Direction of an AC motor revisited

[captainvi...@gmail.com]

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

[Wolfgang Allinger]

On 18 Jun 15 at group /sci/electronics/repair in article 4f695716-1f25-4b1f...@googlegroups.com

Take a DC Motor. The brushes are directly connected to the + -
connector. The permanent field is fixed. If you inverse the Batterie,
the rotor will run in the other direction.

So do the AC Motor. However the brushes and the field is connected to
the mains connector, so changing the mains connector will also change
the field, therefor no change between field and rotor.

But you managed reversing by changing the internal brush connection. So
the rotor is now to the opposite of the field direction.

Hope my Ginglisch is understandable :)


Saludos (an alle Vernünftigen, Rest sh. sig)
Wolfgang

--
Wolfgang Allinger, anerkannter Trollallergiker :) reply Adresse gesetzt!
Ich diskutiere zukünftig weniger mit Idioten, denn sie ziehen mich auf
ihr Niveau herunter und schlagen mich dort mit ihrer Erfahrung! :p
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[John-Del]

On Friday, June 19, 2015 at 5:14:57 AM UTC-4, Wolfgang Allinger wrote:

>
> Hope my Ginglisch is understandable :)
>

The sad thing Wolfgang is that your post was far better than some from people whose native language is *supposed* to be English...

[Wolfgang Allinger]

On 19 Jun 15 at group /sci/electronics/repair in article 530841b1-2bf4-457f...@googlegroups.com

So these natives should try harder if even a bloody Kraut can outperform
them :)

[Phil Allison]

** A regular DC motor is surrounded by a *permanent magne*t - right?

If you reverse the external connections to the rotor, it spins the other way cos the relationship between the fixed and moving magnetic fields is reversed.

With your " AC/DC" motor, the fixed field is provided by the same current that drives the rotor. When fed by an AC or DC supply, the fixed and rotor fields always *change polarity at the same time* so the rotation direction remains the same.

You have to go inside and reverse the connection to the field or rotor to effect a change.


... Phil

[John-Del]

On Friday, June 19, 2015 at 6:12:11 AM UTC-4, Wolfgang Allinger wrote:
> On 19 Jun 15 at group /sci/electronics/repair in article 530841b1-2bf4-457f...@googlegroups.com
> <ohg...@aol.com> (John-Del) wrote:
>
> >On Friday, June 19, 2015 at 5:14:57 AM UTC-4, Wolfgang Allinger wrote:
>
> >> Hope my Ginglisch is understandable :)
>
> >The sad thing Wolfgang is that your post was far better than some from
> >people whose native language is *supposed* to be English...
>
> So these natives should try harder if even a bloody Kraut can outperform
> them :)
>
>
> Saludos (an alle Vernünftigen, Rest sh. sig)
> Wolfgang

If we can only convince them to try harder. They seem to have no will, nor is there any incentive for them to do so.. Seems to get worse as time goes on!

:)

[captainvi...@gmail.com]

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

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

[Samuel M. Goldwasser]

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. :)

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Important: Anything sent to the email address in the message header above is
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[Ralph Mowery]

"Samuel M. Goldwasser" <s...@repairfaq.org> wrote in message
news:87381n8...@repairfaq.org...

> 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.
>

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.

[captainvi...@gmail.com]

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'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]

wrote in message
news:bae9e252-5885-4642...@googlegroups.com...

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]

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.

[captainvi...@gmail.com]

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

[Rheilly Phoull]

wrote in message
news:63e9c726-83d4-49e4...@googlegroups.com...

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]

In article <yMidnVbMHPbGYhjI...@westnet.com.au>,
rhe...@bigslong.com says...

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

[captainvi...@gmail.com]

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

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]

wrote in message
news:b89d9d1a-1a0f-4402...@googlegroups.com...

I think they are all crimped these days, I am no longer active in that
field.

[Michael A. Terrell]

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

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]

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

[captainvi...@gmail.com]

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

[jurb...@gmail.com]

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.

[whit3rd]

I think it makes sense. The commutator selects a winding. The rotation of brushes determines
whether winding #1 puts a new rotor N pole CW of the stator's S pole, or winding #2
puts a new rotor N pole CCW of the stator's S pole

[Wolfgang Allinger]

On 21 Jun 15 at group /sci/electronics/repair in article 88958a1d-8253-423f...@googlegroups.com

<whi...@gmail.com> (whit3rd) wrote:


>I think it makes sense. The commutator selects a winding. The
>rotation of brushes determines whether winding #1 puts a new rotor N
>pole CW of the stator's S pole, or winding #2 puts a new rotor N pole
>CCW of the stator's S pole

on an AC Motor are no permanent S and N poles ;(
Its because Alternating Current = AC!

Saludos (an alle Vernünftigen, Rest sh. sig)
Wolfgang

[M Philbrook]

In article <DJHb4...@allinger-307049.user.uni-berlin>, all2001
@spambog.com says...

>
> On 21 Jun 15 at group /sci/electronics/repair in article 88958a1d-8253-423f...@googlegroups.com
> <whi...@gmail.com> (whit3rd) wrote:
>
>
> >I think it makes sense. The commutator selects a winding. The
> >rotation of brushes determines whether winding #1 puts a new rotor N
> >pole CW of the stator's S pole, or winding #2 puts a new rotor N pole
> >CCW of the stator's S pole
>
> on an AC Motor are no permanent S and N poles ;(
> Its because Alternating Current = AC!
>
>
>
>
> Saludos (an alle Vernünftigen, Rest sh. sig)
> Wolfgang

Yeah but, it's a series motor so that means it can operate
on AC or DC..

As for the communtator being out by 1.5" or so, that isn't anything
to worry about because in the first short running time that should
smooth out, unless there is some bearing play? You really don't
want that.

Jamie

[hrho...@sbcglobal.net]

It's good to know Sam Goldwasser is still around, his posts are almost always 100 correct!!!

[Wolfgang Allinger]

On 21 Jun 15 at group /sci/electronics/repair in article MPG.2ff115271...@news.eternal-september.org

<jamie_...@charter.net> (M Philbrook) wrote:

>In article <DJHb4...@allinger-307049.user.uni-berlin>, all2001
>@spambog.com says...

>> on an AC Motor are no permanent S and N poles ;(
>> Its because Alternating Current = AC!

>Yeah but, it's a series motor so that means it can operate
>on AC or DC..

The OP didn`t say anything about how the field is connected.
It`s likely, but not necessarily a series motor.!
So how do you know?

There are 3 types of brushed Motors with non permanent fields:

Nebenschluss Motor - shunt wound motor
Reihenschluss Motor - series wound motor
and combinations of them.

Mostly but not all are running with DC and low freq. AC (50/60Hz)
Some need a special wound for running properly with AC.

Saludos (an alle Vernünftigen, Rest sh. sig)
Wolfgang

[Arfa Daily]

>
> 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. >

A friend from my youth was an auto-electrician, and apparently, back then,
this was a common occurrence on starter motors and the like. The term that
he used for the condition was "flung" as in 'it's got a "flung" armature'

I knew what that one meant, but the one that I never got in terms of where
the phrase came from was "drop testing" which I believe referred to the
resistance checking of the armature windings across opposite brass
commutator segments, as described here by someone else.

Arfa