>
>
>         That is actually the way one can apply an electronic
> break to an AC motor if one needs to stop one quickly.
>
>        There is a man who has invented a quick stop device to
> stop a table saw blade when it contacts something it shouldn't
> like your fingers. He says it puts a quick pulse of DC on the
> motor and then kills the power to it.
>
> That method wouldn't work fast enough, even with a massive DC pulse.
The youtube demo of  'saw stop' shows that it uses a mechanical claw to
block
the blade instantly. DC method would allow the blade to rotate enough to do
damage (back EMF only works with MOTION).

http://www.youtube.com/watch?v=3DcTUOhYcw4ZY
jump to 1:40 to see how it works, and why the claw has to be replaced every
trigger.
Small price to pay to not lose part of a hand to a blade, but not
inexpensive.
--=20
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