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Welding Forums - Welding of materials for manufacture & repair.
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Posted by Richard Smith on March 21, 2008, 7:26 am
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"Universal motors". These are a classic - work on DC and AC. The
traction motors for railway locos were these (not now that use
power-electronic devices and AC traction motors) - current received
was fast enough AC that you could use a transformer to set the power
through voltage tap, yet slow enough AC that a "universal motor" could
run on it. The tap on the transformer is selected using a big
multi-position switch turned by a big wheel on the driver's console
which looks a bit absurdly like a steering wheel(!).
How the motor works - the current flows through the static "stator"
coils to create the magnetic field - that react against the self-same
currnet continuing via the carbon-brushes through the rotor coils /
windings causing the mechanical force and roatyional movement.
If you are continuity testing a power tool like an angle-grinder
looking for a fault - you need to indpendently continuity test the
rotor coils and the stator coils. Their resistance to DC current for
intact windings is about the same, isn't it?
On AC - when the current reverses, so does the magnetic field it
produces in the stator - so the motor keeps running in the same
direction - the reason why uniquely this motor keeps happily spinning
in one direction producing power whether the current is AC or DC.
I think some claim that angle-grinders, etc run smoother on DC than AC
- maybe that is a claim when using a "Lincoln pipeliner"
Here it is:
"DC Auxiliary Performance
1,750 total watts of DC auxiliary power from a single 120V outlet for
grinders and lights. DC power is less likely to bog down a grinder
compared to AC power. (Not for use with AC voltage equipment.)"
Rich Smith
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Posted by Bob La Londe on March 21, 2008, 10:51 am
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> I think some claim that angle-grinders, etc run smoother on DC than AC
> - maybe that is a claim when using a "Lincoln pipeliner"
Many years ago I used to hang around a gun smith's shop and chat with him
while he worked. He had commented that both his big milling machine, and
his big lather were actually DC motors, and claimed that all the big low
tolerance machining tools like that used DC motors because it ran smoother.
I never dug into the connections, nor I think would he have let me. Those
were some expensive pieces of equipment.
>
> Here it is:
>
> "DC Auxiliary Performance
>
> 1,750 total watts of DC auxiliary power from a single 120V outlet for
> grinders and lights. DC power is less likely to bog down a grinder
> compared to AC power. (Not for use with AC voltage equipment.)"
>
> Rich Smith
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Posted by Richard Smith on March 21, 2008, 2:21 pm
Please log in for more thread options
>
> > I think some claim that angle-grinders, etc run smoother on DC than AC
> > - maybe that is a claim when using a "Lincoln pipeliner"
>
> Many years ago I used to hang around a gun smith's shop and chat with him
> while he worked. He had commented that both his big milling machine, and
> his big lather were actually DC motors, and claimed that all the big low
> tolerance machining tools like that used DC motors because it ran smoother.
> I never dug into the connections, nor I think would he have let me. Those
> were some expensive pieces of equipment.
>
>
>
>
>
> >
> > Here it is:
> >
> > "DC Auxiliary Performance
> >
> > 1,750 total watts of DC auxiliary power from a single 120V outlet for
> > grinders and lights. DC power is less likely to bog down a grinder
> > compared to AC power. (Not for use with AC voltage equipment.)"
> >
> > Rich Smith
Bob
Just recounting what I've been told...
3-phase induction motors have a constant turning torque. It's a
geometric perfection of having 3 phases rising and falling in the
three sets of windings, all balancing eachother out with their peaks
and troughs to give an even turning moment.
So I'd be surprised if common industrial machines had other than
3-phase motors to power them.
Single-phase induction motors have an uneven turning torque and that
can sometimes be seen in a "thrum" in the drive system, can't it? And
single-phase motors are not self-starting, unlike 3-phase motors which
are self-starting, giving a simple and very ideal set-up.
Rich Smith
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Posted by Martin H. Eastburn on March 21, 2008, 11:24 pm
Please log in for more thread options I'm with Rich - Industrial machines use 3, 5, 7, 9 and 11 phase in exotic
machines. These are wyes and stars and twisted stars. More phases the smoother
the movement.
Large can machines use the poly phase power and custom AC control.
Years ago when I taught power in a class, a young electrician under his
dads master sought help in determining which phase came first. Order counts
on some complex machines - and there was an electronic device that measured
just that. Neither he nor his dad had seen the lab instrument at that time.
Now there is a small hand unit that defines phase order.
My surface grinders are 3 phase.
Martin
Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
http://lufkinced.com/
Richard Smith wrote:
>
>>
>>> I think some claim that angle-grinders, etc run smoother on DC than AC
>>> - maybe that is a claim when using a "Lincoln pipeliner"
>> Many years ago I used to hang around a gun smith's shop and chat with him
>> while he worked. He had commented that both his big milling machine, and
>> his big lather were actually DC motors, and claimed that all the big low
>> tolerance machining tools like that used DC motors because it ran smoother.
>> I never dug into the connections, nor I think would he have let me. Those
>> were some expensive pieces of equipment.
>>
>>
>>
>>
>>
>>> Here it is:
>>>
>>> "DC Auxiliary Performance
>>>
>>> 1,750 total watts of DC auxiliary power from a single 120V outlet for
>>> grinders and lights. DC power is less likely to bog down a grinder
>>> compared to AC power. (Not for use with AC voltage equipment.)"
>>>
>>> Rich Smith
>
> Bob
>
> Just recounting what I've been told...
>
> 3-phase induction motors have a constant turning torque. It's a
> geometric perfection of having 3 phases rising and falling in the
> three sets of windings, all balancing eachother out with their peaks
> and troughs to give an even turning moment.
>
> So I'd be surprised if common industrial machines had other than
> 3-phase motors to power them.
>
> Single-phase induction motors have an uneven turning torque and that
> can sometimes be seen in a "thrum" in the drive system, can't it? And
> single-phase motors are not self-starting, unlike 3-phase motors which
> are self-starting, giving a simple and very ideal set-up.
>
> Rich Smith
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> - maybe that is a claim when using a "Lincoln pipeliner"