Old motors: Why so different than today's

They did the same thing with small gas engines. Fifty years ago all mowers had about 3 1/2 HP ratings then about fifteen years ago they took off crazy saying there engines were now 6.75 HP. Big law suit and now there ratings have dropped HP and replaced with cubic ins. Same deal people are gullible ,,Barnum said,, sucker born every minute. Yupp
 
A quick check is to multiply amps x volts = watts. Then divide by 746 to get hp. The output mechanical hp will always be less than this number.

One catch is this should be running amps, not peak amps. A clamp-on ammeter will verify this.

Wouldn't the motor need to be under a load? and then, are you not just calculating the load on the motor?
 
Wouldn't the motor need to be under a load? and then, are you not just calculating the load on the motor?
Yes, it should have a typical load. What you are mesuring is the input power which is always more than the output power. Output power = input power x efficiency. As I recall, typical efficiencies are in the 80% - 90% range.
 
Ok, I'm following. Your just calculating the load on the motor, not what the motor is rated for right? Just like a car, if you can't find the specs, you need expensive equipment to find the max output.
 
Clamp on ac ammeters needn't be expensive. HF has three for under $20.
 
Clamp on Ammeter indicates current at the time.

However a 7.5 hp motor on a compressor may not approach 7.5 hp in current until it reaches full tank pressure.

There does not seem to be any standards for simple comparisons so one needs to read and understand the data sheets and hope they are correct.

Pressure washers use "cleaning unit" where they multiply volume of output X pressure to come up with some sort of common data point that one can use to compare units.

Same could be used for say compressors where amps and operating pressure and volume could be used.
 
I used to have a Hoover vacuum cleaner that had a rating of 12 hp. It would be lucky to actually be generating a 1/2 hp. Marketing!

Please correct me if wrong, I believe it may say 12 Amps on the vacuum, I've seen that stated many times.

A 1750 rpm one Hp Motor will have more torque then a 3450 rpm one Hp Motor, and several times more torque then a 6000 Rpm one Hp Motor. A vacuum requires high rpm not torque. all 3 motors use the same amount of energy - 746 watts X 1 hour = 1 HP.

A high rpm motor can be considerably smaller and use the same amount of energy as the larger higher torque motor, the trade off is speed for torque.

A 1750 rpm motor would look funny on your vacuum, and would turn the brush well enough to rip the carpet out, But couldn't create the vacuum needed with the tinny fan to suck out any dirt due to the rpm of the motor. The small fan has to reach high speeds to create good suction using a high rpm motor.

Pull your vacuum agitator & belt off and look how fast your little motor is going, takes allot of energy to do that.

There is no gimmick here, No magic going on - just volts times amps = watts.
 
Lawn mowers. Yeah, what a joke. My brother bought one years ago that said in big letters something like, "7 HP at 5000 RPM". Then a small sticker said, "Never run above 3000 RPM".
 
Please correct me if wrong, I believe it may say 12 Amps on the vacuum, I've seen that stated many times.

A 1750 rpm one Hp Motor will have more torque then a 3450 rpm one Hp Motor, and several times more torque then a 6000 Rpm one Hp Motor. A vacuum requires high rpm not torque. all 3 motors use the same amount of energy - 746 watts X 1 hour = 1 HP.

A high rpm motor can be considerably smaller and use the same amount of energy as the larger higher torque motor, the trade off is speed for torque.

A 1750 rpm motor would look funny on your vacuum, and would turn the brush well enough to rip the carpet out, But couldn't create the vacuum needed with the tinny fan to suck out any dirt due to the rpm of the motor. The small fan has to reach high speeds to create good suction using a high rpm motor.

Pull your vacuum agitator & belt off and look how fast your little motor is going, takes allot of energy to do that.

There is no gimmick here, No magic going on - just volts times amps = watts.
Unfortunately, that claim was on the packaging which is long since gone. The rating plate on the vacuum says 10.4 amps/120 volt, which would work out to 1.67hp input (that may include the power to the brush motor and light as well)

However, I did buy a new Shop Vac this year with a label in plain sight that proclaims 4.5 peak hp and the rating plate says 9 amps/120 volt. which works out to 1.44 hp input. At 75% efficiency, this would be about a 1 hp motor. I have to say, though, it is the most powerful vacuum that I have ever owned.

As the excerpt I quoted in post #6 explains, vacuum cleaner claims of peak hp are based on a totally unrealistic method of measurement done strictly for marketing purposes and no real indication as to how well the vacuum cleaner will perform.

The point being, though, that you can't trust advertising claims when looking at expected performance. A modern motor may look like an economical replacement for your tired old motor but you may be disappointed with the outcome. If you calculate the horsepower by the rated input power (volts x amps), you may have a better understanding of what to expect. Factor in for efficiency and if the labling says anything like peak, figure a sizable factor for that as well.
 
Unfortunately, that claim was on the packaging which is long since gone. The rating plate on the vacuum says 10.4 amps/120 volt, which would work out to 1.67hp input (that may include the power to the brush motor and light as well)

However, I did buy a new Shop Vac this year with a label in plain sight that proclaims 4.5 peak hp and the rating plate says 9 amps/120 volt. which works out to 1.44 hp input. At 75% efficiency, this would be about a 1 hp motor. I have to say, though, it is the most powerful vacuum that I have ever owned.

As the excerpt I quoted in post #6 explains, vacuum cleaner claims of peak hp are based on a totally unrealistic method of measurement done strictly for marketing purposes and no real indication as to how well the vacuum cleaner will perform.

The point being, though, that you can't trust advertising claims when looking at expected performance. A modern motor may look like an economical replacement for your tired old motor but you may be disappointed with the outcome. If you calculate the horsepower by the rated input power (volts x amps), you may have a better understanding of what to expect. Factor in for efficiency and if the labling says anything like peak, figure a sizable factor for that as well.

You'll get no argument from me on the advertising being somewhat misleading, And efficiency.. well If you lived here I'm sure we could have a great conversation about all this.
 
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