Why is that when you are at one's intellectual worst that the more
complex of discussions occur - solution of the world's problems,
etc !!!

This particular one revolved round ac and dc motors - covering single
phase v. 3 ph induction motors and their relative power /torque
capabilities and how they work, which was hard work 45 years after
university, but what triggered the whole discussion was how Bosch can
claim that a lawnmower with a 36v Li-polymer powered dc motor can have
the same capability as a 1700w ac motor. OK 1700w is a comfortable
2hp but single phase induction motors are not too good on torque, and
if I remember that is where dc motors score but are modern ones going
to match a 1700w ac motor ?

Can anyone help or point me at a site on this topic please.

Rob

In article ,
robgraham writes:
Why is that when you are at one's intellectual worst that the more
complex of discussions occur - solution of the world's problems,
etc !!!

This particular one revolved round ac and dc motors - covering single
phase v. 3 ph induction motors and their relative power /torque
capabilities and how they work, which was hard work 45 years after
university, but what triggered the whole discussion was how Bosch can
claim that a lawnmower with a 36v Li-polymer powered dc motor can have
the same capability as a 1700w ac motor. OK 1700w is a comfortable
2hp but single phase induction motors are not too good on torque, and
if I remember that is where dc motors score but are modern ones going
to match a 1700w ac motor ?

I think most electric mowers are universal motors (i.e. with
brushes and a commutator). Certainly they were 8 years ago
when I last bought one -- I had to go some way off the beaten
track to find an induction motor mower. I've bought two over
the years -- I think they're both German but different makes
(both still working fine, although I've had to replace the
run capacitor in the 15 year old one).

The torque profile of a universal and induction motor is quite
different. An induction motor doesn't have much starting torque,
but when it's nearly up to speed, there's quite a lot of torque
to maintain speed, which makes it good for a mower. A universal
motor has a high starting torque, but low torque when up to
speed, which means it easily slows when under load. That isn't
good for a lawn mower. Universal motors also spin too fast for
direct coupling to a mower blade. You will also find you need
around 30-50% more powerful universal motor mower to get the
same cutting power as an induction motor. Universal motors
seem to get much hotter, but that may just reflect cheap lower
quality motors rather than any inherent reason.

Can anyone help or point me at a site on this topic please.

How many AHrs is the 36v Li-polymer battery?

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

robgraham wrote:
Why is that when you are at one's intellectual worst that the more
complex of discussions occur - solution of the world's problems,
etc !!!

This particular one revolved round ac and dc motors - covering single
phase v. 3 ph induction motors and their relative power /torque
capabilities and how they work, which was hard work 45 years after
university, but what triggered the whole discussion was how Bosch can
claim that a lawnmower with a 36v Li-polymer powered dc motor can have
the same capability as a 1700w ac motor. OK 1700w is a comfortable
2hp but single phase induction motors are not too good on torque, and
if I remember that is where dc motors score but are modern ones going
to match a 1700w ac motor ?

Can anyone help or point me at a site on this topic please.

certainly 36v and about 50A is not unusual in the largest 'DC' model
aircraft motors. Mind you there is no such thing as a DC motor.

They are all 3 phase. - a DC brushed motor simply uses a commutator to
generate the AC..

If you are sticking 1700W in, its got to come out as heat, noise or as
shaft power.

I doubt efficiencies are any less on a brushed PM versus induction
motor, ..


Rob

Andrew Gabriel wrote:
In article
,
robgraham writes:
Why is that when you are at one's intellectual worst that the more
complex of discussions occur - solution of the world's problems,
etc !!!

This particular one revolved round ac and dc motors - covering single
phase v. 3 ph induction motors and their relative power /torque
capabilities and how they work, which was hard work 45 years after
university, but what triggered the whole discussion was how Bosch can
claim that a lawnmower with a 36v Li-polymer powered dc motor can
have the same capability as a 1700w ac motor. OK 1700w is a
comfortable 2hp but single phase induction motors are not too good
on torque, and if I remember that is where dc motors score but are
modern ones going to match a 1700w ac motor ?

I think most electric mowers are universal motors (i.e. with
brushes and a commutator). SNIP

Cetrainly all the 'hovver' mowers would be, an induction motor would be far
to heavy.

Cost is also a factor, all the el cheapo pressure washers have universal
motors because of the cost, commercial machines have induction.


--
Dave - The Medway Handyman
www.medwayhandyman.co.uk

"Andrew Gabriel" wrote in message
...


I think most electric mowers are universal motors (i.e. with
brushes and a commutator). Certainly they were 8 years ago
when I last bought one -- I had to go some way off the beaten
track to find an induction motor mower. I've bought two over
the years -- I think they're both German but different makes
(both still working fine, although I've had to replace the
run capacitor in the 15 year old one).

IIRC qualcast use induction motors even in the little rotary mowers.

dennis@home wrote:


"Andrew Gabriel" wrote in message
...


I think most electric mowers are universal motors (i.e. with
brushes and a commutator). Certainly they were 8 years ago
when I last bought one -- I had to go some way off the beaten
track to find an induction motor mower. I've bought two over
the years -- I think they're both German but different makes
(both still working fine, although I've had to replace the
run capacitor in the 15 year old one).

IIRC qualcast use induction motors even in the little rotary mowers.



My Honda electric mower - about 15 years old with a rust free plastic
deck has an induction motor. I want it to break as my wife that likes
it will let me buy a petrol mower, but it just keeps on going...........

"The Natural Philosopher" wrote in message
...
robgraham wrote:
Why is that when you are at one's intellectual worst that the more
complex of discussions occur - solution of the world's problems,
etc !!!

This particular one revolved round ac and dc motors - covering single
phase v. 3 ph induction motors and their relative power /torque
capabilities and how they work, which was hard work 45 years after
university, but what triggered the whole discussion was how Bosch can
claim that a lawnmower with a 36v Li-polymer powered dc motor can have
the same capability as a 1700w ac motor. OK 1700w is a comfortable
2hp but single phase induction motors are not too good on torque, and
if I remember that is where dc motors score but are modern ones going
to match a 1700w ac motor ?

Can anyone help or point me at a site on this topic please.

certainly 36v and about 50A is not unusual in the largest 'DC' model
aircraft motors. Mind you there is no such thing as a DC motor.

They are all 3 phase. - a DC brushed motor simply uses a commutator to
generate the AC..

??? In a DC motor the field is DC. The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous torque. Not
sure where you get 3 phase from. From a standard single pole pair DC motor
I would call it "single phase". 2 pole pairs on a DC motor is common place
for starter motors. I haven't come across with 3 pole pairs with 3 sets of
brushes?


If you are sticking 1700W in, its got to come out as heat, noise or as
shaft power.

I remain unconvinced about power in and useable power out for mains motors.
At present I would have hoped green thinking would have had some meaningful
measure of real power out, not just turned into heat. There is still the
concept that the more power in the better the motor! Generally small
induction motors are very inefficient, DC motors are inherently very
efficient. AC (brushed) motors are less efficient than DC and the best
thing that could be done would be to rectify the mains first.


I doubt efficiencies are any less on a brushed PM versus induction motor,
..


Rob

Fred wrote:
"The Natural Philosopher" wrote in message
...
robgraham wrote:
Why is that when you are at one's intellectual worst that the more
complex of discussions occur - solution of the world's problems,
etc !!!

This particular one revolved round ac and dc motors - covering single
phase v. 3 ph induction motors and their relative power /torque
capabilities and how they work, which was hard work 45 years after
university, but what triggered the whole discussion was how Bosch can
claim that a lawnmower with a 36v Li-polymer powered dc motor can have
the same capability as a 1700w ac motor. OK 1700w is a comfortable
2hp but single phase induction motors are not too good on torque, and
if I remember that is where dc motors score but are modern ones going
to match a 1700w ac motor ?

Can anyone help or point me at a site on this topic please.

certainly 36v and about 50A is not unusual in the largest 'DC' model
aircraft motors. Mind you there is no such thing as a DC motor.

They are all 3 phase. - a DC brushed motor simply uses a commutator to
generate the AC..

??? In a DC motor the field is DC.

So what?

Its still a three phase motor with the poles switched on one (or two) at
a time via a 2 brush system on a Nx3 commutator element.



The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous torque. Not
sure where you get 3 phase from.

Each winding gets an AC signal. Each winding is switched at 120 degrees
phase to the next one: If I told you that and told you nothing else,
you would say 'ah, a 3 phase AC motor!!'




From a standard single pole pair DC motor
I would call it "single phase". 2 pole pairs on a DC motor is common place
for starter motors. I haven't come across with 3 pole pairs with 3 sets of
brushes?

The simples motor is a single phase. But its not self starting.
Therefore the simplest that works is three phase with two magnet
poles.It ameks no dss as to whether the current is originally DC with
permanent magnets, or AC with a field winding. It will work.

Unless you actyally go for synchronuus motors, the actual AC that drives
the MOTOR as opposed to a high frequency ripple on the magnetic fields,
is generated by brushes and commutators or an electronic switch.






If you are sticking 1700W in, its got to come out as heat, noise or as
shaft power.

I remain unconvinced about power in and useable power out for mains motors.
At present I would have hoped green thinking would have had some meaningful
measure of real power out, not just turned into heat.

On a mains motor, the frequency of commutation is nor far off mains
frequency for typical motors speeds - about 3000 RPM say. So there is
not much extra iron loss using a mains motor or a permanent magnet motor
or an induction motor off DC.

All are capable of better than 90&% efficiency if built well, or as low
as 50% if stamped out in thousands in Taiwan, and operated well off
decent efficiency points.


There is still the
concept that the more power in the better the motor! Generally small
induction motors are very inefficient, DC motors are inherently very
efficient. AC (brushed) motors are less efficient than DC and the best
thing that could be done would be to rectify the mains first.


I dont see why they should be really.

I doubt efficiencies are any less on a brushed PM versus induction motor,
..


yup


Rob

The Natural Philosopher wrote:
Fred wrote:
"The Natural Philosopher" wrote in message
...
robgraham wrote:
Why is that when you are at one's intellectual worst that the more
complex of discussions occur - solution of the world's problems,
etc !!!

This particular one revolved round ac and dc motors - covering single
phase v. 3 ph induction motors and their relative power /torque
capabilities and how they work, which was hard work 45 years after
university, but what triggered the whole discussion was how Bosch can
claim that a lawnmower with a 36v Li-polymer powered dc motor can have
the same capability as a 1700w ac motor. OK 1700w is a comfortable
2hp but single phase induction motors are not too good on torque, and
if I remember that is where dc motors score but are modern ones going
to match a 1700w ac motor ?

Can anyone help or point me at a site on this topic please.

certainly 36v and about 50A is not unusual in the largest 'DC' model
aircraft motors. Mind you there is no such thing as a DC motor.

They are all 3 phase. - a DC brushed motor simply uses a commutator
to generate the AC..

??? In a DC motor the field is DC.

So what?

Its still a three phase motor with the poles switched on one (or two) at
a time via a 2 brush system on a Nx3 commutator element.



The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous torque.
Not sure where you get 3 phase from.

Each winding gets an AC signal. Each winding is switched at 120 degrees
phase to the next one: If I told you that and told you nothing else,
you would say 'ah, a 3 phase AC motor!!'


I think you are wrong a dc motor is not a 3 phase or ac , some motors
might have three poles but that only 1 configuration , is a five pole
motor 5 phase? and a 7 pole 7 phase? and you cant feed a permanent
magnet motor AC current so to call a dc motor ac is simplifiing things
to far


--
Kevin R
Reply address works

In article ,
The Natural Philosopher wrote:
The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous torque.
Not sure where you get 3 phase from.

Each winding gets an AC signal.

No - it gets switched polarity DC. A different thing entirely.

Each winding is switched at 120 degrees
phase to the next one: If I told you that and told you nothing else,
you would say 'ah, a 3 phase AC motor!!'

--
*Two many clicks spoil the browse *

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

Kevin wrote:
The Natural Philosopher wrote:
Fred wrote:
"The Natural Philosopher" wrote in message
...
robgraham wrote:
Why is that when you are at one's intellectual worst that the more
complex of discussions occur - solution of the world's problems,
etc !!!

This particular one revolved round ac and dc motors - covering single
phase v. 3 ph induction motors and their relative power /torque
capabilities and how they work, which was hard work 45 years after
university, but what triggered the whole discussion was how Bosch can
claim that a lawnmower with a 36v Li-polymer powered dc motor can have
the same capability as a 1700w ac motor. OK 1700w is a comfortable
2hp but single phase induction motors are not too good on torque, and
if I remember that is where dc motors score but are modern ones going
to match a 1700w ac motor ?

Can anyone help or point me at a site on this topic please.

certainly 36v and about 50A is not unusual in the largest 'DC' model
aircraft motors. Mind you there is no such thing as a DC motor.

They are all 3 phase. - a DC brushed motor simply uses a commutator
to generate the AC..

??? In a DC motor the field is DC.

So what?

Its still a three phase motor with the poles switched on one (or two)
at a time via a 2 brush system on a Nx3 commutator element.



The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous torque.
Not sure where you get 3 phase from.

Each winding gets an AC signal. Each winding is switched at 120
degrees phase to the next one: If I told you that and told you
nothing else, you would say 'ah, a 3 phase AC motor!!'


I think you are wrong a dc motor is not a 3 phase or ac , some motors
might have three poles but that only 1 configuration , is a five pole
motor 5 phase? and a 7 pole 7 phase?

I cannot think of any motor that does not have a multiple of 3 actual
windings. But I suppose its possible. So OK, they are 5, 7 whatever phse
motors!



and you cant feed a permanent
magnet motor AC current

Yes you can.

I have about 9 of them myself.

so to call a dc motor ac is simplifiing things
to far



I think not. All electric motors have alternating current in the windings.

Realising that takes a lot of bull**** about the so called difference
between 'AC' and 'DC' motors away.

Really there are only two basic types of motor: those that are driven,
either electronically, or by means of commutators, with a phased AC that
synhronises to the motor speed, and those that are synchronous to a
fixed frequency AC source.

The only other variable is whether permanent magnets or electromagnets
provide the field. And if electrical whether they are series or shunt
connected.

Apart from eddy current motors, which are off the topic here.

Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous torque.
Not sure where you get 3 phase from.

Each winding gets an AC signal.

No - it gets switched polarity DC. A different thing entirely.


NO, it is true alternating current in the meaning of the term. Current
that has an average value of zero, but has at any given time, a value
that is not zero.


Switched polarity DC *IS* AC!!

"The Natural Philosopher" wrote in message
...
Fred wrote:
"The Natural Philosopher" wrote in message
...


The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous torque. Not
sure where you get 3 phase from.

Each winding gets an AC signal. Each winding is switched at 120 degrees
phase to the next one: If I told you that and told you nothing else, you
would say 'ah, a 3 phase AC motor!!'


With 3 brushes equally spaced I suppose?

In some respects you're right but for all the wrong reasons!

The Natural Philosopher wrote:

I cannot think of any motor that does not have a multiple of 3 actual
windings. But I suppose its possible. So OK, they are 5, 7 whatever phse
motors!

So how many do you see here?
http://www.physclips.unsw.edu.au/jw/electricmotors.html

Chris
--
Chris J Dixon Nottingham UK


Have dancing shoes, will ceilidh.

"The Natural Philosopher" wrote in message
...
Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous torque.
Not sure where you get 3 phase from.

Each winding gets an AC signal.

No - it gets switched polarity DC. A different thing entirely.


NO, it is true alternating current in the meaning of the term. Current
that has an average value of zero, but has at any given time, a value that
is not zero.


Err no, it's *an* alternating current in *your* meaning of the term "True"
alternating current is that whis is assumed in AC theory and engineering and
in the design of AC motors and equipment and is sinusoidally varying.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not

"The Natural Philosopher" wrote in message
...

I cannot think of any motor that does not have a multiple of 3 actual
windings. But I suppose its possible. So OK, they are 5, 7 whatever phse
motors!

I have a PC fan in front of me with a transparent case.. It has four coils
so you can think of one now.

dennis@home wrote:


"The Natural Philosopher" wrote in message
...

I cannot think of any motor that does not have a multiple of 3 actual
windings. But I suppose its possible. So OK, they are 5, 7 whatever
phse motors!

I have a PC fan in front of me with a transparent case.. It has four
coils so you can think of one now.
but that's an brushless motor as the coils stay still and they are fed
pulses by the electronics

--
Kevin R
Reply address works

The Natural Philosopher wrote:
Kevin wrote:
The Natural Philosopher wrote:
Fred wrote:
"The Natural Philosopher" wrote in message
...
robgraham wrote:
Why is that when you are at one's intellectual worst that the more
complex of discussions occur - solution of the world's problems,
etc !!!

This particular one revolved round ac and dc motors - covering single
phase v. 3 ph induction motors and their relative power /torque
capabilities and how they work, which was hard work 45 years after
university, but what triggered the whole discussion was how Bosch can
claim that a lawnmower with a 36v Li-polymer powered dc motor can
have
the same capability as a 1700w ac motor. OK 1700w is a comfortable
2hp but single phase induction motors are not too good on torque, and
if I remember that is where dc motors score but are modern ones going
to match a 1700w ac motor ?

Can anyone help or point me at a site on this topic please.

certainly 36v and about 50A is not unusual in the largest 'DC'
model aircraft motors. Mind you there is no such thing as a DC motor.

They are all 3 phase. - a DC brushed motor simply uses a commutator
to generate the AC..

??? In a DC motor the field is DC.

So what?

Its still a three phase motor with the poles switched on one (or two)
at a time via a 2 brush system on a Nx3 commutator element.



The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous
torque. Not sure where you get 3 phase from.

Each winding gets an AC signal. Each winding is switched at 120
degrees phase to the next one: If I told you that and told you
nothing else, you would say 'ah, a 3 phase AC motor!!'


I think you are wrong a dc motor is not a 3 phase or ac , some motors
might have three poles but that only 1 configuration , is a five pole
motor 5 phase? and a 7 pole 7 phase?

I cannot think of any motor that does not have a multiple of 3 actual
windings. But I suppose its possible. So OK, they are 5, 7 whatever phse
motors!

you have not done much research, most model boat motors are 5 pole along
with trains
http://www.zscale.org/articles/fivepole.html

but they still are not 3 phase and no dc motor is, as there are not 3
rotating magnetic/electrical feilds there is only 1 field that is
switched in sequence by the commutator


and you cant feed a permanent
magnet motor AC current

Yes you can.

lets see you feed ac into any normal aero style model motor
I have about 9 of them myself.

so to call a dc motor ac is simplifiing things to far



I think not. All electric motors have alternating current in the windings.

are you sure its alternating and not just feeding one set of windings
then the next etc

Realising that takes a lot of bull**** about the so called difference
between 'AC' and 'DC' motors away.

Really there are only two basic types of motor: those that are driven,
either electronically, or by means of commutators, with a phased AC that
synhronises to the motor speed, and those that are synchronous to a
fixed frequency AC source.

The only other variable is whether permanent magnets or electromagnets
provide the field. And if electrical whether they are series or shunt
connected.

Apart from eddy current motors, which are off the topic here.








--
Kevin R
Reply address works

Chris J Dixon wrote:
The Natural Philosopher wrote:

I cannot think of any motor that does not have a multiple of 3 actual
windings. But I suppose its possible. So OK, they are 5, 7 whatever phse
motors!

So how many do you see here?
http://www.physclips.unsw.edu.au/jw/electricmotors.html

Chris
that's just theory no dc brushed motor usually has two poles minimum is
usually 3, which is where Nat gets his 3 phase ac from (which is just
wrong),I believe 3 are used as they have better starting torque the more
poles they have, 3 5 7 are the usual numbers

--
Kevin R
Reply address works

Kevin wrote:

you have not done much research, most model boat motors are 5 pole along
with trains
http://www.zscale.org/articles/fivepole.html

In the model world, maybe, but in the real railway, DC Traction
Motors generally have an even number of poles, most commonly 4 or
6.

Chris
--
Chris J Dixon Nottingham UK


Have dancing shoes, will ceilidh.

Bob Mannix wrote:
"The Natural Philosopher" wrote in message
...
Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous torque.
Not sure where you get 3 phase from.
Each winding gets an AC signal.
No - it gets switched polarity DC. A different thing entirely.

NO, it is true alternating current in the meaning of the term. Current
that has an average value of zero, but has at any given time, a value that
is not zero.


Err no, it's *an* alternating current in *your* meaning of the term "True"
alternating current is that whis is assumed in AC theory and engineering and
in the design of AC motors and equipment and is sinusoidally varying.


Er, no, sinusoidal is not mentioned anywhere in the *definition* of AC.

Fred wrote:
"The Natural Philosopher" wrote in message
...
Fred wrote:
"The Natural Philosopher" wrote in message
...

The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous torque. Not
sure where you get 3 phase from.
Each winding gets an AC signal. Each winding is switched at 120 degrees
phase to the next one: If I told you that and told you nothing else, you
would say 'ah, a 3 phase AC motor!!'


With 3 brushes equally spaced I suppose?

No, three commutator segments spaced equally.

In some respects you're right but for all the wrong reasons!

Kevin wrote:
The Natural Philosopher wrote:
Kevin wrote:
The Natural Philosopher wrote:
Fred wrote:
"The Natural Philosopher" wrote in message
...
robgraham wrote:
Why is that when you are at one's intellectual worst that the more
complex of discussions occur - solution of the world's problems,
etc !!!

This particular one revolved round ac and dc motors - covering
single
phase v. 3 ph induction motors and their relative power /torque
capabilities and how they work, which was hard work 45 years after
university, but what triggered the whole discussion was how Bosch
can
claim that a lawnmower with a 36v Li-polymer powered dc motor can
have
the same capability as a 1700w ac motor. OK 1700w is a comfortable
2hp but single phase induction motors are not too good on torque,
and
if I remember that is where dc motors score but are modern ones
going
to match a 1700w ac motor ?

Can anyone help or point me at a site on this topic please.

certainly 36v and about 50A is not unusual in the largest 'DC'
model aircraft motors. Mind you there is no such thing as a DC motor.

They are all 3 phase. - a DC brushed motor simply uses a
commutator to generate the AC..

??? In a DC motor the field is DC.

So what?

Its still a three phase motor with the poles switched on one (or
two) at a time via a 2 brush system on a Nx3 commutator element.



The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous
torque. Not sure where you get 3 phase from.

Each winding gets an AC signal. Each winding is switched at 120
degrees phase to the next one: If I told you that and told you
nothing else, you would say 'ah, a 3 phase AC motor!!'


I think you are wrong a dc motor is not a 3 phase or ac , some motors
might have three poles but that only 1 configuration , is a five pole
motor 5 phase? and a 7 pole 7 phase?

I cannot think of any motor that does not have a multiple of 3 actual
windings. But I suppose its possible. So OK, they are 5, 7 whatever
phse motors!

you have not done much research, most model boat motors are 5 pole along
with trains
http://www.zscale.org/articles/fivepole.html

but they still are not 3 phase and no dc motor is, as there are not 3
rotating magnetic/electrical feilds there is only 1 field that is
switched in sequence by the commutator


and you cant feed a permanent
magnet motor AC current

Yes you can.

lets see you feed ac into any normal aero style model motor

Well that's what the electronic controllers do.

Three wires coming out. Hard to connect DC to that and get it to work.
Put a scope on any two pairs and you will see AC. Put a scope on all of
them and you will see three phase AC, albeit with a lot of trash due to
throttling and commutation, but motor inductance smooths that out somewhat..





I have about 9 of them myself.

so to call a dc motor ac is simplifiing things to far



I think not. All electric motors have alternating current in the
windings.

are you sure its alternating and not just feeding one set of windings
then the next etc

Yes, in the sense that later on the current gets fed backwards to the
winding that was forwards last time.

Chris J Dixon wrote:
Kevin wrote:

you have not done much research, most model boat motors are 5 pole along
with trains
http://www.zscale.org/articles/fivepole.html

In the model world, maybe, but in the real railway, DC Traction
Motors generally have an even number of poles, most commonly 4 or
6.

Chris
Its general to have an even number of fields or fixed magnet poles, and
windings as a multiple of three.

So it depends what we re talking about.

The normal cheapest electric motor you might find in e.g.an electric
drill will have two magnet poles and three wound armature segments.

Some of the motors I have have 12 wound poles wound as three phases, and
14 magnet poles. For example.

The Natural Philosopher wrote:
Kevin wrote:
The Natural Philosopher wrote:
Kevin wrote:
The Natural Philosopher wrote:
Fred wrote:
"The Natural Philosopher" wrote in message
...
robgraham wrote:
Why is that when you are at one's intellectual worst that the more
complex of discussions occur - solution of the world's problems,
etc !!!

This particular one revolved round ac and dc motors - covering
single
phase v. 3 ph induction motors and their relative power /torque
capabilities and how they work, which was hard work 45 years after
university, but what triggered the whole discussion was how
Bosch can
claim that a lawnmower with a 36v Li-polymer powered dc motor
can have
the same capability as a 1700w ac motor. OK 1700w is a comfortable
2hp but single phase induction motors are not too good on
torque, and
if I remember that is where dc motors score but are modern ones
going
to match a 1700w ac motor ?

Can anyone help or point me at a site on this topic please.

certainly 36v and about 50A is not unusual in the largest 'DC'
model aircraft motors. Mind you there is no such thing as a DC
motor.

They are all 3 phase. - a DC brushed motor simply uses a
commutator to generate the AC..

??? In a DC motor the field is DC.

So what?

Its still a three phase motor with the poles switched on one (or
two) at a time via a 2 brush system on a Nx3 commutator element.



The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous
torque. Not sure where you get 3 phase from.

Each winding gets an AC signal. Each winding is switched at 120
degrees phase to the next one: If I told you that and told you
nothing else, you would say 'ah, a 3 phase AC motor!!'


I think you are wrong a dc motor is not a 3 phase or ac , some
motors might have three poles but that only 1 configuration , is a
five pole motor 5 phase? and a 7 pole 7 phase?

I cannot think of any motor that does not have a multiple of 3 actual
windings. But I suppose its possible. So OK, they are 5, 7 whatever
phse motors!

you have not done much research, most model boat motors are 5 pole
along with trains
http://www.zscale.org/articles/fivepole.html

but they still are not 3 phase and no dc motor is, as there are not 3
rotating magnetic/electrical feilds there is only 1 field that is
switched in sequence by the commutator


and you cant feed a permanent
magnet motor AC current

Yes you can.

lets see you feed ac into any normal aero style model motor

Well that's what the electronic controllers do.

we were talking brushed dc motors not brushless

Three wires coming out. Hard to connect DC to that and get it to work.
Put a scope on any two pairs and you will see AC. Put a scope on all of
them and you will see three phase AC, albeit with a lot of trash due to
throttling and commutation, but motor inductance smooths that out
somewhat..







I have about 9 of them myself.

so to call a dc motor ac is simplifiing things to far



I think not. All electric motors have alternating current in the
windings.

are you sure its alternating and not just feeding one set of windings
then the next etc

Yes, in the sense that later on the current gets fed backwards to the
winding that was forwards last time.


--
Kevin R
Reply address works

The Natural Philosopher wrote:
Chris J Dixon wrote:
Kevin wrote:

you have not done much research, most model boat motors are 5 pole
along with trains
http://www.zscale.org/articles/fivepole.html

In the model world, maybe, but in the real railway, DC Traction
Motors generally have an even number of poles, most commonly 4 or
6.

Chris
Its general to have an even number of fields or fixed magnet poles, and
windings as a multiple of three.

So it depends what we re talking about.

a 5 pole motor has 2 magnet poles and 5 windings & 2 brushes so bang
goes 3 phase theory
The normal cheapest electric motor you might find in e.g.an electric
drill will have two magnet poles and three wound armature segments.

Some of the motors I have have 12 wound poles wound as three phases, and
14 magnet poles. For example.





--
Kevin R
Reply address works

"The Natural Philosopher" wrote in message
...
Bob Mannix wrote:
"The Natural Philosopher" wrote in message
...
Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous torque.
Not sure where you get 3 phase from.
Each winding gets an AC signal.
No - it gets switched polarity DC. A different thing entirely.

NO, it is true alternating current in the meaning of the term. Current
that has an average value of zero, but has at any given time, a value
that is not zero.


Err no, it's *an* alternating current in *your* meaning of the term
"True" alternating current is that whis is assumed in AC theory and
engineering and in the design of AC motors and equipment and is
sinusoidally varying.


Er, no, sinusoidal is not mentioned anywhere in the *definition* of AC.

Oh well, that's all AC current theory out the window then, so that's OK!


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

Kevin wrote:
The Natural Philosopher wrote:
Kevin wrote:
The Natural Philosopher wrote:
Kevin wrote:

and you cant feed a permanent
magnet motor AC current

Yes you can.

lets see you feed ac into any normal aero style model motor

Well that's what the electronic controllers do.

we were talking brushed dc motors not brushless


No, see above. You were talking permanent magnet motors. No mention was
made of brushed or brushless.

Kevin wrote:
The Natural Philosopher wrote:
Chris J Dixon wrote:
Kevin wrote:

you have not done much research, most model boat motors are 5 pole
along with trains
http://www.zscale.org/articles/fivepole.html

In the model world, maybe, but in the real railway, DC Traction
Motors generally have an even number of poles, most commonly 4 or
6.

Chris
Its general to have an even number of fields or fixed magnet poles,
and windings as a multiple of three.

So it depends what we re talking about.

a 5 pole motor has 2 magnet poles and 5 windings & 2 brushes so bang
goes 3 phase theory

Well then its a 5 phase AC motor ;-)

Unusual, but possible with a commutator.

Bob Mannix wrote:
"The Natural Philosopher" wrote in message
...
Bob Mannix wrote:
"The Natural Philosopher" wrote in message
...
Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous torque.
Not sure where you get 3 phase from.
Each winding gets an AC signal.
No - it gets switched polarity DC. A different thing entirely.

NO, it is true alternating current in the meaning of the term. Current
that has an average value of zero, but has at any given time, a value
that is not zero.

Err no, it's *an* alternating current in *your* meaning of the term
"True" alternating current is that whis is assumed in AC theory and
engineering and in the design of AC motors and equipment and is
sinusoidally varying.


Er, no, sinusoidal is not mentioned anywhere in the *definition* of AC.

Oh well, that's all AC current theory out the window then, so that's OK!



Not at all. Sinusoidal merely makes it easy to do calculations based on
single frequency operation.

In te real world, its almost never seen ourtside of ultra low distortin
oscillators.

You have to distinguish between 'electrical theory for dummies' and
'electrical engineering, an advanced course'

"The Natural Philosopher" wrote in message
...
Bob Mannix wrote:
"The Natural Philosopher" wrote in message
...
Bob Mannix wrote:
"The Natural Philosopher" wrote in message
...
Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous
torque. Not sure where you get 3 phase from.
Each winding gets an AC signal.
No - it gets switched polarity DC. A different thing entirely.

NO, it is true alternating current in the meaning of the term. Current
that has an average value of zero, but has at any given time, a value
that is not zero.

Err no, it's *an* alternating current in *your* meaning of the term
"True" alternating current is that whis is assumed in AC theory and
engineering and in the design of AC motors and equipment and is
sinusoidally varying.


Er, no, sinusoidal is not mentioned anywhere in the *definition* of AC.

Oh well, that's all AC current theory out the window then, so that's OK!



Not at all. Sinusoidal merely makes it easy to do calculations based on
single frequency operation.

In te real world, its almost never seen ourtside of ultra low distortin
oscillators.

You have to distinguish between 'electrical theory for dummies' and
'electrical engineering, an advanced course'

Indeed


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

The Natural Philosopher wrote:
Bob Mannix wrote:
"The Natural Philosopher" wrote in message
...
Bob Mannix wrote:
"The Natural Philosopher" wrote in message
...
Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous
torque. Not sure where you get 3 phase from.
Each winding gets an AC signal.
No - it gets switched polarity DC. A different thing entirely.

NO, it is true alternating current in the meaning of the term.
Current that has an average value of zero, but has at any given
time, a value that is not zero.

Err no, it's *an* alternating current in *your* meaning of the term
"True" alternating current is that whis is assumed in AC theory and
engineering and in the design of AC motors and equipment and is
sinusoidally varying.


Er, no, sinusoidal is not mentioned anywhere in the *definition* of AC.

Oh well, that's all AC current theory out the window then, so that's OK!



Not at all. Sinusoidal merely makes it easy to do calculations based on
single frequency operation.

In te real world, its almost never seen ourtside of ultra low distortin
oscillators.

You have to distinguish between 'electrical theory for dummies' and
'electrical engineering, an advanced course'

Any chance of getting you lot back On Topic and answering the original
question.

Bosch claim that this 36v driven machine will mow 300m^2 on one battery
- that's at least 30 minutes continuous running I reckon, or 1.8kwh at
50A, based on the poster mentioning model aircraft motors.

Rob

Rob G wrote:


Any chance of getting you lot back On Topic and answering the original
question.

Bosch claim that this 36v driven machine will mow 300m^2 on one battery
- that's at least 30 minutes continuous running I reckon, or 1.8kwh at
50A, based on the poster mentioning model aircraft motors.


36v at 50A for half an hour? thats a tough call: You would need a 25Ah
battery.

Not impossible, but does it have one?

You could get all that in a couple of pounds weight of motor probably,
if done well. 5lb done cheaply.

Motors I use range from about 60% to 90% efficiency. Thats not such a
huge variation in running time. It is a huge variation in waste heat
though, which is why the less efficient motors need to be bigger to be
able to dump the heat.

As I said, mutatis mutandis, there is no real theoretical efficiency
difference between mains and battery DC powered motors.

Both CAN do better than 90%, most generally do 60-70%, as that is fairly
easy to achieve. The devil is in a lot of tiny details..iron quality and
shape, pole geometry, magnet quality - if PM - quality low friction
bearings..commutator friction and brush design (if brushed) or switching
losses in electronic commutators (if not)...etc etc..

"The Natural Philosopher" wrote in message
...
Fred wrote:
"The Natural Philosopher" wrote in message
...
Fred wrote:
"The Natural Philosopher" wrote in message
...

The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous torque.
Not sure where you get 3 phase from.
Each winding gets an AC signal. Each winding is switched at 120 degrees
phase to the next one: If I told you that and told you nothing else,
you would say 'ah, a 3 phase AC motor!!'


With 3 brushes equally spaced I suppose?

No, three commutator segments spaced equally.

Most motors have far more than 3 commutator segments!

"The Natural Philosopher" wrote in message
...
Bob Mannix wrote:
"The Natural Philosopher" wrote in message
...
Bob Mannix wrote:
"The Natural Philosopher" wrote in message
...
Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous
torque. Not sure where you get 3 phase from.
Each winding gets an AC signal.
No - it gets switched polarity DC. A different thing entirely.

NO, it is true alternating current in the meaning of the term. Current
that has an average value of zero, but has at any given time, a value
that is not zero.

Err no, it's *an* alternating current in *your* meaning of the term
"True" alternating current is that whis is assumed in AC theory and
engineering and in the design of AC motors and equipment and is
sinusoidally varying.


Er, no, sinusoidal is not mentioned anywhere in the *definition* of AC.

Oh well, that's all AC current theory out the window then, so that's OK!



Not at all. Sinusoidal merely makes it easy to do calculations based on
single frequency operation.

In te real world, its almost never seen ourtside of ultra low distortin
oscillators.

You have to distinguish between 'electrical theory for dummies' and
'electrical engineering, an advanced course'

Agreed!

To get the advantages of 3 phase, each waveform has to be close to
sinusoidal.

"Bob Mannix" wrote in message
...
"The Natural Philosopher" wrote in message
...
Bob Mannix wrote:
"The Natural Philosopher" wrote in message
...
Bob Mannix wrote:
"The Natural Philosopher" wrote in message
...
Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous
torque. Not sure where you get 3 phase from.
Each winding gets an AC signal.
No - it gets switched polarity DC. A different thing entirely.

NO, it is true alternating current in the meaning of the term.
Current that has an average value of zero, but has at any given time,
a value that is not zero.

Err no, it's *an* alternating current in *your* meaning of the term
"True" alternating current is that whis is assumed in AC theory and
engineering and in the design of AC motors and equipment and is
sinusoidally varying.


Er, no, sinusoidal is not mentioned anywhere in the *definition* of
AC.

Oh well, that's all AC current theory out the window then, so that's OK!



Not at all. Sinusoidal merely makes it easy to do calculations based on
single frequency operation.

In te real world, its almost never seen ourtside of ultra low distortin
oscillators.

You have to distinguish between 'electrical theory for dummies' and
'electrical engineering, an advanced course'

Indeed


But most dangerous of all is a little bit of knowledge, then they think they
know everything!

Fred wrote:
"The Natural Philosopher" wrote in message
...
Fred wrote:
"The Natural Philosopher" wrote in message
...
Fred wrote:
"The Natural Philosopher" wrote in message
...
The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous torque.
Not sure where you get 3 phase from.
Each winding gets an AC signal. Each winding is switched at 120 degrees
phase to the next one: If I told you that and told you nothing else,
you would say 'ah, a 3 phase AC motor!!'

With 3 brushes equally spaced I suppose?
No, three commutator segments spaced equally.

Most motors have far more than 3 commutator segments!


Depends. Most cheap ones have three. Larger motors have more, but
generally at least 5 are in contact with the brushes at any time.

Fred wrote:
"The Natural Philosopher" wrote in message
...
Bob Mannix wrote:
"The Natural Philosopher" wrote in message
...
Bob Mannix wrote:
"The Natural Philosopher" wrote in message
...
Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous
torque. Not sure where you get 3 phase from.
Each winding gets an AC signal.
No - it gets switched polarity DC. A different thing entirely.

NO, it is true alternating current in the meaning of the term. Current
that has an average value of zero, but has at any given time, a value
that is not zero.

Err no, it's *an* alternating current in *your* meaning of the term
"True" alternating current is that whis is assumed in AC theory and
engineering and in the design of AC motors and equipment and is
sinusoidally varying.


Er, no, sinusoidal is not mentioned anywhere in the *definition* of AC.
Oh well, that's all AC current theory out the window then, so that's OK!


Not at all. Sinusoidal merely makes it easy to do calculations based on
single frequency operation.

In te real world, its almost never seen ourtside of ultra low distortin
oscillators.

You have to distinguish between 'electrical theory for dummies' and
'electrical engineering, an advanced course'

Agreed!

To get the advantages of 3 phase, each waveform has to be close to
sinusoidal.


No it doesn't.

3 phase as far as a motor is concerned, simply means it knows which way
to go round.

"The Natural Philosopher" wrote in message
...
Fred wrote:
"The Natural Philosopher" wrote in message
...
Bob Mannix wrote:
"The Natural Philosopher" wrote in message
...
Bob Mannix wrote:
"The Natural Philosopher" wrote in message
...
Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous
torque. Not sure where you get 3 phase from.
Each winding gets an AC signal.
No - it gets switched polarity DC. A different thing entirely.

NO, it is true alternating current in the meaning of the term.
Current that has an average value of zero, but has at any given
time, a value that is not zero.

Err no, it's *an* alternating current in *your* meaning of the term
"True" alternating current is that whis is assumed in AC theory and
engineering and in the design of AC motors and equipment and is
sinusoidally varying.


Er, no, sinusoidal is not mentioned anywhere in the *definition* of
AC.
Oh well, that's all AC current theory out the window then, so that's
OK!


Not at all. Sinusoidal merely makes it easy to do calculations based on
single frequency operation.

In te real world, its almost never seen ourtside of ultra low distortin
oscillators.

You have to distinguish between 'electrical theory for dummies' and
'electrical engineering, an advanced course'

Agreed!

To get the advantages of 3 phase, each waveform has to be close to
sinusoidal.


No it doesn't.

3 phase as far as a motor is concerned, simply means it knows which way to
go round.

What on earth are you talking about? Are you seriously suggesting that it
doesn't matter what the waveform is for each of the phases, that you can
still tell me which way the motor will turn? Wow.

"The Natural Philosopher" wrote in message
...
Fred wrote:
"The Natural Philosopher" wrote in message
...
Fred wrote:
"The Natural Philosopher" wrote in message
...
Fred wrote:
"The Natural Philosopher" wrote in message
...
The commutator is to ensure the field
in the rotor is aligned wrt the stator to provide continuous torque.
Not sure where you get 3 phase from.
Each winding gets an AC signal. Each winding is switched at 120
degrees phase to the next one: If I told you that and told you
nothing else, you would say 'ah, a 3 phase AC motor!!'

With 3 brushes equally spaced I suppose?
No, three commutator segments spaced equally.

Most motors have far more than 3 commutator segments!


Depends. Most cheap ones have three. Larger motors have more, but
generally at least 5 are in contact with the brushes at any time.

So the brushes are in contact with more commutator segments than the motor
actually has?