Guitarman1

Hello:

I have Sandor Nagyszalanczy'sbook on "Workshop Dust Control", but it is an older edition (1999, as I recall). In it, he describes improving dust collector suction by replacing the existing fan in a unit with a larger diameter retrofit impeller fan, as well as replacing the intake cover with one that has a larger diameter intake pipe.

I have a Grizzly 2 HP, 12 amp single stage collector that I hope to "soup up". As it is, I plan to replace the intake plate with a sheet of plywood that will enable me to secure the fan unit to the output of an add-on cyclone as part of creating a tower. In doing that, I can readily leave a larger opening in the sheet of plywood that will plainly improve the resistance to air intake (the air output on the cyclone is 7" diameter, as opposed to the 6" intake on the existing fan unit).

The problem has been finding a retrofit fan. I have gone to sites of companies recommended by the author in the book, including Oneida, and through Google searches on the topic, but I have been unable to find any such offering. I do not know whether there proved to be some problem with that idea that led to its falling out of favor since the book was published, or if the companies that formerly sold the retrofit fans simply decided not to compete with themselves by making other companies' units function better, or if there is some other reason. Most of the sites I have found are aimed at industry and sell very expensive impellers powered by 3-phase and/or ridiculously powerful motors and diameters that would blow my shop down! I am just curious if anyone has experience in this regard and if they might know of a resource for retrofit fans for a small woodshop dust collector. I hope to replace my 12" fan with a 14" fan. Thanks in advance for any assistance.

Leo G

You will probably burn out your motor doing this. Moving more air requires more HP. If you just increase the fan size and the hood opening then you will allow more air to flow. This will overload the motor. You can't get something for nothing.

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Guitarman1

Thanks for the response.

I've wondered about that, but there is always the issue of what horsepower as reported really represents. I have seen a number of dust collectors advertised as 2 HP that have 10 amp 220 volt motors turning 12" fans, and this one is 12 amp. That represents a 20% increase in power, I imagine, and although I don't know how the power requirement to turn a fan against resistance varies with the diameter of the blades, the increase in diameter of the blades would be only about 16%, so the relative increase in power exceeds the relative increase in fan blade diameter.

I've also seen advertised dust collection units with 2 HP motors that come with 14" fans, so I want to presume that that is not excessive for the motor, in itself, but that Grizzly simply elected to optimize the size of the fan to what they could most competetively sell the unit for.

Beyond that, I also intend to rebuild the unit, replacing the high resistance, two bag filter tower that comes with the unit with a bag house using four 6' long, 1' diameter higher efficiency sleeve filters. That should significantly decrease the resistance to the output from the fan, and I would expect that to reduce the load on the motor, even with the larger fan.

I am not an engineer, but this is my thinking, and it makes sense to me, for the several reasons I have outlined, so I hope this is not so simply a matter of "trying to get something for nothing". The author of the book I mentioned, in fact, stated something to the effect that, if run wide open without the intended resistance of being in line with a system of ductwork, the motor would burn out prematurely, and he advised specifically to avoid running the fan until it was all hooked up, but that is something easily enough avoided, as there would be no good point in doing it in the first place.

In the end, though, I have to ask whether you know this to be a bad idea from some specific knowledge or experience, or if you are simply presuming or guessing it to be so. Regardless of the thinking I have outlined, I certainly do not wish to stubbornly proceed to burn the motor out if there is good evidence/experience that has shown it to be a bad idea. I mean no offense in expressing it this way and again thank you for your response.

chrisgerman1983

if your DC is not enough for your shop, have you tried other options first like adding blast gates and reworking your ducting. are you running the same diameter ducting through the whole shop, or are you running a little bigger before each "Y" and going down a size after? it is very inefficient to run the same size everywhere

rrbrown

If you increase the area for which the same amount of air can leave the system you have done nothing more then decrease the pressure out of the bags for the same amount of air. Now if in doing this you increase the duct, intake and fan size you are moving more air. Now you have inceased the pressure of the exiting air again. I have a 120 v 1 1/2 hp dust collector with a 12" impeller that is rated at 1200 cfm. The impeller, intake and exhaust size along with square inches of the filter determine air flow and for the most part hp needed. However if you increase say from a 12" fan to a 14" fan and increase the intake and exhaust size also you should still be able to use the same hp motor. Just don't jump from a 12" fan to a 16" fan. As for the amps and hp those numbers or manipulated by the companies. There are specific amps per hp ratings listed below. use a Amp meter that clamps around the wire and make sure you are drawing close to the amps listed for the motor size that you have. These motor have overloads on the motor and will trip if you go to far. All that said by the time you get new bags, intake, impeller and probably an amp meter you could probably sell the DC you have and buy a new larger one cheaper.

Amp Draw of Electric Motors
Motor Size /120 volts /240 volts
1/4 hp. /6 amp. /3 amp.
1/3 hp. /7 amp. /3½ amp.
1/2 hp. /10 amp. /5 amp.
3/4 hp. /14 amp. /7 amp.
1 hp. /16 amp. /8 amp.
1½ hp. /20 amp. /10 amp.
2 hp. /24 amp. /12 amp.
3 hp. /34 amp. /17 amp.
5 hp. /56 amp. /28 amp.

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Richard

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Guitarman1

Thanks for the responses.

The table of HP as relates to amperage is interesting. Curiously, I have seen DC's listed as 2 HP that then report having 10 amp motors. I have a multimeter that I've used for doing my own electrical work. Is that adequate to measure the actual amperage draw of the motor?

In truth, I am not considering beefing this up because of any apparent experienced inadequacy. I have used the DC, since I purchased it, as a portable unit, with 4" flexible hose to connect it to a first stage separator that I made of a 55 gallon plastic drum with plastic 90 degree fittings that I used to create a cyclone-like vortex in the drum. It has worked well, as far as I can tell. The collector bag on the second stage DC unit, connected to the first stage separator again with 4" flexible hose, appears to be totally empty. I have simply reconnected the hose to the preseparator to each tool at the time of use.

This all comes up because I have decided to set up a system with rigid metal ductwork, rather than using this stationary DC like a portable unit, and I've been reading up on the topic from all sorts of sources. The idea of increasing the size of the fan was not because I am aware of any inadequacy of the existing fan. It's just the one author, Nagyszalanczy, suggested it as a way to get more out of an existing unit, and I thought, if it made sense and it was reasonably easy to do (including getting a larger impeller in the first place, which has not proved to be easy), I'd just as soon do it as part of the initial set-up, rather than waiting to find out how well it works and then going back to do it later. I've found a cyclone with a 7" output to the fan unit, and I certainly want to do away with the double 4" wye connector that presently is attached to the input of the DC.

Another soul who I suspect many here are familiar with, Bill Pentze, if I remember correctly, has written extensively about the inadequacy of home systems and scared the wits out of me. In the end, he appears to suggest a system based on anything less than a 7.5 HP motor is entirely inadequate and exposes you and your entire household to enough low micron dust to result in horrendous health problems.

There's no way I can afford a unit of that size, either financially or physically--I simply don't have enough headspace in my shop for a unit with a motor that large or the cyclone that would appropriately attach to it. So I want to do the best with what I can manage, and I figured getting the maximum benefit out of the fan I've got would be the optimum approach for me. I've considered the cost of selling what I've got and buying a prepackaged unit, but I think I've devised a system that will fit in my shop and function better, and be less expensive, than what I've found advertised. I think I've devised a system that will save me about $200 over the least expensive pre-packaged system I've found that would do the same thing. Beyond that, to sell the unit I already have would result in a loss, because I could not sell it for what I paid for it. My wife is ready to shoot me as it is, given what I've spent on tools that I need to collect dust from!

For all I know, the system would work just fine with the impeller I have, but I'm trying to investigate this from all angles to optimize it from the get-go. Thanks again for your responses.

Guitarman1

To chrisgerman1983, in response to your response, "if your DC is not enough for your shop, have you tried other options first like adding blast gates and reworking your ducting. are you running the same diameter ducting through the whole shop, or are you running a little bigger before each "Y" and going down a size after? it is very inefficient to run the same size everywhere ."


I am making this change specifically to increase the efficiency of the unit in the context of changing over from using the DC as a portable unit, as I have previously, to using it as the stationary unit it is meant to be. As such, I will be using a main duct system of 6" metal duct primarily with 4" branch ducts to most of the tools and with individual blast gates to all of them.

My shop is not huge, but I have a bulky beam dividing it in half lengthwise, so I plan to run a separate main duct to each half of the shop. I will separate them each other with blast gates, so that during use, it will function as if I have only one main duct. Although that will add somewhat to the expense of running pipe, it will limit the maximum length of any run to about 25'. 6" pipe is the maximum I can use with the input to the cyclone I plan to use. Given that the branch pipes will need to be for the most part 4", I could picture reducing to 5" at some point along the main duct and to 4" at a more distant point. One problem is that I have a relatively large lathe, and the only convenient place I can put it has it at the far end of one of the main ducts. I had thought for that tool it would be ideal to devise a hood with a 6" branch duct, so I had planned on keeping the entire main duct 6", to allow for that.

Because of the limited length of the main duct, the relatively short maximum length of run to any tool, and those specific issues tied to the lathe, I thought it would be most convenient simply to run 6" pipe exclusively for the main ducts. When you say this is very inefficient, do you mean in mechanical terms, or do you mean in economic terms of paying more than I might need to for the few extra lengths of the larger diameter pipe? If it makes a major difference in the mechanical efficiency, I'm sure the lathe would get by with a 4" duct, and it would save some money. Thanks for your input.