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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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.

 

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.

 

That was educational, thanks BJ and Jim for the lesson.

 

+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

 

The NA residential power standard is 120/240V AC single phase. Technically the 240 is two 120V sources 180* out of phase. This gives you 240V between the two hot legs but only 120 from either hot leg to ground. It was chosen to reduce the risk of electrocution since most "shocks" occur between hot and ground. In the NA home, unless you have a shop, 240V is typically only used for electric stoves, electric clothes dryers, electric water heaters and permanent electric heaters.

Typical home circuit breakers are 20A 120V though some people install 15A breakers to get away with smaller wire (14 vs 12 Ga).

NA commercial / industrial power is 3-phase, either 120V/208 Wye or 277/480VAC Wye. The power between phases is 120*, which is the reason why the voltage between two 120V hot legs is 208V instead of 240.

As far as "more dangerous", no... it's arguably safer. What plays in is the rather conservative National Electric Code which is not federally mandated but is typically adopted (with exceptions) by virtually all states.

+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

 

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.

 

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.

 

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.

It was that "unmistakable smell of electrical death" -- sort of gray, acrid, chemical...

 

Hi

Just my 2 cents

I think it comes down to using the right tool for the job, a power hand saw is not made to cut concrete, they make concrete saws, most are gas power but they do make some big elec.ones also, it's like hooking up a trailer to your VW, what do you thing going to happen..

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Agreed!!

 

I understood most of that. So, if I am looking for the most powerful 110v. motor for my router table, am I to look for a high amperage, and ignore the HP rating on the router? That makes a kind of intuitive sense to me.

Thanks again!

 

Hi

At one time I wanted a new door way in the basement, the wall was 10" thick with rebar in it and I called a guy up that did it day in and day out, he said no big deal he did it in 2 hours or less but he said you will need to break it up and take it out of the basement, it cost me a 125.oo bucks but worth every penny, sometime it's worth calling the right guy with the right tools to get the job done..


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You are correct. Any audiophile wants power measured in watts RMS (root mean square) which is more of an average. Router manufacturers get their machines spinning as fast as they can go and then measure how much energy it takes to stop them (essentially brake HP). The crunch is that power is the ability to do work over time so if you shorten the time to make the armature stop it makes the HP level look good. Watts is a more accurate measure. The only other factor involved then is efficiency which is power out/power in x 100 = % efficiency. A 3 1/4 HP router would have to use over 2200 watts of power which the standard North American circuit cannot deliver. A 15 amp circuit can deliver about 1800 watts of power (line voltage x amps= watts i.e. 15 amps x 120 volts = 1800 watts). I too would like to see a little more truth in advertising.

 

Hi

If I run my 3 1/4 HP on a 15amp. breaker it will pop it every time on a full load ,I need to run it on a 20 amp. breaker that is a standard in the states for equipment in the home shop.
15 amp.is for light circuits in the states...

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Unless you have a weak heart, brief exposure to 13amps won't kill you (don't ask !)

You must be talking milliseconds! In defibrillation which lasts about 10 milliseconds currents of close to 100A are not unusual.

However, for a longer exposure even 60 mA can induce ventricular fibrillation.

To have 13 A passed through your body, assuming an average impedance (arm-to-arm) of 1500 ohm one would have to be exposed to something like 20,000 volts!

 

Hi

Wire size in the shop, I used 10/3 for most of my wiring in the shop, this is one place you don't want to go cheap but you don't want to get your wire from HD/Lowes, I always buy that type of stuff from Cash Way Elec.Supply or some other Elec.Supply outlet the place that HD/Lowes gets it from went they run out or short.

That's a little tip always read the box that they have in the stores you will sometimes see it on the box where they got it from...

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"A chain is as strong as its weakest link."

Nothing wrong with oversizing the wire. It reduces the voltage drop along the wire, for a given load. Less voltage sag when a heavy electrical load starts (such as a 3-1/4 HP router.)

However, one needs to consider where the weakest link is. If one runs power from the main power panel to a sub-panel ("pony panel"), best to oversize the run between the panels, in addition to the individual loads on the pony panel.

Cassandra'

 

I know you like to say that speed equals power but that really isn't the case.

Quite right. Power = speed (rpm) x torque x constant (unit-dependent).

 

I think the formula you are refering to is Power= torque x 2pi x rpm/60. Your formula does pass the test for power, i.e. work/time. To put the importance of rpm in perspective try the following test. Turn on your router and get it revved up as fast as it will go. Now shut it off. It stayed in motion under zero load for about 3 to 5 seconds. Once the power was turned off torque went to zero. The 3-5 seconds that the armature kept spinning (under zero load) is the power that was still available due to rotational energy (stored energy or inertia). The formula you quoted is for total energy in the system (i.e. torque, which is constant under a constant load, and rotational energy, which was imparted to the armature by the initial torque that was applied to it.) As I already pointed out, a router armature is too light and has too small a moment arm (diameter) to be able to store any significant amount of energy. If you want power, you need input watts. RPM has almost nothing to do with it no matter how fast you can spin the armature.

 

Power= torque x 2pi x rpm/60.

2pi/60 being the constant which has to be modified further depending on the units.

If you want power, you need input watts.

Yes, that is true of any system that converts one form of power to another.

 

"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. "

Assuming excellent 80 percent efficiency there is no way you can get more than 2.57 HP out of a 20 amp circuit since the circuit blows at 20 amps. So where is the 3.25 HP? It is not possible.

 

Hi Joe

You and some of the members on the north side of the border think the same way , maybe you should tell the mfg. of the 3 1/2HP routers and some 3HP table saws ,they have got it wrong ,they sure sale a ton of them..I don't recall anyone suing for false advertisement many of the 3HP routers items are rated 15amp. by the way..

My table saw as a sticky on it and that states , developing 3 HP., and it's rated at 12 amp.maybe it's the 10" saw blade mass ..

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The scientific formula for horse power vs electrical energy is:

1 horsepower = 745.699872 watts

that may or may not be what manufacturers are using for thier ratings.

watts = volts x amps , what are the manufactureres using for amps? A locked rotor?

 

Harry
I dont want the goverment messing with anything!!!!! I receive few benefits and pay more taxes. Anytime goverment does something it alwasy costs more than if they just left it alone So rgarding power transmissions they already have it overregulated and now you want to give them more control. Wake up goverment takes your freedom everytime you take a handout

God Bless
Bill

 

Thanks for the explanationation on that Jim. I had grown up using perhaps the wrong term to describe what I was attempting to convey. It may have been a regional difference. I know that when I took my air brake course many years ago in British Columbia, we were told that an air brake system was required to produce a stopping force of 50 brake horsepower per wheel. This type of definition is more in line with what I was describing. In the meantime, I have found an excellent article on the web that explains this whole issue of Peak HP vs Actual HP very thoroughly and explains what I was trying to describe. It can be found at

http://www.kevinsbrady.net/motors.pdf

In the article there is a chart that shows real horsepower according to amperage draw and motor efficiency.

Bob,
If your saw is only 110-120vac then it is only a true 1hp according to the above article. My Unisaw is rated at 3 hp and it can't be run on anything but 220-240vac so one manufacturer is lying (actually maybe they both are, one just less than the other). By the way, my Unisaw must have some kind of brake as it stops much quicker than the old Rockwell Beaver 10" I have.

 

http://www.kevinsbrady.net/motors.pdf

This is a good article which re-states much of what has been said here already.

It is instructive to actually measure the current drawn by the various power tools in the workshop:

Kill A Watt™ P4400 Energy Meter - Lee Valley Tools

With this gizmo I have not been able to measure anything approaching the stated HP on the tools I checked so far with the exception of my metal lathe.

One of the more amusing tests was on a Foredom knock off I bought in a local shop: It turned out to be weaker than my Dremel!

 

If you are ever running your tools at peak HP you are really overloading them. Normal use will not even come close to peak HP.

 

Induction motor, universal motor -- if I remember correctly somewhere on the forum is an item showing the different types of electric motors. How does the type of motor relate to the way their "strength" is rated? I have a 3/4 HP motor on my bandsaw. It's absolutely huge, weighs a ton and looks like it could winch in a lake freighter and not work up a sweat. How does it compare with my 3HP Hitachi M12V router that's less than 1/2 the size?

 

Hi

It's sounds like you and I don't have 3HP routers just 1HP to 1 1/2 HP routers :sarcastic::jester: maybe someone should tell Hitachi,Freud,Porter Cable,DeWalt,Triton,Trend,etc. that we want a refund..now that we know Chuck and others are right and they are All wrong,they must know something we don't, now I wonder if my new T4/Colt/DeWalt 1.25hp router is just a 1/4HP router,,...:shout::stop::big_boss:

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Good link, Charles.. and it's straight-shooting about the amps/horsepower relationship. His ratings for 50%/60%/70% efficient is accurate and probably accurate in a lot of true "industrial" motors (big, heavy, live-forever tanks). Newer motors, even the industrial models run towards the 70% and the lighter-duty industrial induction motors are inching towards 80%.

In response to the PC Speedmatic 3hp (and any other manufacturers like-rated router) are pure balderdash. I say that and I own (and really like) my Speedmatic.
As for the smaller routers, BJ, yep.. They scale down in HP too... both our Colts are closer to 1/2hp. That said, a horse is pretty strong!! <g>

 

Good link, Charles.. and it's straight-shooting about the amps/horseaccurate in a lot of true "industrial" motors (big, heavy, live-forever tanks). Newer motors, even the industrial models run towards the 70% and the lighter-duty industrial induction motors are inching towards 80%.

power relationship. His ratings for 50%/60%/70% efficient is accurate and probably In response to the PC Speedmatic 3hp (and any other manufacturers like-rated router) are pure balderdash. I say that and I own (and really like) my Speedmatic.
As for the smaller routers, BJ, yep.. They scale down in HP too... both our Colts are closer to 1/2hp. That said, a horse is pretty strong!! <g>

Thanks Jim,
I agree with you, a good honest horsepower is pretty powerful.
I think the best idea is just to use a factory hp rating to gauge against other size models and pick something in the range you need. I suspect that there isn't that much difference between your Powermatic and my big Hitachi in what they can rout. I would certainly tell someone now not to bother picking one router over another just because it is supposed to be 1/4hp stronger. I would be more concerned with features and durability.
The Colts you and Bob bought will still do the jobs you bought them for no matter what the actual output is. If it is any consolation, at least it appears that all the manufacturers appear to be lying to us equally.

 

I have a 3/4 HP motor on my bandsaw. It's absolutely huge, weighs a ton and looks like it could winch in a lake freighter and not work up a sweat. How does it compare with my 3HP Hitachi M12V router that's less than 1/2 the size?

Size is not necessarily related to power. It *may* be related to efficiency which has a lot to do with how the motor is constructed. I suspect the band saw motor is induction, Hitachi is universal. The "3HP" has been covered here several times as well as in the article linked.

 

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 3¼ HP.

Back to the original question which wasn't really answered completely.

Peak HP just means that the Peak Voltage was used to calculate it. Peak voltage for a 120 volt wall socket is about 170 volts (i.e. 120*sqrt(2)= 120*1.414).

Equation for electrical power: P=VI, P = 170v*15a = 2550 peak watts.

There are 746 watts in 1 horse power, so 2550/746 = 3.42 HP but this is the no load HP. Assuming 5% loss in the bearings and brushes (i.e. 95% efficiency) give:

3.42 * .95 = 3.25 HP.

Induction motors turn much slower than universal motors and have higher torques. this makes them much bigger and heavier.

Small, light weight, high speed, low torque universal motors can have the same power rating (HP) as big, heavy, slow, high torque induction motors; however, the useful power of a universal motor is much lower than for an induction motor, so, although they're rated the same, an induction motor will supply greater useful power than a universal motor. Working efficiencies for unversal motors are around 60-70%; for induction motors, they're around 80-90%.

 

If, for a 120V RMS, the current is 15A RMS, then for the peak 170 V the peak current will be also 15A x 1.414 = 21.2A. Thus the peak power (given a constant load) will be 3604W (4.83HP) at 100% efficiency.

3.25 HP output would then represent 67% efficiency which is perhaps more realistic figure than 95% for any motor.

I think it unlikely though that this is what the manufacturers mean when they refer to "peak power".

 

So, if I'm to understand all of this correctly, it is quite possible that 3.25 HP (peak) is indeed a valid method of stipulating the power of a motor. In essence it is saying that a 3.25 HP motor can continue to function (albeit for a short time) at 170V. Given that our power fluctuations (here in Québec) routinely hit 170V+ it is comforting to know that my M12V isn't going to blow up in my hands!

Now, I read in...

Electric Motor Basics and
http://EzineArticles.com/640680

layman's language of universal and induction motors compared. Everything that has been said in this thread seems to apply only to universal motors.

I have several induction motors in my shop -- bandsaw, tablesaw etc. how do their ratings compare to their labels? Do only induction motors have NEMA ratings?

How is it that induction motors are stuck at 1750 rpm and universal motors can easily hit 30,000 rpm and more?

I'm trying to broaden the scope of this a bit so I can put it into a summary for myself. It helps when I write it out.

Thanks all for the discussion and the contributions.