Watts to Horsepower

[SPYDERLK]

746 watts is one horsepower. That might explain why the power meter on my bicycle says it is rare I get over 800 watts. I am not a horse. There are folks who can do twice the watts as me which is not surprising as I am not a powerful fellow. I can't even round up to claim more HP.

There are highly conditioned athletes who can do multi HP for quite a while. The guy who self powered an ultralight [English Channel?] used both legs and arms. I think he hit a peak of 6hp on takeoff.
A horse can do MUCH more than a HP for a short time, but 1HP is what it can do all day with a break for lunch

 

[buickanddeere]

Maybe for a sprint . Even the doped up Lance Armstrong was limited to 2/3HP continuous for hour while biking . Best I ever did was 2.21HP in a sprint up stairs in high school. Did 1/2 HP for 10 minutes a couple of times on the bike but was awful tired and rubber legged afterwards.

 

[SPYDERLK]

Maybe for a sprint . Even the doped up Lance Armstrong was limited to 2/3HP continuous for hour while biking . Best I ever did was 2.21HP in a sprint up stairs in high school. Did 1/2 HP for 10 minutes a couple of times on the bike but was awful tired and rubber legged afterwards.

I guess Im wrong about the HP peak. Cant find anything. I think it was in a long ago Popular Science article on the human powered flights. ... Anyway, I came up with this - it has a video:
Aug. 23, 1977: Pedal-Powered Gossamer Condor Flies Into Record Books | WIRED

 

[CobyRupert]

What? Watt? Nobody's mentioned volt-amps or vars (reactive power), power factor,? The old: Yes you have a beer mug that accepts a certain quantity, but only some of that input (volt-amps =volts x amps) is beer (real power/watts), some is foam (reactive power/vars). The relationship of the mug size to real beer quantity is your power factor.

 

[buickanddeere]

Coby I mentioned reactive power in a prior post

 

[CobyRupert]

Yes. I just saw and was typing: LD1 & BuickandDeere are correct. A motors efficiency in turning the electrical input power into real shaft output power. Some of the input power goes into overcoming friction ( bearings and air gap) and reactive currents flowing around the coils. Wherever you have coils the magnetic fields which run around the conductors interact and cause s resistance. Technically, it's called an impedance.

 

[doxford jim]

There is also the consideration of starting current for motors - which is usually in the area of six times that of the running current. This is needed to get the motor to turn and get it up to rated speed - once there the current then drops to the rated value. Therefore there must be allowances for this higher starter current or the fuses would blow or breakers trip.

 

[buickanddeere]

Yes. I just saw and was typing: LD1 & BuickandDeere are correct. A motors efficiency in turning the electrical input power into real shaft output power. Some of the input power goes into overcoming friction ( bearings and air gap) and reactive currents flowing around the coils. Wherever you have coils the magnetic fields which run around the conductors interact and cause s resistance. Technically, it's called an impedance.

Capacitance, resistance and reactance all impede current flow but they are not the same.

 

[nova3930]

The ratings could also vary based on the difference between peak and RMS voltage in AC electricity

 

[Soundguy]

your question is missing some important variables.

theoreticle vs real world, and friction... and then you get into efficiency.

that's why when you see pto generators for sale. most specify about 2hp per kw as a rule of thumb.

I was reading yesterdays comics when I got to "Non Sequitur" it read - 745.7 watts equals one horsepower. Which is about 6.21 amps. It didn't seem right so I googled it. Well, it looks like it is correct.

So why does my 1hp bench grinder have a decal on it that says it is a 10 amp motor? And the same with my 1.5hp table saw with an 18 amp motor?

Who's right and why do the rules change?