Thanks to everyone who has given advice on this thread. I've learned a heck of a lot about older drives.
I'm not going to attempt to repair, I'm just going to pull all three drives and replace with something a little more modern - which will probably double the space I have in that cabinet. > From: Jon Elson [mailto:el...@pico-systems.com] > On 03/05/2017 07:38 AM, Ben Potter wrote: > > Interesting - I have to admit I'm still a little bit confused as to > > how these drives work, running 360V AC to the chokes and somehow > > turning that into 140V DC seems... odd. > Well, does it run off 3 Phase power? If not, then it gets hard to drive motors > with any constant torque or speed. Single phase. Well, 180-0-180 on a autotransformer. > Phase angle control from a 3-phase source takes 6 SCRs, and due to the > overlapping waveforms of the 3-phase mains, can give fairly steady power to > the motor. Still, the servo bandwidth will be pretty low. > > With single-phase power, the bandwidth will be really low to avoid the 120 Hz > pulsing from driving everything crazy. Your 120 Hz remark has just made it click in my head. The drive works by controlling the phase offset at which the thyristors trigger - which will control the voltage present when they fire. Typically I'm guessing they should fire 180 degrees out of phase to one another. That was probably obvious to everyone else as soon as I said thyristor - but it took a bit of getting my head around. I'm more used to thinking about MOSFET drives with switching frequencies in the kHz range. > > it seems a bit odd that a signal capacitor caused the failure, but maybe that > fouled up the current control logic to get the SCRs turned on in the wrong > sequence. The cap was part of the opamp feedback driving the control voltage for one phase controller. Assuming it hasn't blown the phase controller completely, that'd be enough to confuse the drive. > > Jon > ------------------------------------------------------------------------------ Announcing the Oxford Dictionaries API! The API offers world-renowned dictionary content that is easy and intuitive to access. Sign up for an account today to start using our lexical data to power your apps and projects. Get started today and enter our developer competition. http://sdm.link/oxford _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
