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Old 12-30-2011, 12:12 PM   #1
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AMPS TO HP using Snap on multimeter


I have a AC 115/230 motor which I don't know the HP. I am using a Sperry DSA-400 meter which has a snap around clamp.

I have the meter set at 20a and using 115 Volts and using the snaparound on one terminal I get a reading of .64

Can I covert that back to HP?

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Old 12-30-2011, 12:15 PM   #2
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AMPS TO HP using Snap on multimeter


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Originally Posted by johndrew View Post
I have a AC 115/230 motor which I don't know the HP. I am using a Sperry DSA-400 meter which has a snap around clamp.

I have the meter set at 20a and using 115 Volts and using the snaparound on one terminal I get a reading of .64

Can I covert that back to HP?
HP = Voltage x Current x Efficiency / 746

http://www.ehow.com/how_5928406_calc...otor_s-hp.html

Also http://www.onlineconversion.com/motor_horsepower.htm

I am coming up with 2hp.

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Old 12-30-2011, 12:46 PM   #3
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AMPS TO HP using Snap on multimeter


No way to know accurately without the data plate. Motor hp is rated at full load.

To give a comparison a 1/6 hp 115 volt rated motor will range from 2 amps to around 4 amps at full load.

Are you running the motor with no load?

Do you know who makes the motor ?
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Old 12-30-2011, 02:16 PM   #4
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AMPS TO HP using Snap on multimeter


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Originally Posted by Stubbie View Post
No way to know accurately without the data plate. Motor hp is rated at full load.

To give a comparison a 1/6 hp 115 volt rated motor will range from 2 amps to around 4 amps at full load.

Are you running the motor with no load?

Do you know who makes the motor ?
The motor has no load and is made by Emerison no other information
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Old 12-30-2011, 05:09 PM   #5
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AMPS TO HP using Snap on multimeter


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Originally Posted by gregzoll View Post
HP = Voltage x Current x Efficiency / 746

http://www.ehow.com/how_5928406_calc...otor_s-hp.html

Also http://www.onlineconversion.com/motor_horsepower.htm

I am coming up with 2hp.
Uh, how? 115V X 0.64A X 80% efficiency / 746 = 0.079 HP. And that is about right. Since the motor has no load on it, it will hardly draw any current and is only "using" a small fraction of a horsepower. You can't determine the horsepower rating of a motor by measuring the current with no load. In fact, you can't determine it by measuring the current under any load, unless you know for sure that the load is exactly the full rated load (which is usually impossible to determine). The only way to know the HP rating for sure is to find it on the nameplate or look it up in the spec sheet. You can sort of guess by the size of the motor and intended application, but it's a rough estimate.
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Old 12-30-2011, 05:34 PM   #6
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AMPS TO HP using Snap on multimeter


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Uh, how? 115V X 0.64A X 80% efficiency / 746 = 0.079 HP. And that is about right. Since the motor has no load on it, it will hardly draw any current and is only "using" a small fraction of a horsepower. You can't determine the horsepower rating of a motor by measuring the current with no load. In fact, you can't determine it by measuring the current under any load, unless you know for sure that the load is exactly the full rated load (which is usually impossible to determine). The only way to know the HP rating for sure is to find it on the nameplate or look it up in the spec sheet. You can sort of guess by the size of the motor and intended application, but it's a rough estimate.
Yup, you're correct.

I bet a decimal was carried in the wrong spot since 80% is actually .8 in decimals.

Also must stress that motors are rated at full load, as Stubbie said.
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Old 12-30-2011, 05:57 PM   #7
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AMPS TO HP using Snap on multimeter


I flipped my numbers around. That is what I get trying to speed through posts, during lunch at home, before going back to the office. So if we find out the pertinent info, and I am close, what do I get?
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Old 12-30-2011, 06:52 PM   #8
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AMPS TO HP using Snap on multimeter


Even if you could load the motor incrementally, there's still no way to know the HP. Current will steadily rise as load is increased until breakdown torque is reached. This is where a small increase in load results in a large decrease in RPM, and usually occurs anywhere from 200% to 400% of full load torque.

The only way to know for sure what the HP is would be to load the motor to a known torque and measure winding temperature. Even this is still somewhat of a guess since the temperature rating of the winding insulation is not known.

A few clues;

1) What is the shaft diameter?

2) What are the dimensions of the base?

3) One or two capacitors?

4) What is the overall length of the motor, including the shaft?

5) Is it open or totally enclosed?

With this info, we can get pretty close.

Rob
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Old 12-30-2011, 06:53 PM   #9
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AMPS TO HP using Snap on multimeter


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Originally Posted by gregzoll View Post
HP = Voltage x Current x Efficiency / 746

http://www.ehow.com/how_5928406_calc...otor_s-hp.html

Also http://www.onlineconversion.com/motor_horsepower.htm

I am coming up with 2hp.
Power factor needs to be included as well.
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Old 12-30-2011, 07:20 PM   #10
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AMPS TO HP using Snap on multimeter


How about this?

"A large horse on a good horsepower treadmill elevated at an angle of 1:4 could actually develop slightly over two horsepower of energy with one horse."
http://wilmingtonnrhs.com/newsletters/2006may.htm

Could this be 4 horsepower?
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Old 12-30-2011, 08:07 PM   #11
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AMPS TO HP using Snap on multimeter


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How about this?

"A large horse on a good horsepower treadmill elevated at an angle of 1:4 could actually develop slightly over two horsepower of energy with one horse."
http://wilmingtonnrhs.com/newsletters/2006may.htm

Could this be 4 horsepower?
LOL. But if you load them down until they stall, do they start smoking?
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Old 12-31-2011, 01:39 PM   #12
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AMPS TO HP using Snap on multimeter


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Originally Posted by micromind View Post
Even if you could load the motor incrementally, there's still no way to know the HP. Current will steadily rise as load is increased until breakdown torque is reached. This is where a small increase in load results in a large decrease in RPM, and usually occurs anywhere from 200% to 400% of full load torque.

The only way to know for sure what the HP is would be to load the motor to a known torque and measure winding temperature. Even this is still somewhat of a guess since the temperature rating of the winding insulation is not known.

A few clues;

1) What is the shaft diameter?

2) What are the dimensions of the base?

3) One or two capacitors?

4) What is the overall length of the motor, including the shaft?

5) Is it open or totally enclosed?

With this info, we can get pretty close.

Rob
The shaft is 5/8
Two capacitors ..running is 189-227 mf 250 volt
The motor is enclosed
The base size is 4x8
The RMP is 1725 determined by using (Professional Digital Laser Photo Tachometer Non Contact RPM Tach) from Amazon $12.95
It says Emerison Economiser on the side.
Overall length is 13" including the shafts.
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Old 12-31-2011, 05:22 PM   #13
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AMPS TO HP using Snap on multimeter


I'm going to guess 1HP.

The base is sort of typical for a 56 frame, though most are more like 4 X 7 or so with two sets of slotted holes in each side. A typical 1-1/2 HP and up will have a 56H frame, the base will be 6.5 X 7 or so.

The 5/8" shaft is very typical of a 56 frame. The only other 5/8" shaft is a 48Z frame, it'll have a smaller base.

The overall dimension is about right for 1HP, slightly long though.

If it has leads (and not a terminal board) and there are 6 leads (labelled T1 through T5 and T8), it's not thermally protected. If it has 7 leads and one of them is labelled P1, then it is thermally protected.

Two capacitors are typical of an energy efficient model. Also somewhat typical of standard efficiency 1-1/2HP and up.
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Old 12-31-2011, 06:33 PM   #14
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AMPS TO HP using Snap on multimeter


I think you are right, one of the 4 motors was a Dayton with the same base and it was rated at 1hp on the plate but the RPM was 3450 vs 1725.
Appreicated the information on the thermo protection.

Thanks for helping two ole grumpy men.
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Old 12-31-2011, 07:50 PM   #15
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AMPS TO HP using Snap on multimeter


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I think you are right, one of the 4 motors was a Dayton with the same base and it was rated at 1hp on the plate but the RPM was 3450 vs 1725.
Appreicated the information on the thermo protection.

Thanks for helping two ole grumpy men.
Glad I could help.

Depending on the date of manufacture, Dayton motors were built by Emerson for quite a few years.

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