4 HP on 115v??

[Greg O]

By useing the same math that Porter Cable uses on my 7 HP air compressor, that draws 15 amps at 240 volts! Greg

[effinperfectionist]

This is hilarious.

4.4HP * 746W = 3282.4W

3282.4W / 15A = 218.83V

If your 110/115/120V (however you want to rate it) circuit EVER reaches that, you're going to melt stuff in your house. Vpeak for 110Vrms is only about 155V. I've measured 125Vrms in the wall before, which is a peak of 177V.

In short, it is IMPOSSIBLE for that saw to ever develop 4.4HP, presuming its stall current is 15A, and it is running on a household 110V circuit (and further presuming that the motor is operating at 100% efficiency, which it is, of course, NOT).

Now, if it can draw 21A at Vpeak (155V) without turning in to a puddle, then it can consume power equivalent to 4.4HP, though it still wouldn't be cutting wood at that rating.

[Al Reid]

Figuring in efficiency and power factor, the best it's gonna be is ~1.5hp.

-- Al Reid

"It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." --- Mark Twain

[Al Reid]

You are playing the same game bu using "theoretical" numbers. You have to look at efficiency and power factor to knoe the actual watts/hp

peak-to-opeak voltave has nothing to do with it.

the 15A is full load current (FLA) not locked rotor current.

Still wrong since you are not taking efficiency and power factor in to account and you are using a ficticious voltage.

The long and short of it is that on a nominal 120vac circuit, a motor drawing 15 amps will produce `~1.5 hp. On a 20 Amp curcuir you can eek out a little more at the expense of heat and speed. If the circuit is not limited, it will continue to slow down and produce more power until it hist 'breakdown' and stalls. at that point it will deaw the Locked rotor current.

I am not sure why the manufacturers have taken to this silly rating game. I have a

1.5 hp Ingersol-Rand air compressor that is 1.5 HP and draws about 16 amps. The same compressor by today's 'standard' is rated at 6hp. That's great, except that in reality, they do the same amount of work for the same power input.

[CW]

No, the best it is ever going to be is 2.41 horsepower. Small motors are rated in INPUT power.

[gabriel]

Ha! So _this_ is how Bosch routers went from 2HP to 2.25HP without a change in the motor!

[Al Reid]

Not according to the NEC and NEMA.

[effinperfectionist]

Al Reid wrote: "Still wrong since you are not taking efficiency and power factor in to account and you are using a ficticious voltage."

No, I'm not wrong. I said IF it could actually DRAW 21A at the peak voltage of 155V, then the math gives you power consupmtion of 4.4HP. Efficiency is not relevant, as I'm talking purely about consumed power (input power). Thus, if a 21A peak coincides with a 155V peak, the power consumption at that moment is 4.4HP. I am NOT talking about power delivered to the cutting teeth, or wherever else you may choose to measure it, I'm talking about the total consumed power of the machine.

And, 155V is not ficticious.......it's the peak instantaneous voltage for a

110V sine wave. (110VACrms / 0.707)

To quote myself:

"> Now, if it can DRAW 21A at Vpeak (155V) without turning in to a puddle, then

[CW]

[DJ Delorie]

All the more reason to use the amp rating instead of the HP rating. The amp rating is more strictly controlled.

[Al Reid]

While that may be true, what is ultimately of importance is the power delivered to the shaft of the motor. That is where HP and torque are traditionally measured. What is better, a 15A motor with a 1.5 HP output or one with a 1 HP output. Efficiency and power factor must be considered. Input power is meaningless if you want to know how much work it will do.

[Al Reid]

It is still meaningless. It is not a DC machine. It is still rated based on the RMS input voltage. Mow if you wnnt to apply a higher (155VRMS) input voltage, then you would be correct.

The only measure that has any value is the HP and torque at the output shaft. I don't care how many amps go in, I want to know how much HP is developed.

[Bridger]

HP "where the rubber meets the road" is of course the only meaningful measurement. it's actually used in some high performance equipment, but output brake horsepower is not something I've ever heard of being measured on small electric motors. instead, the manufacturers seem to be free to engage in whatever flights of fancy they please when writing specifications. Bridger

[Bridger]

I doubt you will ever see that information given for a power tool. I suspect that that number would shock the american buying public, who think that they own 6 HP vacuum cleaners and such. I doubt that output HP on one of sears' 6 HP specials would exceed 1/4 HP or so....

[Everett M. Greene]

No. They're going in opposite directions so they cancel. You get zero amps from your 15A circuit which makes the

4.4 HP even more miraculous.

Less than truth in advertising...

[CW]

Yes, it is. In Europe, motors are rated in watts. That rating has to meet government standards.

[CW]

That's quite true. Why would a manufacturer want you to know the actual work that their product will do? It sounds so much better to rig the numbers.

[Charlie Self]

But it's still less than useful information because you have no idea of duty cycle or motor efficiency.

Charlie Self "Character is much easier kept than recovered." Thomas Paine

[Al Reid]

Check out this link for a series of properly rated motors:

Reid

"It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." --- Mark Twain

[Charlie Self]

Al Reid responds:

Yeah, well Marathon is said to be among the best--and with the 3600 rpm 1-1/2 HP unit listing for $320, they should be!

Charlie Self "Character is much easier kept than recovered." Thomas Paine