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View Willscary's profile

Motor Specifications

by Willscary
posted 09-29-2018 09:43 PM


7 replies so far

View splintergroup's profile

splintergroup

3015 posts in 1766 days


#1 posted 10-01-2018 10:02 PM

Welcome to the mystery of electric motors 8^)

HP ratings are a lot like the stereo amplifier “Watts” battles of the 70’s. Lots of misinformation.

Many motors list a current that is “RLA” or rated load amps and some list FLA or full load amps. Each is dependent upon how the motor was tested. There are standards, but it still is a somewhat sloppy business.

Your motor will most probably run at much less than the nameplate current while under operation because it is not being fully loaded. Lock the motors rotor and turn it on and you might see the 11.4A pop up on the meter.

Sorry, not exactly the explanation you were looking for but your underlying assumptions are correct. Measure the current while running with the rotor not attached to anything. Load the motor up with the tool/machine, read the current difference and use this to calculate the motors applied HP (with an assumed efficiency)

View runswithscissors's profile

runswithscissors

3081 posts in 2569 days


#2 posted 10-02-2018 12:39 AM

Reminds me of when stereo was coming in (so, you can guess how long ago), I went with a friend to check out some hot shot new vendor who was bragging about the output of his speakers. He would play something over the system, and then point to the wiggly line on an oscilloscope to show us how great the frequency range was. Trouble is, he was showing us the oscilloscope’s reading, not the real output of the speakers. As usual, caveat emptor.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

View Willscary's profile

Willscary

25 posts in 464 days


#3 posted 10-03-2018 01:16 AM

As a big “hi-fi” guy myself, I get the inflated specifications part of it. My thought though is that amps are amps, and if this motor is rated at 11.4 amps at 115 volts, that is more than 1-1/8 HP at the 65% common efficiency of motors of this age, size and type.

My thought was that this motor was probably VERY conservativiely rated.

View TheFridge's profile

TheFridge

10859 posts in 2030 days


#4 posted 10-03-2018 02:41 AM

that’s still a beefy motor with even 65% efficiency figured in.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View Nugs's profile

Nugs

67 posts in 2421 days


#5 posted 10-03-2018 06:33 PM

What am I missing? Is there something else to convert?

- Willscary

You are missing the power factor, usually the nameplate will have both the power factor and efficiency on it.

The power equation for a motor is; power = voltage x current x efficiency x power factor

https://en.wikipedia.org/wiki/Power_factor

View Willscary's profile

Willscary

25 posts in 464 days


#6 posted 10-03-2018 07:30 PM

I had originally posted the PF as 1.0, but then noticed that the faceplate did not list the power factor, but instead the service factor = 1.0.

Here is the entire plate:

You are missing the power factor, usually the nameplate will have both the power factor and efficiency on it.

The power equation for a motor is; power = voltage x current x efficiency x power factor

https://en.wikipedia.org/wiki/Power_factor

- Nugs


View splintergroup's profile

splintergroup

3015 posts in 1766 days


#7 posted 10-04-2018 01:45 PM

The power factor changes as a motor is loaded and is one of the primary reasons that for maximum efficiency (most work done for your electric bill payment), you want to run the motor near the maximum load.

Typically people only really care about PF for mulit-HP 3-phase motors, but give this calculator a try (nice revalation Nugs!)

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