RPM of variable speed DC Motors
 

After some web surfing, with HP being the same on a permanent magnet
DC motor, is a lower RPM for the given HP better than a higher RPM for
the same HP?

Motor A: 1HP, 90V, 2500 RPM, 10.7A 4.28A per 1,000 RPM
Motor B: 1HP, 90V, 1750 RPM, 9.2A 5.26A per 1,000 RPM

Since I'm a recovering college graduate, does this mean more kick per
RPM by the lower speed drive?

RPM of variable speed DC Motors
 

"Louis Ohland" wrote: (clip) does this mean more kick per RPM by the lower
speed drive?
^^^^^^^^^^^^^^^^
I've never heard of anyone calculating amps per RPM, and I think that is
because it is meaningless. First question: How do you know that both
motors are developing 1 HP? Are the figures you listed measured or read off
the nameplates? Of course, you get more torque at lower speed for a given
horsepower. If the figures are accurate, then motor A is slightly more
efficient than motor B.

RPM of variable speed DC Motors
 

Leo Lichtman wrote:
"Louis Ohland" wrote: (clip) does this mean more kick per RPM by the lower
speed drive?
^^^^^^^^^^^^^^^^
I've never heard of anyone calculating amps per RPM, and I think that is
because it is meaningless. First question: How do you know that both
motors are developing 1 HP? Are the figures you listed measured or read off
the nameplates? Of course, you get more torque at lower speed for a given
horsepower. If the figures are accurate, then motor A is slightly more
efficient than motor B.



Well, some manufacturers do not make finding their torque graphs readily
available. The amps were off a manufacturer's website, but they are just
summaries. No tables or graphs at all.

Motor A: 1HP, 90V, 2500 RPM, 10.7A 4.28A per 1,000 RPM
Motor B: 1HP, 90V, 1750 RPM, 9.2A 5.26A per 1,000 RPM

Efficiency aside, neglecting heat loss, wouldn't using a motor rated to
deliver 1HP at a lower RPM be better?

RPM of variable speed DC Motors
 

On Sat, 29 Sep 2007 21:09:57 -0500, Louis Ohland
wrote:

After some web surfing, with HP being the same on a permanent magnet
DC motor, is a lower RPM for the given HP better than a higher RPM for
the same HP?

Motor A: 1HP, 90V, 2500 RPM, 10.7A 4.28A per 1,000 RPM
Motor B: 1HP, 90V, 1750 RPM, 9.2A 5.26A per 1,000 RPM

Since I'm a recovering college graduate, does this mean more kick per
RPM by the lower speed drive?

Definitely means more torque. Less reduction required if you need less
than 2500 (0r 1750) RPM.
More torque means mor amops, and vise versa.

--
Posted via a free Usenet account from http://www.teranews.com

RPM of variable speed DC Motors
 

On Sat, 29 Sep 2007 22:22:15 -0500, Louis Ohland wrote:

Leo Lichtman wrote:
"Louis Ohland" wrote: (clip) does this mean more kick per RPM by the lower
speed drive?
^^^^^^^^^^^^^^^^
I've never heard of anyone calculating amps per RPM, and I think that is
because it is meaningless. First question: How do you know that both
motors are developing 1 HP? Are the figures you listed measured or read off
the nameplates? Of course, you get more torque at lower speed for a given
horsepower. If the figures are accurate, then motor A is slightly more
efficient than motor B.



Well, some manufacturers do not make finding their torque graphs readily
available. The amps were off a manufacturer's website, but they are just
summaries. No tables or graphs at all.

A theoretically perfect DC motor has a 1:1 relationship between armature
current and shaft torque, and a 1:1 relationship between armature voltage
and speed. It is, in fact, the same relationship if you use the right
units (Newtons, meters, volts, amps, radians and seconds) to do your
calculation.

Real DC motors, unless they're horribly inefficient, don't stray too far
from the theoretical -- so you can pretty much calculate the torque vs.
current characteristic from the speed vs. voltage characteristic.

Motor A: 1HP, 90V, 2500 RPM, 10.7A 4.28A per 1,000 RPM Motor B: 1HP,
90V, 1750 RPM, 9.2A 5.26A per 1,000 RPM

Efficiency aside, neglecting heat loss, wouldn't using a motor rated to
deliver 1HP at a lower RPM be better?

Define "better". The motor rated to deliver 1HP at the lower RPM is
clearly capable of delivering more torque without overheating. Assuming
that it's bearings and armature construction will stand up to the stress,
you'll be able to get nearly that torque out of it at higher speeds (and
voltages), but it'll probably be bigger.

If you need more than 1750 RPM and you don't want to mess with giving the
motor higher than rated voltage, then the second motor is clearly worse.
If you need more torque than the first motor can give and you'll always be
operating at less than 1750 RPM, the second motor is clearly better. If
neither of these two conditions hold, then you haven't given enough
information.

If you're going to be gearing either of them down no matter what, and you
haven't selected a gear ratio yet, then the speed and torque don't matter,
so you need to look at efficiency (and heat generation), weight, and other
factors that you haven't mentioned.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

RPM of variable speed DC Motors
 

On Sep 29, 9:09 pm, Louis Ohland wrote:
After some web surfing, with HP being the same on a permanent magnet
DC motor, is a lower RPM for the given HP better than a higher RPM for
the same HP?

Motor A: 1HP, 90V, 2500 RPM, 10.7A 4.28A per 1,000 RPM
Motor B: 1HP, 90V, 1750 RPM, 9.2A 5.26A per 1,000 RPM

Since I'm a recovering college graduate, does this mean more kick per
RPM by the lower speed drive?

Certainly you must mean Volts per 1000 RPM. A common specification.
At 52.6 volts per 1000 RPM, 92 volts will drive it to 1.75 K RPM.

Which motor is better? That is like asking which gear is better for a
bicycle.
Won't it depend on what you intend to use it for?
One motor appears to be designed for more RPM, and less torque, (if
they are really both 1 HSP motors)
It appears that the specifications listed are somewhat ambiguous/
questionable.
What are you planing to do? How many RPM do you really want?

RPM of variable speed DC Motors
 

Louis Ohland wrote:
After some web surfing, with HP being the same on a permanent magnet
DC motor, is a lower RPM for the given HP better than a higher RPM for
the same HP?

Motor A: 1HP, 90V, 2500 RPM, 10.7A 4.28A per 1,000 RPM
Motor B: 1HP, 90V, 1750 RPM, 9.2A 5.26A per 1,000 RPM

Since I'm a recovering college graduate, does this mean more kick per
RPM by the lower speed drive?
Motor B has more torque at rated current. The A/RPM is
meaningless, derived by dividing the rated full-load current by
the rated RPM. One interesting observation, though, is that
motor B is 16% more efficient than motor A, since they both
deliver 1 HP at the same voltage, but B draws a lot less current.

Jon

RPM of variable speed DC Motors
 

maybe it will help to understand that horsepower is a measure of power, not
force - torque is "force", RPM is "speed", power is the product, so to
speak. one horsepower is 3300 ft-lbs per minute - e.g. a one horsepower
motor can lift a 3300 pound weight (not mass) one foot in one minute, or it
can lift a 1 pound weight about 2/3 of a mile in the same time.



"Jon Elson" wrote in message
...
Louis Ohland wrote:
After some web surfing, with HP being the same on a permanent magnet DC
motor, is a lower RPM for the given HP better than a higher RPM for the
same HP?

Motor A: 1HP, 90V, 2500 RPM, 10.7A 4.28A per 1,000 RPM
Motor B: 1HP, 90V, 1750 RPM, 9.2A 5.26A per 1,000 RPM

Since I'm a recovering college graduate, does this mean more kick per
RPM by the lower speed drive?
Motor B has more torque at rated current. The A/RPM is meaningless,
derived by dividing the rated full-load current by the rated RPM. One
interesting observation, though, is that motor B is 16% more efficient
than motor A, since they both deliver 1 HP at the same voltage, but B
draws a lot less current.

Jon



--
Posted via a free Usenet account from http://www.teranews.com

RPM of variable speed DC Motors
 

On Sun, 30 Sep 2007 09:15:41 -0700, "William Noble"
wrote:

maybe it will help to understand that horsepower is a measure of power, not
force - torque is "force", RPM is "speed", power is the product, so to
speak. one horsepower is 3300 ft-lbs per minute - e.g. a one horsepower
motor can lift a 3300 pound weight (not mass) one foot in one minute, or it
can lift a 1 pound weight about 2/3 of a mile in the same time.

Ya dropped a zero. 1 HP = 33,000 ft-lbf/min.

RPM of variable speed DC Motors
 

On Sat, 29 Sep 2007 23:44:21 -0500, Tim Wescott
wrote:

On Sat, 29 Sep 2007 22:22:15 -0500, Louis Ohland wrote:

Leo Lichtman wrote:
snip
A theoretically perfect DC motor has a 1:1 relationship between armature
current and shaft torque, and a 1:1 relationship between armature voltage
and speed. It is, in fact, the same relationship if you use the right
units (Newtons, meters, volts, amps, radians and seconds) to do your
calculation.

Real DC motors, unless they're horribly inefficient, don't stray too far
from the theoretical -- so you can pretty much calculate the torque vs.
current characteristic from the speed vs. voltage characteristic.

snip

This is only true of permanent magnet motors or shunt
field motors operated with a fixed field voltage.

In the case of a perfect lossless SERIES field motor
the shaft speed is directly proportionate to supply voltage AND
inversely proportionate to supply current..

Because increase of supply current increases BOTH the
field and the armature excitation, the shaft torque is
proportional to current squared.

With regard to the original query, because the
manufacturer quotes RPM/supply current, these are clearly series
wound motors possibly intended for wheeled transport.

There is little to choose between them. The higher
speed motor is likely to be slightly smaller and lighter than the
lower speed machine. The lower speed machine is a bit more
efficient and the lower speed and higher torque may be an
advantage.

Neither machine is suitable if the main aim is
constant speed with variable load.

Jim

RPM of variable speed DC Motors
 

Theoretical concerns aside, then how can one tell if a DC motor is
appropriate for use on a lathe?


wrote:
Real DC motors, unless they're horribly inefficient, don't stray too far
from the theoretical -- so you can pretty much calculate the torque vs.
current characteristic from the speed vs. voltage characteristic.

snip
With regard to the original query, because the
manufacturer quotes RPM/supply current, these are clearly series
wound motors possibly intended for wheeled transport.

There is little to choose between them. The higher
speed motor is likely to be slightly smaller and lighter than the
lower speed machine. The lower speed machine is a bit more
efficient and the lower speed and higher torque may be an
advantage.

Neither machine is suitable if the main aim is
constant speed with variable load.

Jim

RPM of variable speed DC Motors
 

Ya added an f in lbf ? never heard of that one :-)

Martin
Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Life; 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/


Don Foreman wrote:
On Sun, 30 Sep 2007 09:15:41 -0700, "William Noble"
wrote:

maybe it will help to understand that horsepower is a measure of power, not
force - torque is "force", RPM is "speed", power is the product, so to
speak. one horsepower is 3300 ft-lbs per minute - e.g. a one horsepower
motor can lift a 3300 pound weight (not mass) one foot in one minute, or it
can lift a 1 pound weight about 2/3 of a mile in the same time.

Ya dropped a zero. 1 HP = 33,000 ft-lbf/min.

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RPM of variable speed DC Motors
 

That is to distinguish it as pound (force) as opposed to pound (mass)

lbf .... lbm

Here is a link that discusses the relationship with Newton's second law.

http://engr.nmsu.edu/~etti/winter98/...mann/slug.html



Martin H. Eastburn wrote:
Ya added an f in lbf ? never heard of that one :-)

Martin
Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Life; 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/


Don Foreman wrote:
On Sun, 30 Sep 2007 09:15:41 -0700, "William Noble"
wrote:

maybe it will help to understand that horsepower is a measure of
power, not force - torque is "force", RPM is "speed", power is the
product, so to speak. one horsepower is 3300 ft-lbs per minute -
e.g. a one horsepower motor can lift a 3300 pound weight (not mass)
one foot in one minute, or it can lift a 1 pound weight about 2/3 of
a mile in the same time.

Ya dropped a zero. 1 HP = 33,000 ft-lbf/min.

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News==----
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Newsgroups
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RPM of variable speed DC Motors
 

On Wed, 03 Oct 2007 15:59:21 -0500, Louis Ohland
wrote:

Theoretical concerns aside, then how can one tell if a DC motor is
appropriate for use on a lathe?


wrote:
Real DC motors, unless they're horribly inefficient, don't stray too far
from the theoretical -- so you can pretty much calculate the torque vs.
current characteristic from the speed vs. voltage characteristic.

snip
With regard to the original query, because the
manufacturer quotes RPM/supply current, these are clearly series
wound motors possibly intended for wheeled transport.

There is little to choose between them. The higher
speed motor is likely to be slightly smaller and lighter than the
lower speed machine. The lower speed machine is a bit more
efficient and the lower speed and higher torque may be an
advantage.

Neither machine is suitable if the main aim is
constant speed with variable load.

Jim
If it is shunt or PM feild and enclosed frame of adequate horsepower
at the correct rated speed, it's useable. The motor with the lower
native speed for the same horsepower will be the stronger motor when
used variable speed, as it will provide more torque at lower speeds
than the highspeed motor will.

--
Posted via a free Usenet account from http://www.teranews.com

RPM of variable speed DC Motors
 

I forgot the obscure and not approved terms like kgf, lfg, gf, ozf...ugh.
I was a newton type.
Martin
Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Life; 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/


JohnB wrote:
That is to distinguish it as pound (force) as opposed to pound (mass)

lbf .... lbm

Here is a link that discusses the relationship with Newton's second law.

http://engr.nmsu.edu/~etti/winter98/...mann/slug.html



Martin H. Eastburn wrote:
Ya added an f in lbf ? never heard of that one :-)

Martin
Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Life; 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/


Don Foreman wrote:
On Sun, 30 Sep 2007 09:15:41 -0700, "William Noble"
wrote:

maybe it will help to understand that horsepower is a measure of
power, not force - torque is "force", RPM is "speed", power is the
product, so to speak. one horsepower is 3300 ft-lbs per minute -
e.g. a one horsepower motor can lift a 3300 pound weight (not mass)
one foot in one minute, or it can lift a 1 pound weight about 2/3 of
a mile in the same time.

Ya dropped a zero. 1 HP = 33,000 ft-lbf/min.

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News==----
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120,000+ Newsgroups
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RPM of variable speed DC Motors
 

在 2007年9月30日星期日 UTC+8上�10:09:57，Louis Ohland写�：
After some web surfing, with HP being the same on a permanent magnet
DC motor, is a lower RPM for the given HP better than a higher RPM for
the same HP?

Motor A: 1HP, 90V, 2500 RPM, 10.7A 4.28A per 1,000 RPM
Motor B: 1HP, 90V, 1750 RPM, 9.2A 5.26A per 1,000 RPM

Since I'm a recovering college graduate, does this mean more kick per
RPM by the lower speed drive?

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