Novice question about - Re: L298 goes boom

Ok,

I know that one can 'find' the leads to a stepper coil by touching
two and turning the stepper, when you get the right two, it is
harder to turn. no electronical external connectins, just the
stepper leads.

Now, 'if' a voltage/current/emf or whatever is generated when one
disconnects from any external electronical bits, chips or what have
you, then wouldn't it be logical to short the leads before connecting
or dis-connecting ?

and it this really a problem ?

I would think we all know that disconnection while powered, output
going nowhere so it can feedback on itself. Used to have problems
with VSD's in the early days when someone would open a disconnect and
fry the drive. or disconnect when spinning is bad, motor is acting
as a generator and fries the electronical bits. But is there a
dangerious charge when the rotor is fixed ?

Dave

--- In CAD_CAM_EDM_DRO@y..., "tauscnc" <tauscnc@h...> wrote:
> Hey,
> well I don't know enough about electronics or what how EMF works. I
> do know what if I unplug a running fan from my 110V house outlet
> there is a spark due to the difference in current etc. I assume
this
> is the same thing that occurs if a stepper is at idle (still on) or
> running (still on).
>
> I look at it this way, Dan makes the boards, he designes the
boards,
> he knows what he is doing, HE says NOT to disconnect a stepper when
> the power is on (as every other place I have seen), I figure heck
who
> am I to disagree, hes gotta know what he is doing. Besides, why
> chance it, its not that hard to switch off the power.
>
> just my .02
>
> tauseef
>
>
> --- In CAD_CAM_EDM_DRO@y..., "exeric1" <exeric1@y...> wrote:
> > Hoyt,
> > It normally takes a lot to get me stirred up but you managed it.
> > There is easily enough EMF generated when the magnetic field
> > collapses to jump the gap as the contacts are disconnected. This
> > forum is for "helping" people - not generating bad info that will
> be
> > expensive and discouraging to the people on it. May as well not
> have
> > a forum if information like this gets disseminated.
> >
> > Eric
> >
> > --- In CAD_CAM_EDM_DRO@y..., bjammin@i... wrote:
> > > At 10:57 AM 8/4/02 -0400, RichD wrote:
> > > >You are quite wrong. Any inductance carrying current will
> generate
> > large
> > > >voltages when disconnected as the flux field collapses.
> > >
> > > Not back EMF, by definition. Also, it's not able to affect
> drivers,
> > as it
> > > doesn't occur until disconnected from them. BUT, if you take
> power
> > off
> > > steppers when connected, there *will* be a magnetic field
> collapse
> > that
> > > puts voltage on the drivers ... and nobody even you has
cautioned
> us
> > > against that! Therefore, you need to think these things thru a
> bit
> > more
> > > before writing.
> > >
> > > Regards, Hoyt McKagen
> > >
> > >
> > > Anti-virus request: Please do not add this email addy to
address
> > books
> > > Belfab CNC -
http://www.freeyellow.com/members/belfab/belfab.html
> > > US Best MC -
> http://www.freeyellow.com/members/batwings/best.html
> > > Camping/Caving -
> > http://www.freeyellow.com/members/batwings/caving.html
> > > Hac ahac que haec, hoc, hoc, patui