Design a 30KW Generator: RPM 120-200, Carbon Fibre Components

[sahil2309]

i'm looking to design a generator, can someone just help me out, the following are the main criterias:
It'll have a power rating 30KW
RPM like between 120-200, so basically its a low RPM design;
i plan on using Carbon fibre for all the components on the rotor other than the power generating components.....should basically give very low inertia for the same structural strength as steel...
also can someone tell me how to determine the power rating of the generator based on the magnets and copper windings?

 

[Crazymechanic]

Sahil I don't want to sound rude but do you have built something on the scale of this before?
Also you should realize that the power level 30KW is something one just doesn't build in his home.Devices like these are built in factories by people who have experience and designed by people who have even more of that.

Can I ask you why and for what are you building this?

Also carbon fiber is a dielectric , which means it doesn't conduct electricity and doesn't have magnetic properties , do you know how generators work? The rotor has to be made out of materials that have electromagnetic properties like copper wires and stainless steel armature and so on.You can't make a rotor with carbon because the metal armature in the rotor is what helps to make the induced magnetic field stronger , carbon will not do this and the generator will be with poor efficiency.If any at all.
The wires are moving around in a magnetic field which induces current in them .The basic principle of a generator/electromotor.

If you haven't built anything like this before I suggest to start with a low power 1-2kw generator to understand the working principle and see how it all goes together.You can make a generator out of an old electric motor.

 

[sahil2309]

Hey... Yeah I get what your trying to tell me but can I use carbon fibre In places like the structure to support the magnets?

 

[sahil2309]

And also can you help me design a 2 kw generator?

 

[sahil2309]

Well yeah actually I'm not going to build this at home, like ill get it built buy a manufacturer but I just want to know whether it is possible to reduce the weight and inertia of the rotor by substituting components of the rotor that do not contribute in producing the magnetic field from steel to carbon fibre (eg. Rotor shaft, the frame that holds the magnet in place, etc.) also for my requirements, the copper windings would be on the stator where as the rotor will have the magnets...

 

[Lsos]

Well yeah actually I'm not going to build this at home, like ill get it built by a manufacturer but I just want to know whether it is possible to reduce the weight and inertia of the rotor by substituting components of the rotor that do not contribute in producing the magnetic field from steel to carbon fibre (eg. Rotor shaft, the frame that holds d magnet in place, etc.) also for my requirements, the copper windings would be on the stator where as the rotor will have the magnets...

You probably CAN reduce the inertia, but I'll guess from my limited knowledge that the electrically conductive/ magnetic portion is by far the heaviest part of the generator. And carbon fiber is expensive. You'll probably increase the cost of a normal generator by a large amount for an insignificant loss of mass and/or inertia.

 

[sahil2309]

What percentage of the rotor inertia does the magnet contribute ( on a rough estimate)

 

[cjl]

Also, why are you trying to reduce the inertia? Most generators operate at a constant RPM, so low inertia wouldn't really give any benefit. Once at speed, assuming you use decent bearings, almost 100% of the resistance to turning the generator would come from the magnetic field itself, so all you would achieve with a low-mass design would be to make it substantially more expensive for almost no benefit. Also, a custom manufactured generator would be very expensive - you would probably be better off just buying a commercial generator of the size you need.

 

[sahil2309]

Yeah... Ohhh but is there anyway where I can reduce the input power required to get the rotor moving for the same level of output? Like someway of increasing mechanical advantage or something ?

 

[cjl]

You're basically looking to increase the efficiency, and large generators (admittedly much larger than you're looking at here) can already hit 98%, so there isn't a whole lot to be gained here. What's your application?

 

[sahil2309]

Just want to use an electric motor of lower power rating to get thing moving and harness the surplus power generated...

 

[Crazymechanic]

there is pretty much nothing to take away from the rotor as it has to be 95% metal or metal alloy and copper.Also the 98/99% of the power needed to turn the rotor is opposed or consumed by the magnetic field which actually induced the current in the windings.Only I think like 1% would be due to friction in bearings (assuming they are lubricated and new)

Sahil I think you need to read up about classical physics , electromagnetism , generator / electric motor working principles.
Now I hope you do understand english pretty ok I have some old but very informative videos about this topic.Remember in the generator motor part there are no fundamentally new things so things discovered 50/60 years ago still apply just as back then as now.









Now watch these and you will be better off if you will pay attention to what is said there.

 

[sahil2309]

Hey ill have a look at then and will revert back if I come up with any queries... Btw I'm not pursuing science... I'm a commerce student planning to pursue MBA this year

 

[Crazymechanic]

""""Just want to use an electric motor of lower power rating to get thing moving and harness the surplus power generated... """"" Now I see what your talking about.Probably you have watched some "free energy videos" on youtube or something like that.

Sahil even though many of those people who either because their very uneducated or just fanatically crazy say that mainstream physics is lying about the fact that there is no free energy , I must admit there really is NO FREE ENERGY.
When I was very little I though that one can get free energy but the truth is I grew up and learned that well , you can't.

the motor that will drive the generator will use power , the more load you will put on the generator the more power will be taken to drive it.magnetic field doesn't go for free it tries to stop the generator rotor from moving.It's like arm wrestling you can't win a opponent with a weaker arm, the power doesn't come from "thin air" you have to supply the power to overcome the resistance.

 

[gerbi]

Using carbon fibre in rotor ? Well.. I hope you have any clue what are drawbacks of this idea.
Rotor is quite complex in design, it's not flat like many carbon fibre elements. It has directional mechanical proporties, which can be quite dangerous because many forces are acting in rotor while it is working in the machine. In addition, I'm not so sure about this reducing inertia idea - benefits from it are not worth pursuing it in my opinion.

Second thing, You said you're not familiar with engineering.. please, gain some knowledge in this matter. It's not that easy like "I have an idea, let's do it". You will be wasting your time without deeper understanding of matter discussed here.

 

[sahil2309]

""""Just want to use an electric motor of lower power rating to get thing moving and harness the surplus power generated... """"" Now I see what your talking about.Probably you have watched some "free energy videos" on youtube or something like that.

Sahil even though many of those people who either because their very uneducated or just fanatically crazy say that mainstream physics is lying about the fact that there is no free energy , I must admit there really is NO FREE ENERGY.
When I was very little I though that one can get free energy but the truth is I grew up and learned that well , you can't.

the motor that will drive the generator will use power , the more load you will put on the generator the more power will be taken to drive it.magnetic field doesn't go for free it tries to stop the generator rotor from moving.It's like arm wrestling you can't win a opponent with a weaker arm, the power doesn't come from "thin air" you have to supply the power to overcome the resistance.

Why will the magnetic field try to stop the rotor from moving ?

 

[sahil2309]

As in is there some particular reason ? Or something ?

 

[Lsos]

As you know, magnetic fields attract or repel each other depending on their poles.

Also, when you have electricity flowing through a wire, it generates a magnetic field. Conversely, in order to generate electricity, you move a magnetic field across a wire.

Well, it just so happens that when you try to generate electricity by moving a magnetic field across a wire, the very electricity that gets generated creates its own magnetic field, which opposes the one you are moving in order to create it.

It's the mechanism that keeps you from making energy out of nothing. You'll find that in this universe, there is always some such mechanism.

You can feel this by simply spinning a generator with no load, and then attaching a load to it (such as a light bulb). You'll find that the generator gets much harder to turn. I wish everybody tried this so that they would stop trying to to create energy by some "clever" arrangement of magnets.

 

[sahil2309]

What is this counter electromotive force?

 

[gerbi]

What is this counter electromotive force?

http://en.wikipedia.org/wiki/Counter-electromotive_force

 

[sahil2309]

Hey I read the article but can someone just explain me how will this CEMF have an effect on the generator rotor when it's spinning

 

[gerbi]

Zero effect on rotor. CEMF will be induced in stator winding.

Let's be straight: what are you thinking about ?

 

[sahil2309]

So basically it won't have any effect on the rotor while its in motion?

Yeah I've already mentioned about my intentions a few post earlier just have a look at it and youll know what I'm talking about

 

[gerbi]

Ok, so as I said it in one of my posts. Unless there is a real reason (like generator is drived by a very specific drive) there is no need to reduce rotor mass-> it's inertia.
Inertia moment of rotor is not all bad, it is required to provide adequate dynamic properties to the machine.
Plus: designing (and building) a rotor made of not-steel or so needs deep knowledge and can be extremely dangerous.
Third thing: I'm sorry, but this is not about briliant ideas.. it needs some knowledge.

EDIT: few mor words..

increasing generator efficinecy - this is your goal, right ? Well, this is very hard task even for people doing this for years. I won't elaborate on it. Please search for proper articles/books if you want. Then we can talk about important details in machines design.

 

[jim hardy]

You might find this article more instructive.

http://www.reliance.com/mtr/mtrthrmn.htm

 

[jccamp]

I want to learn how to design a generator but i don't know where should i start first. I've been given the ff conditions:
Power - 3kW
Voltage - 230V
no. of poles - 4
no. of parallel paths - 3
type of winding - lap
-could you anyone help me where to start? thank you!

 

[Alkemist]

i'm looking to design a generator, can someone just help me out, the following are the main criterias:
It'll have a power rating 30KW
RPM like between 120-200, so basically its a low RPM design;
i plan on using Carbon fibre for all the components on the rotor other than the power generating components.....should basically give very low inertia for the same structural strength as steel...
also can someone tell me how to determine the power rating of the generator based on the magnets and copper windings?

Sahil :

I see you as one of the Curious Joe about free energy or wishful thinker. Anyways, I have thought something like you before. So I have few things to share with you.

1] Using Carbon fiber to replace parts other than Magnets and Coils is very expensive. You will end up in spending more than 10-25 times cost of traditional motor.
2] Reducing weight of generator won't give you any advantage. Unless you are trying to use in in Airplane.
3] Having Still/Iron core improves output of the Generator. Air core generator will have less output. You can try this simply by using single coil / magnet and iron piece. Watch this video to see it in action https://www.youtube.com/watch?v=4vyJcdf-nCk
4] Having heavier Rotor will help you in better way as its inertia will help you when the generator is running. Only drawback is at the start you will need more power to rotate it.
5] If you are looking for very light weight generator, then you don't need anything apart from Coils and Magnets + supporting frame for them. You can make it by using any light weight material which can withstand high temperature.
6] Before starting designing such huge generator, try very simple and easy one. https://picasaweb.google.com/116297647808736459252/Mar92014?authkey=Gv1sRgCO2oqueouPGnUw#slideshow/5988894475777428818, which will give you some insights about Generator. e.g. how much output you can expect at particular RPM. Lower the RPM, lower the output.
7] Always remember one thing : No matter what/how/when/where you think, Output of any machine will be always be less than input given.
8] Before going any further, just run a simple test like this: - Make a Copper or aluminium coil of 50 or 100 turns, join both terminals of it [short circuit it], and then move it across the magnet. You will notice the opposite force. That effect may be called as CEMF or simply Newtons third law or Lenz's force or the Force, which will shatter your Dreams of making this big Generator.

Let us know what you decide or see what you make.