Re: [CAD_CAM_EDM_DRO] Re: L298 goes boom

Taus,
One little bit more.
Those big super high speed diodes that Dan specifies and is very
explicit about insertion direction, have you checked them?
Best done with the L298 out and motors pulled off.
These diodes are the protection to snuff (limit) back EMF and
"accidental" disconnects that produce high voltages, but they are not
absolutely guaranteed to save you everytime you abuse the rules.
Any baddies or mistakes here will destroy drivers everytime.
I have never lost an L298 without also having to change the L297.
RichD

tauscnc 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
>
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