Peak horsepower vs. real horsepower? - Router Forums
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post #1 of 119 (permalink) Old 02-05-2011, 11:42 PM Thread Starter
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Default Peak horsepower vs. real horsepower?

I see the term "Peak HP" on some routers. This term makes me a little suspicious, as I remember that "Peak Music Power" was a misleading figure that used to be used to sell amplifiers when I was young.

If I want a 2HP router, am I really getting 2HP from a router that says "Peak 2HP?"

I took grade 10 science a half century ago, and I remember that a HP is about 750 watts, so I'm not sure how a 15 amp (1650 watt) motor can generate 3 HP.

Cheers,
Roger


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post #2 of 119 (permalink) Old 02-06-2011, 12:14 AM
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Hi Roger

It's not the same , speed = HP in this case but with the new routers they have found a way to get around it by letting the motor pull more amps..to a point..at low rpm.to keep the HP up at any speed.

Think of it like your weed wackier very small motor but will tons of HP when the speed comes up (rpm's) ...i.e. the crotch rocket bikes,new table saws as well.

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post #3 of 119 (permalink) Old 02-06-2011, 01:09 AM
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Roger,

The horsepower ratings on routers are technically true, but misleading. First, lets talk about what 3-1/4 hp means. If there are no electrical losses (resistance, friction, heat, etc.) in a motor it takes 746 watts to generate a horsepower. Thus it would take ~2425 watts to generate that much power. In reality there's about 10% wasted due to friction heat, etc. and about 10% lost due to how motors work on AC (in technobabble, the voltage and current waves not being in sync over time). The combined effect is a motor that's in the 80 percent efficient range. At that efficiency, it takes about 25A at 120V to generate 3-1/4hp.

Induction motors behave much differently than induction motors under load. An induction motor delivers its rated power, and that's it. If the load goes up a bit, the motor essentially stops.

With an induction motor, when the load exceeds the rating the motor keeps turning and just draws more and more current (and provides more and more torque) until the resistance in the wiring eventually outweighs the ability for the router to draw more power.

As the power consumed goes up the heat generated by the router goes up very quickly, exceeding the fans ability to cool it. Additionall, the electronics is rated for certain amounts of current and, if overloaded, can fail as well.

The 3-1/4hp rating is the peak horsepower the motor can generate, as its generating heat much faster than it can reject it. Essentially, as it is burning itself up.

A side-note for when people here are using routers with speed control. As you are slowing down the router, you are slowing down the cooling fan. Does this mean you shouldn't slow down your router? No. Just keep an eye on how warm your router is or isn't getting when you are spinning a large bit taking heavy cuts at slow speed for a long time, as the router may warm up. The cooling system should be designed to take it but you're definitely loading the router more than normal, for two reasons.

Just my $0.02.

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post #4 of 119 (permalink) Old 02-06-2011, 03:17 AM
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That was educational, thanks BJ and Jim for the lesson.

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post #5 of 119 (permalink) Old 02-06-2011, 07:14 AM
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Quote:
Originally Posted by BigJimAK View Post
The 3-1/4hp rating is the peak horsepower the motor can generate, as its generating heat much faster than it can reject it. Essentially, as it is burning itself up.
Hi Jim:

I have just spent several months working with concrete. I cut 80' of concrete (1 1/2" to 4" thick) with several circular saws. Both of which functioned until the smoke was thicker than the concrete dust. I was using a diamond blade so that's a pretty tall order. Then, I used my heaviest electric drills to mix concrete in buckets to refill the holes. They performed until the smoke was thicker than the concrete dust. I stopped before either of the drills seized or caught fire. No such luck for the circular saws.

How badly does a motor have to smoke before it becomes unusable? Does "just a little bit" of smoke mean that the drill is still usable at full power? Or, does any smoke = total destruction? Or, let it smoke until it seizes, let it cool and go back at it? Or, somewhere in between?

My collection of smoking tools is increasing so I would appreciate your council. Even relegating them to the non-smoking section doesn't seem to help.

Allthunbs
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post #6 of 119 (permalink) Old 02-06-2011, 07:25 AM
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+1

Perhaps you could explain for me how the North American system works. Unlike most of the rest of the world you are using 120v. How does say, a DW625, differ in the US version from the one the rest of us use running at 230v? How do you get the power from half the voltage without massively uprated circuits?
In the UK, for instance, standard circuits are 13amp. For something like an oven, there would be a separate 30amp circuit.
Unless you have a weak heart, brief exposure to 13amps won't kill you (don't ask !) but higher powered circuits presumably would. Is the US domestic electrical system inherently more dangerous than that in the rest of the world?


Vaguely relevant, but a personal anecdote:

I was kitting out a laboratory outside Riyad some years ago. It had been built something like 7yrs before, but never commissioned. Saudi had no national grid and voltages varied from town to town, depending on who had sold them the town's power station. Some places that had expanded quickly even had two power stations delivering different voltages to different sides of town !
I checked the voltage plates on various things that were there prior to ordering up all the kit as 120v. Some weeks later, my installation engineer came on in a panic. They had switched on the a/c and things were blowing everywhere.
In between building the place and my arrival, the town had got a new power station to replace the old US one. Fortunately, none of our stuff had been unpacked and it all went back to the manufacturers to be replaced with 230v stuff.

Cheers

Peter
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post #7 of 119 (permalink) Old 02-06-2011, 07:29 AM
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Hi Ron

I would have thought that any smoke was a death sentence. Isn't it the insulation on the windings burning? The windings are going to short, if not at the first puff, not long after.

Cheers

Peter
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post #8 of 119 (permalink) Old 02-06-2011, 08:25 AM
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Jim....

Accurate and as well explained as anything I've read anywhere else!!


excellent!



Quote:
Originally Posted by BigJimAK View Post
Roger,

The horsepower ratings on routers are technically true, but misleading. First, lets talk about what 3-1/4 hp means. If there are no electrical losses (resistance, friction, heat, etc.) in a motor it takes 746 watts to generate a horsepower. Thus it would take ~2425 watts to generate that much power. In reality there's about 10% wasted due to friction heat, etc. and about 10% lost due to how motors work on AC (in technobabble, the voltage and current waves not being in sync over time). The combined effect is a motor that's in the 80 percent efficient range. At that efficiency, it takes about 25A at 120V to generate 3-1/4hp.

Induction motors behave much differently than induction motors under load. An induction motor delivers its rated power, and that's it. If the load goes up a bit, the motor essentially stops.

With an induction motor, when the load exceeds the rating the motor keeps turning and just draws more and more current (and provides more and more torque) until the resistance in the wiring eventually outweighs the ability for the router to draw more power.

As the power consumed goes up the heat generated by the router goes up very quickly, exceeding the fans ability to cool it. Additionall, the electronics is rated for certain amounts of current and, if overloaded, can fail as well.

The 3-1/4hp rating is the peak horsepower the motor can generate, as its generating heat much faster than it can reject it. Essentially, as it is burning itself up.

A side-note for when people here are using routers with speed control. As you are slowing down the router, you are slowing down the cooling fan. Does this mean you shouldn't slow down your router? No. Just keep an eye on how warm your router is or isn't getting when you are spinning a large bit taking heavy cuts at slow speed for a long time, as the router may warm up. The cooling system should be designed to take it but you're definitely loading the router more than normal, for two reasons.

Just my $0.02.

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post #9 of 119 (permalink) Old 02-06-2011, 08:40 AM
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Quote:
Originally Posted by istracpsboss View Post
Hi Ron

I would have thought that any smoke was a death sentence. Isn't it the insulation on the windings burning? The windings are going to short, if not at the first puff, not long after.

Cheers

Peter
That's what I'm wondering. Both drills still work. Wondering if it's worth the time to replace brushes and bearings on the cheap Skil saw. I'm not going to waste money on the Porter Cable.

Allthunbs
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post #10 of 119 (permalink) Old 02-06-2011, 09:24 AM
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Depending on what was causing the 'smoke'....

sometimes the smoke could be dirt and oil accumulations on the windings of the motor that have finally gotten hot enough to cook off, but not have damaged the insulation itself. Sometimes the smoke is from the shields or seals in the bearings failing and you're starting to burn off the light portion of the grease as it escapes the bearings. Sometimes, the smoke is the insulation itself, and that's the unmistakable smell of electrical death.

Without seeing the color of the smoke, and smelling the smell, it's hard to determine what the cause was.

Doug
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