Induction motor shopvac?

[Alan Schaffter]

Other than size, weight, RPM, and of course cost, anyone have any idea why they make shopvacs with universal brush-type motors, instead of induction motors?

Seems, once you gear it up and if all the other concerns don't matter to you, an induction motor powered shopvac would be much, much, quieter, more powerful, and more durable than one powered by a universal motor.

[Dan Friedrichs]

I think you hit all the reasons :) Are you considering building one?

I wonder how much quieter it would actually be given the gear and fan you'd still have spinning at high speed.

[Jeff Bratt]

Other than size, weight, RPM, and of course cost...
How many more reasons do you need?


Seems, once you gear it up and if all the other concerns don't matter to you, an induction motor powered shopvac would be much, much, quieter, more powerful, and more durable than one powered by a universal motor.
And it would be bigger, heavier, and cost more... Anyway, an impeller moving air through passages at high enough velocities will still be fairly noisy. Even dust collection systems powered by induction motors aren't quiet. But universal motors - especially in shop vacs - can sure scream unpleasantly.

[Dave Lehnert]

They do make one. They are called Dust Collectors.

[Chip Lindley]

Yep, here's one by Delta! I've used the 2Hp. model for years!

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[Norman Hitt]

I've really never thought about what RPM a shop vac motor turns, BUT, I know that the fan is a very small diameter, very thin, made from VERY thin metal and has a lot of blades in it spaced closely together, Soooo..... I wonder if a fan was made thin like those AND with the same vane spacing as those, but a much larger diameter, say just nearly the size of the body of the dust bin, would the tip speed of the larger fan, if powered with one of the higher rpm induction motors, be the same as the tip speed of the current Vac's fans? If so, that could eliminate the gearing problem and it just might be possible, who knows???

Interesting question to say the least.

[Alan Schaffter]

They do make one. They are called Dust Collectors.


Yep, here's one by Delta! I've used the 2Hp. model for years!

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Two different animals. Shopvacs have a totally different fan design. I'm not talking about a DC with its high CFM/low static pressure, material handling blower which requires large ducting. I'm talking about a shopvac with LOTS of static pressure that will really pull through 2" hose. Typical DC's work at 8" - 12" of static pressure, while a good shopvac like a Fein or Festool suck nearly 100" !!! That's what I want, except one with even greater static pressure, but much quieter.


I've really never thought about what RPM a shop vac motor turns, BUT, I know that the fan is a very small diameter, very thin, made from VERY thin metal and has a lot of blades in it spaced closely together, Soooo..... I wonder if a fan was made thin like those AND with the same vane spacing as those, but a much larger diameter, say just nearly the size of the body of the dust bin, would the tip speed of the larger fan, if powered with one of the higher rpm induction motors, be the same as the tip speed of the current Vac's fans? If so, that could eliminate the gearing problem and it just might be possible, who knows???

Interesting question to say the least.

Not sure if they spin as fast as a router, but shop vac impellers spin fast since they use universal motors like a router. I'm not sure, but the RPM might need to be limited so the impeller tip speed does not go supersonic and lose effectiveness- that is a limitation with airplane propellers which are airfoils. That problem may be limited to airfoil impellers. The bigger the impeller the more difficult it is to balance. Maybe a multi-stage turbine fan would work- but that might make "jet engine noise" :eek: :eek: One other problem might be the filter- could it handle the SP without blowing out? It might be ok since the CFM would still be low like a shopvac (100 - 200 CFM). If the intake were blocked even semi-rigid hose might collapse with that much SP.

I guess I'll keep thinking and researching this.

[Dan Friedrichs]

You need more than 100"? :)

Thinking about the design of a universal motor, I'm trying to think of which part makes that loud noise. I wonder if the majority of the noise comes from loads on the motor (blowers, cooling fans) rather than the rotor itself spinning. To that end, I'm not sure I believe that a geared up induction motor spinning the same blower at the same speed would be much quieter...

[Alan Schaffter]

You need more than 100"? :)

Thinking about the design of a universal motor, I'm trying to think of which part makes that loud noise. I wonder if the majority of the noise comes from loads on the motor (blowers, cooling fans) rather than the rotor itself spinning. To that end, I'm not sure I believe that a geared up induction motor spinning the same blower at the same speed would be much quieter...

Probably a little of both, but look at the noise a router makes!! No blower there and just a small cooling fan.

[Van Huskey]

Alan, I applaud your inventor mind but I have been thinking about this for an hour or so and keep coming back to it being an answer to a question no body else ask. Shop vacs perform well, very well at their task and the biggest issue I ever had with them is noise, Fein for example has done a great job at making that tolerable and if one were willing to give up some of the form factor (which you would have to to use an induction motor) I would think you could quiet even a universal motor down to a whisper. For my next shop I am taking a page from your shop and adding a dose of the Dust Cobra. I am planning to run two large shop vacs in parallel with a separator and hard pipe it through the shop. The dust viper (as I like to refer to it) will be housed in a room along with my DC, it will have electrical outlets throughout the shop that turn it on automatically.

I suppose the Dust Cobra is the closest thing to what you have in mind though it isn't exactly highly portable.

[Alan Schaffter]

Alan, I applaud your inventor mind but I have been thinking about this for an hour or so and keep coming back to it being an answer to a question no body else ask. Shop vacs perform well, very well at their task and the biggest issue I ever had with them is noise, Fein for example has done a great job at making that tolerable and if one were willing to give up some of the form factor (which you would have to to use an induction motor) I would think you could quiet even a universal motor down to a whisper. For my next shop I am taking a page from your shop and adding a dose of the Dust Cobra. I am planning to run two large shop vacs in parallel with a separator and hard pipe it through the shop. The dust viper (as I like to refer to it) will be housed in a room along with my DC, it will have electrical outlets throughout the shop that turn it on automatically.

I suppose the Dust Cobra is the closest thing to what you have in mind though it isn't exactly highly portable.

Maybe what I am looking for is a fixed vac connected like I have already done in my shop (plumbed like a whole house vac), but one that is much quieter and more powerful (150"+?), and has a motor that will never need new brushes and whose bearings will last more like those in an induction motor, not like those in a typical shopvac. I aleady have too many projects, so this pretty low on my list.

[Jason Roehl]

I bet a lot of the noise is from the (cheap) bearings. New, present-day shopvacs aren't all that loud out of the box, but if you let a little water and/or dust into those bearings, they get louder and louder and louder... On a $100 shopvac, there can't be much more than a dollar or two in the build budget for bearings, when a quality bearing of a similar size could be $25 and up.

[Greg R Bradley]

Typical shopvacs are noisy because they are made by companies trying to make something that looks good on a spec sheet and make it for next to nothing so they can sell it to you at a low price and still make a big profit. Trying to keep manufactured cost at $10 and sell it to us for $50-100 means they have to make junk.

If you look at the quality made stuff, it is usually powerful and quiet. They usually have bypass systems so the dirt doesn't get near the bearings. I have one Fein that is 15 years old and still works perfectly - and very quiet. If you want a shop vac that is more powerful than that, others make them. I have a Jamco that has two cords so that you can run it off two separate 15a circuits and run it with only one or both motors running. They don't build it to use 240v so that you can take it somewhere that has normal outlets. With both running, it will require care since it will pull blood out through your skin and give you a nasty hematoma.

[Jim Neeley]

Alan,

Van is dead-on with the Oneida Dust Cobra.. http://store.oneida-air.com/dustcobra-2.aspx Priced at $700 - $1,000, it's specs read like:

Designed for portable tools with dust ports 2.5" or smaller
• Ideal for: panel saws, routers, dremel tools, carving tools, scroll saws, band saws, mini-lathes, chop and miter saws
• 3x the air performance of most shop vacs - 90" w/c, 260cfm (std. shop vacs 70 cfm)
• Amazing high efficiency cyclone - 99.9% separation before the filter, filter won't clog
• HEPA filtration - 99.97% @ 0.3 microns
• Highly portable - 52 lbs.
• No Filter Bags!

Though they don't explicitly say it's an induction, their PDF's reference to avoiding excessive starts and stops is a give-away.....

[Norman Hitt]

Two different animals. Shopvacs have a totally different fan design. I'm not talking about a DC with its high CFM/low static pressure, material handling blower which requires large ducting. I'm talking about a shopvac with LOTS of static pressure that will really pull through 2" hose. Typical DC's work at 8" - 12" of static pressure, while a good shopvac like a Fein or Festool suck nearly 100" !!! That's what I want, except one with even greater static pressure, but much quieter.



Not sure if they spin as fast as a router, but shop vac impellers spin fast since they use universal motors like a router. I'm not sure, but the RPM might need to be limited so the impeller tip speed does not go supersonic and lose effectiveness- that is a limitation with airplane propellers which are airfoils. That problem may be limited to airfoil impellers. The bigger the impeller the more difficult it is to balance. Maybe a multi-stage turbine fan would work- but that might make "jet engine noise" :eek: :eek: One other problem might be the filter- could it handle the SP without blowing out? It might be ok since the CFM would still be low like a shopvac (100 - 200 CFM). If the intake were blocked even semi-rigid hose might collapse with that much SP.

I guess I'll keep thinking and researching this.

One possibility on a larger diameter fan/impeller to keep the SP in the desired range, might be to block off all the vanes except the same number that are on the smaller diameter vacs built now, BUT, this "might possibly" create an internal turbulence and affect the effeciency of the impeller, depending on it's design. Possibly a better way would be to have the outlets of those excess vanes be directed to a different outlet ring near the center of the impeller and exit by being spread out through a larger exit ring/shroud like the High Bypass fan engines on current Jets where the air exits through a large shroud around the thrust exhaust at a much slower speed than the thrust exhaust which gives the insulating cushion between the high speed thrust stream and the zero to relatively low speed air the engine is moving through. This air could possibly be used to cool the motor and/or attenuate the noise level of the vac's exhaust, IF the shroud surrounded the exhaust exit. What you think? (I'm Crazy, huh)?:D

[Alan Schaffter]

Alan,

Van is dead-on with the Oneida Dust Cobra.. http://store.oneida-air.com/dustcobra-2.aspx Priced at $700 - $1,000, it's specs read like:

Designed for portable tools with dust ports 2.5" or smaller
• Ideal for: panel saws, routers, dremel tools, carving tools, scroll saws, band saws, mini-lathes, chop and miter saws
• 3x the air performance of most shop vacs - 90" w/c, 260cfm (std. shop vacs 70 cfm)
• Amazing high efficiency cyclone - 99.9% separation before the filter, filter won't clog
• HEPA filtration - 99.97% @ 0.3 microns
• Highly portable - 52 lbs.
• No Filter Bags!

Though they don't explicitly say it's an induction, their PDF's reference to avoiding excessive starts and stops is a give-away.....

Now don't all you Oneida lovers attack me again, I'm just quoting manufacturers numbers-

Lets compare apples to apples.

The Fein Turbo III has less CFM- 126 (but that is not very important to a ROS, router, etc. anyway) but has higher SP (100 " or 105" depending on where your read) than the Cobra, and which IS important in small tool applications. The Fein is much smaller and costs about half what a Cobra does. I'm too lazy to check, but I think the Festool is rated similar to the Fein.

So why not buy a "real" DC for DC applications (where much higher CFM than the Cobra can pull is a must), leave the small tool dust collection chores to a real shopvac, and save about $500 or spend the extra on more tools.

[Rod Sheridan]

Hi Jim, it looks like there are 2 models;

- the standard vacuum motor model $690

- brushless industrial motor $926

Regards, Rod.

[Noah Katz]

Most vac motors turn between 22k and 28k rpm.

I think the high pitched noise of universal motors is the brushes riding over the segmented commutators.

I also once thought about an induction motor for less noise, but quieting the fan noise will quiet the motor too.

[Van Huskey]

Now don't all you Oneida lovers attack me again, I'm just quoting manufacturers numbers-

Lets compare apples to apples.

The Fein Turbo III has less CFM- 126 (but that is not very important to a ROS, router, etc. anyway) but has higher SP (100 " or 105" depending on where your read) than the Cobra, and which IS important in small tool applications. The Fein is much smaller and costs about half what a Cobra does. I'm too lazy to check, but I think the Festool is rated similar to the Fein.

So why not buy a "real" DC for DC applications (where much higher CFM than the Cobra can pull is a must), leave the small tool dust collection chores to a real shopvac, and save about $500 or spend the extra on more tools.

All I can say is you have to use a Dust Cobra to see its advantages. The thing does exactly what I want but I am going to see what I can do with the parallel system I mentioned before I spend the money on it. In my estimation it works very well with small tool extraction, as well as my Fein or the Festools (have not used the new Festools). I often get caught up in paper numbers as well but especially with anything as complex as fluid dynamics distilling it down to a couple of numbers is almost always folly. In short it is expensive but it works though I do hope to approximate it for a significantly lower cost.

I can see an induction motored "shop vac" being useful, but it will be a niche product in a niche industry which there is nothing wrong with.

[Phil Thien]

Does anyone have a Cobra? I'm wondering what kind of motor powers that thing.