How to specify an electric alternator....

[Rakesh bhatoa]

how we can specify an alternator (which converts rotational energy into electricity) .
how we can calculate the charge given out by alternator in its one revolution .

 

[anorlunda]

Most generators are efficient, so the easiest approximate calculation is electric power out = mechanical power in.

Charge is not power. Electric power is measured in watts and calculated from voltage times current. Mechanical power is calculated from torque times speed.

 

[Rakesh bhatoa]

If we gives the supply of alternator ( which should fitted in a bike) to a heating coil ,then is it possible to produce 250 joule of heat in 4 revolution of alternator

 

[anorlunda]

If we gives the supply of alternator ( which should fitted in a bike) to a heating coil ,then is it possible to produce 250 joule of heat in 4 revolution of alternator

One watt of power is one joule per second. So if your bike pedal rotates once per second, 4 seconds in 4 revolutions, then 250 joules/4 seconds is 62.5 watts. Yes that is possible. See https://en.m.wikipedia.org/wiki/Bicycle_performance

But the alternator is probably connected to the bicycle by a belt or chain so that the alternator makes several revolutions per one bike pedal revolution.

 

[Rakesh bhatoa]

Thanks Sir for reply , I have one another question ,if i use 24 volt 45 ampere alternator then what will be the resistance should the heating coil be provided with , so that it should produce 250 joule of heat in four revolution of alternator, please show me the calculations also sir.

 

[anorlunda]

62.5 watts / 24 volts = 2.6 amps.

24 volts / 2.6 amps = 9.2 Ohms resistance

But I suspect that my answers are not helpful because you asked the wrong questions. Please tell us what you are trying to accomplish. We will try to help. For example, why 250 joules in 4 revolutions?

 

[Rakesh bhatoa]

Sir, i want to supply 250 joule of heat to the air (at constant volume) by electric means, in maximum 4 revolution of an alternator.This is the part of my project about which i m just thinking

 

[Rakesh bhatoa]

Sir,why did you say "my answers are not helpful for you" and what is the meaning of "45 ampere " in alternator specification(in my question)?

 

[anorlunda]

Sir,why did you say "my answers are not helpful for you" and what is the meaning of "45 ampere " in alternator specification(in my question)?

45 amperes is the maximum current the alternator can supply. You don't need that much.

250 joules in 4 revolutions is a strange requirement. Most people need either

1. specific energy (a joule is a measure of energy) to do something like charge a battery. The number of revolutions is not relevant.
2. Or a specific power (measured in joules per second) to do something like supply a light. Pedaling continues as long as power is needed.

Can you explain why 250 joules in 4 revolutions is your requirement?

 

[Rakesh bhatoa]

45 amperes is the maximum current the alternator can supply. You don't need that much.

250 joules in 4 revolutions is a strange requirement. Most people need either

1. specific energy (a joule is a measure of energy) to do something like charge a battery. The number of revolutions is not relevant.
2. Or a specific power (measured in joules per second) to do something like supply a light. Pedaling continues as long as power is needed.

Can you explain why 250 joules in 4 revolutions is your requirement?

sir,i m trying to prepare an engine that will run on air only..

 

[Rakesh bhatoa]

sir,i m trying to prepare an engine that will run on air only..

sir, Is there an effect of time of completion of one revolution on heat energy produced in one revolution.Example ,Is the one revoluiton taking place in 4 sec will give the same heat energy that is provided in one revolution which is taking place in half ( .5 ) second ?

 

[Averagesupernova]

sir,i m trying to prepare an engine that will run on air only..

Compressed air? Tell us more about this engine.

 

[Rakesh bhatoa]

Compressed air? Tell us more about this engine.

Sir read the patents of guy negre on compressed air engine

 

[Rakesh bhatoa]

Sir read the patents of guy negre on compressed air engine

I m using guy negre's concept

 

[Rakesh bhatoa]

I m using guy negre's concept

I m using guy negre's concept

Please answer my question ,anorlunda sir

 

[anorlunda]

sir, Is there an effect of time of completion of one revolution on heat energy produced in one revolution.Example ,Is the one revoluiton taking place in 4 sec will give the same heat energy that is provided in one revolution which is taking place in half ( .5 ) second ?

You need only a small fraction of the rated output. Minimum speed for many alternators is about 1000 RPM. So, yes there is a time effect, one revolution should be completed in less than 0.06 seconds.

Once again, your requirements and your numbers sound unusual and far from reality. The quality of the answers we are able to give you are proportional to the information you are willing to share with us.

Below is a sample alternator performance curve. Note that the key input parameter is not revolutions but revolutions per second, and the key output parameter is not joules but joules per second (watts=joules per second=volts*amps).

 

[Rakesh bhatoa]

You need only a small fraction of the rated output. Minimum speed for many alternators is about 1000 RPM. So, yes there is a time effect, one revolution should be completed in less than 0.06 seconds.

Once again, your requirements and your numbers sound unusual and far from reality. The quality of the answers we are able to give you are proportional to the information you are willing to share with us.

Below is a sample alternator performance curve. Note that the key input parameter is not revolutions but revolutions per second, and the key output parameter is not joules but joules per second (watts=joules per second=volts*amps).

Thnx sir for helping me to understand alternators

 

[Rakesh bhatoa]

Thnx sir for helping me to understand alternators

sir, the project i m thinking is an engine that works on air only .in this engine the air is sucked in the down stroke of the piston ,the air is compressod in the later stroke (air becomes at high pressure),now this pressurised air is supplied to a pre chamber ,the pre chamber will then fully closed , the heat is supplied to the air at the constant volume in the pre chamber ,thus the air is further pressurised upto desired pressure,then this high pressurised air will then supplied to the main engine which give us the rotational power which is used to rotate the tyres of the vehicle ,Now the power of an engine is also supplied to an alternator whose power is supplied to heating element which is fitted in pre chamber to heat the air ,the gear ratio b\w engine and the alternator is set such that in one revolution of engine there are four revolutions of alternator. I required the heat upto 250 joules in the pre chamber in one revolution of engine (or in four revolution of an alternator).Sir this is the thing i want to do...so sir just help me that ,how can i produce this 250 joules of heat (in four revolution of an pertucular aternator)

 

[Rakesh bhatoa]

sir, in graphs that you send what is the meaning of 12volt

 

[anorlunda]

sir, the project i m thinking is an engine that works on air only .in this engine the air is sucked in the down stroke of the piston ,the air is compressod in the later stroke (air becomes at high pressure),now this pressurised air is supplied to a pre chamber ,the pre chamber will then fully closed , the heat is supplied to the air at the constant volume in the pre chamber ,thus the air is further pressurised upto desired pressure,then this high pressurised air will then supplied to the main engine which give us the rotational power which is used to rotate the tyres of the vehicle ,Now the power of an engine is also supplied to an alternator whose power is supplied to heating element which is fitted in pre chamber to heat the air ,the gear ratio b\w engine and the alternator is set such that in one revolution of engine there are four revolutions of alternator. I required the heat upto 250 joules in the pre chamber in one revolution of engine (or in four revolution of an alternator).Sir this is the thing i want to do...so sir just help me that ,how can i produce this 250 joules of heat (in four revolution of an pertucular aternator)

Oh dear, I'm afraid that your project resembles "perpetual motion or free energy ideas", because it would violate the second law of thermodynamics. Those topics are forbidden here on Physics Forums, and the mentors may close this thread.

 

[Averagesupernova]

Somehow I had a feeling that is where this was going. Look into a sterling engine. These are fairly efficient external combustion heat engines. The heat source does not matter. However, you will NEVER get more heat energy out of a generator running a heating element than what the engine requires to turn said generator. Look into these engines since there is a lot of information out there in real actual numbers about their efficiency that you can apply to real actual numbers about the efficiency of alternators. From here you will see that what you are trying to do is not possible. I am surprised this thread was not closed before I posted this.

 

[RonL]

Sir read the patents of guy negre on compressed air engine

I for one think you are looking in the correct area of compressed air, but I feel you need to expand your knowledge base about "heat from electric" best wishes in your thoughts. Lots of study material on the net, wiki might be the best start and as you learn, go to more detailed sites.

 

[Rakesh bhatoa]

Oh dear, I'm afraid that your project resembles "perpetual motion or free energy ideas", because it would violate the second law of thermodynamics. Those topics are forbidden here on Physics Forums, and the mentors may close this thread.

Oh dear, I'm afraid that your project resembles "perpetual motion or free energy ideas", because it would violate the second law of thermodynamics. Those topics are forbidden here on Physics Forums, and the mentors may close this thread.

ok sir , but what is meant 12 volt in graph?

 

[Averagesupernova]

ok sir , but what is meant 12 volt in graph?

It means exactly what it says. 12 volts. What good is a specification sheet if there is no reference to voltage? According to the graph, when the shaft speed hits 5000 RPM the alternator is able to supply about 90 amps at 12 volts. This is about 1080 watts. If the voltage were specified at 5 volts then the output would only be about 450 watts. The voltage regulator that exists in the alternator is responsible for maintaining the voltage at around 12 volts. Typically an automotive alternator regulates at about 14.25 volts.

 

[Rakesh bhatoa]

Sir ,it means voltage varries as the rpm varries (1000 to 5000) or alternator does not supply the current at single voltage (12 v) with varrying rpm?

 

[Averagesupernova]

A modern automotive alternator with a built in voltage regulator will supply a constant voltage over an RPM range. The current supplied depends upon the load. As per the graph, there is only a certain RPM range that the alternator is able to supply a given amount of current.

 

[Rakesh bhatoa]

Sir, i have a new design of engine (not a piston cylinder arrangement) which can produce work output of 55Nm in one revolution of the cranck shaft if we supply the air at 6 bar ,1200 degree celsius,having volm of 100cc, assuming that the air will expand isentropicaly in engine( index of expansion is 1.4, neglecting the heat losses ) which is enough to run a bike , a hero splender bike produce maximum work of 60 Nm in one revolution of cranck shaft (12 bhp at 8000rpm), sir the only thing is ,I have supply 150 to 250 joule of heat energy to air at constant volume to increase its pressure , Sir suggest me the way how can i supply this heat energy to air (only by electric means)

 

[Averagesupernova]

No. Do this work yourself. This forum is about helping people who are willing to help themselves. It is geared towards helping students with coursework and getting feedback from them in a positive forward moving manner. You have been told that using an engine to spin an alternator which generates electricity which in turn is used to heat the air to power this engine is impossible and against forum rules to discuss it. I suggested you research sterling engines and alternator efficiencies to realize what you are attempting is impossible based on accepted and established specs of these machines. You appear to have done nothing of the sort. You continue to ask questions about alternators and in a roundabout way trying to get a one answer solution without understanding any of the details. It is pretty clear that you do not understand the relationship between voltage and current with regards to the load connected. You have been given most of the answers you need in this thread if you bother to understand the relationship between watts, joules, ohms, amps, volts, etc. I suspect you do not understand that by loading an alternator with a heating element you will require more torque to maintain the rotational speed of the alternator. This torque must come from the engine that is turning it. Where will this torque come from? If you want a simple answer from me to this:

Sir suggest me the way how can i supply this heat energy to air (only by electric means)

then I will tell you to run a gasoline engine that turns an alternator which generates electricity that runs a heating element that heats the air in your so-called engine. Seems rather silly doesn't it?

 

[Rakesh bhatoa]

Sorry, for the sillyness, Sir. And thanks for the answers

 

[berkeman]

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