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Posted by Mark Lloyd on July 10, 2007, 4:19 pm
On Tue, 10 Jul 2007 15:25:35 -0400, gfretwell@aol.com wrote:
>On Tue, 10 Jul 2007 17:40:08 -0000, clewis@nortelnetworks.com (Chris
>Lewis) wrote:
>
>>
>>> I used to work with Baldor repulsion/induction motors in the oilfield.
>>> There were all 240v, 15 hp. If memory serves, on the well upstroke they
>>> drew around 30 amps and otherwise around 18.
>>
>>240V at 30A is 7200W, which means that during the upstroke those
>>motors were delivering somewhere around 6-8 HP. Conservative
>>motor selection, given that weather/rig conditions etc could cause
>>the motor to need more.
>>
>>It would have been interesting to compare that with the motor
>>plate ratings, or know what size the fuses/breakers were.
>
>
>Don't let that theoretical 800w per HP confuse you. Motors never get
>close to that efficiency. A typical 1HP motor will pull more like
>12-13a @ 120v (my C/H compressor) and some cheap ones will be more
>like 15-16a.
Lowe's claims to have a 3HP electric chain saw, that still works on a
15A receptacle.
--
Mark Lloyd
http://notstupid.laughingsquid.com
"Unlike biological evolution. 'intelligent design' is
not a genuine scientific theory and, therefore, has
no place in the curriculum of our nation's public
school classes." -- Ted Kennedy
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Posted by Dave Martindale on July 11, 2007, 12:10 am
>Lowe's claims to have a 3HP electric chain saw, that still works on a
>15A receptacle.
Assuming it's not simply a baldfaced lie, that is an intermittent
rating. As in "if you load this motor with a brake to the point where
it produces maximum output in overload, it's producing 3 HP - until the
circuit breaker trips or the motor burns up, whichever comes first".
The rating might actually make a bit of sense for a chainsaw, where
hitting a hard spot *will* cause the motor to put out more power
temporarily, and where you're comparing against gas-powered motors where
the HP rating is the maximum HP available.
But it's not comparable to induction motor ratings, where "1 HP" generally
means it will deliver 1 HP all day, and nearly 2 HP momentarily when
overloaded.
Rating continuous-running things like shop vacs and air compressors in
"peak HP" is completely bogus, of course.
Dave
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Posted by Chris Lewis on July 12, 2007, 2:07 pm
> >Lowe's claims to have a 3HP electric chain saw, that still works on a
> >15A receptacle.
> Assuming it's not simply a baldfaced lie, that is an intermittent
> rating. As in "if you load this motor with a brake to the point where
> it produces maximum output in overload, it's producing 3 HP - until the
> circuit breaker trips or the motor burns up, whichever comes first".
Yes. It's an instantaneous max HP, rather than a safe continuous
rating. Shop vacuums and routers are infamous for using these inflated
figures. Instantaneous max HP is a useful measure on a router or
chain saw in some cases, but is useless to a shop vacuum.
--
Chris Lewis,
Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.
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Posted by Chris Lewis on July 12, 2007, 2:04 pm
> On Tue, 10 Jul 2007 17:40:08 -0000, clewis@nortelnetworks.com (Chris
> Lewis) wrote:
>
> >
> >> I used to work with Baldor repulsion/induction motors in the oilfield.
> >> There were all 240v, 15 hp. If memory serves, on the well upstroke they
> >> drew around 30 amps and otherwise around 18.
> >
> >240V at 30A is 7200W, which means that during the upstroke those
> >motors were delivering somewhere around 6-8 HP. Conservative
> >motor selection, given that weather/rig conditions etc could cause
> >the motor to need more.
> >
> >It would have been interesting to compare that with the motor
> >plate ratings, or know what size the fuses/breakers were.
>
>
> Don't let that theoretical 800w per HP confuse you.
In case it wasn't clear, I wasn't confused ;-)
> Motors never get
> close to that efficiency. A typical 1HP motor will pull more like
> 12-13a @ 120v (my C/H compressor) and some cheap ones will be more
> like 15-16a.
Once you get into multi-horsepower industrial-grade motors,
rule-of-thumb is about 1000 watts per HP. At 1-2HP and below,
they're not as efficient and 12-13A/HP is a reasonable ballpark at
the high end. Once you get to 1/4HP and below, motors can be
stupidly inefficient. Eg: the 1/4HP motor I saw whose label
said 10A.
--
Chris Lewis,
Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.
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Posted by Toller on July 9, 2007, 7:39 pm
>> How did you determine that, and how much, specifically, are you thinking
>> is "a lot" for a fractional hp fan motor???
>
Don't know who you are; I have you blocked for the stupid things you have
said in the past.
For good reason, here is one more!
12a is not a fractional hp motor. Don't you even bother to read the posts?
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