On Mon, 2012-02-27 at 19:31 +0000, Alan wrote: > Thanks for the information. To be honest I thought the 3phase motor > would be better than the dc one. > > I have a small chinese mill and I toasted either the motor or its > controller by pushing the mill beyond its limits. The motor got very hot > and suddenly the house rcd tripped and kept tripping each time I > switched the mill on. I have taken the motor apart and there are no > superficial signs of any shorting across the windings but need to look > further. Also inspected the controller card and again no blackening or > other superficial signs of shorting. > > I am not an electrical engineer so have come to a temporary stop with > the fault finding. Anyway I gave that up when starting to consider using > a 3phase motor. I had assumed that 3phase would be better and easier to > control with regard to the speed. > > The controller card I have is JYMC 220B I which is varaible up to 170vdc > I think for full speed, and the dc motor is a 600w type 91ZYT005. Both > motor and controller are available but I thought that I would need to > get a new controller anyway if I was going to alter the speed through > emc. I do not know where to get a suitable card thats why I was opting > for 3phase. > > So any help or advice would be much appreciated. > > Alan
Well, the plot thickens. Randomly thinking out loud. It looks like the motor driver is an SCR type speed controller like the KBIC controllers. http://www.wallacecompany.com/machine_shop/kbic/ By the way they are fairly easy for LinuxCNC to control using an opto-isolator and a PDM or PWM signal from the parallel port pin or an FPGA signal generator pin. These controllers have a plug in resistor that needs to match the motor size you have. I'm not sure if having a different resistor would have prevented a failure or not. If the motor didn't smoke or smell really bad, my guess is it should be okay. If it is a permanent magnet motor, you could spin it up, maybe with a drill (be careful not to break a wrist) and see if it generates any voltage. I suspect it is a universal type, which has field coil windings in the housing where the magnets would be. Spinning up the motor would not normally produce voltage unless one powers up the field. Simply applying 12 Volts from a battery or power supply should turn the motor if it's okay. Most motors have a crude thermal circuit breaker embedded somewhere: http://gearmotorblog.wordpress.com/2009/09/21/thermal-overload-protectors/ The breaker should restore the circuit when the motor cools down, but some of these are so badly made they only work once. It might be worth checking. If the motor checks out okay, the speed controller may be the problem. They don't take to having the output switched, so if the motor's thermal cutout trips, the controller could be damaged. I'd first check the fuses on the controller. I think there are two, one for the mains input and one for the motor output. Then power it up and see if it puts out any voltage. There may be separate Field terminals that could be checked too. If this is a relabeled KBIC, I think you can download a manual, maybe: http://www.kbelectronics.com/manuals/kbic_manual.pdf With your RCD tripping, if it's like our GFCI, it's indicating there is a short to ground somewhere. You should probably use a meter to check various parts to see if they are shorted to ground, but this takes some electronics knowledge. Another method might be, and it's not really recommended, is to disconnect your speed controller and motor and power up your CNC and see if the RCD trips again. If not, power down, reconnect the controller, but not the motor, power up and check the RCD. If it doesn't trip, power down, reconnect the motor and try again. Now, even if you get everything working again, your problem may just come right back. You can add a system to better shut down the motor before damage is done, or you can upgrade to a bigger motor and driver. Considering DC motors are getting harder to find and more expensive. I may have to say that if one is going to need both a new motor and driver, a three phase motor and VFD would be easier to find, afford and integrate. I've had trouble with my VFD and low end torque with my slower turning heavy lathe spindle and chuck, but my mill has no trouble. Now, I haven't taken the time to tune my lathe VFD, so I may have a solution there. If you decide to go with a three phase motor and VFD, don't throw away your DC motor and speed controller, even broken, they have value. So I may have typed myself back to your original question about VFD's and remote control. I'd say it depends on the VFD. Typically, a VFD will have a set of terminals that are meant to be connected to a pair of switches and a potentiometer. One switch for Run, another for direction and the pot for speed. LinuxCNC can control these or you can switch between LinuxCNC and a switch panel. Newer VFD's feature a serial connection to pass command data to and from LinuxCNC or a remote terminal. Your options there depend on the VFD. Typically there is a setting made from the VFD's control panel that sets where the run, direction and speed commands come from, such as the panel itself, the switch/pot terminals, or the serial port, or some combination. If you want to switch modes, you'll need to use the control panel to bring up the proper register and make the selection. Sometimes this can also be done through the serial port. Any way that's what I can think of so far. Sorry to others on the list, for taking up so much bandwidth lately, but it's warmer in front of the keyboard than outside. -- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/index.html California, USA ------------------------------------------------------------------------------ Try before you buy = See our experts in action! The most comprehensive online learning library for Microsoft developers is just $99.99! Visual Studio, SharePoint, SQL - plus HTML5, CSS3, MVC3, Metro Style Apps, more. Free future releases when you subscribe now! http://p.sf.net/sfu/learndevnow-dev2 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
