On Tue, 28 Apr 2015 19:51:06 -0400, Bob Engelhardt wrote:

A neighbor has a Festool shop vac, er ... "dust extractor" (at $650, it
wouldn't sell as a "shop vac" G).

It has been shutting itself off due to the motor overheating. It's
spec'ed as using 2.9 - 8.3A (depending upon the speed, I assume). So I
put an ammeter on it and measured 9A, at low speed! Ah-ha, something to
work with. Suspecting a blocked air path was putting an extra load on
it, I first removed the dust bag, then the HEPA filter, and then took
the motor-fan out of the housing. No help: in free air, at low speed it
used 7.4A and at high speed 10A!

The rotor turns easily enough, but doesn't spin when given a push. The
brushes are fine and there is no arcing at the commutator.

So, the only thing that _might_ be an abnormality is the less-than-free
rotor. Could that be the basis for such increased current (7.5 vs 2.9)?
The assembly is not meant to be serviced (they'll sell you a new
motor-fan for $95+). I suppose that I don't have anything to lose by
trying to break it down, but I'd like there to be something else to try.

I'm not sure of the exact mechanism, but on home-style vacuum cleaners
when you block the vacuum line the motor speeds up. I assume this means
the motor is unloaded, and I assume it's because the turbine is suddenly
working in rarefied air.

I'd be interested in hearing truth from one who knows.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com