On Sat, 8 Dec 2012 06:19:30 -0800 (PST), "
wrote:

On Dec 7, 12:26*pm, wrote:
On Fri, 07 Dec 2012 08:13:24 -0600, Leon lcb11211@swbelldotnet
wrote:





On 12/7/2012 7:56 AM, wrote:
On Fri, 7 Dec 2012 05:29:58 -0800 (PST), "
wrote:

On Dec 6, 5:18 pm, "Michael A. Terrell"
wrote:
" wrote:

On Dec 6, 11:41 am, "Michael A. Terrell"
wrote:
" wrote:

On Dec 5, 2:50 pm, "Michael A. Terrell"
wrote:
" wrote:

You do realize that turning off the saw via the switch is
very different from a power failure, right? *Using the
switch there is still power available to the protection
circuitry. *During a power failure there is not.

* * A relay with it's coil across the power line when the switch is on
will stop it, if the power fails. *Or configure it with the common
on/off power buttons as a simple motor controller.

It will stop it in 1 ms? * Or at least close enough to instantly
to avoid injury, eh? * You sure about that? *You should go tell
the SawStop guy what a simple, practical new invention you
have. * I say, it just doesn't work.

* * No one claimed that it did, and you just want to whine.

Excuse me, but try to follow the thread. *The discussion was
about the SawStop and what happens if power is lost. *The
claim was made that it still would work. *Then someone claimed
that you could just short the motor and use electromagnetic
braking in case of power loss. * The SawStop halts the saw in
1 ms.

* * Excuse yourself. *It doesn't do that when the power fails, and you're
in the dark with a stil spinning blade. *It's you that can't comprehend
what is happening in this thread. I introduced the magnetic braking to
stop the blade faster when the motor is turned off. *I also told how to
do it in the case of a power failure. It's not my fault that your mother
used to let you play with plastic bags over your head, which caused all
that brain damage.- Hide quoted text -

- Show quoted text -

Let's go back to your first post on this:

Leon:
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.

Michael:
* *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.

In the first sentence of the post you replied to, Leon said "I
questioned Gass about this." * The "this" he was referring to
was the issue if the SawStop still worked in the event of a power
fail. * So, that was the context. *And in posts before that, others
had suggested adding a cap to the SawStop so that it would
work when power was lost.

However, Leon's problem came in the spin-down which wouldn't
necessarily require the SS hardware. *Leon wanted to know if they'd
covered this case. *Michael was noting that this problem could have
been corrected, cheaply, without the expensive SS hardware and without
blowing a SS cartridge and blade when it occurred.

So, you replied about using electromagnetic braking. * Sorry,
but in that context, it sure appeared that you were talking about
adding that in addition to the SawStop, so that it would stop
it in a similar fashion if the power failed. * Or at the very least,
that you were suggesting electromagnetic approach as a safety
device for protection to replace the SawStop.

Replace? *I didn't get that. *In addition, sure.

So, instead of hurling insults, perhaps you should learn
to write less ambiguously.

It was perfectly clear to me. *I understand the issues involved,
though.

Lol to clear this up. *I had turned the saw off. *I had just finished
cutting a dado. *I reached over the blade to remove the fence and my
thumb came in contact with he blade. *No power failure. *The SawStop
would have worked.

Right. *An inexpensive dynamic blade brake would have worked, also.
That's the point I think Michael was making.

That depends on the time between turning off the power and
the saw stopping. And I'm not so sure about the inexpensive
part. I don't buy that all you have to do is disconnect power,
short the leads and the saw stops very quickly. That may
have some effect, but I'd bet to stop it in even a few rotations
requires some external power source.

No, the back-emf of the motor supplies the power for the brake. There
is probably an ideal resistor (impedance matching exercise) to
dissipate the energy optimally. I'm not a power/motor engineer,
though. It works.

If anyone has an spec sheets or examples of saws, motors,
etc with that feature I'd be interested in seeing them.

Have you ever used a miter saw? Same size blade, or larger, so even
more mass to stop, yet they do in a second. Though they tend to be
direct drive rather than belt drive (don't know if that matters).

I contacted SawStop a couple of days ago to learn if the SawStop would
work on a spinning blade if all power was lost. *The answer is that it
would for a second or two until the residual power was absorbed. *After
that if the blade that is cutting wood is still spinning you would be
unprotected.

What does "residual power was absorbed" mean?

I would bet that it means the remaining power in the power
supply circuitry of the SawStop.

Yes, that was explained. Apparently it's just the power left until
the filter caps discharge. Useless.