I have just stripped the 1kW motor from a Black and Decker 10"
circular saw I inherited. It was running erratic with the symptom
indicating the brushes were making poor contact. Sure enough the
brushes were seized in the brush holders,

As it looks like they had got hot I want to check the armature before
ordering brushes and holders. Am I right to think I need to check the
resistance between opposite commutator contacts? I seem to have about
80 Ohms on the few I have checked so far and a few kOhms between
coils, does that seem reasonable?

AJH

wrote:
I have just stripped the 1kW motor from a Black and Decker 10"
circular saw I inherited. It was running erratic with the symptom
indicating the brushes were making poor contact. Sure enough the
brushes were seized in the brush holders,

As it looks like they had got hot I want to check the armature before
ordering brushes and holders. Am I right to think I need to check the
resistance between opposite commutator contacts? I seem to have about
80 Ohms on the few I have checked so far and a few kOhms between
coils, does that seem reasonable?

AJH

I'd expect a small proportion of that to be honest.
In my experience if one of those motors is giving trouble and there is
sparking from the commutator or it has been overheating, the armature is
knackered.
If you take it to a motor rewinders, they should have a thing called a
growler which they can test it with.

Bob Minchin wrote:
wrote:
I have just stripped the 1kW motor from a Black and Decker 10"
circular saw I inherited. It was running erratic with the symptom
indicating the brushes were making poor contact. Sure enough the
brushes were seized in the brush holders,

As it looks like they had got hot I want to check the armature before
ordering brushes and holders. Am I right to think I need to check the
resistance between opposite commutator contacts? I seem to have about
80 Ohms on the few I have checked so far and a few kOhms between
coils, does that seem reasonable?

AJH

I'd expect a small proportion of that to be honest.
In my experience if one of those motors is giving trouble and there is
sparking from the commutator or it has been overheating, the armature is
knackered.
If you take it to a motor rewinders, they should have a thing called a
growler which they can test it with.
I've just measured the armature on my Bosch 1600w saw. 1.6 ohms after
compensating for the test meter leads.

Either your measurement rig is suspect of the armature is not a happy
chappy.

On 22/06/2014 21:03, wrote:
I have just stripped the 1kW motor from a Black and Decker 10"
circular saw I inherited. It was running erratic with the symptom
indicating the brushes were making poor contact. Sure enough the
brushes were seized in the brush holders,

As it looks like they had got hot I want to check the armature before
ordering brushes and holders. Am I right to think I need to check the
resistance between opposite commutator contacts? I seem to have about
80 Ohms on the few I have checked so far and a few kOhms between
coils, does that seem reasonable?

Few Kohms sounds very wrong.

Check resistance between adjacent segments. It should be very constant.

Anything else and its toast.

On Sunday, June 22, 2014 9:03:21 PM UTC+1, wrote:

I have just stripped the 1kW motor from a Black and Decker 10"
circular saw I inherited. It was running erratic with the symptom
indicating the brushes were making poor contact. Sure enough the
brushes were seized in the brush holders,
As it looks like they had got hot I want to check the armature before
ordering brushes and holders. Am I right to think I need to check the
resistance between opposite commutator contacts? I seem to have about

Yup, as the brushes connect

80 Ohms on the few I have checked so far and a few kOhms between
coils, does that seem reasonable?
AJH

if in doubt one can usually bend something to enable old brushes to keep running a while more, and lightly sand the commutator to clean the surface while its running (not on 240v . Then you can assess whether it runs ok - if it does its worth rebrushing.


NT

I'd say the coils should not be connected at all, unless the commutator has
graphite between its segments causing it
Brian

--
From the Sofa of Brian Gaff Reply address is active
wrote in message
...
I have just stripped the 1kW motor from a Black and Decker 10"
circular saw I inherited. It was running erratic with the symptom
indicating the brushes were making poor contact. Sure enough the
brushes were seized in the brush holders,

As it looks like they had got hot I want to check the armature before
ordering brushes and holders. Am I right to think I need to check the
resistance between opposite commutator contacts? I seem to have about
80 Ohms on the few I have checked so far and a few kOhms between
coils, does that seem reasonable?

AJH

Yes, they tend to go shorted turns though not high resistance. Bit odd that
one.
Brian

--
From the Sofa of Brian Gaff Reply address is active
"Bob Minchin" wrote in message
...
Bob Minchin wrote:
wrote:
I have just stripped the 1kW motor from a Black and Decker 10"
circular saw I inherited. It was running erratic with the symptom
indicating the brushes were making poor contact. Sure enough the
brushes were seized in the brush holders,

As it looks like they had got hot I want to check the armature before
ordering brushes and holders. Am I right to think I need to check the
resistance between opposite commutator contacts? I seem to have about
80 Ohms on the few I have checked so far and a few kOhms between
coils, does that seem reasonable?

AJH

I'd expect a small proportion of that to be honest.
In my experience if one of those motors is giving trouble and there is
sparking from the commutator or it has been overheating, the armature is
knackered.
If you take it to a motor rewinders, they should have a thing called a
growler which they can test it with.
I've just measured the armature on my Bosch 1600w saw. 1.6 ohms after
compensating for the test meter leads.

Either your measurement rig is suspect of the armature is not a happy
chappy.

On Sun, 22 Jun 2014 21:03:21 +0100, wrote:

I have just stripped the 1kW motor from a Black and Decker 10"
circular saw I inherited. It was running erratic with the symptom
indicating the brushes were making poor contact. Sure enough the
brushes were seized in the brush holders,

As it looks like they had got hot I want to check the armature before
ordering brushes and holders. Am I right to think I need to check the
resistance between opposite commutator contacts? I seem to have about
80 Ohms on the few I have checked so far and a few kOhms between
coils, does that seem reasonable?

AJH

Those readings rather suggest open circuits between the armature
windings (topologically, the armature is a bunch of electromagnetic
coils all connected in series at each commutator segment forming a
closed loop).

I'd expect a 1HP constant speed universal motor to have the field
connected in shunt, possibly compounded with a series winding to help
stabilise speed with load.

I'd expect the armature DC resistance between opposite segments to
show a reading of around 5 to 7% of the equivilent resistance of a 1KW
heating element (the perfect motor would have zero DC resistance in
the armature windings). In this case, a practical 1HP universal motor,
I'd expect a reading of around 4 ohms with a fraction of an ohm
between adjacent segments.
--
J B Good

On 23/06/2014 13:07, Johny B Good wrote:
On Sun, 22 Jun 2014 21:03:21 +0100, wrote:

I have just stripped the 1kW motor from a Black and Decker 10"
circular saw I inherited. It was running erratic with the symptom
indicating the brushes were making poor contact. Sure enough the
brushes were seized in the brush holders,

As it looks like they had got hot I want to check the armature before
ordering brushes and holders. Am I right to think I need to check the
resistance between opposite commutator contacts? I seem to have about
80 Ohms on the few I have checked so far and a few kOhms between
coils, does that seem reasonable?

AJH

Those readings rather suggest open circuits between the armature
windings (topologically, the armature is a bunch of electromagnetic
coils all connected in series at each commutator segment forming a
closed loop).

I'd expect a 1HP constant speed universal motor to have the field
connected in shunt, possibly compounded with a series winding to help
stabilise speed with load.

I'd expect the armature DC resistance between opposite segments to
show a reading of around 5 to 7% of the equivilent resistance of a 1KW
heating element (the perfect motor would have zero DC resistance in
the armature windings). In this case, a practical 1HP universal motor,
I'd expect a reading of around 4 ohms with a fraction of an ohm
between adjacent segments.

Hmm. A 1kW motor consumes 1kW of power. The motor will be based on cost
that tends to mean a lot of heat and not so much mechanical power.

Often the motor is speed stabilised by a combination of drag by cooling
fan, and the current lagging due to the inductive stator winding. I've
never seen a shunt winding in addition to a series winding, but I could
be wrong in this instance.

All in all a universal motor is a terrible compromise and best run by
rectified mains!

On Mon, 23 Jun 2014 15:09:09 +0100, Fredxxx wrote:

On 23/06/2014 13:07, Johny B Good wrote:
On Sun, 22 Jun 2014 21:03:21 +0100, wrote:

I have just stripped the 1kW motor from a Black and Decker 10"
circular saw I inherited. It was running erratic with the symptom
indicating the brushes were making poor contact. Sure enough the
brushes were seized in the brush holders,

As it looks like they had got hot I want to check the armature before
ordering brushes and holders. Am I right to think I need to check the
resistance between opposite commutator contacts? I seem to have about
80 Ohms on the few I have checked so far and a few kOhms between
coils, does that seem reasonable?

AJH

Those readings rather suggest open circuits between the armature
windings (topologically, the armature is a bunch of electromagnetic
coils all connected in series at each commutator segment forming a
closed loop).

I'd expect a 1HP constant speed universal motor to have the field
connected in shunt, possibly compounded with a series winding to help
stabilise speed with load.

I'd expect the armature DC resistance between opposite segments to
show a reading of around 5 to 7% of the equivilent resistance of a 1KW
heating element (the perfect motor would have zero DC resistance in
the armature windings). In this case, a practical 1HP universal motor,
I'd expect a reading of around 4 ohms with a fraction of an ohm
between adjacent segments.

Hmm. A 1kW motor consumes 1kW of power. The motor will be based on cost
that tends to mean a lot of heat and not so much mechanical power.

Which is why I used a 1HP rather than a 1.25HP figure. :-)


Often the motor is speed stabilised by a combination of drag by cooling
fan, and the current lagging due to the inductive stator winding. I've
never seen a shunt winding in addition to a series winding, but I could
be wrong in this instance.

No, you're probably right. I was just covering the possibility that a
1HP motor _might_ also include a series field winding by using the
phrase "possibly compounded with a series winding". Assuming
(possibly incorrectly) that you'd need constant speed rather the
torque curve speed law of a traction motor for spinning a circular saw
blade.


All in all a universal motor is a terrible compromise and best run by
rectified mains!

Maybe, and if so, _only_ rectified with no 'smoothing' caps. A pulsed
100Hz DC might imbalance the electrical erosion of the brushess (it
remains balanced out on the commutator segments in either case).

Regardless of the detail, one thing seems clear, the armature appears
to have developed open ciruited coil connections.
--
J B Good

On 23/06/2014 17:06, Johny B Good wrote:
On Mon, 23 Jun 2014 15:09:09 +0100, Fredxxx wrote:

On 23/06/2014 13:07, Johny B Good wrote:
On Sun, 22 Jun 2014 21:03:21 +0100, wrote:

I have just stripped the 1kW motor from a Black and Decker 10"
circular saw I inherited. It was running erratic with the symptom
indicating the brushes were making poor contact. Sure enough the
brushes were seized in the brush holders,

As it looks like they had got hot I want to check the armature before
ordering brushes and holders. Am I right to think I need to check the
resistance between opposite commutator contacts? I seem to have about
80 Ohms on the few I have checked so far and a few kOhms between
coils, does that seem reasonable?

AJH

Those readings rather suggest open circuits between the armature
windings (topologically, the armature is a bunch of electromagnetic
coils all connected in series at each commutator segment forming a
closed loop).

I'd expect a 1HP constant speed universal motor to have the field
connected in shunt, possibly compounded with a series winding to help
stabilise speed with load.

I'd expect the armature DC resistance between opposite segments to
show a reading of around 5 to 7% of the equivilent resistance of a 1KW
heating element (the perfect motor would have zero DC resistance in
the armature windings). In this case, a practical 1HP universal motor,
I'd expect a reading of around 4 ohms with a fraction of an ohm
between adjacent segments.

Hmm. A 1kW motor consumes 1kW of power. The motor will be based on cost
that tends to mean a lot of heat and not so much mechanical power.

Which is why I used a 1HP rather than a 1.25HP figure. :-)


Often the motor is speed stabilised by a combination of drag by cooling
fan, and the current lagging due to the inductive stator winding. I've
never seen a shunt winding in addition to a series winding, but I could
be wrong in this instance.

No, you're probably right. I was just covering the possibility that a
1HP motor _might_ also include a series field winding by using the
phrase "possibly compounded with a series winding". Assuming
(possibly incorrectly) that you'd need constant speed rather the
torque curve speed law of a traction motor for spinning a circular saw
blade.

The only time I have seen both series and shunt windings are in motors /
generators designed to run at constant speed / voltage with varying load.


All in all a universal motor is a terrible compromise and best run by
rectified mains!

Maybe, and if so, _only_ rectified with no 'smoothing' caps. A pulsed
100Hz DC might imbalance the electrical erosion of the brushess (it
remains balanced out on the commutator segments in either case).

I don't understand the assertion, that pulsating DC will be any
different to less pulsating (smoother) DC. The stator's inductance will
go some way to reduce ripple current.

I've not come across electrical erosion of brushes, unless you mean
arcing?

Still less arcing than in a universal AC motor where there is
considerable induced voltage between adjacent segments due to
transformer action from AC current flowing in the stator.

Regardless of the detail, one thing seems clear, the armature appears
to have developed open ciruited coil connections.

Yes - very likely.

On Sun, 22 Jun 2014 21:58:04 +0100, Bob Minchin
wrote:

Either your measurement rig is suspect of the armature is not a happy
chappy.


Thanks Bob and others, I was using a digital meter which gave about 40
Ohms when the leads were shorted so I have now reverted to a moving
coil one and am getting less than an Ohm across the coil and between
coils so I guess it's not worth repairing.

AJH

wrote:
On Sun, 22 Jun 2014 21:58:04 +0100, Bob Minchin
wrote:

Either your measurement rig is suspect of the armature is not a happy
chappy.


Thanks Bob and others, I was using a digital meter which gave about 40
Ohms when the leads were shorted so I have now reverted to a moving
coil one and am getting less than an Ohm across the coil and between
coils so I guess it's not worth repairing.

AJH

That is what it should be!! - 1 to 2 ohms would be about right

Bob

On Mon, 23 Jun 2014 19:12:46 +0100, Bob Minchin
wrote:

wrote:
On Sun, 22 Jun 2014 21:58:04 +0100, Bob Minchin
wrote:

Either your measurement rig is suspect of the armature is not a happy
chappy.


Thanks Bob and others, I was using a digital meter which gave about 40
Ohms when the leads were shorted so I have now reverted to a moving
coil one and am getting less than an Ohm across the coil and between
coils so I guess it's not worth repairing.

AJH

That is what it should be!! - 1 to 2 ohms would be about right

Should there be that little resistance between adjacent coils?

AJH

wrote:
On Mon, 23 Jun 2014 19:12:46 +0100, Bob Minchin
wrote:

wrote:
On Sun, 22 Jun 2014 21:58:04 +0100, Bob Minchin
wrote:

Either your measurement rig is suspect of the armature is not a happy
chappy.


Thanks Bob and others, I was using a digital meter which gave about 40
Ohms when the leads were shorted so I have now reverted to a moving
coil one and am getting less than an Ohm across the coil and between
coils so I guess it's not worth repairing.

AJH

That is what it should be!! - 1 to 2 ohms would be about right

Should there be that little resistance between adjacent coils?

AJH

I took the trouble last night to go and open up and measure my saw motor
and gave you the results. Are you saying my measurements are wrong?

On Mon, 23 Jun 2014 19:54:49 +0100, Bob Minchin
wrote:

I took the trouble last night to go and open up and measure my saw motor
and gave you the results. Are you saying my measurements are wrong?

Not at all and thank you again for your trouble.

I think I have a logical problem in that I assumed the adjacent
segments on the commutator should have a higher resistance than
opposite segments, are you suggesting this is not the case?

AJH

wrote:
On Mon, 23 Jun 2014 19:54:49 +0100, Bob Minchin
wrote:

I took the trouble last night to go and open up and measure my saw motor
and gave you the results. Are you saying my measurements are wrong?

Not at all and thank you again for your trouble.

I think I have a logical problem in that I assumed the adjacent
segments on the commutator should have a higher resistance than
opposite segments, are you suggesting this is not the case?

AJH

Only opposite segments are relevant to the motor operation. As others
have said they are often wound in a series ring for convenience.
I would suggest easing the old brushes in the guides and testing the
motor before spending out on spares

On 23/06/2014 20:07, wrote:
On Mon, 23 Jun 2014 19:54:49 +0100, Bob Minchin
wrote:

I took the trouble last night to go and open up and measure my saw motor
and gave you the results. Are you saying my measurements are wrong?

Not at all and thank you again for your trouble.

I think I have a logical problem in that I assumed the adjacent
segments on the commutator should have a higher resistance than
opposite segments, are you suggesting this is not the case?

Adjacent segments should have the lowest resistance. They are
effectively in series when comparing opposite segments.

That way all the copper windings are used all the time independent of
armature position.

On Mon, 23 Jun 2014 17:37:00 +0100, Fredxxx wrote:

On 23/06/2014 17:06, Johny B Good wrote:
On Mon, 23 Jun 2014 15:09:09 +0100, Fredxxx wrote:

On 23/06/2014 13:07, Johny B Good wrote:
On Sun, 22 Jun 2014 21:03:21 +0100, wrote:

I have just stripped the 1kW motor from a Black and Decker 10"
circular saw I inherited. It was running erratic with the symptom
indicating the brushes were making poor contact. Sure enough the
brushes were seized in the brush holders,

As it looks like they had got hot I want to check the armature before
ordering brushes and holders. Am I right to think I need to check the
resistance between opposite commutator contacts? I seem to have about
80 Ohms on the few I have checked so far and a few kOhms between
coils, does that seem reasonable?

AJH

Those readings rather suggest open circuits between the armature
windings (topologically, the armature is a bunch of electromagnetic
coils all connected in series at each commutator segment forming a
closed loop).

I'd expect a 1HP constant speed universal motor to have the field
connected in shunt, possibly compounded with a series winding to help
stabilise speed with load.

I'd expect the armature DC resistance between opposite segments to
show a reading of around 5 to 7% of the equivilent resistance of a 1KW
heating element (the perfect motor would have zero DC resistance in
the armature windings). In this case, a practical 1HP universal motor,
I'd expect a reading of around 4 ohms with a fraction of an ohm
between adjacent segments.

Hmm. A 1kW motor consumes 1kW of power. The motor will be based on cost
that tends to mean a lot of heat and not so much mechanical power.

Which is why I used a 1HP rather than a 1.25HP figure. :-)


Often the motor is speed stabilised by a combination of drag by cooling
fan, and the current lagging due to the inductive stator winding. I've
never seen a shunt winding in addition to a series winding, but I could
be wrong in this instance.

No, you're probably right. I was just covering the possibility that a
1HP motor _might_ also include a series field winding by using the
phrase "possibly compounded with a series winding". Assuming
(possibly incorrectly) that you'd need constant speed rather the
torque curve speed law of a traction motor for spinning a circular saw
blade.

The only time I have seen both series and shunt windings are in motors /
generators designed to run at constant speed / voltage with varying load.


All in all a universal motor is a terrible compromise and best run by
rectified mains!

Maybe, and if so, _only_ rectified with no 'smoothing' caps. A pulsed
100Hz DC might imbalance the electrical erosion of the brushess (it
remains balanced out on the commutator segments in either case).

I don't understand the assertion, that pulsating DC will be any
different to less pulsating (smoother) DC. The stator's inductance will
go some way to reduce ripple current.

It's not whether it's a pulsating or or ripple free DC that might be
a problem, just the fact that it's DC of any flavour. The problem with
using capacitive smoothing is that it may raise the rms voltage to
somewhere in the region of 300 volts or more if you overdo the
smoothing.


I've not come across electrical erosion of brushes, unless you mean
arcing?

There's always some level of 'arcing' involved with commutator brush
gear. The uni-directional current flow (which won't matter to the
commutator segments) may slow down wear on one brush and accelerate it
on the other brush compared to AC current running.

I don't suppose it would be a major problem since dynamos on vintage
motor vehicles seemed to cope well enough. At least, I never saw any
historic articles regarding 'rotating the dynamo brushes' to even out
the wear but dynamos were a vintage thing even back in the sixties so
I may have simply missed seeing such 'sage advice' being published.


Still less arcing than in a universal AC motor where there is
considerable induced voltage between adjacent segments due to
transformer action from AC current flowing in the stator.

I'm not so sure whether the armature would behave like a secondary
winding of a transformer (at least not to the extent you're
suggesting). I think you'd only see a 100Hz modulation of the inter
segment voltage you'd expect anyway on a pure DC supply of the same
rms value.
--
J B Good

"Johny B Good" wrote in message
...
On Mon, 23 Jun 2014 15:09:09 +0100, Fredxxx wrote:

On 23/06/2014 13:07, Johny B Good wrote:
On Sun, 22 Jun 2014 21:03:21 +0100, wrote:

I have just stripped the 1kW motor from a Black and Decker 10"
circular saw I inherited. It was running erratic with the symptom
indicating the brushes were making poor contact. Sure enough the
brushes were seized in the brush holders,

As it looks like they had got hot I want to check the armature before
ordering brushes and holders. Am I right to think I need to check the
resistance between opposite commutator contacts? I seem to have about
80 Ohms on the few I have checked so far and a few kOhms between
coils, does that seem reasonable?

AJH

Those readings rather suggest open circuits between the armature
windings (topologically, the armature is a bunch of electromagnetic
coils all connected in series at each commutator segment forming a
closed loop).

I'd expect a 1HP constant speed universal motor to have the field
connected in shunt, possibly compounded with a series winding to help
stabilise speed with load.

I'd expect the armature DC resistance between opposite segments to
show a reading of around 5 to 7% of the equivilent resistance of a 1KW
heating element (the perfect motor would have zero DC resistance in
the armature windings). In this case, a practical 1HP universal motor,
I'd expect a reading of around 4 ohms with a fraction of an ohm
between adjacent segments.

Hmm. A 1kW motor consumes 1kW of power. The motor will be based on cost
that tends to mean a lot of heat and not so much mechanical power.

Which is why I used a 1HP rather than a 1.25HP figure. :-)


Often the motor is speed stabilised by a combination of drag by cooling
fan, and the current lagging due to the inductive stator winding. I've
never seen a shunt winding in addition to a series winding, but I could
be wrong in this instance.

No, you're probably right. I was just covering the possibility that a
1HP motor _might_ also include a series field winding by using the
phrase "possibly compounded with a series winding". Assuming
(possibly incorrectly) that you'd need constant speed rather the
torque curve speed law of a traction motor for spinning a circular saw
blade.


All in all a universal motor is a terrible compromise and best run by
rectified mains!

Maybe, and if so, _only_ rectified with no 'smoothing' caps. A pulsed
100Hz DC might imbalance the electrical erosion of the brushess (it
remains balanced out on the commutator segments in either case).

Regardless of the detail, one thing seems clear, the armature appears
to have developed open ciruited coil connections.
--
J B Good

There is no point in dismantling the item.
Free off the brushes and test the continuity by connecting your meter to the
power input rotating the armature.
If the meter jumps about, there is a winding OC or SC.

But you don't need a meter.
So long as the brushes are in order (ie free and in contact) , if there is
lots of sparking on the commutator, IE flashing over several segments, the
armature is shagged. There will likely be burn marks on the commutator too.
Cost of repair (new armature) is likely to be uneconomic even assuming you
can get the part.

"DC" series motors whilst theoretically having an infinite no load speed, in
practice, the cooling fan and the fact they are on AC limits the top speed.
If you ran this motor on DC ,it would go lots faster, mainly be cause the
impedence of the field windings would be much reduced.

In days of yore, some DC motors (for traction) had an additional shunt
winding to limit top speed. But they were on DC. These were "cumulatively
compounded machines".
The other possiblity being "differentially compounded machines."

There is in fact no such thing as a DC motor, they are all AC.

"Johny B Good" wrote in message
...
On Mon, 23 Jun 2014 17:37:00 +0100, Fredxxx wrote:

On 23/06/2014 17:06, Johny B Good wrote:
On Mon, 23 Jun 2014 15:09:09 +0100, Fredxxx wrote:

On 23/06/2014 13:07, Johny B Good wrote:
On Sun, 22 Jun 2014 21:03:21 +0100, wrote:

I have just stripped the 1kW motor from a Black and Decker 10"
circular saw I inherited. It was running erratic with the symptom
indicating the brushes were making poor contact. Sure enough the
brushes were seized in the brush holders,

As it looks like they had got hot I want to check the armature before
ordering brushes and holders. Am I right to think I need to check the
resistance between opposite commutator contacts? I seem to have about
80 Ohms on the few I have checked so far and a few kOhms between
coils, does that seem reasonable?

AJH

Those readings rather suggest open circuits between the armature
windings (topologically, the armature is a bunch of electromagnetic
coils all connected in series at each commutator segment forming a
closed loop).

I'd expect a 1HP constant speed universal motor to have the field
connected in shunt, possibly compounded with a series winding to help
stabilise speed with load.

I'd expect the armature DC resistance between opposite segments to
show a reading of around 5 to 7% of the equivilent resistance of a 1KW
heating element (the perfect motor would have zero DC resistance in
the armature windings). In this case, a practical 1HP universal motor,
I'd expect a reading of around 4 ohms with a fraction of an ohm
between adjacent segments.

Hmm. A 1kW motor consumes 1kW of power. The motor will be based on
cost
that tends to mean a lot of heat and not so much mechanical power.

Which is why I used a 1HP rather than a 1.25HP figure. :-)


Often the motor is speed stabilised by a combination of drag by cooling
fan, and the current lagging due to the inductive stator winding. I've
never seen a shunt winding in addition to a series winding, but I could
be wrong in this instance.

No, you're probably right. I was just covering the possibility that a
1HP motor _might_ also include a series field winding by using the
phrase "possibly compounded with a series winding". Assuming
(possibly incorrectly) that you'd need constant speed rather the
torque curve speed law of a traction motor for spinning a circular saw
blade.

The only time I have seen both series and shunt windings are in motors /
generators designed to run at constant speed / voltage with varying load.


All in all a universal motor is a terrible compromise and best run by
rectified mains!

Maybe, and if so, _only_ rectified with no 'smoothing' caps. A pulsed
100Hz DC might imbalance the electrical erosion of the brushess (it
remains balanced out on the commutator segments in either case).

I don't understand the assertion, that pulsating DC will be any
different to less pulsating (smoother) DC. The stator's inductance will
go some way to reduce ripple current.

It's not whether it's a pulsating or or ripple free DC that might be
a problem, just the fact that it's DC of any flavour. The problem with
using capacitive smoothing is that it may raise the rms voltage to
somewhere in the region of 300 volts or more if you overdo the
smoothing.


I've not come across electrical erosion of brushes, unless you mean
arcing?

There's always some level of 'arcing' involved with commutator brush
gear. The uni-directional current flow (which won't matter to the
commutator segments) may slow down wear on one brush and accelerate it
on the other brush compared to AC current running.

I don't suppose it would be a major problem since dynamos on vintage
motor vehicles seemed to cope well enough. At least, I never saw any
historic articles regarding 'rotating the dynamo brushes' to even out
the wear but dynamos were a vintage thing even back in the sixties so
I may have simply missed seeing such 'sage advice' being published.

Total drivel.
The ideal position of the brushes on the commutator varies depending on the
load.
If they are in the "wrong" position, there is a sparking and brush wear.


In days of yore large DC machines had moveable brushes which were manually
changed to suit load.
Later machines had interpoles or compensating windings in series with the
armature which automatically corrected this problem by modifying the field
piece magnetic field.
Of course this costs money and they are not fitted to small machines.
So brushes etc don't last as long and there is arcing.
http://wiki.answers.com/Q/What_is_th...ine?#slide =5

The armature current BTW reverses as it passes under the brush ideally which
is why there is no sparking.
Or it would if it was DC. Not always the case with AC. Which is why power
tools have a life of only hours.

On 25/06/2014 07:46, harryagain wrote:

snip

There is in fact no such thing as a DC motor, they are all AC.

I would beg to differ. I can assure you that a nominal 12V DC is sent to
my starter motor when required.

"Fredxxx" wrote in message
...
On 25/06/2014 07:46, harryagain wrote:

snip

There is in fact no such thing as a DC motor, they are all AC.

I would beg to differ. I can assure you that a nominal 12V DC is sent to
my starter motor when required.

Then you are an idiot.
The commutator is a mechanical inverter/rectifier.
The first thing that happens in a "DC motor" is the DC is converted to AC

With a single laboratory exception, all rotating electrical machines are AC.

On 25/06/2014 17:51, Fredxxx wrote:
On 25/06/2014 07:46, harryagain wrote:

snip

There is in fact no such thing as a DC motor, they are all AC.

I would beg to differ. I can assure you that a nominal 12V DC is sent to
my starter motor when required.

Harry's trying and failing to be a smart alec. And he keeps forgetting
that there *is* a type of electric motor that works on pure DC, with no
internal conversion to AC.

--
Tciao for Now!

John.

On 25/06/14 17:51, Fredxxx wrote:
On 25/06/2014 07:46, harryagain wrote:

snip

There is in fact no such thing as a DC motor, they are all AC.

I would beg to differ. I can assure you that a nominal 12V DC is sent to
my starter motor when required.

What harry probably means is that the commutator inverts it to AC.


--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

On 25/06/14 18:59, John Williamson wrote:
On 25/06/2014 17:51, Fredxxx wrote:
On 25/06/2014 07:46, harryagain wrote:

snip

There is in fact no such thing as a DC motor, they are all AC.

I would beg to differ. I can assure you that a nominal 12V DC is sent to
my starter motor when required.

Harry's trying and failing to be a smart alec. And he keeps forgetting
that there *is* a type of electric motor that works on pure DC, with no
internal conversion to AC.

The SillyNerd?


--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

In article , harryagain
wrote:

"Fredxxx" wrote in message
...
On 25/06/2014 07:46, harryagain wrote:

snip

There is in fact no such thing as a DC motor, they are all AC.

I would beg to differ. I can assure you that a nominal 12V DC is sent
to my starter motor when required.

Then you are an idiot. The commutator is a mechanical inverter/rectifier.
The first thing that happens in a "DC motor" is the DC is converted to AC

With a single laboratory exception, all rotating electrical machines are
AC.

My model railway trains ran with dc motors.

--
From KT24

Using a RISC OS computer running v5.18

On 25/06/2014 19:58, charles wrote:
In article , harryagain
wrote:

"Fredxxx" wrote in message
...
On 25/06/2014 07:46, harryagain wrote:

snip

There is in fact no such thing as a DC motor, they are all AC.

I would beg to differ. I can assure you that a nominal 12V DC is sent
to my starter motor when required.

Then you are an idiot. The commutator is a mechanical inverter/rectifier.
The first thing that happens in a "DC motor" is the DC is converted to AC

With a single laboratory exception, all rotating electrical machines are
AC.

My model railway trains ran with dc motors.

Yawn Which harry will probably remind us again unless he reads this,
turn the DC into AC on the armature internally.

--
Tciao for Now!

John.

John Williamson wrote:

Harry's trying and failing to be a smart alec. And he keeps forgetting
that there *is* a type of electric motor that works on pure DC, with no
internal conversion to AC.

http://youtu.be/EkU_JmtH3PU

On Wed, 25 Jun 2014 08:15:20 +0100, "harryagain"
wrote:


"Johny B Good" wrote in message
.. .
On Mon, 23 Jun 2014 17:37:00 +0100, Fredxxx wrote:

On 23/06/2014 17:06, Johny B Good wrote:
On Mon, 23 Jun 2014 15:09:09 +0100, Fredxxx wrote:

On 23/06/2014 13:07, Johny B Good wrote:
On Sun, 22 Jun 2014 21:03:21 +0100, wrote:

I have just stripped the 1kW motor from a Black and Decker 10"
circular saw I inherited. It was running erratic with the symptom
indicating the brushes were making poor contact. Sure enough the
brushes were seized in the brush holders,

As it looks like they had got hot I want to check the armature before
ordering brushes and holders. Am I right to think I need to check the
resistance between opposite commutator contacts? I seem to have about
80 Ohms on the few I have checked so far and a few kOhms between
coils, does that seem reasonable?

AJH

Those readings rather suggest open circuits between the armature
windings (topologically, the armature is a bunch of electromagnetic
coils all connected in series at each commutator segment forming a
closed loop).

I'd expect a 1HP constant speed universal motor to have the field
connected in shunt, possibly compounded with a series winding to help
stabilise speed with load.

I'd expect the armature DC resistance between opposite segments to
show a reading of around 5 to 7% of the equivilent resistance of a 1KW
heating element (the perfect motor would have zero DC resistance in
the armature windings). In this case, a practical 1HP universal motor,
I'd expect a reading of around 4 ohms with a fraction of an ohm
between adjacent segments.

Hmm. A 1kW motor consumes 1kW of power. The motor will be based on
cost
that tends to mean a lot of heat and not so much mechanical power.

Which is why I used a 1HP rather than a 1.25HP figure. :-)


Often the motor is speed stabilised by a combination of drag by cooling
fan, and the current lagging due to the inductive stator winding. I've
never seen a shunt winding in addition to a series winding, but I could
be wrong in this instance.

No, you're probably right. I was just covering the possibility that a
1HP motor _might_ also include a series field winding by using the
phrase "possibly compounded with a series winding". Assuming
(possibly incorrectly) that you'd need constant speed rather the
torque curve speed law of a traction motor for spinning a circular saw
blade.

The only time I have seen both series and shunt windings are in motors /
generators designed to run at constant speed / voltage with varying load.


All in all a universal motor is a terrible compromise and best run by
rectified mains!

Maybe, and if so, _only_ rectified with no 'smoothing' caps. A pulsed
100Hz DC might imbalance the electrical erosion of the brushess (it
remains balanced out on the commutator segments in either case).

I don't understand the assertion, that pulsating DC will be any
different to less pulsating (smoother) DC. The stator's inductance will
go some way to reduce ripple current.

It's not whether it's a pulsating or or ripple free DC that might be
a problem, just the fact that it's DC of any flavour. The problem with
using capacitive smoothing is that it may raise the rms voltage to
somewhere in the region of 300 volts or more if you overdo the
smoothing.


I've not come across electrical erosion of brushes, unless you mean
arcing?

There's always some level of 'arcing' involved with commutator brush
gear. The uni-directional current flow (which won't matter to the
commutator segments) may slow down wear on one brush and accelerate it
on the other brush compared to AC current running.

I don't suppose it would be a major problem since dynamos on vintage
motor vehicles seemed to cope well enough. At least, I never saw any
historic articles regarding 'rotating the dynamo brushes' to even out
the wear but dynamos were a vintage thing even back in the sixties so
I may have simply missed seeing such 'sage advice' being published.

Total drivel.

You forgot to add the all important "IMO".

The ideal position of the brushes on the commutator varies depending on the
load.

Yes, that's a given.

If they are in the "wrong" position, there is a sparking and brush wear.


A consequence of the distortion of the magnetic field due to the
variation of armature current with loading. On a simple motor with
fixed brushes, it's set to a midway compromise position unless it's
been designed for use with a reversing switch.


In days of yore large DC machines had moveable brushes which were manually
changed to suit load.

That was fine for large industrial DC motors.

Later machines had interpoles or compensating windings in series with the
armature which automatically corrected this problem by modifying the field
piece magnetic field.

A rather neat refinement you're unlikely to see on a typical sub
horsepower universal motor typical of most domestic white goods and
electrical tools.

Of course this costs money and they are not fitted to small machines.

Ok, you 'get it' then. So why nitpick my statements?

So brushes etc don't last as long and there is arcing.
http://wiki.answers.com/Q/What_is_th...ine?#slide =5

The armature current BTW reverses as it passes under the brush ideally which
is why there is no sparking.

The intersegment voltage is pretty close to zero at the ideal brush
location and reaches a max at 90 degrees.

Or it would if it was DC. Not always the case with AC. Which is why power
tools have a life of only hours.

I think you meant to say "tens of hours", still pretty short lived
but in the context of its use, probably sufficient for a few years of
DIY use in most cases.
--
J B Good

On 25/06/2014 18:40, harryagain wrote:
"Fredxxx" wrote in message
...
On 25/06/2014 07:46, harryagain wrote:

snip

There is in fact no such thing as a DC motor, they are all AC.

I would beg to differ. I can assure you that a nominal 12V DC is sent to
my starter motor when required.

Then you are an idiot.

No you're the crass idiot in saying there is no such thing as a DC
motor. Or a motor that won't accept a DC power input.

The commutator is a mechanical inverter/rectifier.

Next you'll be saying a universal motor running on AC doesn't need a
commutator.

The first thing that happens in a "DC motor" is the DC is converted to AC

Have you tried applying an AC current to opposing segments of a motor.
Would you expect anything other than a "hum"?

For a DC motor with a DC field coil, a commutator ensures that a DC
current flows in the appropriate section of armature to maintain a torque.

It is true that any part of an armature will see an alternating current,
but the motor is still driven with DC and is called in all parlances a
DC motor.

With a single laboratory exception, all rotating electrical machines are AC.

Make your mind up.

"Fredxxx" wrote in message
...
On 25/06/2014 18:40, harryagain wrote:
"Fredxxx" wrote in message
...
On 25/06/2014 07:46, harryagain wrote:

snip

There is in fact no such thing as a DC motor, they are all AC.

I would beg to differ. I can assure you that a nominal 12V DC is sent to
my starter motor when required.

Then you are an idiot.

No you're the crass idiot in saying there is no such thing as a DC motor.
Or a motor that won't accept a DC power input.

The commutator is a mechanical inverter/rectifier.

Next you'll be saying a universal motor running on AC doesn't need a
commutator.

Acutally it doesn't.
But it would only run at one speed.



The first thing that happens in a "DC motor" is the DC is converted to AC

Have you tried applying an AC current to opposing segments of a motor.
Would you expect anything other than a "hum"?

For a DC motor with a DC field coil, a commutator ensures that a DC
current flows in the appropriate section of armature to maintain a torque.

The current reverses when the segment passes under a brush.



It is true that any part of an armature will see an alternating current,
but the motor is still driven with DC and is called in all parlances a DC
motor.


Only for the benefit of the ignorant.
Such as you.

With a single laboratory exception, all rotating electrical machines are
AC.

Make your mind up.

"John Williamson" wrote in message
...
On 25/06/2014 17:51, Fredxxx wrote:
On 25/06/2014 07:46, harryagain wrote:

snip

There is in fact no such thing as a DC motor, they are all AC.

I would beg to differ. I can assure you that a nominal 12V DC is sent to
my starter motor when required.

Harry's trying and failing to be a smart alec. And he keeps forgetting
that there *is* a type of electric motor that works on pure DC, with no
internal conversion to AC.

I did mention that.

On 26/06/2014 06:06, harryagain wrote:
"Fredxxx" wrote in message
...
Next you'll be saying a universal motor running on AC doesn't need a
commutator.

Acutally it doesn't.
But it would only run at one speed.

It wouldn't run at all, so you are indeed correct for a change. The only
way a motor without a commutator will run is if it's designed to only
run on AC, which makes it the opposite of a universal machine. The only
way to design a motor to run on AC or DC without a commutator would be
to incorporate an inverter in the design, and a bridge rectifier to
power the inverter, but the motor in this case would be AC only.
Brushless DC motors use electronic switching instead of mechanical.

The first thing that happens in a "DC motor" is the DC is converted to AC

Have you tried applying an AC current to opposing segments of a motor.
Would you expect anything other than a "hum"?

For a DC motor with a DC field coil, a commutator ensures that a DC
current flows in the appropriate section of armature to maintain a torque.

The current reverses when the segment passes under a brush.

If you examine each segment in turn as it passes the same position, the
current always flows in the same direction.


It is true that any part of an armature will see an alternating current,
but the motor is still driven with DC and is called in all parlances a DC
motor.


Only for the benefit of the ignorant.
Such as you.

" ".


--
Tciao for Now!

John.

On 26/06/2014 06:06, harryagain wrote:
"Fredxxx" wrote in message
...
On 25/06/2014 18:40, harryagain wrote:
"Fredxxx" wrote in message
...
On 25/06/2014 07:46, harryagain wrote:

snip

There is in fact no such thing as a DC motor, they are all AC.

I would beg to differ. I can assure you that a nominal 12V DC is sent to
my starter motor when required.

Then you are an idiot.

No you're the crass idiot in saying there is no such thing as a DC motor.
Or a motor that won't accept a DC power input.

The commutator is a mechanical inverter/rectifier.

Only an idiot would think that my car starter motor would not accept 12V DC.

Next you'll be saying a universal motor running on AC doesn't need a
commutator.

Acutally it doesn't.
But it would only run at one speed.

How often are synchronous motors used? Clocks and timers are the only
examples I can think of. They have appalling start characteristics.

The first thing that happens in a "DC motor" is the DC is converted to AC

Have you tried applying an AC current to opposing segments of a motor.
Would you expect anything other than a "hum"?

For a DC motor with a DC field coil, a commutator ensures that a DC
current flows in the appropriate section of armature to maintain a torque.

The current reverses when the segment passes under a brush.

Yes, you're just saying the same thing.

It is true that any part of an armature will see an alternating current,
but the motor is still driven with DC and is called in all parlances a DC
motor.


Only for the benefit of the ignorant.
Such as you.

You have a choice of obfuscating simple explanations in a show of
prowess or you can be helpful.

Resorting to name calling shows you've lost any argument you were trying
to make.

With a single laboratory exception, all rotating electrical machines are
AC.

Make your mind up.

On Thu, 26 Jun 2014 01:03:57 +0100, Fredxxx wrote:

On 25/06/2014 18:40, harryagain wrote:
"Fredxxx" wrote in message
...
On 25/06/2014 07:46, harryagain wrote:

snip

There is in fact no such thing as a DC motor, they are all AC.

I would beg to differ. I can assure you that a nominal 12V DC is sent to
my starter motor when required.

Then you are an idiot.

No you're the crass idiot in saying there is no such thing as a DC
motor. Or a motor that won't accept a DC power input.

The commutator is a mechanical inverter/rectifier.

Next you'll be saying a universal motor running on AC doesn't need a
commutator.

The first thing that happens in a "DC motor" is the DC is converted to AC

Have you tried applying an AC current to opposing segments of a motor.
Would you expect anything other than a "hum"?

For a DC motor with a DC field coil, a commutator ensures that a DC
current flows in the appropriate section of armature to maintain a torque.

It is true that any part of an armature will see an alternating current,
but the motor is still driven with DC and is called in all parlances a
DC motor.

With a single laboratory exception, all rotating electrical machines are AC.

Make your mind up.

Harry's a troll. Oh he's not the foul mouthed class of troll usually
associated with the name Troll but a troll, nonetheless. He's a more
intellectual troll (in most news groups, the worst kind).

His exception, which he could so easily have named, is the Faraday or
homopolar motor or generator which relies on Lorentz force. This type
works on a steady DC current with no internally generated polarity
reversals as used by conventional DC motors.

What he states is, strictly speaking, absolutely correct. The common
or garden DC motor is essentially an AC motor with a mechanical
reversing swith synchronised to the rotational position of the
armature. The current flow in each pole winding isn't constant as in
the case of the homopolar motor but alternating as in the case of an
ac motor. The commutator brush gear just neatly disguises this fact.

See these links for the obvious sources of information on this
subject:-

http://en.wikipedia.org/wiki/Homopolar_generator
http://en.wikipedia.org/wiki/Homopolar_motor
http://en.wikipedia.org/wiki/Railgun

--
J B Good

"Fredxxx" wrote in message
...
On 26/06/2014 06:06, harryagain wrote:
"Fredxxx" wrote in message
...
On 25/06/2014 18:40, harryagain wrote:
"Fredxxx" wrote in message
...
On 25/06/2014 07:46, harryagain wrote:

snip

There is in fact no such thing as a DC motor, they are all AC.

I would beg to differ. I can assure you that a nominal 12V DC is sent
to
my starter motor when required.

Then you are an idiot.

No you're the crass idiot in saying there is no such thing as a DC
motor.
Or a motor that won't accept a DC power input.

The commutator is a mechanical inverter/rectifier.

Only an idiot would think that my car starter motor would not accept 12V
DC.

Next you'll be saying a universal motor running on AC doesn't need a
commutator.

Acutally it doesn't.
But it would only run at one speed.

How often are synchronous motors used? Clocks and timers are the only
examples I can think of. They have appalling start characteristics.


Clearly thinking is not your forte.
They are used for example in all commercial electric cars.
They have excellent start characteristics.
Max torque @ zero revs.
Ideal for traction.
They are used for many of the auxilliary motors in electric cars too.

They are used in many traction applications , eg electric trains, ships.

Domestically they are appearing in vacuum cleaners and washing machines
(elctronics being cheaper than commutators.) "Digital motors". Heh Heh.

There is no difference between a synchronous motor and an alternator.
All electric"motors" can be run as generators.






The first thing that happens in a "DC motor" is the DC is converted to
AC

Have you tried applying an AC current to opposing segments of a motor.
Would you expect anything other than a "hum"?

For a DC motor with a DC field coil, a commutator ensures that a DC
current flows in the appropriate section of armature to maintain a
torque.

The current reverses when the segment passes under a brush.

Yes, you're just saying the same thing.

It is true that any part of an armature will see an alternating current,
but the motor is still driven with DC and is called in all parlances a
DC
motor.

The motor has DC supplied to it. But it doesn't run on DC.




Only for the benefit of the ignorant.
Such as you.

You have a choice of obfuscating simple explanations in a show of prowess
or you can be helpful.

Resorting to name calling shows you've lost any argument you were trying
to make.

With a single laboratory exception, all rotating electrical machines
are
AC.

Make your mind up.

I can't make it any more simple than that for you
Go and read some books.

On 26/06/2014 16:13, Johny B Good wrote:
On Thu, 26 Jun 2014 01:03:57 +0100, Fredxxx wrote:

On 25/06/2014 18:40, harryagain wrote:
"Fredxxx" wrote in message
...
On 25/06/2014 07:46, harryagain wrote:

snip

There is in fact no such thing as a DC motor, they are all AC.

I would beg to differ. I can assure you that a nominal 12V DC is sent to
my starter motor when required.

Then you are an idiot.

No you're the crass idiot in saying there is no such thing as a DC
motor. Or a motor that won't accept a DC power input.

The commutator is a mechanical inverter/rectifier.

Next you'll be saying a universal motor running on AC doesn't need a
commutator.

The first thing that happens in a "DC motor" is the DC is converted to AC

Have you tried applying an AC current to opposing segments of a motor.
Would you expect anything other than a "hum"?

For a DC motor with a DC field coil, a commutator ensures that a DC
current flows in the appropriate section of armature to maintain a torque.

It is true that any part of an armature will see an alternating current,
but the motor is still driven with DC and is called in all parlances a
DC motor.

With a single laboratory exception, all rotating electrical machines are AC.

Make your mind up.

Harry's a troll. Oh he's not the foul mouthed class of troll usually
associated with the name Troll but a troll, nonetheless. He's a more
intellectual troll (in most news groups, the worst kind).

His exception, which he could so easily have named, is the Faraday or
homopolar motor or generator which relies on Lorentz force. This type
works on a steady DC current with no internally generated polarity
reversals as used by conventional DC motors.

What he states is, strictly speaking, absolutely correct. The common
or garden DC motor is essentially an AC motor with a mechanical
reversing swith synchronised to the rotational position of the
armature. The current flow in each pole winding isn't constant as in
the case of the homopolar motor but alternating as in the case of an
ac motor. The commutator brush gear just neatly disguises this fact.

See these links for the obvious sources of information on this
subject:-

http://en.wikipedia.org/wiki/Homopolar_generator
http://en.wikipedia.org/wiki/Homopolar_motor
http://en.wikipedia.org/wiki/

I'm quite aware of what harry is saying, but when he calls someone an
idiot when they say their starter motor runs on 12V, he only shows
himself up as a trolling idiot.

BTW I thought homopolar generators were often used to provide
substantial currents at modest voltages.

On Fri, 27 Jun 2014 00:12:30 +0100, Fredxxx wrote:

On 26/06/2014 16:13, Johny B Good wrote:
On Thu, 26 Jun 2014 01:03:57 +0100, Fredxxx wrote:

On 25/06/2014 18:40, harryagain wrote:
"Fredxxx" wrote in message
...
On 25/06/2014 07:46, harryagain wrote:

snip

There is in fact no such thing as a DC motor, they are all AC.

I would beg to differ. I can assure you that a nominal 12V DC is sent to
my starter motor when required.

Then you are an idiot.

No you're the crass idiot in saying there is no such thing as a DC
motor. Or a motor that won't accept a DC power input.

The commutator is a mechanical inverter/rectifier.

Next you'll be saying a universal motor running on AC doesn't need a
commutator.

The first thing that happens in a "DC motor" is the DC is converted to AC

Have you tried applying an AC current to opposing segments of a motor.
Would you expect anything other than a "hum"?

For a DC motor with a DC field coil, a commutator ensures that a DC
current flows in the appropriate section of armature to maintain a torque.

It is true that any part of an armature will see an alternating current,
but the motor is still driven with DC and is called in all parlances a
DC motor.

With a single laboratory exception, all rotating electrical machines are AC.

Make your mind up.

Harry's a troll. Oh he's not the foul mouthed class of troll usually
associated with the name Troll but a troll, nonetheless. He's a more
intellectual troll (in most news groups, the worst kind).

His exception, which he could so easily have named, is the Faraday or
homopolar motor or generator which relies on Lorentz force. This type
works on a steady DC current with no internally generated polarity
reversals as used by conventional DC motors.

What he states is, strictly speaking, absolutely correct. The common
or garden DC motor is essentially an AC motor with a mechanical
reversing swith synchronised to the rotational position of the
armature. The current flow in each pole winding isn't constant as in
the case of the homopolar motor but alternating as in the case of an
ac motor. The commutator brush gear just neatly disguises this fact.

See these links for the obvious sources of information on this
subject:-

http://en.wikipedia.org/wiki/Homopolar_generator
http://en.wikipedia.org/wiki/Homopolar_motor
http://en.wikipedia.org/wiki/

I'm quite aware of what harry is saying, but when he calls someone an
idiot when they say their starter motor runs on 12V, he only shows
himself up as a trolling idiot.

BTW I thought homopolar generators were often used to provide
substantial currents at modest voltages.

As that last link was supposed to have shown one of the uses for Mega
Ampere generators. I'm not sure how I managed to paste my home page
link instead of the one I meant to post, he

http://en.wikipedia.org/wiki/Railgun

Mention was made in a wiki article on the homopolar generator of
hundreds of volts output (possibly not at a million or more amps
though - 100MW or higher if a 1MA 100 volt generator was involved).

Ah! This is the relavent link:
http://en.wikipedia.org/wiki/Electric_generator#Homopolar_generator

With regard to Harry's trolling, he just wants to start an argument
that he 'knows' he can 'win' on a technicality he hopes is obscure
enough to get a pointless and protracted argument going.

He carefully chooses his subject matter for maximum effect when he's
the thread starter, conveniently forgetting about practicalities that
seem best summed up as "You can't make an omelette without cracking a
few eggs".

He seems to have a Bee in his bonnet when it comes to nuclear power,
choosing to exclude the most pragmatic of solutions to the conflicting
need for more energy and the need to reduce pollution which might
cause the global climate to flip over into yet another Ice Age or a
Global Warm period (it's far from clear as to exactly what the
consequences will be for the climate due to our significant
contributions to the greenhouse gasses in the atmosphere - it's not
just the carbon dioxide we have to worry about in this regard, there's
also the possibility of massive releases of the methane trapped just
below the permafrost of the Tundra, a gas that is 60 times more
effective than CO2 as a greenhouse gas).

As a result of his wilful ignorance of the real world, most of
Harry's spoutings are best ignored and forgotten about. Don't let the
technical truths in his postings suck you into a pointless discussion
over the impracticalities involved in his suggested solutions (most of
which appear to be a case of 'not thinking things through') unless you
like going round and round in circles on a journey to nowhere.
--
J B Good

"Johny B Good" wrote in message
...
On Fri, 27 Jun 2014 00:12:30 +0100, Fredxxx wrote:

On 26/06/2014 16:13, Johny B Good wrote:
On Thu, 26 Jun 2014 01:03:57 +0100, Fredxxx wrote:

On 25/06/2014 18:40, harryagain wrote:
"Fredxxx" wrote in message
...
On 25/06/2014 07:46, harryagain wrote:

snip

There is in fact no such thing as a DC motor, they are all AC.

I would beg to differ. I can assure you that a nominal 12V DC is sent
to
my starter motor when required.

Then you are an idiot.

No you're the crass idiot in saying there is no such thing as a DC
motor. Or a motor that won't accept a DC power input.

The commutator is a mechanical inverter/rectifier.

Next you'll be saying a universal motor running on AC doesn't need a
commutator.

The first thing that happens in a "DC motor" is the DC is converted to
AC

Have you tried applying an AC current to opposing segments of a motor.
Would you expect anything other than a "hum"?

For a DC motor with a DC field coil, a commutator ensures that a DC
current flows in the appropriate section of armature to maintain a
torque.

It is true that any part of an armature will see an alternating
current,
but the motor is still driven with DC and is called in all parlances a
DC motor.

With a single laboratory exception, all rotating electrical machines
are AC.

Make your mind up.

Harry's a troll. Oh he's not the foul mouthed class of troll usually
associated with the name Troll but a troll, nonetheless. He's a more
intellectual troll (in most news groups, the worst kind).

His exception, which he could so easily have named, is the Faraday or
homopolar motor or generator which relies on Lorentz force. This type
works on a steady DC current with no internally generated polarity
reversals as used by conventional DC motors.

What he states is, strictly speaking, absolutely correct. The common
or garden DC motor is essentially an AC motor with a mechanical
reversing swith synchronised to the rotational position of the
armature. The current flow in each pole winding isn't constant as in
the case of the homopolar motor but alternating as in the case of an
ac motor. The commutator brush gear just neatly disguises this fact.

See these links for the obvious sources of information on this
subject:-

http://en.wikipedia.org/wiki/Homopolar_generator
http://en.wikipedia.org/wiki/Homopolar_motor
http://en.wikipedia.org/wiki/

I'm quite aware of what harry is saying, but when he calls someone an
idiot when they say their starter motor runs on 12V, he only shows
himself up as a trolling idiot.

BTW I thought homopolar generators were often used to provide
substantial currents at modest voltages.

As that last link was supposed to have shown one of the uses for Mega
Ampere generators. I'm not sure how I managed to paste my home page
link instead of the one I meant to post, he

http://en.wikipedia.org/wiki/Railgun

Mention was made in a wiki article on the homopolar generator of
hundreds of volts output (possibly not at a million or more amps
though - 100MW or higher if a 1MA 100 volt generator was involved).

Ah! This is the relavent link:
http://en.wikipedia.org/wiki/Electric_generator#Homopolar_generator

With regard to Harry's trolling, he just wants to start an argument
that he 'knows' he can 'win' on a technicality he hopes is obscure
enough to get a pointless and protracted argument going.

He carefully chooses his subject matter for maximum effect when he's
the thread starter, conveniently forgetting about practicalities that
seem best summed up as "You can't make an omelette without cracking a
few eggs".

He seems to have a Bee in his bonnet when it comes to nuclear power,
choosing to exclude the most pragmatic of solutions to the conflicting
need for more energy and the need to reduce pollution which might
cause the global climate to flip over into yet another Ice Age or a
Global Warm period (it's far from clear as to exactly what the
consequences will be for the climate due to our significant
contributions to the greenhouse gasses in the atmosphere - it's not
just the carbon dioxide we have to worry about in this regard, there's
also the possibility of massive releases of the methane trapped just
below the permafrost of the Tundra, a gas that is 60 times more
effective than CO2 as a greenhouse gas).

As a result of his wilful ignorance of the real world, most of
Harry's spoutings are best ignored and forgotten about. Don't let the
technical truths in his postings suck you into a pointless discussion
over the impracticalities involved in his suggested solutions (most of
which appear to be a case of 'not thinking things through') unless you
like going round and round in circles on a journey to nowhere.

There are alot of poorly educated people here.
I can't abide ignorance and those that perpetrate stupid theories
Especially the people that come up with homespun theories to account for
things they have never bothered to research.
Easy these days with the internet.

And no-one has yet explained to me how nuclear waste is disposed of.
Only the homespun theories and crap about the likes of future thorium
Let alone if it can be done economically.
I have found plenty of evidence on the internet to the contrary.


If everything was so easy, it would be happening. And it isn't.
Plus we have been told so many liesin the past by the nuclear industry.