- Direction of an AC motor revisited - 8 Updates
- Newbie Question: Filing Down Component Leads - 1 Update
| "Rheilly Phoull" <rheilly@bigslong.com>: Jun 21 08:03AM +0800 wrote in message news:63e9c726-83d4-49e4-901a-45ae13b980a8@googlegroups.com... > out that reversing the brushes did indeed reverse the direction of the > motor. We can't argue with success, but I still don't fully understand why > this is so. Can anyone please explain this to me? Thanks, Lenny I don't have access to the growler any more but can't I use my Simpson? I'm thinking that I should have continuity between each of two segments 180 degrees apart. Is that correct? Lenny Sure, use the Simpson on low ohms, once you have located a winding's bars go around and check each winding. Start with a winding with clean bar edges and then move up to the burnt ones. If you find an open or hi resistance check the crimp or soldering at those bars. |
| M Philbrook <jamie_ka1lpa@charter.net>: Jun 20 09:02PM -0400 In article <yMidnVbMHPbGYhjInZ2dnUU7-K-dnZ2d@westnet.com.au>, rheilly@bigslong.com says... > around and check each winding. Start with a winding with clean bar edges and > then move up to the burnt ones. If you find an open or hi resistance check > the crimp or soldering at those bars. I use a LCR meter these days to check for shorts on the poles. lot quieter than a growler. Use a megger for those HV leaks. Jamie |
| captainvideo462009@gmail.com: Jun 21 04:54AM -0700 > Just wanted to get back to the group about this AC motor that was running in reverse after being disassembled and then put back together. It turns out that reversing the brushes did indeed reverse the direction of the motor. We can't argue with success, but I still don't fully understand why this is so. Can anyone please explain this to me? Thanks, Lenny There was a term commonly used years ago which I haven't heard for a long time. Many commutators would fail because they "threw solder". The point on the commutator that was soldered to the individual rotor winding had heated, melted the solder, and "threw" it out of the connection, leaving that winding either open or intermittent at best. The connections on this commutator, (and in fact others I've worked on over the past few years) are (and have been) clean and look like they were crimped. Is soldering to commutator segments no longer done? Lenny |
| "Rheilly Phoull" <rheilly@bigslong.com>: Jun 21 09:29PM +0800 wrote in message news:b89d9d1a-1a0f-4402-af73-b168b471d8a6@googlegroups.com... > out that reversing the brushes did indeed reverse the direction of the > motor. We can't argue with success, but I still don't fully understand why > this is so. Can anyone please explain this to me? Thanks, Lenny There was a term commonly used years ago which I haven't heard for a long time. Many commutators would fail because they "threw solder". The point on the commutator that was soldered to the individual rotor winding had heated, melted the solder, and "threw" it out of the connection, leaving that winding either open or intermittent at best. The connections on this commutator, (and in fact others I've worked on over the past few years) are (and have been) clean and look like they were crimped. Is soldering to commutator segments no longer done? Lenny I think they are all crimped these days, I am no longer active in that field. |
| "Michael A. Terrell" <mike.terrell@earthlink.net>: Jun 21 09:36AM -0400 > Just wanted to get back to the group about this AC motor that was running in reverse after being disassembled and then put back together. It turns out that reversing the brushes did indeed reverse the direction of the motor. We can't argue with success, but I still don't fully understand why this is so. Can anyone please explain this to me? Thanks, Lenny By changing the connections, you change the magnetic poles of the armature. Just like changing the polarity on a permanent magnet DC motor, changes it direction. |
| "Michael A. Terrell" <mike.terrell@earthlink.net>: Jun 21 09:43AM -0400 > On Friday, June 19, 2015 at 12:19:59 AM UTC-4, captainvi...@gmail.com wrote: > > Just wanted to get back to the group about this AC motor that was running in reverse after being disassembled and then put back together. It turns out that reversing the brushes did indeed reverse the direction of the motor. We can't argue with success, but I still don't fully understand why this is so. Can anyone please explain this to me? Thanks, Lenny > I don't have access to the growler any more but can't I use my Simpson? I'm thinking that I should have continuity between each of two segments 180 degrees apart. Is that correct? Lenny It also test for shorts between coils, usually caused by a short between segments of the commutator. https://en.wikipedia.org/wiki/Growler_%28electrical_device%29 |
| captainvideo462009@gmail.com: Jun 21 08:56AM -0700 If anyone could please comment on my "bounce" question below from an earlier post in this thread I would be very grateful. Lenny The commutator does not appear to have worn down much during it's lifetime. A growler test shows no shorted windings to ground, The areas between some of the the segments however appear to be a little ragged and opened a bit from the arcing, no doubt. A dial indicator on the commutator shows an out of round condition totaling 1.5 thousandth's, on each side for a total of three thousandth's for the entire piece. According to a machinist we consulted this doesn't seem like enough to warrant turning the commutator, but I've been considering something else. With this motor spinning at 9000 RPM would a 1.5 thousandth's out of round condition be enough to "bounce" the brushes and make them arc? Brushes are now trued to the commutator, holders are new, and each brush is mounted stationary, and it's relationship to the position on the commutator cannot be altered. I can't figure out what else could be causing this? Lenny |
| jurb6006@gmail.com: Jun 21 09:53AM -0700 Sam ! haven't heard from you for a while. Nice to know you are still alive and kicking, provided you are kicking the right people. |
| norman.yarvin@gmail.com: Jun 20 03:49PM -0700 On Thursday, June 18, 2015 at 1:53:09 PM UTC-4, Phil Hobbs wrote: > > I've always wondered what the tenacious oxide is. > > George H. > I don't know. It seems to be some sort of organic crud iirc. I'm not sure if you're talking about the same stuff, but the organic crud I've encountered on old wires I've interpreted as being plasticizer from the PVC insulation -- the same sort of stuff that coats the insides of car windshields in the summer. -- Norman Yarvin http://yarchive.net/blog |
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