Watts & HP - how puny are you?

[strantor]

I've grown up around this term "horsepower" and I know what it means, but I guess I never really had a full grasp of what was going on around me. My thinking has always been that there's no way that 1 horsepower is equal to the amount of power that 1 horse can produce. I remember reading that the term origininated from observing how fast a horse could lift a weight, but what about my lawn mower? It's 5HP, does that really mean it's as powerful as 5 horses? No way, I thought. I've assumed for a long time that HP is just a measurement unit and shouldn't be thought of in terms of the power of horses, because there's just no way that a Kia Optima is as powerful as 200 horses.



Recently, I've become interested in how much power a human could produce on a treadmill or on a generator bike. I figured I could probably put out a couple of HP. Started looking around and found this (ignore the picture, there is good info on that page):

As I watch the Tour they occasionally display a rider’s instantaneous power output on the screen. They are able to do this because the cyclist has a power meter on their bike and this transmits data to the broadcasting network.... This power usually ranges anywhere between 250 Watts if they are just cruising along with the pack, or 400-500 Watts if they are pushing hard up a steep climb

(watt-hours)

The International Cycling Union (UCI) maintains records for the Hour Record, which is an ongoing contest to see who can ride the farthest in one hour. ...The current record holder for the Hour Record is Ondrej Sosenka and the website BikeCult.com has an estimate of his average wattage during his Hour Record at 430 Watts! If Ondrej’s bike were attached to a bicycle generator and it was super efficient, Ondrej would have been generating enough power to light up 7 60-Watt light bulbs! Since I pay about 10 cents/kWh, if I were to pay Ondrej for the energy he produced over the hour he was pedaling he would have almost earned a whole nickel (430 Watts • 1 hour = 430 Watt-hours = .43 kWh)!... As you can see, the best human efforts at producing power over the course of an hour on a bicycle are around 300-400 Watts. To put this in perspective, when my AC is running full blast my house can consume about 4,000 Watts or 4 kW. I would need over 10 of the best cyclists in the world attached to bicycle generators to power my house when it is consuming this much power!

So, trained & determined athletes can generate about 500W max, and 300-400W per hour.

In my <athlete shape I now estimate I could put out half that, so 250W max and maybe 125W/hour. So I'm roughly 1/6HP at best. I think that sounds about right if you're looking at horsepower in terms of horses; Not hard to believe that a horse is 6X as powerful as me. But, when I consider my vacuum cleaner, it still sounds counterintuitive. My vacuum pulls 12A, says that right on the label. 12A on a 120V circuit is 1440W. so my vacuum is 11.5X as powerful as I am! does that sound right? Not to me, at first, but let's consider what it's doing:

pulling a 16" long hair brush through the carpet at 150mph
Drawing probably 5000X as much suction as I can with my lungs
powering a bulb in the front (the bulb alone would probably be considerable strain for me to power)
Driving it's own wheels a little bit
(and it's doing all this continuously)

So, maybe it is 11.5X as powerful as I am. I sure don't feel up to the job.



Another example; my oscillating room fan. It & myself are probably in the same weight class. It seems like a puny appliance to me, but then I consider that if I wanted to spin that blade as fast as the fan, I would need some up-gearing which would require a lot more torque from my arm. If I got the gearing right so I could keep up with the fan, it would definatel be a heck of a chore, and I would peter out long before the fan does.



This epiphany about power makes me even more determined to try out a concept I had before - A treadmill generator to power your TV. I was thinking that if you installed this device in your house, with no way to power your TV other than by building up sufficient charge by riding a bike or treadmill, then obesity would have a serious adversary. Now I'm just wondering how long you would have to ride or run to be able to watch a 30min program. You would pay a serious sweat premium for surround sound.



Imagine if people took a more active role in the production of their power. There would be a lot more awareness of energy waste, and therefore a lot less of it. We would strive for efficiency in every way.

 

[hjns]

I like your way of thinking. However, I have a little bit of trouble understanding the last statement. I think that from efficiency point of view, humans should NOT "generate" energy, not even when being rewarded with 30 min of TV. The amount of energy it takes (eating, sleeping, etc) in order for us humans to perform any distinguishable action is just not worth it, and efficiency would be expressed in single digits in my case.

I think it is much better to let heavy actions be done with the right equipment. Electricity for lawn-mowers, vacuum suction devices, bikes, cars, etc is much more efficient than walking, cutting gras by hand, or cleaning carpets by hand, let alone generating electricity to power your TV. From a health perspective, you are absolutely correct, and a minimum amount of exercise should be done every day in order to be fit and prevent obesity, which may include actually turning off the TV set (even more efficient). Other than that, I just prefer to enjoy the advantages of technology...

Just my 0.02

 

[strantor]

I like your way of thinking. However, I have a little bit of trouble understanding the last statement. I think that from efficiency point of view, humans should NOT "generate" energy, not even when being rewarded with 30 min of TV. The amount of energy it takes (eating, sleeping, etc) in order for us humans to perform any distinguishable action is just not worth it, and efficiency would be expressed in single digits in my case.

Yes I see I wasn't very clear. My meaning wasn't that we should strive to generate more energy to power our everyday routines, but that, if we were able to make ourselves aware of just how much energy we waste, by comparing what we use to what we are capable of producing, then we might have a greater respect for it, and use less of it. I see a similar thing happen with my wife; she is from another country, where the currency is different. Things cost less there, people make less there. So when she goes shopping and see some shirt she wants and it's 30$, she converts it to her currency and realizes just how expensive it is (that could feed a family of 6, 3 meals/day for a week in her country) and she doesn't buy it. Maybe if people realized when they sit down in front of the big screen, with the surround sound turned up and the lights on the bathroom for no reason, and the computer on, etc. that they would have to pedal a bike for month to keep up with that kind of energy consumption, they would change their ways. Doubtful, becaus cheap energy is abundant right now, but we'll see what happens...

 

[liveforphysics]

1hp means lifting 550lbs upward at 1ft per second.

Its the rate of power a donkey could deliver over an 8hr shift.


Strong big horses can burst >20hp for 10sec bursts.

 

[Architectonic]

Strong big horses can burst >20hp for 10sec bursts.

And a Tour de France sprinter can burst, something like 2 hp for a few seconds?

 

[strantor]

So HP was intended to be averaged over time? Instead of just HP, should it be HPH, like KWH, since we use HP to represent instantaneous power?

While in my quest for for "how much power can a human produce" I ran across someone doing math for the power output of the World's Strongest Man, world record deadlift. They said he put out about 6HP for an instant, and that is the most I've found documented.

 

[Kingfish]

A Horse is a horse of course, of course…
The donkey-hp relationship sounds correct for measurement of typical horse power, although the units were used to compare the output of mechanical power, at the time being steam engines - to draft horses.

OT: My neighbor to the south of me had several Norwegian Draft Horses (unsure of the specific breed), and these were by far the largest horses I had ever seen. They were used in my wedding to pull my future ex-wife to the ceremony. Beautiful blonde… the horses, not the wife. The farmer said he had won “several gold medals” in horse-pulling contests. In retrospect, I should have paid him to haul her away from and not towards the ceremony, but I digress...

Two other strong large breeds are the Clydesdales (think: Clyde River, Glasgow, Scotland) and the Shires (I believe) from the Midlands of England. I can’t find historical references to the Norwegian Draft Horse, but the Clydes are supposed to be descendants of those brought over by invading Vikings (so the story goes). I once observed the same neighbor pull a very large stump out of the ground with his team; very impressive and much more effective than my 15 hp tractor! When I was young and in the YCC, we worked to restore a meadow from water erosion and used a draft team of work horses to haul logs in a place where a tractor would have become bogged down and torn it all to hell. A work crew was blasting the road ahead to make it wider and forgot to tell us; when the blast went, the team broke and jammed the attached log several feet into the side of the embankment (where it remains to this day) and severely bent the steel singletree, rendering it unusable without repair. From that point, the value of biological horse power in the most literal sense was not lost!

To evaluate human wattage in comparison: On level ground, pedal forward whilst effecting Regen Braking and note the reverse current. Try two tests: Consistent for a long distance, and burst mode. That is now your personal measurement of output. Kinda wimpy when you think about it, and not really a good indicator of the potential available. The best use of human wattage is with the brain to figure out mechanical advantage by other means because we are (for good or for bad) the ultimate toolmaker on the planet.

Circling, the OP suggests (if I read it right) that we should be aware of the efficiency of our conveniences in human terms. He’s right, we should. The way we can affect changes in our consumption is to first go out and create the measure of our own personal wattage, then look at the monthly power bill (easiest if all-electric) and divide that into personal human hours and in hp. It is a sobering prospect to be sure. This is why we should instead spend the energy on creative engineering to devise ways that make us more efficient, such as utilizing LCD TVs, convection ovens, heat pumps coupled with radiant floor heating, and um… walking to the markets:

Walking to the market, wearing a backpack, filling it up, and walking home is the most effective use of the food I eat. I might have said that “thinking” was my best use, though I’d wager some might disagree… Walking to feed my face though seems like a safe bet.

Now if I could just figure out how to rub my two hands together to cook the food that would be marvelous.
Conservatively, KF

 

[liveforphysics]

You would use less energy riding your electric bike to the market to shop without taking a single pedal stroke.

 

[veloman]

Yes, I read that one horsepower is the rate of work that one horse can produce all day.

Your numbers of endurance cycling are correct. Now look at world class track cyclist sprinters. The highest recordings are around 2500watts peak - that's for one second. The top of the chart for peak power is 26 watts/kg. I myself like sprinting and trained my peak power a lot, and did reach over 2000watts a few times (measured by a Powertap power meter), which correlated to about 26w/kg, but I weigh less than most track sprinters at 80kg.

We normally hit 1200-1500watt peaks in road cycling racing during a fast acceleration or sprint. The top road sprinters peak around 1800-2000w. Peak wattage doesn't mean much during a 15 second sprint though. It's more about your tactics, timing, and power over the entire sprint. That's where I lost (wasn't a pro), I couldn't hold 1500watts on a flat road sprint long enough. Hill sprints are easier to hold higher power.


My acceleration on my road bike (spandex, pedaling) still embarrasses my respectable 1200watt Mac ebike. 0-20mph in about 2 seconds is mucho fun. :lol:

 

[dogman dan]

Was just about to say just that. Cavendish defintitely puts out at least 2000w at times, but only for about 5 seconds or less.

The duration is cruicial, sprint early at 1500 m, and you will be putting out only 200w by the finish line and come in 50th. That's why Cavendishes lead out train is so deadly, 2 guys also putting out 1500w for 5 seconds, pulling him to that last 50 feet.

Damn impressive though, to see him put out 500w for the last 2k, then still have 2000w for 50 feet! 2k at 500w would put many of us old crocks in the hospital. I call 100w a sprint nowdays.

 

[MidnightRider]

Along the same lines I was wondering how many calories we typically burn in a 1 hour eBike ride with pedaling. Knowing 1 horsepower is equivalent to 746 watts or 2,545 BTU, and 1 BTU is equal to 1,055 joules, or 252 gram-calories or 0.252 food Calories. Presumably, a horse producing 1 horsepower would burn 641 Calories in one hour if it were 100-percent efficient. If we're saying a person is 300-400 watts or about 1/2 a hp then it seems we burn a little over 300 Calories. Not sure that's correct since it seems like I burn more than that on my 55 minute ride to/from work. Also looking at some online Calorie calculators indicate that we burn 600-700 Cals with moderate or vigorous pedaling. Seems that I've lost weight from eBiking 40 miles a day and need to up my Calories to compensate.

 

[veloman]

From what I remember, 300watt hours equals about the same energy as 1200 calories - when produced by a trained competitive cyclist.

So I think it's a 1:4 ratio of watts per calorie.

3 cents in electricity or 1200 calories of food. In food, that would cost me about $6 given my typical average consumption of 2000 calories a day and $70/week on groceries.


Is what's also really amazing about guys like Cavendish is that they are SUPERB endurance athletes FIRST. Then they train their sprint. They are like 99% better than everyone else in these disciplines, at BOTH energy systems. Incredible. What other sport in the world has that sort of combination of explosive power and insane endurance? Sure the time trial guys and climbers are great with endurance, but their sprints are usually lacking in comparison. I remember when I trained endurance, my sprint got dulled. It was definitely hard to keep both up really high.

Dogman, you are right that it's also amazing how they can put out 500watts for minutes before their sprint, AND then unleash their full sprint. In my case, that is where I failed badly - once I got above my lactate threshold in racing, my sprint power was maybe 60% of what it would be if I was aerobic before I did the sprint.

I like events where I do my sprint while fresh. Street sprints, sprint hill climbs (<30seconds), drag races from a light, are my domain. :lol:

 

[Brentis]

I can only bench like 90lbs.
How puny is that?

 

[Dauntless]

You see a lawnmower with a gas engine on it and it says "3hp" on it, you can be sure it's about 50cc. If you looked into that engine they might list the output as "1,200 watts." So you start to think that if you divide the rated wattage by the horsepower, you'll learn how many watts in 1hp. There's just one problem. For reasons I've never understood, they've called every 16cc of a gas engine "1hp" for the longest time, so that "3hp" on your gas lawnmower means NOTHING.

 

[strantor]

I posted this on another forum and got some pretty interesting feedback there as well. I thought I would share it with you guys:

Another thought that puts it in perspective is to consider the energy content of food.

I have long maintained that, while man is real good at making things that can only hold small amounts of energy but can release it really fast, nature is good at just the opposite -- making things that are real good at holding large amounts of energy but only capable of releasing it really slowly.

So I thought I would look up some examples that I've thought about from time to time and run some numbers.

A food calorie (Calorie or kcal) is 4184 J (joules) of energy. Thus, at an average of 9Cal/gm, fat stores approximately 38kJ/g or 38MJ/kg of energy.

A stick of dynamite is generally considered to contain 2.1MJ of energy with a density of about 7.5MJ/kg. Thus the energy density of fat is about five times that of dynamite. Notice that the energy equivalent of a stick of dynamite is almost exactly 500 Calories, which is about the same as a typical king size candy bar. For someone eating the FDA RDA of 2000 Cal/day, this means that they consume the energy equivalent of four sticks of dynamite a day.

Since fat is generally also considered to have 3500 Calories per lb, that means that a pound of fat is equivalent to 7 sticks of dynamite. For someone like me who has, sadly, something in the vicinity of 200lb of excess fat on him (not counting the fat I would still have at a healthy weight), that means that I am carrying around the equivalent of 1400 sticks of dynamite. Imagine if some suicide bomber ever did figure out how to release that energy quickly! And let's not bring this to the attention of DHS or TSA -- if you think the searches at airports were intrusive now!!

The TNT equivalent that we always hear with regards to really big booms is defined such that 1 ton of TNT is 4.184GJ or 1MCal. For someone eating the FDA RDA of 2000 Cal/day, this means that a ton of TNT has the same energy as what they consume in 500 days. But consider that the Hiroshima device (Little Boy) is generally considered to have yielded 15kt of TNT and that the population at the time was in the vicinity of 350,000. That means that the yield per person was about 0.04 tons of TNT, or about 20 days worth of food (on a contemporary American diet, not a wartime Japanese diet).

Thus, the total energy released over Hiroshima was something on the order of the energy released by it's population just in the food they consumed over the prior month.

The weight of Little Boy was just under 10,000 lb, meaning that it yielded about 1.5t of TNT per pound, or about 3.3t/kg, which is 13,800 MJ/kg, or about 363 times the energy density of fat. While, on the one hand, this indicates that man IS capable of cramming more accessible energy into a pound than mother nature, we had to resort to nuclear weapons to do it and, even then, only achieved a few hundred times the density. I wonder what the highest density is with modern weapons?

Now, the smallest nuke that I could find reference to has a yield of as low as 0.3kt of TNT, or about 300kCal, which is then about 85lb of fat. So I'm walking around with a couple of those! And, again, don't even THINK of mentioning this to the TSA! A kiloton of TNT has the same energy as about 285 pounds of fat, so there are definitely people out there walking around with a kiloton weapon on them.

Imagine that someone (perhaps an alien) develops a technology that allows them to irradiate (or use a beam) food in an area such that it releases its food energy on the same timescale as a conventional explosive. Such a beam, in theory, wouldn't require much energy itself since it is merely triggering the release of what is already there. That would make an interesting sci-fi tale. Perhaps it could be a sequel to Mars Attacks and the beam only works on dog biscuits, or tomatoes, or something like that (I don't know what might be a good tie to the movie, since it has to be food and not music recordings).

 

[kevo]

Yes it is quite intimidating how powerful the pros really are.
On the other hand electric bikes rock - levels the playing field