Hook vacuum to a dimmer switch?

Using a dimmer switch on most any AC motor or transformer will
eventually burn it out. It may start an electrical fire--don't do
it.

Thanks all,

You confirmed my suspicions. In my simplistic thinking, I was thinking
the motor would overheat because it was engineered to run at specified
fix speed, slowing it down would cause overheating and then a cascade
of bad events afterword.

I don't think it's a univeral motor? I'll check the specs. If not I
guess I'll be building that vac box sooner rather than later.

Thanks for advice

-Kevin

Kevin-

I'm not familiar with the FEIN, but all 9 vacuums (2 Craftsman, 4 Shop-Vac,
3 Kenmore) in our house have universal, not induction, motors, and control
quite nicely with SCR speed controls (essentially lamp dimmers).

Universal motors have brushes and can run on either DC or AC. Most
hand-held power tools (drill motors, routers, etc), vacuums, and even
portable planers and cheaper table saws use universal motors because they
can provide high speed and power in a small package. To control them I use
a couple of $20 speed controllers, like Harbor Fright has at:
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=43060

In my larger Craftsman vac I built in an SCR speed controller. Unless I'm
cleaning up a big mess, I usually cut down the speed a bit so I don't feel I
need to don my hearing protectors. The vac does lose power when you slow it
down significantly, but often it's still enough.

Actual "lamp dimmers" might not do the job, because motors are inductive
loads and the SCRs in the dimmers have trouble shutting off (to slow speed)
unless a couple of extra components are used in the dimmer. You'd have to
try it, if you have one lying around. Otherwise, I'd think HomeDespot, etc,
might have a controller like the HarborFright unit in their tool dept.

Reminder - this is only if your FEIN has a "universal" motor. Induction
motors, like in most table saws, jointers, drill presses, furnace fans, etc,
do NOT control well with such controllers.

-Dave

Kevin -

Unless that's a DC motor, and it is *way* unlikely, I don't think your
solution will work. AC motors are fixed speed. Lowering the voltage with a
dimmer will increase the amp draw to provide the proper amount of power to
the motor and putting a dimmer on it would be very similar to making it run
during a "brownout". The motor would overheat.

Others here have FAR more EE experience, and I'm sure they will weigh in. I
wouldn't mind having a "variable speed" for my shop vac either. The sticker
on the vac says it has more than TWICE the power of my 3 HP tablesaw and I'm
STILL trying to figure out how they do that on 110V. Those engineers at
Craftsman, is there NOTHING they can't do?

How about buying a longer hose and putting on the far end o' the shop?

HTH,

John Moorhead
Lakeport CA

"Dave Plumpe" wrote

Snip of some outstanding information ...

> ... Induction
> motors, like in most table saws, jointers, drill presses, furnace fans,
etc,
> do NOT control well with such controllers.
>
> -Dave


If you DO need to control the speed of a single phase induction motor, you
can start here: http://www.anaconsystems.com/text/eagle1.html ... but note
these VFDs (Variable Frequency Drives) are NOT inexpensive.

Found this by a google search (single phase induction motor speed control).

If you want to roll your own, here's a great start:
http://www.cae.wisc.edu/~ece734/project/f00/yaorpt.pdf

and another at
http://gdansk.bradley.edu/iecon02/limited/cdrom_backup/html/pdf/SF-003115.pdf

HTH

Rick

On Tue, 06 Jan 2004 18:21:25 -0800, Kevin wrote:

> Hi all,
>
> Would it be safe to run a FEIN vac (the small one 920watts) off a
> dimmer switch so I can further quiet it down when I'm working in
> stealth mode (3 month old and 3 year old sleeping upstairs). I will
> be building a vac box in the future, but the dimmer would be a $3
> quick solution for now.
>
> I don't want to screw up the motor via trial and error, so am asking
> anyone's thoughts before I do this. Thanks.
>
> -Kevin
>
> I have a MIELE housevac and sure wish they made a shop vac.


Not a wise move. Even if you were able to slow down the motor, the
suction would change.

If the noise bothers you, get ear protection, just one alternative to
replacing an expensive vacuum.

Kevin-

Dave's response is the best one posted so far.
I have yet to see a shop vac with a motor other than a universal
one.

I just went out in the garage and tried both my shop vac and
an upright vac with:
1. Router speed control - worked fine.
2. X10 lamp dimmer module - worked fine.
3. Wall plate light dimmer switch - worked fine.

I see no problem with using any of the above with a shop vac.
The slower speed does reduce the noise and suction of the
vac. It also slows the airflow over/thru the motor but it also
reduces the power into the motor so there shouldn't be any
problem with overheating.

The only negative I see is that it appears that the suction falls
off faster than the noise level does as the speed drops (I
have no quantitative data here, just my ears and hands). So
to get to the noise level you want, you may find that the suction
is too weak to be of any use.

Art

"Dave Plumpe" <[email protected]> wrote in message
news:[email protected]...
> Kevin-
>
> I'm not familiar with the FEIN, but all 9 vacuums (2 Craftsman, 4 Shop-Vac,
> 3 Kenmore) in our house have universal, not induction, motors, and control
> quite nicely with SCR speed controls (essentially lamp dimmers).
>
> Universal motors have brushes and can run on either DC or AC. Most
> hand-held power tools (drill motors, routers, etc), vacuums, and even
> portable planers and cheaper table saws use universal motors because they
> can provide high speed and power in a small package. To control them I use
> a couple of $20 speed controllers, like Harbor Fright has at:
> http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=43060
>
> In my larger Craftsman vac I built in an SCR speed controller. Unless I'm
> cleaning up a big mess, I usually cut down the speed a bit so I don't feel I
> need to don my hearing protectors. The vac does lose power when you slow it
> down significantly, but often it's still enough.
>
> Actual "lamp dimmers" might not do the job, because motors are inductive
> loads and the SCRs in the dimmers have trouble shutting off (to slow speed)
> unless a couple of extra components are used in the dimmer. You'd have to
> try it, if you have one lying around. Otherwise, I'd think HomeDespot, etc,
> might have a controller like the HarborFright unit in their tool dept.
>
> Reminder - this is only if your FEIN has a "universal" motor. Induction
> motors, like in most table saws, jointers, drill presses, furnace fans, etc,
> do NOT control well with such controllers.
>
> -Dave
>
>

On 6 Jan 2004 18:21:25 -0800, [email protected] (Kevin) wrote:


>I don't want to screw up the motor via trial and error, so am asking
>anyone's thoughts before I do this. Thanks.

I wouldn't do it. Dimmers are not meant for motors, and Feins are
expensive.

Alternatives? Scrape instead of sanding. Sweep instead of vacuuming.

Barry