Motor speed control via back-EMF detection

[JosephKK]

Well, no, the point is that high end turntables like the Rek-O-Kut did
not use gear drive or toothed belt drive because of the tooth passing
noise these produce; they used flat belt drive and the seldom needed
adjustment was to compensate for wear - or allow slight pitch
adjustment for those with perfect pitch . (I might have one of
those stored in my barn somewhere too, but I think I threw it out.)

BTW synchronous motors not run from variable frequency drives have a
second rotor winding for starting purposes (amortisseur winding), so
the motor starts as an induction motor with slip then locks in as
synchronous.

Some of them do. There is a variation called a salient pole motor,
some are spun up by induction motors before applying power; and some
are just "hard started". Almost all synchronous motors are 3 phase.

 

[JosephKK]

[snip]

BTW synchronous motors not run from variable frequency drives have a
second rotor winding for starting purposes (amortisseur winding), so
the motor starts as an induction motor with slip then locks in as
synchronous.

My customer with the Fox Theater pipe organ in his basement had a 6HP
electric motor to generate the air flow ;-)

Easy on your new hip there ...

I'm fine. Didn't you catch my comment that I'm trimming my own trees
now ?

That's how it always should have been! Now you can listen to them old
bluegrass records. For youngsters: These are those huge black CDs.

I have a few hundred LP's, mostly classical, but some '50s, early
'60's rock-n-roll, and a lot of Dixieland jazz. I should get it down,
learn to use a sound card and write them all over to CD's

...Jim Thompson

I think you will be pleasantly surprised at just how much of that has
been converted to CD. Watch out for remasters though, the sound may
well be not the same. I might be interested in processing yours when
i get through my own collection (about 300 LPs). There are
commercial services as well, but be careful. Oh, don't use a sound
card, use semipro gear, it is not that expensive and does a much
better job. Get premium noise reduction software, Diamond cut AC5
minimum. With careful use you can even remove noises that are present
in source material earlier in the recording chain than stamping and
playback.

 

[JosephKK]

Except in the Hammond organ here. You push in one switch, helper motor
spools up, then throw main motor switch, clutch engages, wait three
seconds, hope for the best, disengage starter motor switch, clutch
disengages. When all the tubes have heated up the organ runs. Or not.

Yup, an induction motor starter for a synchronous motor.

 

[Jan Panteltje]

Then they are not synchronous.

Maybe Asynchronous is what you're thinking of?

No, read the links.
Mains operated synchronous usually have an extra winding so they can start
in the first place, and only become synchronous once at speed.
If you break those, they will simply drop in speed, not stop.
3 phase variable frequency driven will skip phases too if over loaded.

 

[Jan Panteltje]

On Tue, 02 Sep 2008 07:51:26 -0700, Joerg

Jim Thompson wrote:
On Mon, 01 Sep 2008 17:54:08 -0700, Joerg

[snip]
Variable pulley ratio... you dig?

No grok here

Again:

Synchronous motor -> no slip -> always in sync with your utility's 60Hz.

Strobe disk -> lamp -> lamp also always in sync with utility.

So, where's the value in this measurement?

If I can change the pulley ratio I can adjust the PLATTER speed.

But what for? If the pulley diameters are fixed and there is a
synchronous motor the platter speed can never deviate from nominal. All
it can do with age is drop to zero upon a gummed up shaft, when the belt
snaps or something.

What part of variable diameter (tapered) do you still not read? I am
not used to you being obtuse like this, please quit it.

I think Joerg is referring to some other turntables, I had a Garrard, it
had fixed shaft diameters (and no stroboscope ;-) ), IIRC Lenco had a conical
shaft, but really it is too long ago.
There are plenty of pictures and projects about the old players on the internet
though.

 

[Jan Panteltje]

Jan, you have a "terminology" issue. Synchronous motors do not "slip"
ever. They can and do "cog" at near stall conditions. All of the
drops are full electrical / mechanical cycle steps, not loosing a
fraction of an mechanical rotation with each electrical cycle. That
is why the terminology is different. If your little tape player was
cogging it needed a serious tear down, cleaning, and re-lubrication.
Unless you are interested in what you might learn from such work it is
far cheaper to replace.

A synchronous moter driven from a variable frequency generator,
will slip, it will not 'stall', it will just have speed modulation
at the driving frequency, what was, in the case of my cassette player,
several hundred Hz, thus FM modulating (no flywheel!) the singer / song/ instrument).
Other synchronous motors, mains driven, have an extra winding,
so they become normal motors when loaded to the point where they slip,
and do not stall either.
There is a synchronous motor in my washing machine (yes now 20 years old), that I replaced
coil in, that has a mechanism so it can only turn one way (else the clock would run backwards),
With that one it is pretty much 'go or no go', but it drives a huge gear and has not
much mass itself to keep it going, so maybe yo urefer to that one.

 

[Jeroen Belleman]

[...]
There is a synchronous motor in my washing machine (yes now 20 years old), that I replaced
coil in, that has a mechanism so it can only turn one way (else the clock would run backwards),
[...]

Ah! That reminds me an anecdote showing the different attitudes towards
repairing equipment in different countries:

When I had a washing machine with a broken clock motor in France,
I had to buy not only the motor, but the whole (mechanical) program
switch assembly with it. When confronted with the same problem in the
Netherlands, they couldn't sell me the whole assembly. Not even just
the motor. But they *could* sell me just the motor *coil*. I was
flabbergasted.

That was 25 years ago. These days, they'd try to sell you a whole
new machine...

Jeroen Belleman

 

[Jan Panteltje]

[...]
There is a synchronous motor in my washing machine (yes now 20 years old), that I replaced
coil in, that has a mechanism so it can only turn one way (else the clock would run backwards),
[...]

Ah! That reminds me an anecdote showing the different attitudes towards
repairing equipment in different countries:

When I had a washing machine with a broken clock motor in France,
I had to buy not only the motor, but the whole (mechanical) program
switch assembly with it. When confronted with the same problem in the
Netherlands, they couldn't sell me the whole assembly. Not even just
the motor. But they *could* sell me just the motor *coil*. I was
flabbergasted.

That was 25 years ago. These days, they'd try to sell you a whole
new machine...

Jeroen Belleman

Exactly, they will try to sell you the timer too,
but I wound my own coil.... then one day I noticed 'een crouzet spoel'
for sale on the internet, and that is the name of the thing it seems,
ordered it, put it in (230V).
The one I made had same ampere windings, but less turns and worked
via a transformer.

 

[Joerg]

Jim Thompson wrote:
On Tue, 02 Sep 2008 07:51:26 -0700, Joerg

Jim Thompson wrote:
On Mon, 01 Sep 2008 17:54:08 -0700, Joerg

[snip]
Variable pulley ratio... you dig?

No grok here

Again:

Synchronous motor -> no slip -> always in sync with your utility's 60Hz.

Strobe disk -> lamp -> lamp also always in sync with utility.

So, where's the value in this measurement?
If I can change the pulley ratio I can adjust the PLATTER speed.

But what for? If the pulley diameters are fixed and there is a
synchronous motor the platter speed can never deviate from nominal. All
it can do with age is drop to zero upon a gummed up shaft, when the belt
snaps or something.

What part of variable diameter (tapered) do you still not read? I am
not used to you being obtuse like this, please quit it.

I think Joerg is referring to some other turntables, I had a Garrard, it
had fixed shaft diameters (and no stroboscope ;-) ), IIRC Lenco had a conical
shaft, but really it is too long ago.
There are plenty of pictures and projects about the old players on the internet
though.

Yeah, the Lenco is the only one with a tapered shaft I remember. It was
used by European ballroom dance schools a lot. For anything else a
tapered shaft doesn't make any sense IMHO. They used it to vary the
speed, mostly slow it down to show the steps. When I started ballroom at
an, ahem, advanced age the Lencos were all gone.

 

[Joerg]

Yup, an induction motor starter for a synchronous motor.

Took me a whopping 20 work hours to free the fully seized shaft. The
previous owner hadn't oiled the organ in more than 10 years but
occasionally played it anyways. Arrgh!

It does have the occasional squeal, needs 2-3 start attempts to works
sans squeal. But what a sound! It's like sitting in a big cathedral.

 

[Jamie]

No, read the links.
Mains operated synchronous usually have an extra winding so they can start
in the first place, and only become synchronous once at speed.
If you break those, they will simply drop in speed, not stop.
3 phase variable frequency driven will skip phases too if over loaded.

No, that isn't true.. there is still slip in that type of motor.
Now, if you were referring to an energized rotor type of motor that
employs slip rigs I might then agree more with you but even then you
have slip conditions because that was one way, speed control was done
many moons ago.

I won't get no deeper into this because it's obvious many here are
colleged educated with no real world facts to get the clouded education
that has confused many out of their heads.




http://webpages.charter.net/jamie_5"

 

[Joerg]

A synchronous moter driven from a variable frequency generator,
will slip, it will not 'stall', ...

Nope. Once it slips it's almost done, way beyond the point of reliable
operation.

... it will just have speed modulation
at the driving frequency, what was, in the case of my cassette player,
several hundred Hz, thus FM modulating (no flywheel!) the singer / song/ instrument).
Other synchronous motors, mains driven, have an extra winding,
so they become normal motors when loaded to the point where they slip,
and do not stall either.

Then they are not truly synchronous motors. Maybe shaded-pole? Yes, most
of them can re-start after a stall but only if the load that caused a
stall is at least partially removed.

 

[Joerg]

No, that isn't true.. there is still slip in that type of motor.
Now, if you were referring to an energized rotor type of motor that
employs slip rigs I might then agree more with you but even then you
have slip conditions because that was one way, speed control was done
many moons ago.

I won't get no deeper into this because it's obvious many here are
colleged educated with no real world facts to get the clouded education
that has confused many out of their heads.

Colleges and universities actually do teach about motors. At least at my
university, until it came out of our ears. And this part of the
education was down to earth stuff, taught by guys who had designed
megawatt motors and generators.

 

[JosephKK]

No, that isn't true.. there is still slip in that type of motor.
Now, if you were referring to an energized rotor type of motor that
employs slip rigs I might then agree more with you but even then you
have slip conditions because that was one way, speed control was done
many moons ago.

I won't get no deeper into this because it's obvious many here are
colleged educated with no real world facts to get the clouded education
that has confused many out of their heads.

http://webpages.charter.net/jamie_5"

May i suggest a quick sorting question?

If you can explain the two forms of power angle for standard AC
motors and the difference between them, you may continue to
participate, otherwise please stand down and read only in case you get
a change to learn something.

 

[JosephKK]

Colleges and universities actually do teach about motors. At least at my
university, until it came out of our ears. And this part of the
education was down to earth stuff, taught by guys who had designed
megawatt motors and generators.

They can. They have mostly quit now. I had only two courses. Did
some real work later on.

 

[Jamie]

May i suggest a quick sorting question?

If you can explain the two forms of power angle for standard AC
motors and the difference between them, you may continue to
participate, otherwise please stand down and read only in case you get
a change to learn something.

Oh please, spare me the idiocy.

Not to push any one's buttons other than those that carry some
extra weight on their shoulders trying to maintain an audience level
of their liking, I find it very surprising how twisted and out of whack
people get such basic subject matter displaced and then along comes
people like your self spewing out comments as stated above.

For your information, I deal with EE's on a daily bases that are in
all sorts of aspects of the field. I know what is to be expected from
those that actually adhere to their fields.

Most of them that I associate with actual have years of hands on
experience. That's a lot more than I can say for a few here..

It's more like entertainment for me to sit here watch the pew scroll
by.

If, what I have to say really bothers you that much, please put me on
your filter.. I wouldn't want you to go into agony over me!

http://webpages.charter.net/jamie_5"

 

[JosephKK]

Oh please, spare me the idiocy.

Not to push any one's buttons other than those that carry some
extra weight on their shoulders trying to maintain an audience level
of their liking, I find it very surprising how twisted and out of whack
people get such basic subject matter displaced and then along comes
people like your self spewing out comments as stated above.

For your information, I deal with EE's on a daily bases that are in
all sorts of aspects of the field. I know what is to be expected from
those that actually adhere to their fields.

Most of them that I associate with actual have years of hands on
experience. That's a lot more than I can say for a few here..

It's more like entertainment for me to sit here watch the pew scroll
by.

If, what I have to say really bothers you that much, please put me on
your filter.. I wouldn't want you to go into agony over me!

http://webpages.charter.net/jamie_5"

You personally were not the cause of my issues. I was trying to
consolidate with you as i saw that you really do know the material. I
am a practicing EE with many years of varied experience. I do know
stuff outside of my college specialty of digital, but what is not like
about good grades (B average) that are easy.