On Sat, 2008-01-12 at 07:47 +0000, Steve Blackmore wrote: > On Fri, 11 Jan 2008 16:28:14 -0800, you wrote: > > >On Sat, 2008-01-12 at 00:01 +0000, Steve Blackmore wrote: > > > >> I use KBIC speed control on my mill, I simply reverse the DC output > >> using a 20A DP/DT relay. > > > >You don't switch it while the motor is running, do you? The KBIC manual > >says that you will damage the controller by doing that. I have had > >another look at the schematic and I am thinking that if you disconnect > >the armature, you will get a voltage spike high enough to cause SCR1 to > >conduct in reverse. If SCR2 is on, which is likely, you will have a > >direct short between the mains, L1 and L2. > > No - there's a delay set on CW/CCW. > > >I think if inhibit is invoked long enough ( 20ms ?) to insure that both > >SCR's are off, switching the armature will be okay. I just won't know > >for sure until I try it. Which will have to wait until I get the parts > >to fix the controller due to my last experiment. > > It needs to be long enough to ensure there is no output from the KBIC or > back emf generated by the motor under any condition - I use 1 second.
I think the SCR's and diodes are rated for 1kV, so if the back EMF is kept to a couple of hundred Volts, it should be okay, especially if a braking resistor is used. I think a short inhibit should be enough to get through the initial switching spike. > On a mill that should be plenty, on a lathe, however, where there may be > lots of inertia due to a heavy chuck, it may need to be longer. > > >I am playing with ideas on how EMC could be used to enhance what people > >already have. These KBIC controllers seem to be quit popular. > > EMC should already run one fine, if you use an external isolator board. > > Steve Blackmore My vision is to have EMC be able to control the spindle from full forward to stop, or full reverse within a second. Or, at least, well enough to do rigid tapping. -- Kirk Wallace (California, USA http://www.wallacecompany.com/machine_shop/ Hardinge HNC lathe, Bridgeport mill conversion, doing XY now, Zubal lathe conversion pending) ------------------------------------------------------------------------- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
