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Amps to Horsepower Comparison?
- Thread starter lbperry
- Start date
mike93lx
ALLIANCE MEMBER
1 hp is about 750 watts. amps are watts divided by voltage, so 1 hp at 120v is about 6 amps.
keep in mind that HP rating on most small motors are at "locked rotor condition"which is basically the power it will draw when stopped from turning before it burns up. This is how shop vacs are rated at 6hp but only draw ~12amps
keep in mind that HP rating on most small motors are at "locked rotor condition"which is basically the power it will draw when stopped from turning before it burns up. This is how shop vacs are rated at 6hp but only draw ~12amps
kd3pc
Well-known member
MIke has it in the easy form, and is close enough for most things.
HP = (V * a * e) / 746
Where, h = Horsepower (HP) v = Voltage a = Full Load Amps e = Efficiency...is a tad more accurate, if you know the variables.
There are books written about this, when you are talking hybrid and battery electric cars and kinetic and converters and electric machine construction. And so on.
Mike's will do great for your OP
HP = (V * a * e) / 746
Where, h = Horsepower (HP) v = Voltage a = Full Load Amps e = Efficiency...is a tad more accurate, if you know the variables.
There are books written about this, when you are talking hybrid and battery electric cars and kinetic and converters and electric machine construction. And so on.
Mike's will do great for your OP
jallyn
Well-known member
1 hp is about 750 watts. amps are watts divided by voltage, so 1 hp at 120v is about 6 amps.
Ther is a bit of wastage as well so I think the number is closer to 7-8 amps per HP on a 120v (at ~80% efficient). A 1 HP motor should be about that, and say a 5HP moto on a 240v is about 20AMPs again for a comparison.
edit:see post number 3 has the longer formula
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mike93lx
ALLIANCE MEMBER
MIke has it in the easy form, and is close enough for most things.
HP = (V * a * e) / 746
Where, h = Horsepower (HP) v = Voltage a = Full Load Amps e = Efficiency...is a tad more accurate, if you know the variables.
There are books written about this, when you are talking hybrid and battery electric cars and kinetic and converters and electric machine construction. And so on.
Mike's will do great for your OP
thanks for adding that clarity. In the context of small homeowner-level power tools, efficiency is probably pretty comparable across brands, so I would think that efficiency wouldn't really need to be worried about much. if the motor is sizable enough to justify a separate feed, the nameplate should provide the current draw info needed.
American Locomotive
Well-known member
For 120v motors, 6.2 amps is one "electrical" horsepower, for 240v motors, 3.1 amps is 1 "electrical" horsepower.
It gets tricky because electric motors have varying efficiency, so 1 electrical horsepower doesn't translate into 1 mechanical horsepower. For most large single phase motors (~1 horsepower and up) you can ballpark it with an efficiency of around 75%. So a 1HP 120V motor will probably use around 8-8.5 amps. Modern "premium" high efficiency motors are around 80-85% efficient, so a 1HP motor would only use ~7-7.5 amps.
Things get a little dicey when you get into the fractional horsepower motors (like 3/4, 1/2, 1/6). These motors tend to be far less efficient in general, and the efficiencies of these motors can be all over the place - anywhere from ~50% to ~80%. A lot of them seem to hover around the 60-70% mark. All of that makes it hard to determine horsepower from the nameplate amps in fractional power motors.
If the nameplate current is less than 7 amps, it's just about guaranteed to be less than 1HP. If the tool doesn't advertise its horsepower, or prominently advertises its "amps", chances are it's a garbage inefficient motor that hardly puts out any power.
It gets tricky because electric motors have varying efficiency, so 1 electrical horsepower doesn't translate into 1 mechanical horsepower. For most large single phase motors (~1 horsepower and up) you can ballpark it with an efficiency of around 75%. So a 1HP 120V motor will probably use around 8-8.5 amps. Modern "premium" high efficiency motors are around 80-85% efficient, so a 1HP motor would only use ~7-7.5 amps.
Things get a little dicey when you get into the fractional horsepower motors (like 3/4, 1/2, 1/6). These motors tend to be far less efficient in general, and the efficiencies of these motors can be all over the place - anywhere from ~50% to ~80%. A lot of them seem to hover around the 60-70% mark. All of that makes it hard to determine horsepower from the nameplate amps in fractional power motors.
If the nameplate current is less than 7 amps, it's just about guaranteed to be less than 1HP. If the tool doesn't advertise its horsepower, or prominently advertises its "amps", chances are it's a garbage inefficient motor that hardly puts out any power.
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So the 8.6 amp rated Wen drill press is roughly equivalent to 1 hp? And their 13 amp model would be roughly 2 hp? Sounds a little bit optimistic but not knowing all the variables about the motors makes it possible, I guess.
Thanks for all the replies,
Thanks for all the replies,
American Locomotive
Well-known member
The 8.6 amp one is probably close to 1HP. the 13 amp would be more like 1.5 HP, not 2.
By the way, I believe those Wen drill presses came up on here before, and the general consensus was you'd probably be a lot better off buying used.
By the way, I believe those Wen drill presses came up on here before, and the general consensus was you'd probably be a lot better off buying used.