On Sunday 13 December 2015 00:27:50 Jon Elson wrote: > On 12/12/2015 08:32 PM, Gene Heskett wrote: > > As I'd druther not have to listen to those contactors humm & buzz > > when powered by 120 AC, my thoughts are to use that transformer as a > > step down, feeding the nominally (I haven't measured it yet) into a > > bridge, feeding the contactor coils with somewhat filtered DC from > > that, which ought to silence them. > > > > But I suspect that 90 volts (cap input filter) is still way too much > > for those coils over any time period in excess of 2 or 3 minutes. > > > > So, how much more do I need to reduce the coil voltage in order to > > run them at a reasonable temperature on DC? > > This won't work. AC contactors depend on the change in > inductance when the armature slams home into the stator. > So, they pull a lot of current when in the un-energized > position, and then the current drops drastically when > pulled-in. The only way to do this is to have an NC contact > that delivers full current to the coil until it is pulled > in, then opens to put a resistor in series with the coil. > > Jon > That was also addressed in a google finding, but from a different angle, by noting that the DC relay normally had a non-magnetic shim between the poles, maintaining a fixed separation that reduced the possibility of a residual magnetism hang closed when the coil was turned off. Those that I have seen often used a piece of kaptan or similar sheeting, sometimes thin brass shim stock just 2 or 3 thou thick.
I haven't removed one of these from the box yet so I've no clue how difficult that might be with this relay type. Another article I read last night said that coil currents would be similar at an applied voltage in the 34 volt range. Power disappation in the coil is about 1/3rd to 14 what it would be when driven by std line voltage, a definite plus. Whether that would give a solid pullin will have to be determined. Because they are 3 phase, 3PST, I'll use all 3 contacts in series as insurance against one of them becoming momentarily welded on closeing. All this will be done in the AC line input, so its basically an unplug that supplies power cord from the switched strip, plug this box into the empty socket, and plug that supply into a duplex on the output of this box. A 51 ohm 200 watt wirewound bypassed by the second, delayed action contactor, will supply the initial soft current limit. Switch it all with some hal code looking at the 2nd button from the left at the top of the axis screen. Thats tallied by the hal pin motion.motion-enabled IIRC. No clue how much progress I'll make today, I have to clean myself up as we are headed to a motel next to the hospital where Dee will get a cataract removed first thing Monday morning, then we do it all over again for the other eye a week later. So this project might be on hold until later Monday afternoon after my lady is back home & cared for. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Some mill pix are at: Genes Web page <http://geneslinuxbox.net:6309/gene/GO704-pix> ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
