What is Horsepower?

[SawTroll]

horsepower needs torque to exist

torque does not need horsepower to exist

That sure is correct!

 

[belgian]

I've read post by these three guys who claim to be engineers and physicist. What they say about the relationship between HP & Torque make me think they don't have their facts straight.

They keep talking like HP & Torque are two different things and not related - they're not.

Maybe you should also read what you don't like to read. HP and Torque are two different things, but sure are related. Just look at the formula's, and tell me again there's no relation between them.

For all the folks that seem offended, I am truly sorry for being an engineer. :monkey:

 

[Lakeside53]

I don't care

I like torque

 

[RiverRat2]

Me 2 + 1 =

I like torque

What he said,,,,,,,

 

[Sprig]

Me 3+1!

What he said,,,,,,,

What he said he said, *passes RR mug o' SSI Dark Ale*

 

[ShoerFast]

me+ TQ is = 2 power

I can say it again.

This is the LAST time I will try to explain it ok?

Power = Torque * angular velocity (since we are talking a rotating movements)

Now we have the famous formula:

M1*v1 = M2*v2 (that’s in a perfect world where you don’t have any mechanical losses on the way but that doesn’t matter here.)

Now let’s take the car example again:
M1 = torque on the engine’s crank shaft
V1 = speed of engines crank shaft
M2= torque on the rear wheels (where you want it! This torque will cause the acceleration)
V2= speed of rear wheels.

Since we are interested in M2 we have:

M2 = M1 * v1/v2 now use eq.1…… M1*v1 is ….. P! Engine power. Engine hp!

Hence M2 = P / v2

So where did the engine torque go? We lost is somewhere in the transmission!
Now what happens as the speed increases? The wheels will turn faster right?
V2 will increase. In order to continue the acceleration we need to keep our M2. So what do we need? More P, more hp.

So the fundamentals of all this is: The ability to cut more chips from a log or drive faster with a car is directly dependent on the power, raw kW.
(prefer kW over hp since hp is not unambiguous, depends for example on where on earth you live because of different g-constants)

A 600hp with 500Nm of torque will pull a heavy truck up the hill just as fast as the 600hp 2500Nm truck diesel engine. Engine torque as specified in car magazines only tells you what the characteristics of the engine look like. What the power vs. rpm looks like. It has nothing to do with the ability to accelerate fast or reaching high top speed.

Peter

There is a chance that your just having language barriers making your point.

Or are have a problem understanding what others are saying?

In hope that this will help, and back the the thread. As a chainsaw enters a cut, to make it simple, cutting a block of firewood , cutting a round.

At first the saw cuts a strip of bark, not much TQ demand, then starts into the wood, as the saw gets closer to the middle of the log, the chain demands more TQ to pull it through the wider cut, as the saw passes the middle or widest portion on the cut, the TQ demand gets less.

Just as the car in your explanation will need more TQ as it starts up a hill to maintain the same speed.

And further, the 600HP trucks going up the same hill, the 500nm truck will start to shift gears, while the 2500nm truck will shift lanes , and pass the 500nm truck, every day of the week.

 

[Lou]

Not all engineers are tools. Some actually make me think about tools or the best tool to use. I calibrate things for a living. Force (tensile testing) and engineering are very closely linked. In a perfect world a 1" cylinder with 3000 PSI applied yields 3000 lbf. It isn't a perfect world. Makes my job secure. An engineer willing to listen to input from the poor working slob can actually improve the poor slobs life... unfortunately not many do. Kind of like Peter hung up on the numbers or a definition.

 

[Al Smith]

I have nothing bad to really say about engineers,I work with them on a daily bassis.Some are good,some not so good.A few are somewhat arrogant until shown the errors of their ways.Those make my day as I delight in blowing the wind out of some smart azzs sails.

Here's a little example of torque/horsepower.My folks motor home is rated at 300 HP.However the torque rating is 1680 foot pounds at 2400 rpm.Now it stands to reason that this engine would pull a long steep grade with much more ease than say the same HP at 500 foot pounds.

Often times manufactures use missleading information.An example regarding electric motors.The only true measurement of HP is 746 Watts per .Often times they market their products as "develops 5 HP".In reality however it only produces 2.8 when using the correct formula.Some times it seems that the salabilty of products is directly tied to Madison avenue hype and hoopla.

 

[Woodie]

Often times manufactures use missleading information.An example regarding electric motors.

LOL! Kinda like my shop vac...a 12-amp 110v universal motor somehow manages to produce 6.5 horsepower, while my lil' ol' cabinet saw, with an 18-amp 220v induction motor, manages to struggle-out a measley 3 horses....

Sears/B&D/Pick-one ought to be shot for what they've done to electrical-motor power ratings.

 

[sperho]

18-amp 220v induction motor, manages to struggle-out a measley 3 horses....

If it truly will draw 18A under working loads, that's a 5 horse motor...

 

[Woodie]

If it truly will draw 18A under working loads, that's a 5 horse motor...

The issue there is "working loads," though. Generally speaking, the motor's amperage rating is the max it will draw, usually at start-up or under severe (essentially stall speed) loading.

That's why a dust collector needs E or F class insulation...by definition its working load is fairly close to its max draw.

As I recall, a true 5 hp motor has a max draw around 25A at 220v.

 

[Al Smith]

If it truly will draw 18A under working loads, that's a 5 horse motor...

Again,it could be misleading.Service factor rating of the motor is a factor that must be considerd.
A single phase ,3 HP,1725 rpm motor with a 1.15 service factor would draw 19 amps at 240 .

Adding somewhat of a snag to the subject,a 5 HP single phase 240 volt,3450 rpm motor with a 1. service factor draws 19.6 amps.Clear as mud.

 

[SawTroll]

Not all engineers are tools. .....

No, hopefully not, it would be pretty odd if they were.......:hmm3grin2orange: :hmm3grin2orange:

...sorry, just couldn't resist.......

 

[spacemule]

Here's a little example of torque/horsepower.My folks motor home is rated at 300 HP.However the torque rating is 1680 foot pounds at 2400 rpm.Now it stands to reason that this engine would pull a long steep grade with much more ease than say the same HP at 500 foot pounds.

That conflicts with my understanding. Given two engines with the same hp ratings but different peak torques, the lower torque motor will have to be turning at much faster rpms to have the same hp output. This will be compensated by a gearbox that is designed to run the engine at the higher rpm.
In the example given, the lower torque motor would have to be turning 8064 rpm to achieve the same hp. If an engine is designed to operate at such high rpm's, then it really isn't pulling the load with any more difficulty.

 

[sperho]

As I recall, a true 5 hp motor has a max draw around 25A at 220v.

I think it also depends whether it's single or three phase...

 

[Al Smith]

It just goes back to which bassis the power is rated at,Rex.In days of old,the HP rating of the old steamers was actually based on how much a horse could pull.

If for example and old Case steam engine was rated at a lowely 40 HP,it could pull as much as 40 horses.Of course they never gave the horse sizes,Could be 40 Shetland ponies or 40 Clydsdales,with or without the Budwieser girls.

 

[Al Smith]

I think it also depends whether it's single or three phase...

The rule of thumb on a 3 phase motor is 2.5 amps/HP@ 240 volts.

 

[ShoerFast]

The issue there is "working loads," though. Generally speaking, the motor's amperage rating is the max it will draw, usually at start-up or under severe (essentially stall speed) loading.

That's why a dust collector needs E or F class insulation...by definition its working load is fairly close to its max draw.

As I recall, a true 5 hp motor has a max draw around 25A at 220v.

Having rebuilt and tested AC starter motors, and watch 1 1/4" copper cables jump about 2 feet off the ground the first time you spin them is a sight to see. The first wiggle an amp gauge makes is near the 8000A range, that wattage or HP is pure TQ spinning up the armature. Once to speed, there draw would be around 850A as it spins the turbine up, dropping off as the engine spools up(less TQ demand). Once you start dumping fuel to the engine, the amp draw increases again, as it takes more TQ to maintain cranking speed with a fuel fog on the turbine-blades.

Once the engine is burning and turning on it's own, and the amp draw nears 350-400A, it's safe to turn the starter off.

Jet starters are shunt-would, hi-TQ motors, rated in HP (27HP 24V is the biggest I ever worked on) , but watching just one jet engine start will show you all you ever never wanted to know about why we like TQ

 

[Woodie]

I think it also depends whether it's single or three phase...

I should have qualified that...all mine are single-phase.

 

[belgian]

I have nothing bad to really say about engineers,I work with them on a daily bassis

Some are good,some not so good.

isn't that a universal truth for all individuals, workers, dealers, teachers, engineers, loggers, wifes, .... so could we please all shut up wining about engineers, it's starting to get on my nerves :deadhorse: