CAD CAM EDM DRO - Yahoo Group Archive

Re:low cost stepper driver

on 2012-10-03 04:36:09 UTC
very well laid out for the layman. Thanks.

but are we chasing unicorns ?

how often do people remove motors from operating units ?

When one is using old steppers from old printers, the cost is insignificant for the motor, and then if the table top etcher is cutting something simple like foam or wax, the needed power is small.

but, it boils down to a question of how often ? it took mariss a couple years before he offered a self protecting unit.

Dave



--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Tony Smith" <ajsmith1968@...> wrote:
>
> > This is what I was wondering. I appreciate that you get a back-EMF spike
> when
> > it's disconnected, but it's *DISCONNECTED* - it's not the driver
> transistor
> > switching off so it shouldn't reach the driver. But intermittent
> connections (or a
> > spark that jumps the gap, as Tony suggested) is possibly the reason.
> >
> > I note that some good quality drivers have tranzorbs which can presumably
> > absorb more energy than the internal diodes (and also don't dump it into
> the
> > power supply).
>
>
> You get back-EMF when the coil stops being energized, unplugging the motor
> is just one way of doing that.
>
> Think of the coil as a spring; you push down on it (apply power), the spring
> resists somewhat (inductance), when you let it go it'll spring back at you
> (back EMF) at high speed (high voltage).
>
> The classic circuit is a relay activated by a transistor. Your
> microprocessor or parallel port provides a small signal that switches the
> transistor on, and current flows through it to the coil.
>
> When you turn the transistor off, the coil is still charged. That power
> needs to go somewhere.
>
> As said the magnetic field promptly collapses and generates a current in the
> wire. This has two properties that interest us; one is the polarity is
> reversed, and the other is the voltage is much higher than we used to charge
> it.
>
> Transistors don't like power going backwards across them (reverse bias) so
> that can cause damage, but it's the high voltage that causes more hassles.
> The high voltage can cause arcing in the transistor itself, causing damage
> that may not show until months later. Worse it can escape, travelling down
> the path to your uC or port. The high voltage can damage or disrupt that.
> Optocouplers have a gap the high voltage can't jump, that's how they save
> your parallel port.
>
> The diode placed across the relay coil the only allows power to flow in one
> direction, so when the back EMF is generated the diode absorbs it.
>
> Years ago a local firm had up some alarm boards made for me, nice boards but
> they didn't work properly. Yep, they left the diode off the relay, and
> that'd cause the uC to glitch.
>
> For unipolar steppers (6 or 8 wire) their driver boards are (at a basic
> level) no more complicated than driving a relay. You have 4 coils, and you
> turn them on and off. Across each coil you place a diode for protection.
> Indeed you can make a driver with nothing more than 4 transistors, not
> recommended though.
>
> Bipolar steppers get more complicated as you need to reverse the voltage
> across the coils, so now the diode trick doesn't work. Back EMF causing a
> problem with reversed polarity isn't that much of a problem as the drivers
> expect that. H-bridge circuits do have diodes, but across the transistors
> rather than the coil to deal with that. If you read up on those you can see
> how the protection works.
>
> So long as the motor remains connected the driver can deal with the back
> EMF, however if you disconnect it then you may create the spike when the
> driver isn't ready for it, and that can damage it.
>
> Transorbs are like diodes that allow current in both directions, but they
> clamp the high voltage spikes. They cost money, and are only useful in very
> few circumstances (the oops! ones) so are left off the board. Well, the
> boards we're talking about anyway.
>
> Don't forget the other half of wire damage is short circuits, but that's
> another story.
>
> Some drivers are smart enough to monitor the current, notice when something
> goes wrong and protect themselves.
>
> Tony
>

Discussion Thread

turbulatordude 2012-06-25 17:51:22 UTC low cost stepper driver Ron Thompson 2012-06-26 04:33:51 UTC Re: [CAD_CAM_EDM_DRO] low cost stepper driver Jamie Cunningham 2012-06-26 04:55:38 UTC Re: [CAD_CAM_EDM_DRO] low cost stepper driver Tony Smith 2012-06-26 06:06:24 UTC RE: [CAD_CAM_EDM_DRO] low cost stepper driver Ron Thompson 2012-06-26 06:53:07 UTC Re: [CAD_CAM_EDM_DRO] low cost stepper driver Tony Smith 2012-06-26 07:16:46 UTC RE: [CAD_CAM_EDM_DRO] low cost stepper driver Dan Mauch 2012-06-26 07:43:39 UTC RE: [CAD_CAM_EDM_DRO] low cost stepper driver jeffalanp 2012-06-26 11:54:37 UTC Re: low cost stepper driver Nelson Collar 2012-06-26 12:58:22 UTC Re: [CAD_CAM_EDM_DRO] Re: low cost stepper driver Dr Stuart Harrison 2012-06-26 15:00:53 UTC RE: [CAD_CAM_EDM_DRO] low cost stepper driver jeffalanp 2012-06-26 16:38:30 UTC Re: low cost stepper driver Nelson Collar 2012-06-26 18:18:08 UTC Re: [CAD_CAM_EDM_DRO] Re: low cost stepper driver jeffalanp 2012-06-27 11:50:50 UTC Re: low cost stepper driver David G. LeVine 2012-06-27 17:33:58 UTC Re: [CAD_CAM_EDM_DRO] Re: low cost stepper driver John Dammeyer 2012-06-28 17:35:07 UTC RE: [CAD_CAM_EDM_DRO] Re: low cost stepper driver Lester Caine 2012-06-30 06:45:37 UTC RE: [CAD_CAM_EDM_DRO] low cost stepper driver John Dammeyer 2012-06-30 06:50:12 UTC RE: [CAD_CAM_EDM_DRO] Re: low cost stepper driver artgartg 2012-09-30 19:44:58 UTC Re: low cost stepper driver Ron Ginger 2012-10-01 04:23:09 UTC Re:low cost stepper driver turbulatordude 2012-10-01 04:41:13 UTC Re:low cost stepper driver Jamie Cunningham 2012-10-01 05:01:05 UTC Re: [CAD_CAM_EDM_DRO] Re:low cost stepper driver rwwink 2012-10-01 06:13:45 UTC RE: [CAD_CAM_EDM_DRO] Re:low cost stepper driver Jeffrey Birt 2012-10-01 06:49:39 UTC RE: [CAD_CAM_EDM_DRO] Re:low cost stepper driver John Dammeyer 2012-10-01 08:34:28 UTC RE: [CAD_CAM_EDM_DRO] Re:low cost stepper driver David G. LeVine 2012-10-01 12:22:27 UTC Re: [CAD_CAM_EDM_DRO] Re:low cost stepper driver Tony Smith 2012-10-01 13:15:24 UTC RE: [CAD_CAM_EDM_DRO] Re:low cost stepper driver Ron Thompson 2012-10-01 13:59:56 UTC Re: [CAD_CAM_EDM_DRO] Re:low cost stepper driver turbulatordude 2012-10-01 16:57:37 UTC Re:low cost stepper driver Dr Stuart Harrison 2012-10-01 20:27:49 UTC RE: [CAD_CAM_EDM_DRO] Re:low cost stepper driver Tony Smith 2012-10-01 22:51:44 UTC RE: [CAD_CAM_EDM_DRO] Re:low cost stepper driver Lester Caine 2012-10-02 00:23:21 UTC Re: ***SPAM*** [CAD_CAM_EDM_DRO] Re:low cost stepper driver wotisname 2012-10-02 04:20:51 UTC Re:low cost stepper driver artgartg 2012-10-02 12:10:13 UTC Re:low cost stepper driver artgartg 2012-10-02 12:10:41 UTC Re:low cost stepper driver artgartg 2012-10-02 12:10:56 UTC Re:low cost stepper driver Joe 2012-10-02 12:11:27 UTC Re:low cost stepper driver Stephen Muscato 2012-10-02 12:31:11 UTC Re: [CAD_CAM_EDM_DRO] Re:low cost stepper driver John Dammeyer 2012-10-02 22:15:21 UTC RE: [CAD_CAM_EDM_DRO] Re:low cost stepper driver Tony Smith 2012-10-03 02:46:10 UTC RE: [CAD_CAM_EDM_DRO] Re:low cost stepper driver turbulatordude 2012-10-03 04:36:09 UTC Re:low cost stepper driver Tony Smith 2012-10-03 08:31:49 UTC RE: [CAD_CAM_EDM_DRO] Re:low cost stepper driver