On 12 May 2013 02:45, Gene Heskett <[email protected]> wrote: > Greetings all; > > As I install the motor on my mini-lathe, it occurs to me that if I do a set > of ice cube relays driven by those toys on the C41 board, it strikes me > that with that huge flywheel fan combo, even an e-stop will coast several > revolutions of the spindle. > > When I did the PMDX-106 for the mill, I used 2 relays, one to switch > between the output of the controller with its DPDT poles, the back side of > which dropped a 10 ohm 20 watt resistor across the motor to make use of its > generating ability as a means of stopping it fairly rapidly. As in 2500 > revs to zero in just a hair over 1 second. The 2nd relay was used in the > usual DPDT reversing circuit. > > There isn't that much inertia in that setup, but this will have a cast iron > fan cum flywheel that weighs a good 2 pounds to stop. So a 10 ohm 20 > watter, taking the dump from 7000 rpm, is likely to be considerably hotter > than bright red internally by the time its down to 100 rpms as that will > translate to about a kilowatt of stored energy. > > 20 ohms won't have to take quite as much of a rapid thermal shock, but the > wattage will be similar, so I don't see any way to make it work that > doesn't involve a panel of at least 8 similar resistors. > > Unless someone else has a better idea? How about I find some sockets for > the 500 watt halogen lamp sticks & use 2 of them in series? > > Basically anything I can make off the local walmart shelves (for under 50 > bucks that is). > > Cheers, Gene >
One option is to just remove the flywheel. I've taken many of them off, some can be difficult though. I have also done the resistor trick, but found the value was quite different to what I had in mind. The generated voltage is a lot lower than the input power. On the resistor, find an old hair-dryer, or visit the local dump for one. Crack it open and now you can tap the filament wire at any point to find the ideal resistance. Very unlikely to burn out. Alternatively, visit a heater-element shop and buy a few metres of Ni-Chrome wire, the highest resistance/m (15R ?) and make up a simple resistor. I would just go with a horizontally supported air-core, mounted in an old, punched PSU case. Regards Roland ------------------------------------------------------------------------------ Learn Graph Databases - Download FREE O'Reilly Book "Graph Databases" is the definitive new guide to graph databases and their applications. This 200-page book is written by three acclaimed leaders in the field. The early access version is available now. Download your free book today! http://p.sf.net/sfu/neotech_d2d_may _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
