Paul Dalton
03-10-2019, 8:04 PM
I am trying to figure out the differences between motors of the same horsepower rating where the published amperage requirement is different.
In this regard, it seems that when a power tool manufacturer publishes a horsepower rating for a motor, the specs also identify the AC voltage (usually 120, but sometimes 110 or 130), frequency in Hertz (usually 60, sometimes 50) and the amperage requirements for that same motor. My problem is when the same horsepower rating is claimed from a motor running at the same voltage and frequency but with differing amperage requirements.
Perhaps some manufacturers "fudge" their horsepower rating up or down a bit, but -- assuming they aren't -- I think seeing different amperages used by different electric motors to produce the same horsepower at the same voltage and frequency should tell me something useful about one motor versus another. But I'm just not sure what that tells me and how it should assist me in comparing the motors for real world use.
For example, in comparing different drill presses from different manufacturers, I found the following published information for several different motors operating at 120VAC and 60 Hz:
Motor
HP
Amps
A
0.6
3.85
B
0.67
5
C
0.75
7.5
D
0.75
7.2
E
0.67
8.6
F
1
13.5
G
1.5
13
So I tried to compare them on the basis of how much amperage the motor requires to produce the same amount of horsepower and got this:
Motor
HP
Amps
Amps/HP
A
0.6
3.85
6
B
0.67
5
7
C
0.75
7.5
10
D
0.75
7.2
9
E
0.67
8.6
12
F
1
13.5
13
G
1.5
13
8
The problem for me is that I really don't know what this is telling me. Am I seeing comparable efficiency of these motors or something else (or nothing of any real value)?
As a person who obviously doesn't have a sufficiently deep understanding of electric motor principles, I would really appreciate any explanations or suggestions about trying to compare electric motors based on their horsepower and amperage ratings.
By the way, I read the earlier thread about converting AMPS to HP (at https://sawmillcreek.org/showthread....-or-Visa-Versa (https://sawmillcreek.org/showthread.php?6316-Formula-for-converting-HP-to-AMPs-or-Visa-Versa)) and I'm sure it's just my own ignorance keeping me from being able to use that information to understand what I'm looking at above . . . or even whether I'm looking at it in the correct manner. Anyway, I started to post this question there, but thought that thread might be considered too old for new posts.
In this regard, it seems that when a power tool manufacturer publishes a horsepower rating for a motor, the specs also identify the AC voltage (usually 120, but sometimes 110 or 130), frequency in Hertz (usually 60, sometimes 50) and the amperage requirements for that same motor. My problem is when the same horsepower rating is claimed from a motor running at the same voltage and frequency but with differing amperage requirements.
Perhaps some manufacturers "fudge" their horsepower rating up or down a bit, but -- assuming they aren't -- I think seeing different amperages used by different electric motors to produce the same horsepower at the same voltage and frequency should tell me something useful about one motor versus another. But I'm just not sure what that tells me and how it should assist me in comparing the motors for real world use.
For example, in comparing different drill presses from different manufacturers, I found the following published information for several different motors operating at 120VAC and 60 Hz:
Motor
HP
Amps
A
0.6
3.85
B
0.67
5
C
0.75
7.5
D
0.75
7.2
E
0.67
8.6
F
1
13.5
G
1.5
13
So I tried to compare them on the basis of how much amperage the motor requires to produce the same amount of horsepower and got this:
Motor
HP
Amps
Amps/HP
A
0.6
3.85
6
B
0.67
5
7
C
0.75
7.5
10
D
0.75
7.2
9
E
0.67
8.6
12
F
1
13.5
13
G
1.5
13
8
The problem for me is that I really don't know what this is telling me. Am I seeing comparable efficiency of these motors or something else (or nothing of any real value)?
As a person who obviously doesn't have a sufficiently deep understanding of electric motor principles, I would really appreciate any explanations or suggestions about trying to compare electric motors based on their horsepower and amperage ratings.
By the way, I read the earlier thread about converting AMPS to HP (at https://sawmillcreek.org/showthread....-or-Visa-Versa (https://sawmillcreek.org/showthread.php?6316-Formula-for-converting-HP-to-AMPs-or-Visa-Versa)) and I'm sure it's just my own ignorance keeping me from being able to use that information to understand what I'm looking at above . . . or even whether I'm looking at it in the correct manner. Anyway, I started to post this question there, but thought that thread might be considered too old for new posts.