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.

Any ideas?

Thanks,
Bob

One thing to keep in mind is that the current draw of a centrifugal
blower will usually go down as its output is restricted. The current
is more closely related to the airflow than to the back pressure. So
it's not surprising that you saw an increase in current when you
removed all the restrictions.

--
Ned Simmons