Horsepower change

Not long ago I was reading that the horsepower listed on electric motors was not the same that it would have been 50 years ago. As I remember the horsepower rating now used is not as high a number as it used to be. What happened in the electric motor world that caused a change to horsepower ratings.

The laws of physics have not changed but there have long been multiple ways to rate electric motor power and tort attorneys and state and federal agencies are, no doubt, more involved than 50 years ago,
causing manufacturers to try to avoid becoming targets.

Remember the lawn mower HP controversy a few years ago that generated enormous fees for tort attorneys but little or nothing for consumers?

Would need to read language to be more specific.

Dean

Kind of ran into this a few years ago, my cousin had a nice 60 gallon upright compressor that the motor went south. He took it in to get fixed and the replacement motor was more than the whole unit new. He
owed me some money so I took the unit home. They said he need a 5 hp motor, I had a 3/4 farm duty motor laying around, put it on and just needed to buy a different pulley for the motor, all good for 5+ years.

That is common on various power tools, especially compressors, vacuum cleaners, circular saws, etc. Manufacturers tend to err (lie) on the plus side when describing their product.

When comparison shopping, or sizing a circuit, or repowering a compressor, always go by the FLA (full load amps) on the motor tag, not the claimed horsepower.

There is the calculated horsepower and the real working horsepower. That is why we need to be very careful buying table saws and compressors. Crapsman used to advertise their 10 inch table saw as 3 HP but down underneath the saw table where the customer can not see, the tag on the motor read 1 1/2 HP. Sears could get with calling it 3 HP because it was theoretically 3 HP by calculating amps and volts and RPM.

Well, there are a couple of things going on. First off, there's the rated power of the motor versus the claimed "maximum power" on the product on which it's installed. Many manufacturers grossly exaggerate the latter and the motors they use aren't marked with the rated horsepower. Horsepower ratings for table saws and air compressors are often totally fictitious. Although the rated horsepower isn't marked, it's pretty easy to derive from rated current and voltage; multiply current and voltage to get the volt-amps, then multiply the VA by the power factor to get the rated power in watts. If the power factor isn't marked, assume 0.7. Then divide the watts by 746 to get the horsepower. My air compressor has a decal that says "6.5 max hp", yet the actual horsepower is closer to 3. Yes, this should be against the law but it isn't.

The other thing is that any induction motor will put out as much power as is demanded, up until it stalls out. This is different from internal combustion engines, which only put out so much torque and slow down if the demand for torque is greater than what the engine can produce. This means the motor manufacturer can honestly claim a horsepower rating greater than what might be prudent for motor operation at a 100 percent duty cycle. The motor will get hot at the rated power, but it can produce that power nonetheless.

There are various SAE standards defining exactly how manufacturers rate the horsepower of internal combustion engines. I'm not aware of similar industry standards for electric motors.

What happened was the advent of smoke
and mirrors in the tool industry geared
toward consumers with no knowledge of
actual hp other than higher is better.
Using starting current and no load
conditions they can claim ridiculous
numbers. The major electric motor
companies didn't do it.

(quoted from post at 04:27:40 12/31/20) What happened was the advent of smoke
and mirrors in the tool industry geared
toward consumers with no knowledge of
actual hp other than higher is better.
Using starting current and no load
conditions they can claim ridiculous
numbers. The major electric motor
companies didn't do it.

Click to expand...

M-MAN, if you were going to build and market a piece of electrical equipment and you could choose between two valid and accepted HP ratings you would choose the lower of the two?

Once you installed the smaller drive pulley . Your comparison became apples and oranges .

As previously mentioned . Some electric motors were advertised as Peak HP vs continuous HP . Sure the motor can make peak power for several seconds prior to burnout or tripping the protective devices .
This is related to where some people get it in their head that a 5HP electric motor is more powerful than a 10HP gasoline or diesel motor .
Some people take the 250% torque rise on an overloaded electric motor as being more power than the 125% torque rise on a diesel/gasoline reciprocating engine .
Take a grain auger that requires 15HP to operate and operates just fine with a 15HP diesel/gasoline engine . A 10HP electric motor will run the auger for a few minutes then trip the thermal overload protection .

I like the 6hp shop vacs. A true 6hp would require more than double what a 110v 20a circuit can produce