always found spec'ing DCs with HP ratings to be a few items down on the check list of priorities when looking at DCs. The size of the impeller is always #1 and its blower housing size and fan curves. Next would be duct work losses. Next would be exhaust set up (outside or filter...and what kind of filter). Next would be style of DC (cyclone?). Then the motor rating might come into play.

[Tom M King]

I have a 3hp four bagger Woodtek, and a 2 hp two bagger Grizzly. I don't know what the specs are, but just judging by a hand close to the intake of a 6" flex on the 3hp, and 4" flex on the 2hp, there is a B I G difference. The 3hp pulls much harder on the 6" than the 2hp does on the 4". I run the 3 hp on three machines without blast gates, and the 2hp is dedicated to a 24" resaw bandsaw. I wouldn't think about using the 2hp for what the 3hp does for me.

[Dan Friedrichs]

I have a 3hp four bagger Woodtek, and a 2 hp two bagger Grizzly. I don't know what the specs are, but just judging by a hand close to the intake of a 6" flex on the 3hp, and 4" flex on the 2hp, there is a B I G difference. The 3hp pulls much harder on the 6" than the 2hp does on the 4". I run the 3 hp on three machines without blast gates, and the 2hp is dedicated to a 24" resaw bandsaw. I wouldn't think about using the 2hp for what the 3hp does for me.

I believe you, but you might also say with equal accuracy, "My dust collector that is painted grey does a much better job than the one that's pained blue". Clearly, though, the paint color does not affect performance. Likewise, there is no difference in performance between a 3HP motor and a 2HP motor (if they were spinning the same blower in the same system without exceeding their current ratings). Double the filter (bags), and you've certainly significantly increased the airflow - you might find that hooking the 4 bag filter to the 2HP blower gives you equal performance to the 3HP system. Or you may find that the impeller on the 3HP system is much larger. The difference in performance could be attributed to many things.....but not the motor.

[Chris Padilla]

All these motors spin at the same speed: 3450 rpm. It is the LOAD on that impeller that makes the difference. And the load comes from a variety of things like the ducts, the filters, and the impeller size and design.

[Steve Peterson]

I'm with Dan. I've always found spec'ing DCs with HP ratings to be a few items down on the check list of priorities when looking at DCs. The size of the impeller is always #1 and its blower housing size and fan curves. Next would be duct work losses. Next would be exhaust set up (outside or filter...and what kind of filter). Next would be style of DC (cyclone?). Then the motor rating might come into play.

Your 2HP system might be designed with the same blower as the 3HP version and may operate perfectly fine with the stock filters. The 2HP system could be a perfectly balanced system with the motor running close to it's rated limits. Adding a 3HP motor to the same system would still consume around 2HP of electricity because it would move the exact same amount of air. The motor would run slightly cooler and probably last a bit longer.

Adding larger filters or venting outdoors would allow either system to move more air. This could overload the 2HP motor while the 3HP motor would be perfectly fine. If nothing else changes in your system, then there is no advantage to swapping a working 2HP motor with a 3HP motor. The only way it would make sense is if you get a bigger impeller or better filters that allow more airflow.

Steve

[Art Mann]

I don't think this is true, if the impeller is really the same.

Come to think of it, you are exactly right!

[Mike Chalmers]

Thanks everyone for your thoughts. What I am getting out of this is that a 3hp unit will perform a little better based solely on the increase in filter area, not the stronger motor.
I am guessing that the perceived improvement would not justify the extra cost.
My own research tells me that the only way I'll really improve my set up is to move to a true cyclone, such as the Clearvue or Oneida. Now, that is a big difference in bucks.

[glenn bradley]

Another factor often brushed over in these discussions is that the systems are designed as they are designed. Putting a cyclone separator in front of the blower blows the original design specs. I'm not saying not to use a separator, you should to keep your filters clean. Its just that cyclones are designed to be cyclones, baggers are designed to be baggers. I have yet to find a bagger sold with an appropriately sized bag.. Filter cartridges come closer but . . . for 2300 CFM you want about 450 square feet of filter media . . . Looking at Wynn's woodworking filters, their larger one is about 300 sq. ft. and I imagine it is better than what might come with a unit. There's just so much info and so many variables; its like trying to decide on a cell phone or cable TV package ;-)

[Jim Andrew]

Personally, I would not waste money buying a bagger, when a cyclone is what you really need. The cyclones have the bigger impellers, and would not get anything less than a 3hp unit. I have a 2hp, and plan to upgrade.

[Mike Chalmers]

Personally, I would not waste money buying a bagger, when a cyclone is what you really need. The cyclones have the bigger impellers, and would not get anything less than a 3hp unit. I have a 2hp, and plan to upgrade.Personally, I would like to have been able to afford a true cyclone, however, that was not, and is not, the case.

[glenn bradley]

Personally, I would like to have been able to afford a true cyclone, however, that was not, and is not, the case.

Just more food for thought. I have a 2HP cyclone because I could not fit a 3HP into the shop. We all have restrictions be they monetary, vertical clearance, floor space, etc. Dust collection threads always seem to head toward suggestions of monster systems with super performance. This is because monster systems with super performance are what we should all be using for health reasons.

These discussions are similar to asking "how little should I smoke to remain healthy"; answer . . . not at all. There is no middle ground in theory. fortunately we work in reality. Unfortunately we can't always have the dust collection that would be "best". We should always strive to make it "better" though ;-)

One reason for a cyclone is to make the return air safe if you have to return it to your breathing space. If I could vent outside with impunity I would skip the cyclone (they put a terrible hit on your airflow) and just blow everything outside (I also live where it is warm). In reality I have to breathe my return air so I have a cyclone and a good filter rig that I keep clean. Perfect? No. Better? Yes.

Shoot for the best that you can afford/fit. If you are going to pre-separate the air path to a machine that is not designed for it, go as big as you can. That's a little non-scientific but, I want to spend my time building things so I K.I.S.S.

[Wade Lippman]

Okay, now that the OP's question is thoroughly answered, I have a related question.
The grizzly 3hp cyclone and the 5hp cyclone both draw 22a! The 5hp is 16" versus 15.5", and double the filter area, so shouldn't it draw more current?
I have measured the 3hp at 22a, so that is accurate; I can only presume the 22a is accurate for the 5hp as well.

My only guess is that the 3hp motor is just horribly inefficient; but why would they do that?

[Chris Padilla]

While you've stated a few important design specs on the two cyclone DCs, we don't have everything. What's the intake size of the two blowers? That will tell us the area there for air to move through. Assuming it is different, there you go. If it is the same, then the difference might be coming from the the different size of the impellers not to mention the actual design of the impeller's vanes (how many, angle, geometry, etc.). Also, are the cyclones the same? Lots to look at and compare/contrast.