On Sunday 13 December 2015 05:26:48 Andy Pugh wrote: > > On 13 Dec 2015, at 02:32, Gene Heskett <[email protected]> wrote: > > > > I have managed to source ancient motor controller box, originally > > intended to serve as a bidirectional motor controller serviced by a > > 3 phase circuit. > > How about a different plan? > > Feed the cap bank through a resistor. > Use a (cheap $5) solid state relay to bypass that resistor when > LinuxCNC is turned on. > I've had a chance to remove one of them and play a bit. The concern about a reliable turn off from residual magnetism is valid I think. My test psu is only 15.5 volts, so I have to give it a push to close, but the self opening as I turn down the voltage is about an even 5 volts, so it will definitely need a shim laid on the poles. Current draw was about 75 mills as 15.5 volts. The face of the poles is a fairly decent area, so I am going to see how it behaves with a sheet of 24lb paper for a gap setter. As for closing, it may be that I'have to use a resistor to limit the current from a higher voltage, and give it a boost with a capacitor to slam it down initially. Not impossible of course, but my junk box isn't equipt with suitable 10 watt R's or caps to supply the initial strong bump. I'd have to assume the time constant wouldn't have to be over .1 seconds. Time to get out my calculator... But first a shim, I'd like it just thick enough that the dropout is close to what my test supply can do.
These look to have silver bars for contacts, and the label says 35 amp CW, 150 amps interrupt at 230 volts in case of a locked rotor, down to 100 amps at 660 volts. And surprisingly small. Without counting the spade lugs sticking out, nominally 2.5" cubes. I think I hit one, for carrying it off as the price. :) I took a sheet of laser printer photo paper out and cut a shim, .004" thick, raises the dropout to about 10.3 volts. Its coil R is 246 ohms. Now, heres the real kicker. A 1.5k resistor would hold it in nicely once closed, passing 72 mills for holding power. AND it has an aux set of contacts, SPDT, that could switch in that 1.5k resistor as it closes. And my copy of kcalc says that resistor could be a 1/4 watter? Fudge, quit trying to run kcalc with a mouse, you have to click way too long to get it to register. Punch buttons again but from keyboard. Current is V/R, so 126/(1500+246)=0.072 amps. Thats plenty of holding current. Power is i2*r, so adding the coil r to get the holding current, call it 1750 ohms total. That gets me 7.776 watts in the resistor, and 1.275264 watts in the coil. I can live with that. Now to find 5 pack of 1500 ohm 20 watt R's. But how about I steal some current from the 60 volt Z motor supply? As Yoda might say thought food, is that. Progress, I think. Till reality hits me over the head. :) If I have a small 2/1 toroid, I'll see about using it to isolate the coil supply. Goes off to check stock room. 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
