Hi guys,

I have a 0.5HP 230V single phase motor that I want to use to make an
electric hacksaw. I'd like to vary the speed of it if possible (in
additon to conventional gearing) and as simply as possible. Could I
get away with using a light dimmer for this or is the inductive nature
of the load likely to cause an early "phut!"? If so, what's a workable
alternative?

cheers,

cd

On 15/07/14 21:07, Cursitor Doom wrote:
Hi guys,

I have a 0.5HP 230V single phase motor that I want to use to make an
electric hacksaw. I'd like to vary the speed of it if possible (in
additon to conventional gearing) and as simply as possible. Could I
get away with using a light dimmer for this or is the inductive nature
of the load likely to cause an early "phut!"? If so, what's a workable
alternative?


It should work.

Try and see - at the worst you will destroy the dimmer triac.

cheers,

cd



--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

On Tuesday, July 15, 2014 10:19:29 PM UTC+1, The Natural Philosopher wrote:
On 15/07/14 21:07, Cursitor Doom wrote:

Hi guys,



I have a 0.5HP 230V single phase motor that I want to use to make an

electric hacksaw. I'd like to vary the speed of it if possible (in

additon to conventional gearing) and as simply as possible. Could I

get away with using a light dimmer for this or is the inductive nature

of the load likely to cause an early "phut!"? If so, what's a workable

alternative?





It should work.



Try and see - at the worst you will destroy the dimmer triac.



cheers,



cd







--

Everything you read in newspapers is absolutely true, except for the

rare story of which you happen to have first-hand knowledge. - Erwin Knoll

Ummmm - if it's an induction motor, which you would be able to see by the plate on the motor showing an 'rpm', you could destroy the controller and possibly the motor. Induction motors are mains synchronous and don't like 'dropping out' of that with overload or low voltage.

On Tue, 15 Jul 2014 15:03:43 -0700 (PDT), robgraham
wrote:


Ummmm - if it's an induction motor, which you would be able to see by the plate on the motor showing an 'rpm',
you could destroy the controller and possibly the motor. Induction motors are mains synchronous and don't like
'dropping out' of that with overload or low voltage.

Is that a definitive method of identifying such a motor, then? A fixed
RPM shown on the plate?

On 15/07/14 23:26, Cursitor Doom wrote:
On Tue, 15 Jul 2014 15:03:43 -0700 (PDT), robgraham
wrote:


Ummmm - if it's an induction motor, which you would be able to see by the plate on the motor showing an 'rpm',
you could destroy the controller and possibly the motor. Induction motors are mains synchronous and don't like
'dropping out' of that with overload or low voltage.

Is that a definitive method of identifying such a motor, then? A fixed
RPM shown on the plate?

No commutator.

And a capacitor starter.
brushed motors are in general NOT induction motors.


--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

On Tue, 15 Jul 2014 23:44:03 +0100, The Natural Philosopher
wrote:

On 15/07/14 23:26, Cursitor Doom wrote:
On Tue, 15 Jul 2014 15:03:43 -0700 (PDT), robgraham
wrote:


Ummmm - if it's an induction motor, which you would be able to see by the plate on the motor showing an 'rpm',
you could destroy the controller and possibly the motor. Induction motors are mains synchronous and don't like
'dropping out' of that with overload or low voltage.

Is that a definitive method of identifying such a motor, then? A fixed
RPM shown on the plate?

No commutator.

And a capacitor starter.
brushed motors are in general NOT induction motors.

So is it the case that to know for sure, you have to take the damn
thing to bits?? That seems daft. They really should put something on
the plate to save aggro and for the avoidance of doubt!

In article ,
Cursitor Doom wrote:
On Tue, 15 Jul 2014 15:03:43 -0700 (PDT), robgraham
wrote:


Ummmm - if it's an induction motor, which you would be able to see by
the plate on the motor showing an 'rpm', you could destroy the
controller and possibly the motor. Induction motors are mains
synchronous and don't like 'dropping out' of that with overload or low
voltage.

Is that a definitive method of identifying such a motor, then? A fixed
RPM shown on the plate?

A universal motor - the type that can be easily speed controlled, will
have brushes. Assuming no gearbox, the spindle speed will also be much
higher than an induction one. Induction motors usually around 2000 rpm -
universal 10,000+

Induction motors are usually pretty quiet - universal pretty noisy.

--
*A closed mouth gathers no feet.

Dave Plowman London SW
To e-mail, change noise into sound.

"Cursitor Doom" wrote in message
...
On Tue, 15 Jul 2014 23:44:03 +0100, The Natural Philosopher
wrote:

On 15/07/14 23:26, Cursitor Doom wrote:
On Tue, 15 Jul 2014 15:03:43 -0700 (PDT), robgraham
wrote:


Ummmm - if it's an induction motor, which you would be able to see by
the plate on the motor showing an 'rpm',
you could destroy the controller and possibly the motor. Induction
motors are mains synchronous and don't like
'dropping out' of that with overload or low voltage.

Is that a definitive method of identifying such a motor, then? A fixed
RPM shown on the plate?

No commutator.

And a capacitor starter.
brushed motors are in general NOT induction motors.

So is it the case that to know for sure, you have to take the damn
thing to bits??

Nope, you don't have to take it to bits to see if its got brushes or a
commentator.

That seems daft. They really should put something on
the plate to save aggro and for the avoidance of doubt!

Not when so few even try to speed control them.

On Wed, 16 Jul 2014 00:21:58 +0100, "Dave Plowman (News)"
wrote:

In article ,
Cursitor Doom wrote:
On Tue, 15 Jul 2014 15:03:43 -0700 (PDT), robgraham
wrote:


Ummmm - if it's an induction motor, which you would be able to see by
the plate on the motor showing an 'rpm', you could destroy the
controller and possibly the motor. Induction motors are mains
synchronous and don't like 'dropping out' of that with overload or low
voltage.

Is that a definitive method of identifying such a motor, then? A fixed
RPM shown on the plate?

A universal motor - the type that can be easily speed controlled, will
have brushes. Assuming no gearbox, the spindle speed will also be much
higher than an induction one. Induction motors usually around 2000 rpm -
universal 10,000+

Induction motors are usually pretty quiet - universal pretty noisy.

Well, in the mean time I've found some sellers on ebay advertising
mains motor speed controllers up to around 2kw for only around 5 quid
inc. so couldn't resist ordering one. If the motor turns out to be
unsuitable when I've had a better chance to examine it, I'll just swap
it for a better one. Can't beat 5 quid!

I'm sure I've seen drill speed controls being sold, and I'd imagine they
work as you require.
Most dimmers seem unable to manage the inductive loads, probably the
reverse current on parts of the waveform. Seem to recall drill speed
controllers came in two types, what I call brute force, ie they were
protected against the phase issues of inductive loads by being just plain
big, and zero switching types, which to me at least nearly always seemed to
puldse the motor erratically at slow speeds, but much water has passed under
many bridges since then, so hopefully the issue is solved now.

Brian

--
From the Sofa of Brian Gaff Reply address is active
"robgraham" wrote in message
...
On Tuesday, July 15, 2014 10:19:29 PM UTC+1, The Natural Philosopher wrote:
On 15/07/14 21:07, Cursitor Doom wrote:

Hi guys,



I have a 0.5HP 230V single phase motor that I want to use to make an

electric hacksaw. I'd like to vary the speed of it if possible (in

additon to conventional gearing) and as simply as possible. Could I

get away with using a light dimmer for this or is the inductive nature

of the load likely to cause an early "phut!"? If so, what's a workable

alternative?





It should work.



Try and see - at the worst you will destroy the dimmer triac.



cheers,



cd







--

Everything you read in newspapers is absolutely true, except for the

rare story of which you happen to have first-hand knowledge. - Erwin Knoll

Ummmm - if it's an induction motor, which you would be able to see by the
plate on the motor showing an 'rpm', you could destroy the controller and
possibly the motor. Induction motors are mains synchronous and don't like
'dropping out' of that with overload or low voltage.

No induction motors have no brushes!
I'm assuming brushed motors here. Induction motors need to be driven with
some sort of variable AC frequency, not something trivial to build.
Brian

--
From the Sofa of Brian Gaff Reply address is active
"Cursitor Doom" wrote in message
...
On Tue, 15 Jul 2014 15:03:43 -0700 (PDT), robgraham
wrote:


Ummmm - if it's an induction motor, which you would be able to see by the
plate on the motor showing an 'rpm',
you could destroy the controller and possibly the motor. Induction motors
are mains synchronous and don't like
'dropping out' of that with overload or low voltage.

Is that a definitive method of identifying such a motor, then? A fixed
RPM shown on the plate?

In message , Brian Gaff
writes
No induction motors have no brushes!
I'm assuming brushed motors here. Induction motors need to be driven with
some sort of variable AC frequency, not something trivial to build.

I think you can get away with a variable voltage speed control if the
load torque increases more than that available from an increase in
supply voltage.

Hence fan speed control where the fan load is a square law.

--
Tim Lamb

On 16/07/14 09:00, Brian Gaff wrote:
No induction motors have no brushes!
I'm assuming brushed motors here. Induction motors need to be driven with
some sort of variable AC frequency, not something trivial to build.
Brian

Can have slip rings in some types.


--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

On Wed, 16 Jul 2014 08:59:10 +0100, "Brian Gaff"
wrote:

I'm sure I've seen drill speed controls being sold, and I'd imagine they
work as you require.

Good point, I'd guess.

I've had a chance to look at the motor plate now and it seems a bit
contradictory. On the one hand it states a speed of 2850rpm which
implies from what someone wrote above that it's induction type, yet it
also states in big letters that it's an asynchronous motor, which I'm
guessing implies it isn't.
Have to confess to a certain amount of confusion as a result. Can
anyone clarify if this is an induction type or not?

On 15/07/2014 21:07, Cursitor Doom wrote:
Hi guys,

I have a 0.5HP 230V single phase motor that I want to use to make an
electric hacksaw. I'd like to vary the speed of it if possible (in
additon to conventional gearing) and as simply as possible. Could I
get away with using a light dimmer for this or is the inductive nature
of the load likely to cause an early "phut!"? If so, what's a workable
alternative?

A lathe I used to have, which had stepless speed control, used a 5HP DC
motor to achieve it.

--
Colin Bignell

Cursitor Doom wrote

I've had a chance to look at the motor plate now and it seems a bit
contradictory. On the one hand it states a speed of 2850rpm which
implies from what someone wrote above that it's induction type,

Yes it is.

yet it also states in big letters that it's an asynchronous motor,

Those two are the same name for the same type of motor.
http://en.wikipedia.org/wiki/Induction_motor

which I'm guessing implies it isn't.

No.

Have to confess to a certain amount of confusion as a result.
Can anyone clarify if this is an induction type or not?

Yes it is.

On Wed, 16 Jul 2014 09:50:24 +0100, "Nightjar \"cpb\"@" "insert my
surname here wrote:

On 15/07/2014 21:07, Cursitor Doom wrote:
Hi guys,

I have a 0.5HP 230V single phase motor that I want to use to make an
electric hacksaw. I'd like to vary the speed of it if possible (in
additon to conventional gearing) and as simply as possible. Could I
get away with using a light dimmer for this or is the inductive nature
of the load likely to cause an early "phut!"? If so, what's a workable
alternative?

A lathe I used to have, which had stepless speed control, used a 5HP DC
motor to achieve it.

I'm much more comfortable with DC motor speed control, but am guessing
that a DC motor of any decent power (from a couple of HP up) is going
to be considerably more expensive than its AC counterpart?

On 16/07/2014 10:20, Cursitor Doom wrote:
On Wed, 16 Jul 2014 09:50:24 +0100, "Nightjar \"cpb\"@" "insert my
surname here wrote:

On 15/07/2014 21:07, Cursitor Doom wrote:
Hi guys,

I have a 0.5HP 230V single phase motor that I want to use to make an
electric hacksaw. I'd like to vary the speed of it if possible (in
additon to conventional gearing) and as simply as possible. Could I
get away with using a light dimmer for this or is the inductive nature
of the load likely to cause an early "phut!"? If so, what's a workable
alternative?

A lathe I used to have, which had stepless speed control, used a 5HP DC
motor to achieve it.

I'm much more comfortable with DC motor speed control, but am guessing
that a DC motor of any decent power (from a couple of HP up) is going
to be considerably more expensive than its AC counterpart?

No idea. It came with the CNC lathe :-)

--
Colin Bignell

In article ,
Cursitor Doom wrote:
I'm much more comfortable with DC motor speed control, but am guessing
that a DC motor of any decent power (from a couple of HP up) is going
to be considerably more expensive than its AC counterpart?

Probably not as they're smaller and lighter. The main difference in use is
an induction motor is fine for running more or less continuously. A
universal one (as used on mains drills, routers, vacuum cleaners etc) is
more designed for short periods of use, as it gets hot in service.

--
*Vegetarians taste great*

Dave Plowman London SW
To e-mail, change noise into sound.

On 16/07/14 09:49, Cursitor Doom wrote:
On Wed, 16 Jul 2014 08:59:10 +0100, "Brian Gaff"
wrote:

I'm sure I've seen drill speed controls being sold, and I'd imagine they
work as you require.

Good point, I'd guess.

I've had a chance to look at the motor plate now and it seems a bit
contradictory. On the one hand it states a speed of 2850rpm which
implies from what someone wrote above that it's induction type, yet it
also states in big letters that it's an asynchronous motor, which I'm
guessing implies it isn't.
Have to confess to a certain amount of confusion as a result. Can
anyone clarify if this is an induction type or not?

Three types.

Universal. DC or AC. Brushes and commutator and for AC wound field and
rotors.

Induction. AC only and generally has wound rotor and stator and my have
slip rings but no commutator. On single phase generally has a starter
capacitor.

Synchronous. Can have PM rotor or stator (unwound) and will operate at
mains frequency.


--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

On 16/07/14 10:20, Cursitor Doom wrote:
On Wed, 16 Jul 2014 09:50:24 +0100, "Nightjar \"cpb\"@" "insert my
surname here wrote:

On 15/07/2014 21:07, Cursitor Doom wrote:
Hi guys,

I have a 0.5HP 230V single phase motor that I want to use to make an
electric hacksaw. I'd like to vary the speed of it if possible (in
additon to conventional gearing) and as simply as possible. Could I
get away with using a light dimmer for this or is the inductive nature
of the load likely to cause an early "phut!"? If so, what's a workable
alternative?

A lathe I used to have, which had stepless speed control, used a 5HP DC
motor to achieve it.

I'm much more comfortable with DC motor speed control, but am guessing
that a DC motor of any decent power (from a couple of HP up) is going
to be considerably more expensive than its AC counterpart?

Not really at all.

In fact a universal motor (brushes and commmutator) is called that
because it works on AC and DC ...

--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

On 16/07/14 10:57, Dave Plowman (News) wrote:
In article ,
Cursitor Doom wrote:
I'm much more comfortable with DC motor speed control, but am guessing
that a DC motor of any decent power (from a couple of HP up) is going
to be considerably more expensive than its AC counterpart?

Probably not as they're smaller and lighter. The main difference in use is
an induction motor is fine for running more or less continuously. A
universal one (as used on mains drills, routers, vacuum cleaners etc) is
more designed for short periods of use, as it gets hot in service.

Er no.

They may be designed to pack a lot of power in a small package and
thereby get hot, but that's not intrinsic to the design.


Induction motors are not good at starting torque and wide speed ranges
and power ranges. Nor are they compact.

But they are simple and they are cheap.


--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

Cursitor Doom wrote:
Hi guys,

I have a 0.5HP 230V single phase motor that I want to use to make an
electric hacksaw. I'd like to vary the speed of it if possible (in
additon to conventional gearing) and as simply as possible. Could I
get away with using a light dimmer for this or is the inductive nature
of the load likely to cause an early "phut!"? If so, what's a workable
alternative?

cheers,

cd

Single phase induction motors are designed to run at full voltage and
constant speed. Causing the speed to reduce by any means. changing
voltage, running on part cycles or reducing the frequency will all cause
the starter winding to kick back in (usually with a centrifugal switch)
which will cause problems.

For a hacksaw, the best option is to seek out a 6 pole motor which will
run around 950 rpm and reduce the speed with a belt drive.
A four pole (1425rpm in uk) will be Ok with a smaller motor pulley but
the 2 pole (2850 in Uk) will be just too fast for the application.

The very successful Kennedy saws use a flat belt drive giving good grip
on a small diameter crowned motor pulley and a flywheel around 6-9"
according to model to drive the crank.
Modern source for flat belt drive is to use a toothed belt running on
its back. My kennedy model 90 has been running like that for several
years perfectly.

In article ,
The Natural Philosopher wrote:
On 16/07/14 10:57, Dave Plowman (News) wrote:
In article ,
Cursitor Doom wrote:
I'm much more comfortable with DC motor speed control, but am guessing
that a DC motor of any decent power (from a couple of HP up) is going
to be considerably more expensive than its AC counterpart?

Probably not as they're smaller and lighter. The main difference in
use is an induction motor is fine for running more or less
continuously. A universal one (as used on mains drills, routers,
vacuum cleaners etc) is more designed for short periods of use, as it
gets hot in service.

Er no.

They may be designed to pack a lot of power in a small package and
thereby get hot, but that's not intrinsic to the design.

Ok smart arse, give some examples of a universal motor designed for
continuous operation.


Induction motors are not good at starting torque and wide speed ranges
and power ranges. Nor are they compact.

Really? I can think of some very powerful induction motors. As regards
speed, you use a gearbox. Just as you do with a universal motor.

But they are simple and they are cheap.

Can you give some direct examples of the relative costs? With power tools
where mostly intermittent use gives a choice of either, the more expensive
variety usually has an induction motor. My guess is for a given (small)
size like say 1HP, a universal type is cheaper to make.

--
*I don't have a solution, but I admire your problem. *

Dave Plowman London SW
To e-mail, change noise into sound.

On 16/07/14 13:08, Dave Plowman (News) wrote:
Ok smart arse, give some examples of a universal motor designed for
continuous operation.

Give me an example of ANY electric motor designed for continuous operation?




--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

On Wed, 16 Jul 2014 13:01:48 +0100, Bob Minchin
wrote:

Cursitor Doom wrote:
Hi guys,

I have a 0.5HP 230V single phase motor that I want to use to make an
electric hacksaw. I'd like to vary the speed of it if possible (in
additon to conventional gearing) and as simply as possible. Could I
get away with using a light dimmer for this or is the inductive nature
of the load likely to cause an early "phut!"? If so, what's a workable
alternative?

cheers,

cd

Single phase induction motors are designed to run at full voltage and
constant speed. Causing the speed to reduce by any means. changing
voltage, running on part cycles or reducing the frequency will all cause
the starter winding to kick back in (usually with a centrifugal switch)
which will cause problems.

For a hacksaw, the best option is to seek out a 6 pole motor which will
run around 950 rpm and reduce the speed with a belt drive.
A four pole (1425rpm in uk) will be Ok with a smaller motor pulley but
the 2 pole (2850 in Uk) will be just too fast for the application.

The very successful Kennedy saws use a flat belt drive giving good grip
on a small diameter crowned motor pulley and a flywheel around 6-9"
according to model to drive the crank.
Modern source for flat belt drive is to use a toothed belt running on
its back. My kennedy model 90 has been running like that for several
years perfectly.


Well, it seems I've got a half horse 230V single phase 2850RPM
induction motor and will have to make the best of it. Since electronic
speed control seems to be out of the question, I'll just have to
fabricate a gear train to get the reduction necessary. Two strokes of
the blade per second ought to be about right so the maths is simple
enough (damn sight simpler than cobbling up the gear train but that's
life). Fortunately I have a lathe and a mill so things could be worse.
:-/

In article ,
The Natural Philosopher wrote:
On 16/07/14 13:08, Dave Plowman (News) wrote:
Ok smart arse, give some examples of a universal motor designed for
continuous operation.

Give me an example of ANY electric motor designed for continuous
operation?

Showing your stupidity again.

--
*My wife has a slight impediment in her speech. She stops to breathe.

Dave Plowman London SW
To e-mail, change noise into sound.

Cursitor Doom wrote:
On Wed, 16 Jul 2014 13:01:48 +0100, Bob Minchin
wrote:

Cursitor Doom wrote:
Hi guys,

I have a 0.5HP 230V single phase motor that I want to use to make an
electric hacksaw. I'd like to vary the speed of it if possible (in
additon to conventional gearing) and as simply as possible. Could I
get away with using a light dimmer for this or is the inductive nature
of the load likely to cause an early "phut!"? If so, what's a workable
alternative?

cheers,

cd

Single phase induction motors are designed to run at full voltage and
constant speed. Causing the speed to reduce by any means. changing
voltage, running on part cycles or reducing the frequency will all cause
the starter winding to kick back in (usually with a centrifugal switch)
which will cause problems.

For a hacksaw, the best option is to seek out a 6 pole motor which will
run around 950 rpm and reduce the speed with a belt drive.
A four pole (1425rpm in uk) will be Ok with a smaller motor pulley but
the 2 pole (2850 in Uk) will be just too fast for the application.

The very successful Kennedy saws use a flat belt drive giving good grip
on a small diameter crowned motor pulley and a flywheel around 6-9"
according to model to drive the crank.
Modern source for flat belt drive is to use a toothed belt running on
its back. My kennedy model 90 has been running like that for several
years perfectly.


Well, it seems I've got a half horse 230V single phase 2850RPM
induction motor and will have to make the best of it. Since electronic
speed control seems to be out of the question, I'll just have to
fabricate a gear train to get the reduction necessary. Two strokes of
the blade per second ought to be about right so the maths is simple
enough (damn sight simpler than cobbling up the gear train but that's
life). Fortunately I have a lathe and a mill so things could be worse.
:-/

2850 might a bit fast for simple, open gears. Perhaps OK for a worm drive.
Big snag with gears on a reciprocating mechanism is that the last gear
in the train will wear asymmetrically.
Belts avoid this and should be easier.
There are a few kits around which might same a whole load of design
time. Blackgates used to do one, maybe Hemingway too.

"robgraham" wrote in message
...
On Tuesday, July 15, 2014 10:19:29 PM UTC+1, The Natural Philosopher wrote:
On 15/07/14 21:07, Cursitor Doom wrote:

Hi guys,



I have a 0.5HP 230V single phase motor that I want to use to make an

electric hacksaw. I'd like to vary the speed of it if possible (in

additon to conventional gearing) and as simply as possible. Could I

get away with using a light dimmer for this or is the inductive nature

of the load likely to cause an early "phut!"? If so, what's a workable

alternative?





It should work.



Try and see - at the worst you will destroy the dimmer triac.



cheers,



cd







--

Everything you read in newspapers is absolutely true, except for the

rare story of which you happen to have first-hand knowledge. - Erwin Knoll

Ummmm - if it's an induction motor, which you would be able to see by the
plate on the motor showing an 'rpm', you could destroy the controller and
possibly the motor. Induction motors are mains synchronous and don't like
'dropping out' of that with overload or low voltage.

Induction motors do not run at synchronous speed.
The rpm given is the no load speed.
It drops slightly as the motor is loaded up.
Reducing the voltage to an induction motor will slow it down up to a point
but you must de-rate the output power of it because the iron losses increase
unduely causing overheating. But only around 10% speed reduction is
advisable.
So probably no good to you.
The traditional way is by variable sized "cone" pullys".

The proper way to proceed is with a proper motor speed control which
rectifies the ACand then puts out a variable frequency.

"Cursitor Doom" wrote in message
...
On Tue, 15 Jul 2014 23:44:03 +0100, The Natural Philosopher
wrote:

On 15/07/14 23:26, Cursitor Doom wrote:
On Tue, 15 Jul 2014 15:03:43 -0700 (PDT), robgraham
wrote:


Ummmm - if it's an induction motor, which you would be able to see by
the plate on the motor showing an 'rpm',
you could destroy the controller and possibly the motor. Induction
motors are mains synchronous and don't like
'dropping out' of that with overload or low voltage.

Is that a definitive method of identifying such a motor, then? A fixed
RPM shown on the plate?

No commutator.

And a capacitor starter.
brushed motors are in general NOT induction motors.

So is it the case that to know for sure, you have to take the damn
thing to bits?? That seems daft. They really should put something on
the plate to save aggro and for the avoidance of doubt!



If it's an induction motor.
Assuming you are in the UK the speed will be either just under 3000rpm ,
just under 1500rpm or just under 1000rpm.
This is because we have 50 Hz /3000 cycles per minute mains supply.
You are very inlikely to come across anything else.
99% of motors are induction motors because they are cheap to make.

"Brian Gaff" wrote in message
...
No induction motors have no brushes!
I'm assuming brushed motors here. Induction motors need to be driven with
some sort of variable AC frequency, not something trivial to build.
Brian



Some induction motors have brushes.
There are wound rotor induction motors,
The brushes are connected to external resistors.
It's to do with improving the starting torque not speed control.
Haven't seen one for years though.
Commonly used on large conveyors etc.
In days of yore.

There are also Schrage motors which are true variable speed AC motors that
can run at super and sub synchronous speeds
Haven't seen one of these for years either.

In article ,
harryagain wrote:
99% of motors are induction motors because they are cheap to make.

Are you sure about that?

In the average house, most will have more universal motors than induction,
I'd guess. Mainly because they are easier to control the speed of.

Different matter in a pro workshop or factory.

--
*Don't worry; it only seems kinky the first time.*

Dave Plowman London SW
To e-mail, change noise into sound.

"The Natural Philosopher" wrote in message
...
On 16/07/14 13:08, Dave Plowman (News) wrote:
Ok smart arse, give some examples of a universal motor designed for
continuous operation.

Give me an example of ANY electric motor designed for continuous
operation?


Any fan motor
Virtually all pumps.

"Cursitor Doom" wrote in message
...
On Wed, 16 Jul 2014 13:01:48 +0100, Bob Minchin
wrote:

Cursitor Doom wrote:
Hi guys,

I have a 0.5HP 230V single phase motor that I want to use to make an
electric hacksaw. I'd like to vary the speed of it if possible (in
additon to conventional gearing) and as simply as possible. Could I
get away with using a light dimmer for this or is the inductive nature
of the load likely to cause an early "phut!"? If so, what's a workable
alternative?

cheers,

cd

Single phase induction motors are designed to run at full voltage and
constant speed. Causing the speed to reduce by any means. changing
voltage, running on part cycles or reducing the frequency will all cause
the starter winding to kick back in (usually with a centrifugal switch)
which will cause problems.

For a hacksaw, the best option is to seek out a 6 pole motor which will
run around 950 rpm and reduce the speed with a belt drive.
A four pole (1425rpm in uk) will be Ok with a smaller motor pulley but
the 2 pole (2850 in Uk) will be just too fast for the application.

The very successful Kennedy saws use a flat belt drive giving good grip
on a small diameter crowned motor pulley and a flywheel around 6-9"
according to model to drive the crank.
Modern source for flat belt drive is to use a toothed belt running on
its back. My kennedy model 90 has been running like that for several
years perfectly.


Well, it seems I've got a half horse 230V single phase 2850RPM
induction motor and will have to make the best of it. Since electronic
speed control seems to be out of the question, I'll just have to
fabricate a gear train to get the reduction necessary. Two strokes of
the blade per second ought to be about right so the maths is simple
enough (damn sight simpler than cobbling up the gear train but that's
life). Fortunately I have a lathe and a mill so things could be worse.
:-/

You can't vary the speed of and induction motor by varying the voltage.
You can vary it by varying the frequency.
You can buy a motor speed control that does this.
But be sure it is a frequency changer.

They are quite common on new cheap lathes for example, saves having a
gearbox.

On Wed, 16 Jul 2014 17:52:32 +0100, "harryagain"
wrote:

You can't vary the speed of and induction motor by varying the voltage.
You can vary it by varying the frequency.
You can buy a motor speed control that does this.
But be sure it is a frequency changer.

They are quite common on new cheap lathes for example, saves having a
gearbox.


I'm suitably impressed by Bob's suggestion of a wormdrive. A simple
and elegant solution to the problem - at least until the next
fault-finder throws another spanner in the works!

harryagain wrote:
"Cursitor Doom" wrote in message
...
On Wed, 16 Jul 2014 13:01:48 +0100, Bob Minchin
wrote:

Cursitor Doom wrote:
Hi guys,

I have a 0.5HP 230V single phase motor that I want to use to make an
electric hacksaw. I'd like to vary the speed of it if possible (in
additon to conventional gearing) and as simply as possible. Could I
get away with using a light dimmer for this or is the inductive nature
of the load likely to cause an early "phut!"? If so, what's a workable
alternative?

cheers,

cd

Single phase induction motors are designed to run at full voltage and
constant speed. Causing the speed to reduce by any means. changing
voltage, running on part cycles or reducing the frequency will all cause
the starter winding to kick back in (usually with a centrifugal switch)
which will cause problems.

For a hacksaw, the best option is to seek out a 6 pole motor which will
run around 950 rpm and reduce the speed with a belt drive.
A four pole (1425rpm in uk) will be Ok with a smaller motor pulley but
the 2 pole (2850 in Uk) will be just too fast for the application.

The very successful Kennedy saws use a flat belt drive giving good grip
on a small diameter crowned motor pulley and a flywheel around 6-9"
according to model to drive the crank.
Modern source for flat belt drive is to use a toothed belt running on
its back. My kennedy model 90 has been running like that for several
years perfectly.


Well, it seems I've got a half horse 230V single phase 2850RPM
induction motor and will have to make the best of it. Since electronic
speed control seems to be out of the question, I'll just have to
fabricate a gear train to get the reduction necessary. Two strokes of
the blade per second ought to be about right so the maths is simple
enough (damn sight simpler than cobbling up the gear train but that's
life). Fortunately I have a lathe and a mill so things could be worse.
:-/

You can't vary the speed of and induction motor by varying the voltage.
You can vary it by varying the frequency.
You can buy a motor speed control that does this.
But be sure it is a frequency changer.

They are quite common on new cheap lathes for example, saves having a
gearbox.


This is ******** Harry. You should know better
A single phase motor running on reduced frequency will switch in the
start winding. The start winding and capacitor are designed for 50hz.

You can only change the speed of a 3 phase motor with a variable
frequency supply.

Cursitor Doom wrote:
On Wed, 16 Jul 2014 17:52:32 +0100, "harryagain"
wrote:

You can't vary the speed of and induction motor by varying the voltage.
You can vary it by varying the frequency.
You can buy a motor speed control that does this.
But be sure it is a frequency changer.

They are quite common on new cheap lathes for example, saves having a
gearbox.


I'm suitably impressed by Bob's suggestion of a wormdrive. A simple
and elegant solution to the problem - at least until the next
fault-finder throws another spanner in the works!

But the worm wheel will wear asymmetrically due to the load of a saw.

Gear trains should be designed so that the load wear is distributed
evenly which is why most gear ratios are non integral.

On Wed, 16 Jul 2014 17:52:32 +0100, "harryagain"
wrote:

They are quite common on new cheap lathes for example, saves having a
gearbox.

But how would you do screwcutting and whatnot if you can't change the
speed of the saddle independently of the chuck? I can't see any way of
avoiding a gearbox (or a set of changewheels) in such circumstances.

Cursitor Doom wrote:
On Wed, 16 Jul 2014 17:52:32 +0100, "harryagain"
wrote:

They are quite common on new cheap lathes for example, saves having a
gearbox.

But how would you do screwcutting and whatnot if you can't change the
speed of the saddle independently of the chuck? I can't see any way of
avoiding a gearbox (or a set of changewheels) in such circumstances.

Sorry CD - this is just more Harry ********!

Cheap lathes have brush motor with drill speed type pulse width
modulation speed controllers.
They do away with having geared heads in this was but still have
standard changewheels for screwcutting.

There is quite a lot of work going on under the amateur electronic
leadscrew project where the leadscrew is driven by a stepper motor but
electronically synchronised with the lathe mandrel for a near infinite
range of screw cutting pitches. proper CNC lathes have nearly always
done it this way but I digress!

"The Natural Philosopher" wrote in message
...
On 16/07/14 13:08, Dave Plowman (News) wrote:
Ok smart arse, give some examples of a universal motor designed for
continuous operation.

Give me an example of ANY electric motor designed for continuous
operation?

The ones used in what the yanks call swap coolers.

And the ones used in fans.