Hi I'm a Quebecer, silly question but I know a (random figure) 500watt vehicle alternator must spin for at least 1 hour to actually deliver said 500 watts, may I ask how fast it needs to spin to achieve that ? I believe a car engine typically goes 800 rpm on idle and higher rpm the faster it gets, please forgive me if this is a dumb question but I want to learn.

 

I know a (random figure) 500watt vehicle alternator must spin for at least 1 hour to actually deliver said 500 watts

Eh? The time it runs for is irrelevant. If it's producing 500W then its doing that on an on-going basis.
And there's no 'one-size-fits-all' answer to your question. Different alternators produce their rated outputs at different rpm. You need to check the manufacturer's manuals/datasheets.

 

And another thing, if the engine is running at 800 rpm, how fast is the alternator turning?

 

And another thing, if the engine is running at 800 rpm, how fast is the alternator turning?

well typically the drivebelt turns at the same speed as the crankshaft i guess

so.. no way to produce 500 watts with lets say a bicycle wheel and a belt ???? or hell even hand crank ?

 

so.. no way to produce 500 watts with lets say a bicycle wheel and a belt ???? or hell even hand crank ?

Absolutely no way. Even an Olympic athlete couldn't do that for any useful amount of time.

 

On every car I have ever seen, the diameter of the alternator pulley is smaller than that of the crankshaft pulley. I would guess about a 1:2 ratio. Hence at 800 rpm, the alternator is rotating at about 1600 rpm. By the laws of electromagnetic induction, it is the rpm that matters, not the number of rotations.

 

gotcha,,, and if i use a bicycle with a belt and different sized gears ???? or should i use a DC generator instead ??? i just want to fill 2 batteries that are parallel linked in 2 hours so that i can have 1200 watts at my disposal

 

gotcha,,, and if i use a bicycle with a belt and different sized gears ???? or should i use a DC generator instead ??? i just want to fill 2 batteries that are parallel linked in 2 hours so that i can have 1200 watts at my disposal

I suggest that you revisit this topic when you have thoroughly understood the difference between power and energy.
If you charge a 1000uF capacitor to 12V then you can have 1200W available, but only for 60us.
Energy is the amount of work done.
Power is the rate of doing work.
Hence Energy = Power x Time.

 

You are confusing power and energy.
Power (watts) is the instantaneous amount of energy delivered.
What you want is energy, which is power x time, in units of watt-hours.

If you want 1200 watts for 2 hours, that is 2400 watt-hours.

A typical alternator running at 2000 rpm could generate 100 A @ 12 V = 1200 W.
You would have to run the alternator for 2 hours to generate 2400 watt-hours of energy.

How much power can a cyclist generate assuming 80% efficiency of converting mechanical energy to electrical energy?
An average cyclist can generate 100 W of electrical power. The cyclist would have to pedal a full 24-hour day in order to generate 2400 watt-hours of energy.

In other words, the cyclist would have to pedal a full 24 hours in order to generate 2 hours of 1200 W power.

 

If You can't find at least hundreds of examples of other people doing what You want to accomplish,
then the first thing You must do is ask yourself Why.

There is no such thing as a "Free-Lunch",
somebody, or something, paid for that Lunch,
and they paid for that Lunch with more Energy than the Lunch will result in by being eaten.
.
.
.

 

You are confusing power and energy.
Power (watts) is the instantaneous amount of energy delivered.
What you want is energy, which is power x time, in units of watt-hours.

If you want 1200 watts for 2 hours, that is 2400 watt-hours.

A typical alternator running at 2000 rpm could generate 100 A @ 12 V = 1200 W.
You would have to run the alternator for 2 hours to generate 2400 watt-hours of energy.

How much power can a cyclist generate assuming 80% efficiency of converting mechanical energy to electrical energy?
An average cyclist can generate 100 W of electrical power. The cyclist would have to pedal a full 24-hour day in order to generate 2400 watt-hours of energy.

In other words, the cyclist would have to pedal a full 24 hours in order to generate 2 hours of 1200 W power.

i got it thank you... and what i remember from basic Tesla claas in elementary is that watts is a combinatino of volts and amps....

so here goes anotgher question.. those wind thingies... wind generator ? generator spun by the wind.. if its rated at 400 watts... and if the wind isnt very strong... but its still making 360 degree rotations... can it in fact produce 400 watts at lower wind speeds ? , not certain if a wind generator has an alternator or dc generator inside... letgs say generator, i guess what im asking is, what can i do for 1 hour to produce 1000 watts so that my computer can run on for at least 5-10 hours.... i have 2 batteries linked in parallel.. totalling 1200 watts in capacity (each battery is 12v 50ah)

yes of course i can do solar... Philippines has a crap ton of sun .. and i have 1 solar panel that peaks at 320 watts and its quite big... i rent here in the Philippines and my large solar panel took alot of convincing to get up there.. landlord isnt a chipper dude...

and of course im not a young guy, i cant pedal for 24 hours

 

If 400W is the RATED OUTPUT, then It will produce 400W at its RATED SPEED.
The energy in the wind is proportional to the cube of wind speed,
so when the wind speed is HALF the RATED SPEED, then the output is ONE EIGHTH of the RATED OUTPUT.

 

what can i do for 1 hour to produce 1000 watts

If you are talking about using your muscles to produce that power — you cannot.

 

You are still making the same mistake.
Each 12 V battery does not have 600 watts in capacity. It has 600 watt-hours capacity.
Hence, theoretically, it can deliver 50 A @ 12 V for one hour, or 5 A @ 12 V for 10 hours, in other words, 60 W for 10 hours.

Assuming 100% efficiency, which it is not, in order to recharge the battery in one hour, you would have to replace the energy with the same amount, i.e. 600 W for one hour. You would need 12 average cyclists pedaling for one hour to generate 1200 watts.

 

i have 2 batteries linked in parallel.. totalling 1200 watts in capacity

You are still confusing power with energy (power x time).
The battery capacity is 1200 Watt-hours (energy), not 1200 Watts (power).
Taking the post #9 figure of 100 Watts as an example of human power possible, it would take 1200Wh/100W = 12 hours to fully charge those batteries. By which time you would have totally drained your own energy! Or else you would have some very unhappy cyclists.

 

If you are talking about using your muscles to produce that power — you cannot.

hey bud long time no see

 

You are still making the same mistake.
Each 12 V battery does not have 600 watts in capacity. It has 600 watt-hours capacity.
Hence, theoretically, it can deliver 50 A @ 12 V for one hour, or 5 A @ 12 V for 10 hours, in other words, 60 W for 10 hours.

Assuming 100% efficiency, which it is not, in order to recharge the battery in one hour, you would have to replace the energy with the same amount, i.e. 600 W for one hour. You would need 12 average cyclists pedaling for one hour to generate 1200 watts.

thank you for the correction.. i was hoping to add a 3rd battery 600 ah in capacity.. but that is hefty and pricy so no hurry

 

You are still confusing power with energy (power x time).
The battery capacity is 1200 Watt-hours (energy), not 1200 Watts (power).
Taking the post #9 figure of 100 Watts as an example of human power possible, it would take 1200Wh/100W = 12 hours to fully charge those batteries. By which time you would have totally drained your own energy! Or else you would have some very unhappy cyclists.

thank you for the correction.. i kind of saw watts as fluid in a bottle that you cam consume it at any speed... so.. i guess the only time i can draw from the battery is when the solar panel is giving me the 200 watts that i need.. i just need to wait for a functional pwm.. the fake mppt that i got , i cannot set the stop charging voltage to 14.3v

 

hey bud long time no see

Sure, but could you answer the implied question? Where is the mechanical power to run this generator coming from?

 

thank you for the correction.. i kind of saw watts as fluid in a bottle that you cam consume it at any speed...

If you want to use the fluid analogy, which is usually grossly inadequate, think of fluid in a tank as charge (in coulombs), not power in watts. What comes out of the tap is coulombs per second, or amps. Now imagine the the tap is connected to a pressure washer which can blast you and peel your skin off your body quickly depending on the pressure (volts). Now that is power in watts, which is volts times amps.

Energy is power multiplied by time, i.e. power times how long it takes to peel your skin off your body.