Hello Gene, seems that we have different descriptive names for things, especially motors, in the US and Germany (which is .de-country, Deutschland). We have 230 V AC, 50 Hz here (single phase speaking, it's part of a 400 volts three-phase system). Nowadays, as everybody puts photovoltaic collectors on their roofs, this may rise up line voltage to over 250 V single phase.
My suggestion to use 117 V one way rectified amounts to 58 V eff. voltage and it was supposed for 117 Volts countries. In Europe, this would be about twice as much, but motors are built for this voltage, too. Some 30 years ago, I put a 24 V transformer into the switch box of my home made wood lathe, and it turned out to be a little weak. A 60 volts transformer would have been better to brake down a heavy log turning at 2000 rpm but I didn't happen to have one. For the reason of coming loose I didn't use threads to fasten the chuck or faceplate to the spindle but used a morse taper to hold the workpieces. It seems that they use different kinds of iron in the US, because there is no magnetism whatever in my motors after voltage is turned off. I have experienced, however, that the main relay of my metal lathe, running on 24 DC, sometimes keeps sticking a few seconds after I turned it off. This could be detrimental to an emergency stop. I happen to have a large circular saw for firewood cutting (70 cm diam.) with a 10 kW motor. When I turn it on, it accelerates in star mode (or whatever you call that) at one sixth of full power and later on, it switches to triangle mode. When I turn it off, it takes about a minute to come to a stop. So much for angular momentum. I bought a cheap battery drill/screw machine for 30 Euros. Even this little device has a brake built in so I can cut threads up to the very end of the threading bit. Best greetings Peter gene heskett schrieb: > On Wednesday, June 01, 2011 11:14:32 PM Peter Blodow did opine: > > >> Gene, I suppose that your "AC universal motor" is an induction motor >> with a field winding and a cage rotor. >> > > Nope. > > >> (If it were a motor with rotor >> windings and a brush armature, it would be a AC-DC-universal motor >> > > It is, complete with replaceable brushes. > > >> and >> the following recipe would not apply). When the power supply is cut off, >> there is no magnetic field any more to exert a braking momentum. >> > > Normally, due to hysteresis in the iron, there will be just enough residual > magnetic field to get the generator started. But a dead short has > absolutely zero effect on two modern motors. I say modern, that Skil > router is at least 10 years old. > > >> Therefore with that sort of a motor you need an additional field >> supply, say 24 V DC or even better 117 V one phase rectified. After >> power off, this voltage must be applied for a few seconds (time relay), >> and it will bring the rotor to a stop very quickly. Machines without >> this feature are not allowed to be sold or applied in Germany. >> > > What is the line voltage in .de land? > > >> The only other way would be a mechanical spring loaded brake right on >> the saw shaft, held open by the supply voltage as long as the motor is >> running. >> >> In any case, be sure that your saw blade is secured with one or two >> dowel pins protruding from the flange through the saw blade, preventing >> the left hand thread fastening nut from turning lose by the braking >> momentum or else you might catch the blade hopping through the shop with >> your hands..... I have seen a what a 45 cm blade coming lose at 3000 rpm >> can do, and I almost experienced it myself when a (smaller) blade came >> lose that I used with a shaft locked in my lathe chuck when I stopped >> the lathe. >> > > Yes, I have had that happen with my Dewalt 12" chop saw, but it only > loosened the nut enough to let the blade spin, which made an odd noise that > prompted me to tighten the nut to about 1/16th turn from broke. Dewalt > doesn't supply a decent spindle lock, so the best you can do is snap a > honking big set of vice-grips on the blade so that you can torque on the > nut till happy. They do a spindle lock on the $75 angle grinder, seems > remiss to me that a nearly $500 chop saw doesn't have one. > > Now I am wondering how that chop saw stops itself as well as it does. It > did not come with a schematic. :( > > ------------------------------------------------------------------------------ Simplify data backup and recovery for your virtual environment with vRanger. Installation's a snap, and flexible recovery options mean your data is safe, secure and there when you need it. Data protection magic? Nope - It's vRanger. Get your free trial download today. http://p.sf.net/sfu/quest-sfdev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
