Thread: The Generic 2HP DC

Finally, all is completed


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Modified dust separator with the 150 mm inlet is now connected, the 125 mm blocked and the system up and running.

The results??

Before fitting the modified dust separator. the best flow with a fully conditioned needle felt filter was 634 CFM with the drop down flexy and connection to the table saw disconnected from the horizontal pipe.

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Its now 733 CFM so a gain of close on 100 CFM.

If I compare that to the original figures I first measured, not knowing the pleated filter was partially block, its a huge improvement - 456 to 733 CFM

The best the system could give me, with the filter disconnected and the rectangular outlet from the impellor housing fully exposed and the inlet not connected to any tool, was 886 CFM so I think I've achieved all the system is going to give me.


With the total system connected to the table saw, so close on 9 m of pipe and flexy, I have 638.5 CFM.

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I also have a separate shop vac connected to the overhead dust chute on the saw table which is around 85 CFM

So I'd say the modifications were well worth the time effort.

Originally Posted by Lappa

I also have a separate shop vac connected to the overhead dust chute on the saw table which is around 150 CFM

So I'd say the modifications were well worth the time effort.

Sounds good.

The Shop vac few rate is impressive, how are you measuring it?

Your right Bob re the Super Vac. I forgot to change the parameters in the program so actual flow is 85 CFM.

Thanks for picking that up. I've edited the post to reflect the actual readings.

Originally Posted by Lappa

Your right Bob re the Super Vac. I forgot to change the parameters in the program so actual flow is 85 CFM.

Thanks for picking that up. I've edited the post to reflect the actual readings.

85 CFM Through your saw guard with that tight corner is still pretty good.

The only vacs I have seen pull more than about 125 CFM are those jumbo vacs that use 50 mm hose. The Festools claim 137 CFM but the 2 machines I measured I could only measure about 125 CFM and that was if no hose was used. Once the 27 mm hose was used the flow dropped even further.

There is a lot of good information here and a whole bunch of things that bother me considerably. I spent way too much time looking over this thread and years trying to address the same basic problem. Fine airborne dust is so easily blown around that the only way to ensure safe air quality is to pull in the fine dust before normal room air currents blow it all over. Over fifty years of experience by the pros who guarantee customer air quality found that we must start by upgrading our hoods. Most blades, bits, cutters, and sandpaper launch fine dust at over 100 miles an hour versus most dust collection systems move air at around 40 miles an hour. That race is always lost unless our hoods contain, direct and deliver the fast moving dust filled air streams for collection. Even with really good hoods, almost all traditional stationary tools also leak fine dust from all around their working areas. Again decades of research and experience by those who guarantee customer air quality found we have to have at least 50 feet per minute air speed out to a distance of not less than about 15.25" in all directions to pull in this fine dust or normal room air currents will blow the fine dust all over. Both doing the math and doing the testing shows that most small shop tools need right at 1000 CFM airflow to build up big enough low pressure area to get the needed air speed out to the needed distance to pull in the fine dust. Blower technology is mature meaning if you buy the same type, size, and speed blower from any of the major professional blower makers you will get near identical performance. Dust collection blowers intentionally use self cleaning backward curved bladed impellers to both handle material hits and to minimize noise. If you add up the worst case meaning most distant tool resistances in a typical two-car garage sized shop we have our hoods, flex to the hoods, duct, duct elbows, duct wyes, then our DC or cyclone, its filter, and the resistance from the filter being dirty. We also size our blower motor based on when we move the most air which means calculating the resistance for the shortest run with clean new filters. Putting the numbers into a good static calculator using all 6" diameter ductingg shows most shops have a minimum resistance of 4 water column inches which with a dust collector and at least 7.5 water column inches for a DC, about 11.5" for a typical cyclone and only 9.75" for my high efficiency cyclone design. Using a good commercial blower table such as shared on Cincinnati Fan at https://www.cincinnatifan.com/catalo...1-internet.pdf shows that it takes not less than a 14" diameter impeller turning at 3450 RPM for a DC to move our real 1000 CFM. Checking the low resistance for that same impeller shows we need at least a 3 hp motor for our DC. Likewise, it takes a 15.5" diameter impeller turning at 3450 RPM by at least a 5 hp motor for a typical cyclone and if we interpolate can get by with a 15" for my cyclone design. Anything less will not pull in enough air for good fine dust collection.

Far too many are limited in terms of being able in terms of finances or power to install a motor of ample size to provide the real 1000 CFM we need at most stationary tools to get good fine dust collection. It seemed to me that a 1.5 hp blower that could move a real 1100 CFM or 2 hp that could move a real 1200 should be able to be made to work. They can but only if we use very short lengths of very smooth interior walled flex where we move our collector right next to each machine. Adding the additional static pressure to support ducting and filters causes a serious lack of the needed airflow.

I've learned lots from spending far too much time playing with many of the different DCs which are almost all Chinese imports. This thread mostly deals with the 2 hp units that have a roughly 12" diameter impeller. Few of the import dust collectors are that well engineered. An ideal DC setup would elevate the motor and blower to blow directly into the separation ring, but for safety sake must keep the motor shaft horizontal. It turns out most of the DC methods for securing the impeller presume a horizontal motor shaft, so using a vertical shaft orientation can have bad consequences. I've had two impellers separate from the motor shafts, not good. DC blower housings need much better engineering. We not only need to worry about airflow, we also have to ensure that the blower and impeller are setup so that if a wedge of wood gets collected it does not act like a doorstop and jam the impeller into an abrupt stop. These kinds of stops will shift the shaft electronics which can immediately or soon ruin our motors. Most DC vendors protect against pulling too many amps by either intention or sloppy design. As we clean up the bottlenecks such as in the output of the blower, blower inlet, improved blower housing, better connection to the DC separation ring, etc., we can get in trouble. That trouble comes far more quickly today than it did ten or twenty years ago. The problem is many vendors have been bumping up the sizes of their impellers and keeping all else the same. The larger impellers provide better advertising specifications as they move lots more air at low resistance levels. These larger sized impellers are pretty obvious as the clearances between the blower sides and impeller drop considerably. These larger impellers are dangerous from the vantage of lacking the clearances on top and to the sides of the impeller to pass heavier large object through without jamming. They also pose serious potential problems when it comes to our making all real efficient, so an amp meter is a must to ensure our shortest most open run does not move so much air it over stresses the motor.

Not sure if this helps...

Thanks Bill for your input.

Very informative and of course slightly disturbing. We are probably all far too complacent with our own DC arrangements. I know I am.

Regards
Paul

Originally Posted by bill pentz

There is a lot of good information here and a whole bunch of things that bother me considerably. I spent way too much time looking over this thread and years trying to address the same basic problem. Fine airborne dust is so easily blown around that the only way to ensure safe air quality is to pull in the fine dust before normal room air currents blow it all over.

Far too many are limited in terms of being able in terms of finances or power to install a motor of ample size to provide the real 1000 CFM we need at most stationary tools to get good fine dust collection. It seemed to me that a 1.5 hp blower that could move a real 1100 CFM or 2 hp that could move a real 1200 should be able to be made to work. They can but only if we use very short lengths of very smooth interior walled flex where we move our collector right next to each machine. Adding the additional static pressure to support ducting and filters causes a serious lack of the needed airflow.

Not sure if this helps...

So going by this, the 2hp extractor has to be next to the machine with as short and as smooth a pipe as possible. This then rules out having the extractor in an enclosure or outside the workshop. Therefore the fine dust problem is not going to go away as we are told all extractors leak and no filters will filter fine enough.
In reality, in the average wood workers workshop/shed, it's a lose, lose situation because finances, as you say limit the extractor type. I know for a fact that if I had $4000 plus to spend, it would go on a bandsaw and a thicknesser/jointer and not an extractor system.

I've modified my system as far as it can go so I guess I'll live with it as it's a vast improvement on what I had. No, I don't have a particle counter and I'm told a bright light is a waste of time re fine dust but a bright light has shown a great improvement on my dust collection and I'll wear a face mask.

thanks for your input.

Bill, your site and information has been a source of inspiration for those of us who started out down this dust collection path. I know that Bobl is always quoting your site and findings, I think after years of trying to convert people, he finally came to the collusion that if most "cash strapped" DIY woodworkers were going to use a 2HP DC then those with a desire to improve what they could afford may as well get the most out of the piece of crap - but as always, with extra precautions like dust masks and cross flow ventilation.

Often discussed in the forums here is overloading the Motor, however one thing to keep in mind in Australia is that we run @ 50Hz, and I know you have discussed this on your site, our DC machines are imported and were designed to run at 60Hz and 3,400 RPM, here they spin at around 2800 RPM - I'm not going to look up the exact figure - the point is that a 2HP DC will be lucky to be running at 1.5HP, and a 3HP and 14" impeller will be lucky to make 2.8 HP, and most are turning 12" and 13" impellers, so opening up ports and other mods are unlikely to overload a motor here, however it's always suggested in these forums that the user check the AC current just to be sure. A VFD and 3 Phase motor are options that have been discussed for many years.

Finally, everything you have written about has, at least to myself, been proven true. I find that the "minimum" in my small workshop is cross flow venting, a 3HP DC turning a 14" impeller (mounted outside), keeping the filters clean, even cleaning every few weeks with sanding or working MDF, using short 6" ducting runs and using as little flex as possible - smooth wall when needed.

Thanks again for all that effort, work, and documentation. Still saving for that Cyclone - along your design of course and with VFD and 15" impeller.


EDIT: I feel my need to clean filters regularly (I also monitor filter resistance) is due in part to our lower 50Hz fan speed and resulting borderline flow rate - even with 3hp and 14".

Originally Posted by MandJ

Often discussed in the forums here is overloading the Motor, however one thing to keep in mind in Australia is that we run @ 50Hz, and I know you have discussed this on your site, our DC machines are imported and were designed to run at 60Hz and 3,400 RPM, here they spin at around 2800 RPM - I'm not going to look up the exact figure - the point is that a 2HP DC will be lucky to be running at 1.5HP, and a 3HP and 14" impeller will be lucky to make 2.8 HP.

I seriously doubt that are the same motors
Of the dozen or so cheaper (1-3HP) Chinese motors I have tested (including 2 from dust extractors) with my HP testing rig, all have registered their true/rated HP ratings.
The rig measures output torque which combined with the radius of the fly wheel being turned and the RPM allows the power to be determined.

While testing for HP I also simultaneously measure the current being drawn and the applied V.
What I found was that the current drawn by the motor was a poor guide to its rating, it is after all really a measure of the load being imposed on the motor.

I have only measured the currents drawn by 2 modified 2HP DCs and they were not significantly greater especially with ducting machinery connected into the inlet and when the filters are conditioned . Of course this does not mean you should not test your modified setup. I think I have encouraged folks I speak to personally about modifying their system.

I agree with BP about potential problems with a vertical shaft and poor impeller connections to the motor. This was why the modified 2HP DC has the mounted underneath and the impeller on top, AND the modified mounting directly supports the Motor and not the impeller housing. This way if the impeller get loose it is at least still sitting on top of the motor. If the motor is on top and the impeller gets loose and falls into the housing all hell could break loose.

OTOH the fact that these DCs enclosure/impellers/connections have been designed to operate with motors running at 60Hz is significant to the issue.
It means that running then at 50Hz will result in a significantly lower (44%) of a Kinetic energy load on their mechanical properties which should make some difference to these matters.

I have noticed more and more DCs with vertical shafts e.g. the motor on my Carbatec 2 bag 3HP unit hangs vertically off the impeller housing with no direct support. The same applies to all the 2 bag Carbatec DCs. The general construction and connection of the motor to the impeller housing of these DCs is not exactly what I would call sturdy and no different to the horizontal mounted DCs.. The new timbecon 2 bag units also have the motor on top and the impeller upside down - it would be interesting to see the mechanical connection of the impeller to the motor.

If you are at all worried about this, then yet another good reason to locate the DC outside in an enclosure.

The modified DC was never meant to be an alternative to "proper" dust extraction. I just did the mods to see what it could do. The fact that folks want to run with it for whatever reason is up to them.

Originally Posted by BobL

I seriously doubt that are the same motors
Of the dozen or so cheaper (1-3HP) Chinese motors I have tested (including 2 from dust extractors) with my HP testing rig, all have registered their true/rated HP ratings.
The rig measures output torque which combined with the radius of the fly wheel being turned and the RPM allows the power to be determined.

Yes this is likely the case, and I should have worded that differently to mean that the DC impeller is likely designed to run on 60Hz, the lower speed and loss of flow rate when compared to a 3HP DC running on 60hz is the problem.

However I would like to know, given a 3HP motor turning the same 14" impeller, one running at 60 Hz and 3400 RPM and one at 50Hz and 2700 RPM, how can a 3HP motor turning the same impeller at a lower speed not draw less current?

Originally Posted by MandJ

However I would like to know, given a 3HP motor turning the same 14" impeller, one running at 60 Hz and 3400 RPM and one at 50Hz and 2700 RPM, how can a 3HP motor turning the same impeller at a lower speed not draw less current?

Ah ha - I now understand what you mean.
It will indeed draw less current so will indeed generating less HP and that is exactly what we see.
The same applies across most wood working machines that cannot use gears or pulleys to increase the drive speed.

Originally Posted by Bushmiller

... We are probably all far too complacent with our own DC arrangements...

Originally Posted by Lappa

...I've modified my system as far as it can go so I guess I'll live with it as it's a vast improvement on what I had.

Originally Posted by MandJ

Often discussed in the forums here is overloading the Motor ... - the point is that a 2HP DC will be lucky to be running at 1.5HP

Thanks for the kind words.

A few clarifications. Complacency is fine unless you are looking long term or build an allergic reaction. An allergic reaction can happen in as little as a few hours exposure when working with cocobolo, rosewood, ebony and a few other high sensitizing woods. Long term damage is a combination of a buildup of silica and other wood carried chemicals combined with scaring and damage from the sharp edges and points found on wood dust particles. This latter damage is so little per exposure that most never even know they are developing a problem until they develop health issues. There is a pretty scary Facebook forum https://www.facebook.com/groups/dddawareness/ that provides far more medical info and more crass language than I can handle about the dangers of fine dust, particularly dusts like wood that contain high amounts of silica. Remember protection is easy, put on a good dual cartridge NIOSH approved respirator mask and turn on a strong fan that blows fresh air through your shop. With the mask and fan you can then just concentrate on good chip collection.

For my cyclones I dealt with the 50 MHz power situation by recommending only using 16" diameter or larger impellers to those with 50 MHz power. Almost all Chinese imported DCs do something similar. They replace the 11" diameter DC impellers for the 60 MHz market with 12" diameter DC impellers. Unlike my solution that uses a larger blower housing, most of these importers make zero change to the blower housing creating a much higher potential for a wedge jamming the impeller forcing a rapid halt, plus the tighter clearances end up with making the blower a bit more efficient, meaning it can move about 5% more air. So doing the math shows that an 11" diameter backward curved impeller at 3450 RPM produces a real airflow of about 1100 CFM and that same impeller when turning at 50 MHZ speed gives 50/60 = 83.3333% resulting in a blower speed of 2875 and real airflow of only about 916 CFM. Bumping that now 2875 RPM motor up to a 12" diameter impeller increases the impeller circumference from 34.55 to 37.7 inches which we then have to multiply by the 3875 RPM giving us still a loss over the 11" diameter blower wheel down to 90.90% which when multiplied by 1100 CFM gives 1000 CFM. But, the tighter clearances give back about 5% more efficiency so we end up with the 12" blower wheels at 50 MHz speeds giving a real roughly 1050 CFM maximum airflow. That means the amp draws, etc. should be pretty close and the same concerns apply whether at 50 MHz or 60 MHz if the wheels have been upgraded. In other words don't think that your 50 MHz power protects you, especially when you start dealing with the even larger impellers used in bigger DCs and cyclones.

What is far more telling though, is the impact on the working areas of the fan curves. The larger the diameter the higher the pressure and more air we actually move when dealing with higher working resistance levels, so chip collection becomes far better with these larger diameter impellers as the resistance increases.

Originally Posted by bill pentz

That means the amp draws, etc. should be pretty close and the same concerns apply whether at 50 MHz or 60 MHz if the wheels have been upgraded. In other words don't think that your 50 MHz power protects you, especially when you start dealing with the even larger impellers used in bigger DCs and cyclones. .

The best way to be sure is to always measure the current drawn by the DC before and after the modification.
As I mentioned elsewhere I have measure the currents of 2 of these generic 2HP modified DCs and the changes in current drawn were only marginally different which suggested the impeller design is pretty choked. None of this takes away the responsibility of modifiers to check their before and after currents.
I also recommend not butchering the DC but to keep the original inlets and make a new inlet so the original can be restored if there is a problem.

The stock impeller 2HP DC has a 4.5" round inlet and a rectangular outlet that is nearly the same cross sectional area of a 6" round duct.
The motors have a name plate rating of 7.7A but the current drawn by DC (with 4" intakes and filters attached) is 5.0A
The same 2HP motor is used on a well know budget level planer/thicknesser that I have and note that while operating it can run at around 7A and up to 9A when thicknessing.

The stock impeller (no bags and a naked 4.5" inlet) draws around 5.5 A.
The modified impeller ((no bags and a naked 6" Bell mouth hood inlet) draws 5.7A.
The start up currents are greater for a modified DC taking around 5 seconds to drop to less than 10A while the stock impeller rakes about 3-4 seconds.
When filters, ducting and machinery is connected the operating currents I saw were all less than 5.5A.

These sub 5% current changes are not significant for this motor.
I have seen a more significant change on an old twin bag 3HP DC where the current jumped from 9.3A to 10.9A (17%) when the inlet and bags were removed.
In one post in this thread I recommend not connecting the modified DC to an expander board as the start up current may trip the board breaker.

BobL, just reading over this whole thread again and I have some questions/clarifications re. the measurements in Post 18

The Generic 2HP DC

You state a flow without the 5" outlet or bag, and with a 6" inlet at 1060/1008 cfm and show an airspeed of just over 14m/s (blue graph) at 140mm from the wall. Now 14m/s is 2755.91 ft/sec and the area of the 6" pipe is 0.196375 ft2. This gives a cfm of 541. Am I reading this wrong?
Cheers