Delta Contractor's Saw Motor (34-444)
Paul Houtz
Okay, I called Delta. I called their parts ordering and service line.
I asked them what the story is regarding the Contractor's Saw II and
Contractor's Saw (34-444) motors.
ALL Delta Contractor's saws are now shipping with the 12.8 amp motors.
They are rated at 1.5 HP. They are a new motor design that puts out
the same power as the previous 14.8 amp motor but does not draw as much
amperage.
This means there is less problem with overheating in longer extension
cords and of course, an energy savings over the older 14.2 amp motors.
Of course, this makes it even more complex figuring out the power of
various saws, since there is aparently now a new type of motor that
shifts all the traditional Voltage * Amperate * k formulas.
So, taiwan manufacturers can ship incredibly inefficient motors that
draw 15 amps and call them 2 HP when they are really more like 1 HP,
and Delta ships incredibly efficient motors that draw 12.8 amps and
put out 1.5 HP motors.
What fun.
--
*******************************************************************************
*G. Paul Houtz * "Leave it as it is. You cannot improve on it. The *
*Hewlett Packard * "ages have been at work and man can only mar it." *
*gph@zeppelin\ * -Theodore Roosevelt *
*.pa.itc.hp.com * "Of what value are forty freedoms without a blank" *
* * "spot on the map?" -Aldo Leopold *
*******************************************************************************
Kevin Pausche
>So, taiwan manufacturers can ship incredibly inefficient motors that
>draw 15 amps and call them 2 HP when they are really more like 1 HP,
>and Delta ships incredibly efficient motors that draw 12.8 amps and
>put out 1.5 HP motors.
Actually, my Rexon (Taiwan) saw draws 18 amps and is rated at 2 HP.
Wouldn't this satisfy the traditional HP rule, 9 amps to one HP,
therefore my saw is 2 HP. And I seriously doubt my motor is
"incredibly inefficient", that is unless you actually own a Taiwan
table saw and know what you're talking about.
Paul Houtz
First, your "traditional HP rule" is wrong.
Here are the 3450 rpm figures from the 1988 Grainger's catalog:
1/2 HP 9.8 amps
3/4 HP 11.8 amps
1 HP 13.0 - 15.0 amps
1-1/2 HP 16.4 - 19.6 amps
2 HP 19.0 - 23.0 amps
So, as you can see, your motor falls pretty securely into the
1-1/2 HP range. You can judge for yourself the manufacturer's
claim of 2 HP.
On the other hand the Delta had better be some new kind of motor
of it falls below the 1 HP range. !!!!
So, the picture is muddled even further.
I actually owned a Taiwan bandsaw and still own a Taiwan jointer.
The Taiwan bandsaw claimed a 1 HP motor that drew 11 amps and was actually
weaker than the Delta 3/4 HP TEFC motor in my current bandsaw. It was
a Rexon motor.
I suspect people who actually own Taiwan saws don't really know what they are
talking about anyway. One would have to do directo torque comparisons
at the same time they are measuring amperage draw. Any other conclusion
is strictly a seat of the pants WA guess. Mine is WA guess, but here
is the data I used:
My 3/4 HP Delta 14" can easily get through 9" thick maple while my old
Rexon 1 HP bogged down in 5" maple.
Dull sawblades, etc., can skew these figures pretty significantly, too.
Bill DuBroff
Here are the 3450 rpm figures from the 1988 Grainger's catalog:
1/2 HP 9.8 amps
3/4 HP 11.8 amps
1 HP 13.0 - 15.0 amps
1-1/2 HP 16.4 - 19.6 amps
2 HP 19.0 - 23.0 amps
So, as you can see, your motor falls pretty securely into the
1-1/2 HP range. You can judge for yourself the manufacturer's
claim of 2 HP.
On the other hand the Delta had better be some new kind of motor
of it falls below the 1 HP range. !!!!
So, the picture is muddled even further.
I don't understand this. In the "ideal" world, 1 HP = 746 watts. For
115 volts, 1.5 HP = 9.73 amps. Delta rates their CS motor at 12.8 amps,
which implies a power factor (actual power to apparent power) of 0.76. I
don't know the statistics, but in my experience, AC induction motors have
power factors in the 0.7 to 0.8 range. Delta's "old" rating was 14.2,
which implies a power factor of 0.68, which seems a bit low for motors
and would be an incentive to improve efficiency. So Delta's motor
appears to be in the average range.
In addition, when comparing motors, everything else being equal, it is
essential to know whether the current rating is for full load or
continuous operation, in order to compare "apples with apples."
wd
Chris Lewis
Bill DuBroff <wdu...@coe-nw.eng.clemson.edu> wrote:
>Paul Houtz says:
>
> Here are the 3450 rpm figures from the 1988 Grainger's catalog:
>
> 1/2 HP 9.8 amps
> 3/4 HP 11.8 amps
> 1 HP 13.0 - 15.0 amps
> 1-1/2 HP 16.4 - 19.6 amps
> 2 HP 19.0 - 23.0 amps
>
> So, as you can see, your motor falls pretty securely into the
> 1-1/2 HP range. You can judge for yourself the manufacturer's
> claim of 2 HP.
>
> On the other hand the Delta had better be some new kind of motor
> of it falls below the 1 HP range. !!!!
>
> So, the picture is muddled even further.
>I don't understand this. In the "ideal" world, 1 HP = 746 watts. For
>115 volts, 1.5 HP = 9.73 amps. Delta rates their CS motor at 12.8 amps,
>which implies a power factor (actual power to apparent power) of 0.76. I
>don't know the statistics, but in my experience, AC induction motors have
>power factors in the 0.7 to 0.8 range. Delta's "old" rating was 14.2,
>which implies a power factor of 0.68, which seems a bit low for motors
>and would be an incentive to improve efficiency. So Delta's motor
>appears to be in the average range.
The Grainger catalogue seems unduly pessimistic. Engineering rule-of-thumb
is 1Kw/HP. Hence 12.8A could be around 1.5HP.
--
Chris Lewis: _Una confibula non sat est_
Phone: Canada 613 832-0541
Latest psroff: FTP://ftp.uunet.ca/distrib/chris_lewis/psroff3.0pl17/*
Latest hp2pbm: FTP://ftp.uunet.ca/distrib/chris_lewis/hp2pbm/*
Lenny
requires a motor to produce 200% torque for short periods of times. Some
manufactures use this to their advantage in marketing but saying "rated up
to 2 HP" when in actuality you have a 1HP motor that can develope 2 HP for
short duration. A good example of this is the craftsman shop vac. The HP
they state is actually twice what the motor is rated. I believe this is
what you mean when you say full load versus continuous operation, though
continuous operation is full load.
The numbers you state for calculating current from horsepower do not take
into account efficiency. You mention it at the end as relating to power
factor but these two figure have nothing to do with each other. The power
factor is cause by a motor being an inductive load. The extra current
caused by power factor is "free", that is you meter measures true power,
not apparent power. The efficiency factor is caused by the resistive copper
losses in the windings.
If you have a 1.5 HP motor, the output power is 1119 watts. If you assume a
80% PF and a 90% efficiency, you would get 1554 volt*amps, or 13.5 amps at
115V. Keep in mind that if you're calculating the input power, the power
factor never comes into play, just the efficiency.
In article <3tgthk$9...@hubcap.clemson.edu>, wdu...@coe-nw.eng.clemson.edu
says...
>
>Paul Houtz says:
>
> Here are the 3450 rpm figures from the 1988 Grainger's catalog:
>
> 1/2 HP 9.8 amps
> 3/4 HP 11.8 amps
> 1 HP 13.0 - 15.0 amps
> 1-1/2 HP 16.4 - 19.6 amps
> 2 HP 19.0 - 23.0 amps
>
> So, as you can see, your motor falls pretty securely into the
> 1-1/2 HP range. You can judge for yourself the manufacturer's
> claim of 2 HP.
>
> On the other hand the Delta had better be some new kind of motor
> of it falls below the 1 HP range. !!!!
>
> So, the picture is muddled even further.
>
>
>I don't understand this. In the "ideal" world, 1 HP = 746 watts. For
>115 volts, 1.5 HP = 9.73 amps. Delta rates their CS motor at 12.8 amps,
>which implies a power factor (actual power to apparent power) of 0.76. I
>don't know the statistics, but in my experience, AC induction motors have
>power factors in the 0.7 to 0.8 range. Delta's "old" rating was 14.2,
>which implies a power factor of 0.68, which seems a bit low for motors
>and would be an incentive to improve efficiency. So Delta's motor
>appears to be in the average range.
>
David Elliston
>Actually, my Rexon (Taiwan) saw draws 18 amps and is rated at 2 HP.
>Wouldn't this satisfy the traditional HP rule, 9 amps to one HP,
>therefore my saw is 2 HP. And I seriously doubt my motor is
>"incredibly inefficient", that is unless you actually own a Taiwan
>table saw and know what you're talking about.
I would be interested to know how you might know that your Taiwanese
motor efficiently uses the input power to produce output power. How
did you measure it? I would suspect that the motors produced
domestically (in the US, that is) by such notables as GE, Baldor,
Marathon, etc would be more efficient users of input power than those
produced in the ROC to a marketing "specification".
You might consider that these same factories in the ROC use the
formula so heavily marketed by the likes of Sears etc to artificially
define the HP rating of their products. On the other hand, if y'all
weren't so pre-occupied with amps, and just concentrated on the true
HP rating (746 watts) you would be less likely to be misled, or
confused. For example, a 1 HP (that is 746 watts) motor running on 115
volts draws 6.5 amps, so is it likely that a motor drawing 13 amps
would therefore be rated at 13 amps. For 230 volts you can reduce the
amperage to half that stated.
d...@dnsns.navy.gov.au
Canberra ACT Australia
Chris Lewis
>>Actually, my Rexon (Taiwan) saw draws 18 amps and is rated at 2 HP.
>>Wouldn't this satisfy the traditional HP rule, 9 amps to one HP,
>>therefore my saw is 2 HP. And I seriously doubt my motor is
>>"incredibly inefficient", that is unless you actually own a Taiwan
>>table saw and know what you're talking about.
>I would be interested to know how you might know that your Taiwanese
>motor efficiently uses the input power to produce output power. How
>did you measure it? I would suspect that the motors produced
>domestically (in the US, that is) by such notables as GE, Baldor,
>Marathon, etc would be more efficient users of input power than those
>produced in the ROC to a marketing "specification".
>You might consider that these same factories in the ROC use the
>formula so heavily marketed by the likes of Sears etc to artificially
>define the HP rating of their products.
Standard form factor induction motors are commodity items, heavily
relying on industry for sales, and are designed to be absolutely
interchangeable. Like grain, hog bellies etc. No manufacturer would
commit suicide by selling false-rated or substandard motors to industry.
Not to mention that various standards associations would revoke their
approvals.
>On the other hand, if y'all
>weren't so pre-occupied with amps, and just concentrated on the true
>HP rating (746 watts) you would be less likely to be misled, or
>confused. For example, a 1 HP (that is 746 watts) motor running on 115
>volts draws 6.5 amps, so is it likely that a motor drawing 13 amps
>would therefore be rated at 13 amps. For 230 volts you can reduce the
>amperage to half that stated.
Ahem. For all intents and purposes amps are interchangeable with watts
here. Telling people to ignore amps in favour of watts is rather like
telling people to don't worry about how many tires a car has, choose on
the basis of the number of wheels...
746 watts is, indeed, exactly 1 HP. But, motors aren't 100% efficient.
You'd be extremely lucky to get even a 1/2 HP motor drawing 6.5A at 110V.
Most 1/4HP motors are rated around 4-6A.
Lenny
says...
On the other hand, if y'all
>weren't so pre-occupied with amps, and just concentrated on the true
>HP rating (746 watts) you would be less likely to be misled, or
>confused. For example, a 1 HP (that is 746 watts) motor running on 115
>volts draws 6.5 amps, so is it likely that a motor drawing 13 amps
>would therefore be rated at 13 amps. For 230 volts you can reduce the
>amperage to half that stated.
You fail to take into consideration the power factor and the efficiency of
the motor. If you assume 0.8 for the power factor and 0.9 for the
efficiency, the the current draw would be 9 amps. If your motor was less
efficient, you would obviously draw more amps. Therefore, current draw is a
way for manufacturer's of crappy motors to appear powerful when they
actually arent.
I know of no ac motor that is not an inductive load, nor know of any motor
that has no resistance in the winding. Power factor and efficiency must be
taken into account.
Lenny
efficient motors, there are no 100% resistive ac motors
In article <DBEyy...@ferret.ocunix.on.ca>, cle...@ferret.ocunix.on.ca
says...
>
>In article <3tlqkd$v...@fantale.cbr.fidonet.org>,
>David Elliston <d...@dnsns.navy.gov.au> wrote:
>>mar...@Direct.CA (Kevin Pausche) wrote:
>
>>>Actually, my Rexon (Taiwan) saw draws 18 amps and is rated at 2 HP.
>>>Wouldn't this satisfy the traditional HP rule, 9 amps to one HP,
>>>therefore my saw is 2 HP. And I seriously doubt my motor is
>>>"incredibly inefficient", that is unless you actually own a Taiwan
>>>table saw and know what you're talking about.
>
>>I would be interested to know how you might know that your Taiwanese
>>motor efficiently uses the input power to produce output power. How
>>did you measure it? I would suspect that the motors produced
>>domestically (in the US, that is) by such notables as GE, Baldor,
>>Marathon, etc would be more efficient users of input power than those
>>produced in the ROC to a marketing "specification".
>
>>You might consider that these same factories in the ROC use the
>>formula so heavily marketed by the likes of Sears etc to artificially
>>define the HP rating of their products.
>
>Standard form factor induction motors are commodity items, heavily
>relying on industry for sales, and are designed to be absolutely
>interchangeable. Like grain, hog bellies etc. No manufacturer would
>commit suicide by selling false-rated or substandard motors to industry.
>Not to mention that various standards associations would revoke their
>approvals.
>
>>On the other hand, if y'all
>>weren't so pre-occupied with amps, and just concentrated on the true
>>HP rating (746 watts) you would be less likely to be misled, or
>>confused. For example, a 1 HP (that is 746 watts) motor running on 115
>>volts draws 6.5 amps, so is it likely that a motor drawing 13 amps
>>would therefore be rated at 13 amps. For 230 volts you can reduce the
>>amperage to half that stated.
>
Paul Houtz
: Ahem. For all intents and purposes amps are interchangeable with watts
: here. Telling people to ignore amps in favour of watts is rather like
: telling people to don't worry about how many tires a car has, choose on
: the basis of the number of wheels...
: 746 watts is, indeed, exactly 1 HP. But, motors aren't 100% efficient.
: You'd be extremely lucky to get even a 1/2 HP motor drawing 6.5A at 110V.
: Most 1/4HP motors are rated around 4-6A.
I buy that amps and watts are interchangeable (at the same voltage, of
course!). Can't help it since my major was in physics :-).
So, according to what you write, Delta is simply lying when they say
their new 12.8 amp motor is a true 1-1/2 HP motor and their previous
14.2 amp motor is also a true 1-1/2 HP motor. If 746 wats is
always exactly 1 HP as you say, then there must be some equally hard
figure for 1-1/2 HP and it can't be both 1562 watts AND 14.08 watts.
So are you saying that the HP figure is derived from the wattage
drawn by the motor, and has NO relationship to the amount of work the
shaft is capable of?
This is all very confusing, to me, and to others.
Paul Houtz
I wrote:
: > If 746 wats is
: > always exactly 1 HP as you say, then there must be some equally hard
: > figure for 1-1/2 HP and it can't be both 1562 watts AND 14.08 watts.
: >...
: > This is all very confusing, to me, and to others.
: You're simply confusing input with output. Amperage or wattage ratings are
: input ratings - what the motors consume. HP ratings are output ratings -
But Bennett, he said that 746 watts is always exactly 1 HP.
I'm not confusing anything. I am just asking for a clarification.
If, as you say, some motors put out more heat, then 746 watts will
not ALWAYS be 1 HP, unless I am missing something...
Steve Waite
: But Bennett, he said that 746 watts is always exactly 1 HP.
: I'm not confusing anything. I am just asking for a clarification.
: If, as you say, some motors put out more heat, then 746 watts will
: not ALWAYS be 1 HP, unless I am missing something...
:
746 Watts is exactly 1 HP. What you are confusing is input versus output
power. In the case of an electrical motor, which converts electrical power
to mechanical power, the input is generally measured in Watts and the output
measured in Horsepower. However, it would be equally correct to say that
Delta's motor requires 1.8 HP input to produce 1119 Watts of cutting power.
There, now that's clear as mud,
Steve Waite
Bennett Leeds
> Bennett Leeds (ben...@mv.us.adobe.com) wrote:
> {Paul Houtz} wrote:
> : > If 746 wats is
> : > always exactly 1 HP as you say, then there must be some equally hard
> : > figure for 1-1/2 HP and it can't be both 1562 watts AND 14.08 watts.
> : >...
> : > This is all very confusing, to me, and to others.
>
> : You're simply confusing input with output. Amperage or wattage ratings are
> : input ratings - what the motors consume. HP ratings are output ratings -
>
It is. Just like 12 inches is exactly 1 foot.
> I'm not confusing anything. I am just asking for a clarification.
Well, call it what you will, but you *are* confusing input with output.
> If, as you say, some motors put out more heat, then 746 watts will
> not ALWAYS be 1 HP, unless I am missing something...
What you're missing is the distinction between input and output power.
Despite your claim to the contrary, you *are* confusing them.
A motor that puts *out* 746 watts via the shaft is, by definition, putting
out exactly 1 HP. Whether that motor *consumes* 747 watts or 900 watts or
99,999 watts in the process is just a matter of the motor's efficiency.
The output is still 746 watts, and 746 watts is 1 HP.
Think of it this way: take a motor that consumes 900 watts. That is, for
110 volts the amerage rating is 8.2. Say it outputs 154 watts of heat and
746 watts via its shaft. It's a 1 HP motor. You can measure that by
looking at the amount of work per second the rotating shaft performs.
If you know the input and output power (expressed as wattages), you can
calculate the motor's efficiency. In this example, this motor is 746/900,
or 83%, efficient.
The amerage ratings on motor nameplates indicate what the motor consumes,
not what it outputs. Don't confuse the two. A motor with a rating of 8.2
amps and an efficiency of 83% puts out the same power as a motor with a
rating of 15 amps and an efficiency rating of only 45%: 1 HP.
Since motor efficiencies vary by make and model, if you don't know the
actual efficiency of a motor in question, you cannot calculate its output
solely from what energy the motor consumes. Two variables and only one
equation, you see.
But, since many motors have had similar efficiencies, it has been reasonable
to use a rule of thumb that enabled one to estimate the approximate output
power from the input power consumed. Now that considerably more efficient
motors are available, it appears that applying this rule of thumb universally
is not a good thing to do except where rough calculations will suffice.
- Bennett Leeds
ben...@mv.us.adobe.com
A horse is a horse, of course (of course), unless, of course, the
measurer of the horse is the "lying," "wrong factoid" spreading, Mr. Leeds.
Bennett Leeds
> Chris Lewis (cle...@ferret.ocunix.on.ca) wrote:
> : 746 watts is, indeed, exactly 1 HP. But, motors aren't 100% efficient.
> : You'd be extremely lucky to get even a 1/2 HP motor drawing 6.5A at 110V.
> : Most 1/4HP motors are rated around 4-6A.
>
> their new 12.8 amp motor is a true 1-1/2 HP motor and their previous
> 14.2 amp motor is also a true 1-1/2 HP motor.
No, according to what he's written, Delta's new motor is at the high end
of motor efficiencies, while their old one was less efficient - consuming
more watts to produce the same useful output.
> If 746 wats is
> always exactly 1 HP as you say, then there must be some equally hard
> figure for 1-1/2 HP and it can't be both 1562 watts AND 14.08 watts.
>...
> This is all very confusing, to me, and to others.
You're simply confusing input with output. Amperage or wattage ratings are
input ratings - what the motors consume. HP ratings are output ratings -
what the motors put out. Output is always somewhat less than input, but
how much less depends on the motor's efficiency. You'll probably find that
the more efficient motors put out less heat since less of the input energy
is converted to heat - more of it goes towards useful work.
A useful analogy might be to think of light bulbs. A 40 watt Flourescent
bulb puts out a lot more light than a 40 watt incadescent bulb. The energy
wasted by the incadescent is released as heat instead of useful light.
- Bennett Leeds
ben...@mv.us.adobe.com
Stuart Staniford-Chen
: : > If 746 wats is
: : > always exactly 1 HP as you say, then there must be some equally hard
: : > figure for 1-1/2 HP and it can't be both 1562 watts AND 14.08 watts.
: : >...
: : > This is all very confusing, to me, and to others.
: : You're simply confusing input with output. Amperage or wattage ratings are
: : input ratings - what the motors consume. HP ratings are output ratings -
: But Bennett, he said that 746 watts is always exactly 1 HP.
: I'm not confusing anything. I am just asking for a clarification.
: If, as you say, some motors put out more heat, then 746 watts will
: not ALWAYS be 1 HP, unless I am missing something...
:
From a physics standpoint, both Watts and HP are measures of power. Watts
are the SI unit of power, and HP are an older unit. So, in principle, they
are completely interchangeable (since they measure the same thing) and the
conversion factor is 746 W/HP. (I didn't check this number independently -
I'm just quoting it).
Motors take in electrical energy and convert it to kinetic energy in the
form of the spinning shaft, pulleys etc. Power is defined to be energy
per unit time. Thus, with a very slight abuse of language, we can
consider the motor to be taking in electrical power and putting out
mechanical power (kinetic power).
In principle, we could measure the input electrical power in either Watts
or Horsepower, and the output mechanical power in either Watts or HP.
However, it is conventional to express the input power in Watts, and the
output power in Horsepower.
Now, the input power and the output power are not the same numerically,
because the motor is imperfect and loses some energy as heat, noise etc.
Thus, as physical units, 746 Watts = 1 HP. However, a motor that takes
in 746 watts of electrical power will output less than 1 HP of mechanical
power. (Typically in the range of 0.6 - 0.9 HP I believe).
Is this any clearer?
Stuart. (PhD Physics)
--
===================================================================
Stuart Staniford-Chen | Dept of Computer Science
stan...@cs.ucdavis.edu | UC Davis, CA 95616
h:(916) 756-8697; w:(916) 754-9157 | and
http://seclab.cs.ucdavis.edu/~stanifor/ | N St Cohousing Community
====================================================================
Jim Cathey
>I know of no ac motor that is not an inductive load, nor know of any motor
>that has no resistance in the winding. Power factor and efficiency must be
>taken into account.
A synchronous motor can be forced to run capacitively. (By
over-exciting the field? It's been so long...) I've never seen one
in use on machinery the size of what we talk about here, though.
--
Jim Cathey
Olivetti North America | One Design to rule them all; one Design to find them.
TAF-C8; | One Design to bring them all and in the darkness bind
Spokane, WA 99220 | them. In the land of Mediocrity where the PC's lie.
Chris Lewis
Bennett Leeds <ben...@mv.us.adobe.com> wrote:
>Paul Houtz writes
>> But Bennett, he said that 746 watts is always exactly 1 HP.
>It is. Just like 12 inches is exactly 1 foot.
Precisely.
>> I'm not confusing anything. I am just asking for a clarification.
>Well, call it what you will, but you *are* confusing input with output.
He did say he was confused.
This is the crux. Paul, you have to think of watts and HP as _both_
being measurements of power. Mechanical power is usually rated in HP,
and electrical in watts. But they are absolutely interchangeable
measurements at 746 watts/HP. Like inches per foot. Metres per yard.
Drams per hogshead ;-) Etc. If your car engine puts out 100HP, it's
generating 74600 watts of _mechanical_ power.
However, when you need to convert one form of power (electrical) to
another form of power (mechanical), you have to pay a conversion fee -
the efficiency factor. Which is why a motor consuming 746W of
electrical power _cannot_ produce 746W, aka 1HP, of mechanical power.
In larger motors, the rule of thumb is 900-1000 watts of _input_
electrical power for 1HP of mechanical output power. Below about 2HP
this becomes non-linear, and a 1/4HP motor frequently draws 4-6A (440-660
watts).
The above was efficiency factor - watts of power in versus watts of power
out. There is another confusing factor - power factor. Watts are
volts x amps. However, with AC, you can only calculate watts as volts
x amps when they are exactly in phase with each other. Since motors
are inductive, current _lags_ voltage, and the delivered _power_,
which is calculated by integrating voltsxamps over the whole AC power
cycle, is _less_ than RMS VoltsxAmps. Hence the amperage of a motor
will be _higher_ than the actual _power_ draw would indicate.
So for example (with a little handwaving for numbers), say you have
a motor drawing 9A at 110V. Because of _power factor_, the motor
is not drawing 9x110 = 990W, it's actually drawing around 850W, because
amps lag volts. Furthermore, since the electric to mechanical power
conversion isn't 100% efficient (bearings heat up, eddy currents, etc),
it's not producing 850/746 (1.14) HP, it's only producing _1_ HP.
hau...@mbi.org
>From: ben...@mv.us.adobe.com(Bennett Leeds)
>Subject: Re: Delta Contractor's Saw Motor (34-444)
>Date: Tue, 11 Jul 1995 19:44:44 GMT
Bennett explains:
>Think of it this way: take a motor that consumes 900 watts. That is, for
>110 volts the amerage rating is 8.2.
Actually, 7.5 amps at 120volts. Who has 110 volts? Not me. It usually runs
120 to 122. That's why saying '220' is also wrong. It's 240. Practice with
me. Two forty.
Say it outputs 154 watts of heat and
>746 watts via its shaft. It's a 1 HP motor. You can measure that by
>looking at the amount of work per second the rotating shaft performs.
Now, Bennett, 900 minus 746 minus 154 leaves zero watts left over for light
and noise. Granted, there's not much light, but noise takes up several watts.
Think I'm nitpicking yet?
>The amerage ratings on motor nameplates indicate what the motor consumes,
>not what it outputs. Don't confuse the two. A motor with a rating of 8.2
>amps and an efficiency of 83% puts out the same power as a motor with a
>rating of 15 amps and an efficiency rating of only 45%: 1 HP.
Yes, but you're using that ole 110 again.
>Since motor efficiencies vary by make and model, if you don't know the
>actual efficiency of a motor in question, you cannot calculate its output
>solely from what energy the motor consumes. Two variables and only one
>equation, you see.
>But, since many motors have had similar efficiencies, it has been reasonable
>to use a rule of thumb that enabled one to estimate the approximate output
>power from the input power consumed. Now that considerably more efficient
>motors are available, it appears that applying this rule of thumb universally
>is not a good thing to do except where rough calculations will suffice.
Well explained, bennett! It's hard to believe people don't understand the
above, but obviously some don't.
>A horse is a horse, of course (of course), unless, of course, the
>measurer of the horse is the "lying," "wrong factoid" spreading, Mr. Leeds.
Nice ending, B!
Rich
Paul Houtz
: In article <1995Jul11....@adobe.com>,
: >> But Bennett, he said that 746 watts is always exactly 1 HP.
: >It is. Just like 12 inches is exactly 1 foot.
: Precisely.
: >> I'm not confusing anything. I am just asking for a clarification.
: >Well, call it what you will, but you *are* confusing input with output.
: He did say he was confused.
: This is the crux. Paul, you have to think of watts and HP as _both_
: being measurements of power. Mechanical power is usually rated in HP,
: and electrical in watts. But they are absolutely interchangeable
: measurements at 746 watts/HP. Like inches per foot. Metres per yard.
: Drams per hogshead ;-) Etc. If your car engine puts out 100HP, it's
: generating 74600 watts of _mechanical_ power.
Chris, I am deeply indebted to you for going further than a sound
bite and actually clearing up my confusion. I take back everything
I have ever said about you :-) :-)
Randy Kesselring
>What you're missing is the distinction between input and output power.
>Despite your claim to the contrary, you *are* confusing them.
>A motor that puts *out* 746 watts via the shaft is, by definition, putting
>out exactly 1 HP. Whether that motor *consumes* 747 watts or 900 watts or
>99,999 watts in the process is just a matter of the motor's efficiency.
>The output is still 746 watts, and 746 watts is 1 HP.
I think that the most important question in regard to this issue is can we
rely on the horsepower figure imprinted on the metal tag attached to the
motor? If you cannot rely on the horsepower number printed on the motor
and there is no economical way to calculate efficiency, the output power of
the motor becomes an unknown.
I have noticed that many of the Taiwanese clones appear to use motors that
are physically larger and draw more amps than motors used by, for example,
Delta. Both motors, however, list horsepower as 1 1/2. I have always
assumed that both the horsepower and amp ratings were accurate and that
Delta just used a more efficient motor. Is this assumption wrong?
Randy Kesselring
Bennett Leeds
> In article <1995Jul11....@adobe.com> ben...@mv.us.adobe.com(Bennett
Leeds) writes:
> >Think of it this way: take a motor that consumes 900 watts. That is, for
> >110 volts the amerage rating is 8.2.
>
> Actually, 7.5 amps at 120volts. Who has 110 volts? Not me. It usually runs
> 120 to 122. That's why saying '220' is also wrong. It's 240. Practice with
> me. Two forty.
Well, then the scene in "Mr. Mom" where Michael Keaton's character (Jack) is
trying to show his wife's boss how manly he is should have gone as follows:
Jack (wearing overalls and carrying a running chainsaw): "Yeah, I'm
gonna take some walls out and redo the whole room, plumbing,
electrical...."
Wife's Boss: "You gonna put in 240?"
Jack: "Uh, 240, 241 - whatever it takes."
- Bennett Leeds
ben...@mv.us.adobe.com
Chris Lewis
>In article <1995Jul11....@adobe.com> ben...@mv.us.adobe.com(Bennett Leeds) writes:
>Bennett explains:
>>Think of it this way: take a motor that consumes 900 watts. That is, for
>>110 volts the amerage rating is 8.2.
>Actually, 7.5 amps at 120volts. Who has 110 volts? Not me.
Sure you do. How long is that extension cord?
>It usually runs 120 to 122.
With or without load?
>That's why saying '220' is also wrong. It's 240. Practice with
>me. Two forty.
Read the electrical wiring FAQ. Your utility provides 240V +/- 5% to
your panel. Which means it can be as low as 228V (dual 114) at your
panel. _Then_ you have to consider voltage drop in the circuit - the
NEC allows as much as _another_ 5%, which means it could be as low as
216V (108V). Or a lot lower if you use that 100foot 16ga extension
cord...
Half the time the motor plate ratings say 110V. There's a reason for
that...
Chris Lewis
>Chris Lewis (cle...@ferret.ocunix.on.ca) wrote:
>: This is the crux. Paul, you have to think of watts and HP as _both_
>: being measurements of power. Mechanical power is usually rated in HP,
>: and electrical in watts. But they are absolutely interchangeable
>: measurements at 746 watts/HP. Like inches per foot. Metres per yard.
>: Drams per hogshead ;-) Etc. If your car engine puts out 100HP, it's
>: generating 74600 watts of _mechanical_ power.
>
> Chris, I am deeply indebted to you for going further than a sound
> bite and actually clearing up my confusion. I take back everything
> I have ever said about you :-) :-)
Including the nice things you said when you asked me those questions about
electrical wiring in your shop and whether I thought PVC plumbing was a
good idea for compressor lines? Awwww. ;-)
Paul Houtz
: In article <3u3djc$c...@hpscit.sc.hp.com>, Paul Houtz <g...@pa.itc.hp.com> wrote:
: >Chris Lewis (cle...@ferret.ocunix.on.ca) wrote:
: >: This is the crux. Paul, you have to think of watts and HP as _both_
: >: being measurements of power. Mechanical power is usually rated in HP,
: >: and electrical in watts. But they are absolutely interchangeable
: >: measurements at 746 watts/HP. Like inches per foot. Metres per yard.
: >: Drams per hogshead ;-) Etc. If your car engine puts out 100HP, it's
: >: generating 74600 watts of _mechanical_ power.
: >
: > Chris, I am deeply indebted to you for going further than a sound
: > bite and actually clearing up my confusion. I take back everything
: > I have ever said about you :-) :-)
: Including the nice things you said when you asked me those questions about
: electrical wiring in your shop and whether I thought PVC plumbing was a
: good idea for compressor lines? Awwww. ;-)
No Chris, I don't take back the nice things.
But, I do feel bad about that nasty flame I gave you a couple
of years ago.
Seriously, I have learned a lot from you and I appreciate your patience
in working through this. I especially apprecate you not calling me
stupid even though I may have sounded that way.
Your postings are the kind of resource that makes the usenet worth
talking about and worth getting involved in. (gush, gush).
Anyway, thanks again!