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Old 01-26-2011, 08:12 PM   #1
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Default If 1 HP Electric Motor = 0.746KW

Does that mean it uses 0.746 KW for one hour?
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Old 01-26-2011, 08:24 PM   #2
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Only if you run it at full power for one hour.

Power is a function of time. It describes the amount of work (force acting over a distance) done in a given unit of time.
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Old 01-26-2011, 08:43 PM   #3
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One horsepower equals 550 foot pounds per second. 746 watts also equals 550 foot pounds per second.
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Old 01-26-2011, 09:08 PM   #4
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An electric motor is not 100% efficient. A 1 horse motor is normally 78.8% efficient.
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Old 01-26-2011, 09:20 PM   #5
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Quote:
Originally Posted by JoesC5 View Post
An electric motor is not 100% efficient. A 1 horse motor is normally 78.8% efficient.
Is the motor 1 HP on the output shaft or electric usage?

Input = .746 KW / 120 V = 6.2 amps in.

To output 1 HP assuming 100% efficient (1/.746) /129 = 11.2 amps input.
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Old 01-26-2011, 09:36 PM   #6
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So.............

If my 1 HP motor runs 300 hours and the cost per KW is 13.1 cents the total costs is $29.10?
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Old 01-26-2011, 09:46 PM   #7
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KW x hours = KWH.

.746 KW x 1 Hr = .746 KWH

KW (kilowat) is like horsepower
hour is time
KWH is a measure of power consumed. Kilowatt hours (your electric meter reads in KWH)

If you only run it 10 minutes it only would register 0.124 kwh.

But that is at 100% efficiency of converting electric energy inti mechanical energy. Effiencies vary but on small motors are typically around 80%. So a real 1 hp motor will use .746/0.8 or 0.93 KW.

Run it 1 hour and your electric meter will read .93 kwh.

I use 1hp = 1kw for typical energy cost calculations. It's close enough as all motors vary slightly in efffiency. Some new high effiency motors are better.
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Old 01-26-2011, 09:49 PM   #8
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Quote:
Originally Posted by OHSIXX View Post
So.............

If my 1 HP motor runs 300 hours and the cost per KW is 13.1 cents the total costs is $29.10?
At 80% effiency it actually would cost $36.27.

LJ
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Old 01-26-2011, 10:03 PM   #9
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What happens if it's on a treadmill?
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Old 01-26-2011, 10:15 PM   #10
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Quote:
Originally Posted by Chicago View Post
What happens if it's on a treadmill?
plane crash
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Old 01-26-2011, 10:31 PM   #11
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Quote:
Originally Posted by OHSIXX View Post
Does that mean it uses 0.746 KW for one hour?
All I know is I just went from air/air heat pump to water/air for the heat exchanger for unwanted heat.....

1/2 horse pump subbing for 1/2 horse outdoor fan motor....

BUT there is NO reverse heat cycle, it's just runs like a furnace....102f out the stack.... house WARM now, not fighting it....
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Old 01-26-2011, 11:06 PM   #12
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Quote:
Originally Posted by Chicago View Post
What happens if it's on a treadmill?
It would lose that ugly fat around the middle.
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Old 01-27-2011, 12:28 AM   #13
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Quote:
Originally Posted by OHSIXX View Post
So.............

If my 1 HP motor runs 300 hours and the cost per KW is 13.1 cents the total costs is $29.10?
The motor may be rated at (i.e., capable of) 1 hp, but it's likely producing far less power... And thereby consuming far less electrical power.

Corvette LS1 engine is rated at 345 hp. How often is it actually called on to produce that much?
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Old 01-27-2011, 12:50 AM   #14
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Quote:
Originally Posted by OHSIXX View Post
Does that mean it uses 0.746 KW for one hour?
it would use .746KWH in one hour. Electrical Energy = power x time
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Old 01-27-2011, 08:08 AM   #15
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Quote:
Originally Posted by mrvette View Post
All I know is I just went from air/air heat pump to water/air for the heat exchanger for unwanted heat.....

1/2 horse pump subbing for 1/2 horse outdoor fan motor....

BUT there is NO reverse heat cycle, it's just runs like a furnace....102f out the stack.... house WARM now, not fighting it....
What's the water source? Well water?
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Old 01-27-2011, 11:41 AM   #16
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A simple question and 40 forensic responses. Love it.

The answer to your question is yes.

Now if you want details, read the above post.
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Old 01-27-2011, 11:43 AM   #17
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Quote:
Originally Posted by OHSIXX View Post
Does that mean it uses 0.746 KW for one hour?
Depends on if we're talking about horsepower-minutes or horspower-hours.

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Old 01-27-2011, 11:47 AM   #18
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HP = T X RPM/5252
HP = 33,000 lbs/ft/min
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Old 01-27-2011, 12:07 PM   #19
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Quote:
Originally Posted by 1Patriot View Post
...The answer to your question is yes...
Except he's mixing his units.

HP is Power.
0.746KW is Power.
"0.746 KW for one hour" is Energy.

In an engineering class, the answer would be No.

But that's only because he didn't ask the question correctly.
The answer to "what he really meant" is Yes.

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Old 01-27-2011, 12:19 PM   #20
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Depends. You may have the peak start up HP. Typically the start up draw is double typical run power. You may find that it runs on 3 amps, and starts on 7 amps. The work that it needs to perform makes a difference in actual use, not just the rating. And as other guys pointed out, the efficiency makes a difference. So the rating is a ball park number, and YMMV.
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