On Thursday, June 02, 2011 09:37:05 AM Peter Blodow did opine: > 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.
Certainly would. Most of these control relays have an air gap to stop that which prevents the armature from making a direct metal to metal contact with the pole piece, often a piece of clear kaptan or similar tape just 2 or 3 thou thick placed on the face of the pole piece or bottom of the armature. Repeated use over the years could eventually pound that down or dislodge it. I have used other plastic tapes there, but with only mixed, temporary success, mainly because the plastic hot flows & eventually the adhesive itself begins to make it sticky. Best results for me so far has been a bit of thin paper, glued to the armature face, not the pole piece, so that only the paper, no glue, occupies the space on top of the pole. That old GE transmitter, now out of service, probably has at least 10 such relays treated that way in it. Not much else I could do when the relays maker has been gone for 30 years. That transmitter was a good one, made in 1957, updated for color in 1961, and ran till 2009. > 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. We call that delta, and in tv transmitters it is a common feature, allowing us to test at 50 or 60% of full voltage. But for that, it was a huge switch whose operating lever was usually propelled by a foot as we were dealing with 100 kw or more, with as many as 4 750mcm conductors per phase. Nothing automatic about it, and often interlocked so it couldn't be moved without it causing the main contactor to open first. The knife blades would have been destroyed by the arcing if switched under power. > When I turn it off, it takes about a minute > to come to a stop. So much for angular momentum. To stop in a minute, I'd assume there is an active braking circuit. Heck, even my 14" bandsaw will coast for 30 seconds or more. Or did till I changed guides from $4 a tube of 10 ball bearings to Kool blocks on the sides, and carbide shoes behind the blade. Now it stops a little quicker. And cuts a heck of a lot smoother without the rumble of those ultra cheap bearings. I can take a 12.25" long piece of poplar 1x6 and make 2 insert panels by slicing it just over 1/4" thick, edge gluing each pair in bookmark style, run it through the planer to clean up the saw marks, and a session with 120-220-320 paper on an RO sander, done except for the finish. I'm routing the frame slots for the panels with a 1/4" bit. > 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. Even here, it seems my pair of 14 volt Hitachi drill/drivers have that. Sweet. > Best greetings > > Peter -- 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) <http://tinyurl.com/ddg5bz> <http://www.cantrip.org/gatto.html> FORTUNE PROVIDES QUESTIONS FOR THE GREAT ANSWERS: #19 A: To be or not to be. Q: What is the square root of 4b^2? ------------------------------------------------------------------------------ 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
