Jim & Rich,Thanks for the info. My motor is definitely a Universal motor with carbon brushes. The brushes are in excellent shape and the armature runs true. The main problem I'm having is shorts, as opposed to opens. The motor runs until a load is applied, then you can basically shut it down with your fingers. The "REAL" problem that I have had is due to our geographical location - North Carolina. There are some very good motor shops, but they won't mess with a small problem motor that doesn't generate any return business. If you find a mom & pop operation, they work whenever they get around to it... I left it with one place and the owner promised he would get to it in a week - two months later I went back to check and it was still sitting on his desk in the same place I left it. Another said he could rewind it, then quit his job. Another guy sent it to Michigan to someplace that was willing to work on it, but wanted $900 with no guarantees that they could fix it. As far as electrical engineers go, 99.9% of the population probably don't know what electrical engineers do for a living and they are not in abundance around here, except at the nuclear power plant. The guy who works on your motor may or may not have graduated high school and knows how to fix one or two common motors that are used commercially - give him a challenge and it ends right there. I am tired of being asked by people in motor shops - "What are you going to use it for?" or "What's wrong with it?" If I knew what was wrong and how to fix it, I wouldn't be asking them. What difference does it make what I'm going to use it for? I just want it to run... AND if I did explain that I wanted to use it in a lamp phonograph... you get the picture. Do I sound stressed?
> Date: Fri, 15 Feb 2013 16:50:01 -0600 > From: rich-m...@octoxol.com > To: phono-l@oldcrank.org > Subject: Re: [Phono-L] Turntable Motor Question > > Some of these motors have round brushes constructed from tightly rolled > up brass screen. If this motor has that type of brush they are most > likely dirty and oxidized. They are the first thing to check and they > are cleaned by removing and soaking in carburetor cleaner. Do not sand > them or the commutator surface. > > As to how to get them fixed you have to find some old retired person who > has the time to fiddle with it and possibly make new parts. This will be > someone who collects early electrical equipment and keeps it running. > > On 02/15/2013 03:15 PM, Jim Nichol wrote: > > If this is a "Universal" motor, it can be easily identified by having > > carbon brushes riding on a commutator. A Universal motor is really a DC > > motor that has been specially designed to also work on AC. Whereas an > > Induction motor is AC-only, and is an entirely different thing (no > > brushes). Any motor repair shop that knows anything about DC motors should > > be able to analyze a Universal motor. As a matter of fact, the first thing > > to check before getting it repaired is to see if the carbon brushes are > > worn down, and the springs that push them against the commutator are > > working. Often the brushes get stuck in their brush holder slots from > > carbon dust and grime, and are no longer making contact with the > > commutator. Freeing up the brushes so they slide easily will fix such a > > motor. > > > > A DC motor (and a Universal motor) have two sets of windings called FIELD > > windings and ARMATURE windings. The Field coils are stationary, and are > > often bolted to the inside of the motor frame. The Armature coils are wound > > onto the rotor. The brushes and commutator bars are used to connect the > > power source to the Armature (rotor) windings. > > > > It is possible for DC motors to be made in two configurations. The Field > > and Armature windings can be wired in parallel with each other, or they can > > be wired in series. Such DC motors are called either "parallel" or "series" > > wound. Universal motors are usually series wound. Series motors (unlike > > parallel) have huge torque at slow or stalled speeds, and very low torque > > at high speeds. This is because if the mechanical load stalls the motor, it > > slows down, which increases the current in the Armature. Because the > > Armature and Field are in series, they then BOTH get more current, more > > magnetism in BOTH Armature and Field, and thus more torque squared. This is > > great for home use, like drill motors, vacuum cleaners, and for phonographs > > with heavy tonearms. The slower it goes, the more torque is created to > > compensate. There are two drawbacks for series motors. At high speeds they > > have very low torque, and secondly, they can theoretically reach infinite > > speed if there is no mech an > ic > > al load and fly apart. Some even have fans to provide a little load at > > high speeds. > > > > Jim Nichol > > > > On Feb 15, 2013, at 3:04 PM, Rich<rich-m...@octoxol.com> wrote: > > > >> He was advised that it was a short. You are correct that the correct > >> condition condition description is OPEN Circuit. If the fields happen to > >> be in parallel then that would be where I would start looking. > >> > >> On 02/15/2013 01:04 PM, Jim Nichol wrote: > >>> Al didn't say you had a "short". He said you had an "open". They are > >>> opposites of each other. He only mentioned "shorted turns" to imply that > >>> they are NOT likely to be the problem. > >>> > >>> A broken wire is an "open", resulting in zero current. A "short" is two > >>> wires touching each other, causing the current to take a shorter path > >>> than intended. In a lamp cord a short would blow a fuse, whereas an > >>> "open" would prevent current from flowing. I recommend not saying > >>> "short" when you mean "open" (though many electrical novices do). If you > >>> said you thought "the motor has a short" at a repair shop, it would mark > >>> you as unknowledgeable, maybe setting yourself up to be ripped off. > >>> > >>> The symptom of an "open" in your motor would be that nothing happens at > >>> all. On the other hand, saying the motor has a short (or more > >>> specifically "shorted turns") means that a few of the loops of wire in > >>> the coils are shorted together, causing the current to bypass them. This > >>> would lower the overall resistance of the coils, thus increasing the > >>> current. The motor would still run, but would have less magnetic torque > >>> (because some of the turns of wire are not carrying current), and the > >>> remaining turns would get hot. > >>> > >>> Sorry for the lecture, but as an electrical engineer, this is one of my > >>> pet peeves. > >>> > >>> Jim > >>> > >>> On Feb 15, 2013, at 8:53 AM, Vinyl Visions<vinyl.visi...@live.com> > >>> wrote: > >>> > >>>> Al,Thanks for the reply. As you noted, I have been advised that it was a > >>>> short in the motor somewhere. The problem seems to be that this motor is > >>>> wound for three different types of power - AC/DC and maybe 220. So, > >>>> either the shops don't know what the problem is or they just don't want > >>>> to mess with it... I'm tending toward the latter, since the guys I sent > >>>> it to are very knowledgeable. There is a picture of the motor on our > >>>> website: www.carolinaphonosociety.com > >>>> A shortcut to the pic is: > >>>> http://open1234.wix.com/camps-site/twilight-zone-2#!__fairy-phono-lampCurt > >>>> > >>>>> To: phono-l@oldcrank.org > >>>>> From: clockworkh...@aol.com > >>>>> Date: Fri, 15 Feb 2013 04:01:17 -0500 > >>>>> Subject: Re: [Phono-L] Turntable Motor Question > >>>>> > >>>>> > >>>>> Induction motors that lack torque can usually be traced to an open > >>>>> field coil or an open armature loop. A shorted turn will eat torque > >>>>> but the motor will let you know by getting hot. How about a photo of > >>>>> the motor? Most good motor shops can fix anything from fractional > >>>>> horsepower to 100 HP. Do you know of a fan collector in your area? > >>>>> I have repaired fan motors that lost power and have the same symptoms > >>>>> of your phonograph. These things are not rocket science. > >>>>> > >>>>> Best wishes, > >>>>> Al > >>> > >>> _______________________________________________ > >>> Phono-L mailing list > >>> http://phono-l.org > >>> > >>> > >> _______________________________________________ > >> Phono-L mailing list > >> http://phono-l.org > > > > _______________________________________________ > > Phono-L mailing list > > http://phono-l.org > > > > > _______________________________________________ > Phono-L mailing list > http://phono-l.org _______________________________________________ Phono-L mailing list http://phono-l.org
