On Wed, 5 Dec 2012 09:46:12 -0800 (PST), "
wrote:

On Dec 5, 10:15*am, "Michael A. Terrell"
wrote:
Leon wrote:

10+ years ago before the SawStop was in production I questioned Gass
about this. *My TS accident happened after I finished a cut and had
turned the saw off. *The blade was coasting down to a stop when I was
cut. *I wanted to know back then it those bases were covered also.

* *A modification can be made to table saws with induction or split
phase motors. *You change the power switch from SPST to SPDT, add a
diode & electrolytic capacitor that charges when the motor is running.
When you switch the motor off, the capacitor discharges through the
motor, causing a rapid braking effect. *This can't be done with
universal motors, since they will run on DC.


Even if this could work, it would have to be one hell
of a huge cap to hold enough energy to stop a spinning motor
and saw blade in the time to prevent injury. The cap might
be bigger than the saw. And I have my
doubts about it working at all, ie simply feeding DC into an
AC motor that has lost power being effective at braking.

It does work. You're not trying to turn the rotor backwards, just
stop it. The DC source isn't even needed, just short the thing. This
is how dynamic braking is done in diesel-electric trains, and such,
though hey use resistor banks to change the braking characteristics.

But beyond that, why on earth would you? The energy
that it would take to keep the SawStop system active for
a minute during spin-down following loss of power has
to be tiny compared to what it would take for the electric
motor braking approach.

Firing the SawStop mechanism is a one-shot event. After you clean
your shorts, you get to replace the mechanism and the blade. Dynamic
braking is a freebie and can be done every power cycle.