- Direction of an AC motor revisited - 6 Updates
- What sort of cap is this ? - 1 Update
| sam@repairfaq.org (Samuel M. Goldwasser): Jun 19 04:13PM -0400 Common (non-solid state/brushless) motors: * Series DC motor, shunt DC motor, universal AC DC motor: Direction determined by relative wiring of stator and brushes. * Permanent magnet motor: Direction determined by polarity of DC (or PWM etc.) input. * 3 phase AC induction motor: Direction determined by phase relationship of 3 connections. Swap any two pairs to reverse motor. * Single phase AC induction motor: Direction determine by relative phase of run and start windings during starting. Start winding only used during starting, cut off by centrifugal switch, starting relay, or other starting device. Main winding conencted directly to mains; start winding through capacitor or has different inductance/resistance to provide phase shift. * Split phase AC induction motor: Direction determined by relative phase of two windings. Main winding conencted directly to mains; phase winding through capacitor or has different inductance/resistance to provide phase shift. Both windings powered when running. There are many variations. :) -- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/ Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/ +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html Important: Anything sent to the email address in the message header above is ignored unless my full name AND either lasers or electronics is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. |
| "Ralph Mowery" <rmowery28146@earthlink.net>: Jun 19 05:53PM -0400 "Samuel M. Goldwasser" <sam@repairfaq.org> wrote in message news:87381n8nj8.fsf@repairfaq.org... > PWM etc.) input. > * 3 phase AC induction motor: Direction determined by phase relationship > of 3 connections. Swap any two pairs to reverse motor. One more thing to add to this that hapened where I worked. I don't recall the type of motor, but it was around 100 HP and had 4 sets of brushes and was driven by a varitable speed drive. Two people changed the brushes and said they did not touch the wires. It ran backwards. Several others looked at it and could not determin why it was running backwards. I went up and asked a few questions. I solved the problem for them. They had loosened the plate that holds the brushes and rotated it some to make it easier to replace the brushes. When they rotated it back, they had put it in the wrong place. By rotating it back to the correct position it ran the correct way. |
| captainvideo462009@gmail.com: Jun 19 04:01PM -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 I'm just curious, when this plate was moved did all the brushes rotate the same amount, or perhaps just two? Because if you think about that if they all moved the same as a group it doesn't make any sense. Lenny |
| "Rheilly Phoull" <rheilly@bigslong.com>: Jun 20 09:02AM +0800 wrote in message news:bae9e252-5885-4642-b02f-4041fef3ee25@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 Thanks everyone for the great explanations. It makes more sense now. The original owner of this thing apparently tried to replace the brushes himself. I can only surmise that he didn't realize that the bakelite brush holders were held into the housing with small set screws. So he did what any idiot would do. He used a "bigger hammer". Some people should never pick up a tool. It looks like he tried to pry the holders out without releasing the screws and cracked them into many pieces. The field is connected to the brush holders with push on connectors. That's a good thing too because to get it out he must have ripped it loose from the remnants of the brush holders. Luckily the field wasn't damaged. At this point he apparently gave up and gave the tool to my son who has been working on it since. So in dis assembly the correct orientation of the field then become unknown, and after replacing the brushes and holders we evidently switched the brush positions. So he now has the direction problem resolved but the new brushes arc really bad. Perhaps the old ones did too and maybe that's why Mr Wizard tried to replace them in the first place but we don't know. 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 and 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 The "ragged" wear and arcing would indicate open circuits in the armature windings. Put it back on the growler and drag a hacksaw blade across the gap in each slot. There should be an arc en you do that, if not most likely that winding is open. |
| "Rheilly Phoull" <rheilly@bigslong.com>: Jun 20 09:39AM +0800 The "ragged" wear and arcing would indicate open circuits in the armature windings. Put it back on the growler and drag a hacksaw blade across the gap in each slot. There should be an arc en you do that, if not most likely that winding is open. Also I forgot to mention you have to rotate the armature after testing each slot. |
| captainvideo462009@gmail.com: Jun 20 07:46AM -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 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 |
| "Arfa Daily" <arfa.daily@ntlworld.com>: Jun 20 02:10AM +0100 > So to get that capacity in that package , they must be seriously multi > MLCC. Was it actually dead short or very low resistance. Very low resistance, I guess. Decimals of an ohm. Low enough for me to consider it to be 'dead short', anyway ... Arfa |
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