On Sunday 12 May 2013 09:34:55 Roland Jollivet did opine: > 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. This thing is all one piece machined casting, cooling fan on back, of a 9/16" thick, 6" diameter flywheel with a 6 groove polygroove belt pulley on the front, screws on with a 2 start ccw thread I'll no doubt have to superglue in place to keep it from unscrewing when I brake the motor.
> 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. Oh? I haven't actually checked that, but will. I do see about 88 volts average at the controller output when running wide open. > 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 Thanks Roland. Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> is up! My views <http://www.armchairpatriot.com/What%20Has%20America%20Become.shtml> You can prove anything by mentioning another computer language. :-) -- Larry Wall in <[email protected]> A pen in the hand of this president is far more dangerous than 200 million guns in the hands of law-abiding citizens. ------------------------------------------------------------------------------ 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
