Hi,
I suppose it depends on the alternator.

Is this a renewable energy question? For windmill? Or?

Gary

No easy answer
All are wound differently depending on desired output at different loads and RPM's.
The average 60a could be about 1,400 to 2,000 rpm at shaft to achieve 50% rated output, which on average consumes 3/4 hp.

Like what if I put it on a pedal bike? Saw something like it on tv, but they never went into details about it.

Hmmm.. Sound like you're expecting to get 25-30 amps off a bicycle..not going to happen. You need between 12-15 HP to get 25-30 amps from a 110 volt generator. RPMs are not the only issue...when you talk 'amps', you should really talk 'watts' as that is the true measure of power (watts = amps X volts). Also, when you say 'alternator', are you thinking of using an automobile alternator? Those can provide 30 amps but at 12 volts, 1/10 the power of 30 amps in your house at 120 volts. In addition, the automotive unit includes diodes that rectify the AC to DC. DC isn't too handy, especially at 12 volts.

Nonsense. For anything pedal powered you will NEED to make DC, because you'll need a battery arrangement to buffer/filter it. If you were looking at a direct generation to ac you would have to keep up a steady speed, not very practical.

There may be special alternators built now for alternate power generation, but I would think the vast majority are just repurposed automotive ones.

Looking at it roughly, most car engines idle around 750rpm or so, and idling is not considered adequate to charge a battery with the load of ignition, accessories etc, although I guess a car should be able to run at idle indefinitely, but there would be little or no current left over to charge the battery. A pedal arrangement is not going to be driving much else. So 750rpm is not looking quite so bad. I don't know what the op is looking at doing but say he/she wants to exercise whilst watching tv, and wants an incentive to do so - I've always thought this'd be the perfect system, as you'd need to charge your battery in order to watch.

Either use a 12v tv or a decent inverter that would connect to the battery. Again the battery operates as a buffer.

Looking at a car and most pulley arrangements, the driving pulley on the engine is a fair bit larger than the pulley on the alternator, which means the alternator gets more rpms, of course, at the cost to the engine of more hp needed (no free lunch)

I've attached a spec sheet for Bosch alternators, just the first thing I came across.

Again, don't know what the original poster wants to do. I think you'd be pedalling pretty hard and you'd need an arrangement with a flywheel to smooth out the rpms I guess, looks like you'd need to be pedalling pretty hard but depending on what you want to do, it's possible I guess. If you're looking at some sort of off-grid application, it could only be a supplement unless you're talking about charging a cellphone or laptop or something.

The best sorts of alternative energy setups that I know of are a bit diversified for stability, ie, a mixture of wind and solar, if possible. A bike could be a possibility but it'd be like chopping wood - it warms you at least twice ;)

Here is a link that might be useful: Bosch alternators

PJB... I was looking at both his posts where he mentioned 25-30 amps and the bicycle idea. Those together don't work... My point was the bike wasn't going to provide the power he seemed to be looking for...It takes a lot of work to turn a generator/alternator connected to a load. True you can use the bike to charge a battery then use an inverter but you are still talking about a very small amount of generated power. Right now any alternative source is still trumped by increasing how efficiently you use energy...you never realize how cheap the power company is providing power until you try to make it yourself.

That is very true, and I guess the major reason change is slow to come.

When generating any power from mechanical energy in to electrical energy, 1 horse power is 746 watts of power.
When turning ac generators at 110v at 30 amps, this is ((110*30)/746)=4.42 hp, but this is only the power you put in to get out. One thing people forget is the amount of power needed to get up to the 3600 rpm's needed to get 60hz (3600/60)=60hz.
A average 5kw will need about 10 hp to keep up with loads and rpm's.(5000/746)=6.7hp . It takes about 1.2hp just to turn a generator at the speed of 3600 rpm's, the extra hp is call peek output.

30 amps alternator with a output say 13v is (30*13)=390 watts
390/746=.52hp at 1200 rpms you will need a constant torque of (5252/1200)*.52=2.28 foot pounds or 27.31in/lb at 1200 rpm's

Don't keep fixating on the theoretical by-the-book math. In the real world, you'll need a 12-15HP motor to provide a usable 30 amps since that 30 amp load is going to also need some more ummph to get whatever it is going. There is so much efficiency lost in all the converting, whether from gas engine to electric output or 12 volts DC from an alternator (one conversion there already) to an inverter to provide 110AC. Again, most activity directed at alternate energy would be put to better use tweaking the final load's efficiency. We need a real breakthru such as EEstor or NanoSolar before the alternate energy scenario becomes really cost effective. Irritates me so seeing reporting on some yahoo spending 100K and having an energy hog house completely offline. Why? He could have spent a fraction of that on practical, efficiency-boosting strategies, and paid the remaing power bill on just the interest of the money he had left.

i know for a fact that if u give alittle back to the prosess thats giving it will continue to do so and ive built a happy all electric generator and i want to sell it

Not less than 1500 rpms, but it's beter to be about 3000 rpms, the alternator generates power at any speed, even less than that .. OK

On the average the alternator runs two to three times faster
then the engine. If you notice that the lights dim when idling
then you need a little more rpm to get the alternator to charge above the battery voltage. About 13.5 volts. The average alternator is now between 1,300 to 2,100 rpm.
I set up an old 35 amp alternator to run off a 1/3 hp 1,750 rpm washing machine motor at a 1:1 belt ratio. Using the stock regulator would stall the 1/3hp motor. I put a large adjustable resister on the field connection of the alternator. The output was adjusted by the field resister so the motor would start charging a low battery and not get too hot. This was about 20 amps in my case.
A human can only put out about 1/4 hp. So that would be about 14 amp. How long could the average humane do this?
I would guess about 5 minuets. 13.5v x 14 amp = 189 watts or about 1/4 hp.

If I connect the alternator to the rare wheel of an two wheeler bike can it generate 48v current

What I have in mind is to use a small Solar or Wind generator or both to run a 1500w inverter. I would then use the power from the inverter to run a 5 - 10 hp electric motor. I would then use the electric motor to run a series of alternators (say about 5 - 10). Each alternator would charge a seperate 12 battery. Each 12 volt battery would run a seperate 8000w - 10000w inverter. I would then connect each inverter to seperate breakers in my electric panel. This systen would cost me less than $10,000.00 and should in theory supply all the electricity I consume monthly. My question is what are the technical challenges that could undermine my theory.

Basic math problem: you want to power 5 to 10 inverters, each with a capacity of 8-10 kW. This means you presumably want a total output power of from 40kW to 100kW.

But you want to use a 5-10 HP motor to drive alternators producing 40-100kW. Ten HP is about 7.5kW. Not possible. You can't get out more than you put in.

And you want to run the 7.5kW (7500 Watt) motor driving the alternators charging the batteries powering the inverters with a 1.5kW (1500 Watt) inverter. Not possible. Again, you can't get more out than you put in.

Basic electrical problem: you can't just connect 5-10 cheap DC to AC inverters in parallel (through breakers into a power panel). Their waveforms won't sync up. The most likely result will be blown inverters. You could have an explosion and/or fire.

You might be able to do this with grid-tie inverters -- if you can solve the above problem. But they're not going to be cheap.

Even if you can solve those problems, I'm sorry to say that this idea still isn't practical. You'll lose big time on (in)efficiency.

If your inverters are top quality (expensive) ones, each will lose only 5-15% of the energy in conversion. But my guess is that you're looking for a low cost fix, so you'll probably use Chinese Cheapies. These simple "modified sine" (really modified square wave) inverters are designed for the lowest possible price, not for efficiency. Typical efficiency is poor, 65-75%.

Large, expensive motors can get well into the 90s for efficiency, but a typical mass produced induction motor (think circular saw or washing machine) will be 75-85% efficient (losing 15-25% of its input as heat) at full load. When powered from the crummy waveform a cheap inverter produces, it'll be even less efficient.

I assume you want to use vehicle alternators -- again, they're cheap. For the automakers, low cost is everything. They don't care about efficiency. Typical auto and light truck factory alternator losses run 40% (60% efficiency).

The charging efficiency of a lead battery can be 95% when it's charged with a really good charger. But your alternators won't come close to that. Most likely they'll overcharge your batteries, wasting at least 20-40% of the energy they produce.

Then you lose another 25-35% with another cheap inverter downstream of the batteries.

So let's look at the bottom line, with cheap inverters and automotive alternators. As an example, we'll start with 100 Watt hours of energy produced by your PV or wind machine.

100 Wh * 70% efficient inverter == 70 Wh to motor
70 Wh * 75% efficient motor == 52.5 Wh to alternator
52.5 Wh * 60% efficient alternator == 31.5 Wh to battery
31.5 Wh * 80% efficient battery charging efficiency == 25.2 Wh to inverter
25.2 Wh * 70% efficient inverter == 17.6 Wh available for use

So, overall, your system -- even if it worked without blowing up -- would be only 17.6% efficient. It would lose over 80% of the energy it produced before you could do anything with that energy!

The problem is all those conversions -- from DC to AC in the first inverter, from electrical to mechanical energy in the motor, back to electrical energy in the alternators, from AC to DC (also in the alternators), then from DC to AC (in the inverters). You lose energy at every conversion.

Ideally, you'd use the energy your PV and wind machine produce directly. That's often impractical, but there's plenty of good quality commercial renewable energy gear available. A typical brand name PV inverter runs at 90-95% efficiency.

Of course, it might cost more than your idea would -- or it might not, especially if you buy used gear. In any case, you'll save money on the PV panels and wind machines by not needing as many for a given amount of usable energy.

Sometimes the standard solution really is the most practical and most affordable one.

DavidR, thank you for your insight in response to my inquiry. Thanks also for this information about effiency ratio etc. Notwithstanding, I am still a practical guy and I am also aware that there have many things that could not have been done until they were done for the first time.

Now back to the matter of the use of regular automobile alternators to charge my batteries - I can always upgrade to more efficient one as required. These were designed to charge the battery at a given rate providing that the required RPM was is met.

If I ensure that each alternator is rotating at the required RPM, I see no reason why each battery should not be charged at the requisite level to keep the Inverter running at the maximum efficiency that can be epected for that particular Inverter. It seem that my real problem is to ensure that I have an efficient electrical motor to turn my alternators at the RMP required.

If I slove the problem of the electric motor, I would then have to turn my attention to the source of energy that I need to keep that motor running at maximum capacity. That would mean ensuring that my solar panel and/or wind source has/have the capacity to keep the motor running.

This is my thinking without the technical knowledge (such as you possess) in support of this theory. Where do I fatler technically on this issue? I would further appreciate any added insight you may be able to offer before I dive into it and make a very costly mistake.

What else can I say? Build it and see what happens.

But read my caution above about the inverters. I'm not responsible for any strange or bad things that happen if you ignore that advice.

DavidR, I appreciate your advise, I really do. I am just trying to find an answer to a once "impossible" situation.

Thank you for your input my friend. Will let you know about all the pitfalls and mishaps. If there's anything new I learn, I will share that also.

DavidR, you suggested that I would run into problem wiht my plan to attach each inverter to my grid seperately. If I were using more than one inverter, without a grid tie inverter, how do you suggest that multiple inverters could be tied into your grid?

Your inverters need to be able to synchronize their output waveforms. Grid tie inverters do this by "watching" each other (actually, they all watch the grid, and sync to that).

If you're not going to use grid tie inverters, you need stackable inverters. These are designed specifically to be connected in parallel (for more current) or series (for more voltage). They have communication links so they can talk to each other and synchronize their waveforms.

A web search will turn up some manufacturers, including Chinese companies of unknown reputation, if that's your speed. Be sure you follow the manufacturer's instructions for stacking your inverters.

You seem to have your heart set on doing this, so let me remind you one more time not to put the cart before the horse.

Right now, you shouldn't be worrying about how to couple your PV or wind output to your home electrical system. That should be way down your list.

First, you need to figure out how much energy you really use in a typical month.

Then, you need to figure out how many PV panels or wind machines you need to supply that much energy. Worry about peak power later.

Most likely, your next step will be to figure out how to reduce your energy use, to make your solar or wind system practical and affordable.

But just for fun, let's see what it would take to give you a system capable of supplying 40kW from solar panels, using the power conversion system you've described.

Because your proposed system has low efficiency, less than 20%, you need 5 times as much power going in as you want to get out. So you need enough solar panels to supply 200,000 Watts.

That's one heck of a lot of solar panels.

For example, let's consider the LG 335N1C panel. It's rated to produce 335 watts. That's at high noon under a clear sky, and most of the day it will output much less. But to make the math easy, we'll make believe that it's high noon all day long where you live.

This panel is 67" x 40", weighs 40lb., and costs $380 here. (The link is meant as an example, and is not an endorsement of the product or vendor.)

For 40kW at your distribution panel, you'll need (200,000 / 335) = 597 of those panels.

Time for a reality check.

1. Do you have a south-facing roof that's 11,100 square feet? That would require a one-story home (30 degree roof) of about 19,000 square feet, or a two-story home (45 degree roof) of about 32,000 square feet. (The average US home is 2,600 square feet.)

2. Can your roof support an extra 12 tons?

3. Can you find $226,860.00 to pay for those solar panels? (I guess that if you have a 19,000 - 32,000 square foot house, you probably can. :)

You are certainly giving me a harsh dose of reality but I am stubborn, I will keep pushing until I find an affordable solution. Thank you David.

Hello. Please is it real about self running generator, i yes, I have a 50kW brushless alternator that I want to use as a self run generator to supply electricity for my village people, how many kW motor do i need to run it to give out power that will be able to supply itself and at the same time giving current to my people. Thanks in advanced.