Just been dismantling an old and very dead Ferguson music centre,
probably from the 70s. Nice little DC motor that powered the turntable,
for which I have another use in mind.

Using a bench power supply, the motor spins well at 5v, but I don't know
the voltage the motor was designed for, there being nothing stamped or
marked on it. Were these things fairly standard, and is 12v likely to
be the maximum voltage, or is that 'how long is a piece of string' ?
--
Graeme

Some of these on both cassette and turntable had built in speed control.
Very non sophisticated and seems mainly to be of two main types. The cheap
and nasty ones use an old fashioned governor that disconnects power when a
certain speed is reached. These tend to generate a lotof interference.
The second sort have a little pcb in the back end of the motor that somehow
monitors current anbut not actual speed. I did read these worked from some
kind of clever back emf action, but they were not mega stable over time as
no true servo control was used.


Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"News" wrote in message
...

Just been dismantling an old and very dead Ferguson music centre, probably
from the 70s. Nice little DC motor that powered the turntable, for which
I have another use in mind.

Using a bench power supply, the motor spins well at 5v, but I don't know
the voltage the motor was designed for, there being nothing stamped or
marked on it. Were these things fairly standard, and is 12v likely to be
the maximum voltage, or is that 'how long is a piece of string' ?
--
Graeme

Incidentally, assuming it was a belt drive device, there is probably a
little hole in the bottom of the motor to tweak the speed. a few made by
Mitsubishi seemed to actually have some servo based on pulses fed from the
turntable drive itself.


It is as you say going to be difficult without the circuit diagram to figure
out what the voltage range was.
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"News" wrote in message
...

Just been dismantling an old and very dead Ferguson music centre, probably
from the 70s. Nice little DC motor that powered the turntable, for which
I have another use in mind.

Using a bench power supply, the motor spins well at 5v, but I don't know
the voltage the motor was designed for, there being nothing stamped or
marked on it. Were these things fairly standard, and is 12v likely to be
the maximum voltage, or is that 'how long is a piece of string' ?
--
Graeme

In message , Brian Gaff
writes
Incidentally, assuming it was a belt drive device,

Thanks Brian. Yes, it is belt drive.

Thinking aloud, mainly because I didn't study physics at school, does
reducing the voltage, and therefore the speed of the motor then result
in a reduction of power, or torque?

--
Graeme

On 19/05/16 06:45, News wrote:

Just been dismantling an old and very dead Ferguson music centre,
probably from the 70s. Nice little DC motor that powered the turntable,
for which I have another use in mind.

Using a bench power supply, the motor spins well at 5v, but I don't know
the voltage the motor was designed for, there being nothing stamped or
marked on it. Were these things fairly standard, and is 12v likely to
be the maximum voltage, or is that 'how long is a piece of string' ?

Ah well, be prepar3ed for an education lesson.

Small DC magnetted Electric motors do not really have a 'voltage' rating.

Ther is a little motor that was/is used in electric tooth brushes on 1-3
V. Rebadged and sold with a gearbox this little motor was used to power
model planes running of 7.2v or thereabouts packs. IT was a bit gutless.

I ran them on a much higher gear ratio on 11V, and got better life and
power out of them. Simply because the higher voltage meant less current,
and what broke them was brush burn.


If you delve into the theory of these motors, there are two basic groups
of losses. Loses that represent a fixed current draw irrespective of the
RPM or voltage, due to things like friction, and hysteresis losses. And
looses that go up with the square of the load current which are
basically resistive losses in the copper.

For a given heat dissipation, you can solve a slightly complex equation
and get the best power and or the best efficiency of the motor. *If
either of those is of interest* and trust me. largely they are NOT.

I.e. the motors in my car windows are DESIGNED TO STALL as that provides
a way to tell when the window is fully open, or closed.

So a basic little battery motor can do massively more than you expect by
putting it on a far higher voltage and letting the revs climb. For a
given copper heating, you have a given current, and that means a given
torque, available. If that torque is delivered at 50,000 RPM (by no
means beyond reason for a small motor) rather than 5,000, you have 10
times the power for the same heating. Of course your FIXED current
losses are ten times higher, but as long as these are not dominant, you
have enormous potential.


IN model planes, we were always searching for performance, and what
limited motors was mechanical issues by and large.

- Uber high RPM caused brush bounce and brush burnup due to excessive
arcing. Solid state commutation (brushless motors) solved that.
- Uber high RPM caused physical disintegration of the rotors. Kevlar
wrapping and gluing in place solved that to a degree.
- Uber high propellor RPM just makes noise, not thrust, so rather large
reduction gearboxes were needed adding to cost weight and losing a bit
of efficiency.

So there is no real concept of 'voltage rating' - it tends to be an
arbitrary number stamped on the motor by the manufacturer, but in
reality it means almost nothing.

Current rating is far more pertinent,. but no one ever quotes that.



--
Truth welcomes investigation because truth knows investigation will lead
to converts. It is deception that uses all the other techniques.

On 19/05/16 08:17, News wrote:
In message , Brian Gaff
writes
Incidentally, assuming it was a belt drive device,

Thanks Brian. Yes, it is belt drive.

Thinking aloud, mainly because I didn't study physics at school, does
reducing the voltage, and therefore the speed of the motor then result
in a reduction of power, or torque?

It results in a reduction in RPM

Torque will rise to match the applied load, until current exceeds the
safe limit, and then the magic smoke comes out

There is another effect we learnt in the model plane arena. Before the
magic smoke comes out completely, the magnets get so hot that they go
beyond the curie point and lose magnetism, which results in the
effective back EMF falling, the mntir trying to speed up even MORE to
generate it, drawing even MORE current and a positive and destructive
feedback takes place. We learnt to listen for an unexplained rise in ROM
and close the throttle..sometimes the motor was saved.


--
How fortunate for governments that the people they administer don't think.

Adolf Hitler

In message , The Natural Philosopher
writes

So there is no real concept of 'voltage rating' - it tends to be an
arbitrary number stamped on the motor by the manufacturer, but in
reality it means almost nothing.

Thank you! Bottom line, apply my 5v as before, and gradually increase
the voltage. My ears will tell me when I need to back off.

Actually, high speed is not important. Just the opposite, in fact.
Vague plan is to use this record turntable as a toy train loco
turntable, so slow speed is good. How quickly the TT will stop rotating
once power is cut, I don't know yet, Assuming not terribly quickly,
either some form of indexing will be required, or a lot of practice!

Next step is to try and find a replacement drive belt, which may not be
easy.
--
Graeme

On Thursday, 19 May 2016 06:46:57 UTC+1, News wrote:

Just been dismantling an old and very dead Ferguson music centre,
probably from the 70s. Nice little DC motor that powered the turntable,
for which I have another use in mind.

Using a bench power supply, the motor spins well at 5v, but I don't know
the voltage the motor was designed for, there being nothing stamped or
marked on it. Were these things fairly standard, and is 12v likely to
be the maximum voltage, or is that 'how long is a piece of string' ?

6v, 9v or 12v. Try 6, if no go try 9, if no go try 12. Usually they were voltage marked, and usually one can get the psu working easily to check V.


NT

On Thursday, 19 May 2016 11:47:07 UTC+1, News wrote:

Actually, high speed is not important. Just the opposite, in fact.
Vague plan is to use this record turntable as a toy train loco
turntable, so slow speed is good. How quickly the TT will stop rotating
once power is cut, I don't know yet, Assuming not terribly quickly,
either some form of indexing will be required, or a lot of practice!

or physical stops.

Next step is to try and find a replacement drive belt, which may not be
easy.

Many stationery rubber bands last well, some don't. Superglue a few end to end to get a usable size.


NT

On Thu, 19 May 2016 03:53:29 -0700 (PDT), wrote:

Actually, high speed is not important. Just the opposite, in
fact.
Vague plan is to use this record turntable as a toy train loco
turntable, so slow speed is good. How quickly the TT will stop
rotating once power is cut, I don't know yet, Assuming not
terribly
quickly, either some form of indexing will be required, or a lot
of
practice!

I think if you want to stop the turntable and drive a loco off
without touching the turntable you'll need some form of indexing.

or physical stops.

Moving ones so turntable can do 360 degrees plus. Hole in edge of
turntable, lighly spring loaded to engaged position solenoid operated
pin that is retracted when the motor is powered.

Next step is to try and find a replacement drive belt, which may
not be
easy.

Many stationery rubber bands last well, some don't. Superglue a few end
to end to get a usable size.

Or see what CPC have...

--
Cheers
Dave.

On 19/05/16 11:40, News wrote:
In message , The Natural Philosopher
writes

So there is no real concept of 'voltage rating' - it tends to be an
arbitrary number stamped on the motor by the manufacturer, but in
reality it means almost nothing.

Thank you! Bottom line, apply my 5v as before, and gradually increase
the voltage. My ears will tell me when I need to back off.

Actually, high speed is not important. Just the opposite, in fact.
Vague plan is to use this record turntable as a toy train loco
turntable, so slow speed is good. How quickly the TT will stop rotating
once power is cut, I don't know yet, Assuming not terribly quickly,
either some form of indexing will be required, or a lot of practice!

Next step is to try and find a replacement drive belt, which may not be
easy.

Ah, All sounds fun

try here for belts and gears

http://www.technobotsonline.com/

--
The biggest threat to humanity comes from socialism, which has utterly
diverted our attention away from what really matters to our existential
survival, to indulging in navel gazing and faux moral investigations
into what the world ought to be, whilst we fail utterly to deal with
what it actually is.

On Thursday, 19 May 2016 13:23:02 UTC+1, The Natural Philosopher wrote:
On 19/05/16 11:40, News wrote:
In message , The Natural Philosopher
writes

So there is no real concept of 'voltage rating' - it tends to be an
arbitrary number stamped on the motor by the manufacturer, but in
reality it means almost nothing.

Thank you! Bottom line, apply my 5v as before, and gradually increase
the voltage. My ears will tell me when I need to back off.

Actually, high speed is not important. Just the opposite, in fact.
Vague plan is to use this record turntable as a toy train loco
turntable, so slow speed is good. How quickly the TT will stop rotating
once power is cut, I don't know yet, Assuming not terribly quickly,
either some form of indexing will be required, or a lot of practice!

Next step is to try and find a replacement drive belt, which may not be
easy.

Ah, All sounds fun

try here for belts and gears

http://www.technobotsonline.com/

VCRs used to be a good source. Old ones, not so much the later ones.


NT

On Thursday, 19 May 2016 12:05:06 UTC+1, Dave Liquorice wrote:
On Thu, 19 May 2016 03:53:29 -0700 (PDT), tabbypurr wrote:

Next step is to try and find a replacement drive belt, which may
not be
easy.

Many stationery rubber bands last well, some don't. Superglue a few end
to end to get a usable size.

Or see what CPC have...

elastic also works.


NT