Generator construction

[Generator]

Greetings everybody. Just joined this forum, to get better options for my Generator, I know everyone talks about Motors here but...
Anyways, I've started working on Single phase Axial flux generator. I'm open to move on to Radial flux type, if that is better option.
I get around 6 V out of one coil having resistance of 0.6 Ohm. When I short it, I get 10 Amp. This output is just for one coil.
I want to supply 30 V, 120 Amp to a load whose resistance is 0.05 Ohm. I'm wondering what could be best way to achieve this?

Any comments?

 

[major]

I want to supply 30 V, 120 Amp to a load whose resistance is 0.05 Ohm. I'm wondering what could be best way to achieve this?

Any comments?

Learn Ohm's Law. V = I * R. And maybe use an automotive or truck alternator.

 

[friendly1uk]

This is a subject I'm going to look at more closely in the future. I know alternators are commonly used, with the rotor swapped out for permanent magnets. Regulation being done off-board. In a vehicle regulation is covered by modulating the rotor power instead. You could rework the regulator for any voltage within reason. Making 30v and 120 Amp almost on the shelf.

I'm interested in wind power, and I know from testing alternators that not a lot happens till it's doing a few thousand rpm, with about 12,000 rpm being a typical maximum. My wind farm would sound like a helicopter.

 

[Generator]

Thanks for your comment Major.
V = I * R : If this was so true or simple in case of Generators, I would not have started this thread at all
And maybe use an automotive or truck alternator : I'm building my own, I know I could get one in market for $ 10 or less from junk yard, but I've spent way more than I imagined initially for this Generator.

 

[major]

Thanks for your comment Major.
V = I * R : If this was so true or simple in case of Generators, I would not have started this thread at all
And maybe use an automotive or truck alternator : I'm building my own, I know I could get one in market for $ 10 or less from junk yard, but I've spent way more than I imagined initially for this Generator.

So you don't believe in Ohm's Law and are building a 3.6kW generator from scratch to save $10. That will be a good learning experience for you. Good luck.

 

[Generator]

No, I didn't say Ohm's law is not applicable here. That's the universal truth. But here is the problem :

When coil is rotating relatively at 1600 RPM across 16 magnets, I get somewhere around 6 v and 10 amp when I short it. I wonder how many coils I need, to produce 30 volts, which will give 120 Amps to flow through 0.05 Ohm resistor. What should be the arrangement of coils [Parallel or in Series]?

I'm not saving $ 10, one magnet cost is more than $ 25, which I'm using, so this is something I'm doing for understanding generator inside out.

I think understanding motor is straight forward thing, but generator is little difficult, so I believe this will be good thread.

?

 

[major]

When coil is rotating relatively at 1600 RPM across 16 magnets, I get somewhere around 6 v and 10 amp when I short it.

Assuming constant flux and RPM, and 6V is open circuit generated voltage on the coil, then 10A short circuit current implies a coil resistance of .6Ω.

I wonder how many coils I need, to produce 30 volts...

5 of those coils in series would give you 30V open circuit at the same flux and RPM. Those 5 coils in series would have a resistance of 3Ω and a short circuit current of 10A.

which will give 120 Amps

12 of those 5 coil sets in parallel (with the same flux and RPM) would yield a short circuit current of 120A and have a equivalent resistance of 0.25Ω.

which will give 120 Amps to flow through 0.05 Ohm resistor.

120A through a 0.05Ω load requires a terminal voltage of 6V. Assuming the same flux and RPM, 6 coils in series gives an open circuit voltage of 36V. This allows an I*R drop across the armature of 30V. Iteration using your 0.6Ω coil shows 15 parallel coil sets gives an equivalent armature resistance of 0.24Ω. So the circuit resistance is 0.29Ω. This means 124A would flow through the 0.05Ω load with 6.2V at the generator output terminals. It would have a open circuit voltage of 36Vand a short circuit current of 150A.

What should be the arrangement of coils [Parallel or in Series]?

That would be 90 of your coils (0.6Ω) in a 6S15P connection. There are in fact other combinations of series parallel solutions of that particular coil which could be employed and get you closer to your desired 120A possible.

Of course this gives no consideration to the suitability of the thermal case for the armature design, or the possibility of construction, as in, being able to physically place the coils in the magnetic field and not altering it when loaded.

I think understanding motor is straight forward thing, but generator is little difficult, so I believe this will be good thread.

Motors and generators behave the same. The armature current is opposite direction and thus alters the polarity of the voltage drop in the circuit equation; that's all.

 

[Generator]

Greetings All -
Per F=BIL I can calculate quantity of Force on coil (or magnet), when I draw certain amount of current from the generator.
So I need your inputs in calculating the Force and then weight equivalent of it. Let's say I have Single coil generator [wire length = 92 meter, 300 turns on 3x1x1 inch block], when I move that coil over Magnets in short circuit condition, I sense the opposite force [F] as current [I = 5 amp] passes through the coil. I calculate the amount of opposite force, being exerted on coil for that current as: B = (0.5 T)

F = 0.5 * 5 * 92 = 230 N/Amp.m [Am I correct in Units?], this means I feel the force of 230 N/Amp.m continuously.

Now I want to know how can I relate this force to weight equivalent? I mean when I hold 1 kg weight in my hand I feel F = 9.8 kg.m/s.s

Any comments?

 

[Generator]

Great.
The load is 3600 Watt. I think I might have missed something in your explanation. 90 coils, how did you reach to that number?
For now I can fit in 64 coils in present setup, but I can always increase number of magnets and fit more coils. I'm not worried about the construction possibility and thermal issues for now.

Thank you 8)

 

[major]

Great.
The load is 3600 Watt. I think I might have missed something in your explanation. 90 coils, how did you reach to that number?
For now I can fit in 64 coils in present setup, but I can always increase number of magnets and fit more coils. I'm not worried about the construction possibility and thermal issues for now.

Thank you 8)

What I did was an attempt to show you how. It was by no means a design. First off, as I tried to point out before, your load specifications don't make any sense. So I chose to use 0.05Ω and 120A using the coil you defined. Note that resulted in an output voltage of 6.2V. Or a power to the load of 769W. Far from your desired 3600W.

Also, it would be a horrid machine operating there for any more than a transient condition. At that 769W output, the I²R loss in the armature is 3690W.

90 coils, how did you reach to that number?

Like I said, I started with your coil and 2 of the 3 load parameters. Figured the simple circuit using Ohm's Law and took a stab. Then did a couple of iterations to arrive close to 120A on a 0.05Ω load.

With the popularity of DIY wind turbine generators, I think you should be able to find web sites outlining generator design. Take a look.

 

[Generator]

I know but the load I have are 2 Motors and their internal resistances are 0.01 Ohm and 0.04 Ohm, which I cannot change or control.
I couldn't find a nice tutorial or book online, which can explain how to design a better Generator, if we know what output we want.

 

[major]

I know but the load I have are 2 Motors and their internal resistances are 0.01 Ohm and 0.04 Ohm, which I cannot change or control.

A motor can be represented by its resistance only at stall (zero rotation). Otherwise there is a generated voltage in the armature to consider, often called bemf (back emf).

I couldn't find a nice tutorial or book online, which can explain how to design a better Generator, if we know what output we want.

If you go here: http://endless-sphere.com/forums/viewforum.php?f=30 You can find links. As in this one: http://endless-sphere.com/forums/viewtopic.php?f=30&t=240 And: http://www.reliance.com/mtr/mtrthrmn.htm Which also covers generators.

 

[Generator]

Thank you for the links, I guess they will keep me busy for few more days.

I started another thread here : http://endless-sphere.com/forums/viewtopic.php?f=30&t=57466#p857018 to understand/learn that motor.

 

[jkbrigman]

Greetings everybody. Just joined this forum, to get better options for my Generator, I know everyone talks about Motors here but...
Anyways, I've started working on Single phase Axial flux generator. I'm open to move on to Radial flux type, if that is better option.

Hey Generator; (good nom-de-forum!) I got me three things to say to you:

First:
If you are interested in Axial Flux machines, what I am about to tell you, you might already know. There are two "canonical books" you need to own if you are trying to build an Axial Flux machine:
Wind Power Workshop by Hugh Piggot (The "father" of modern homebuilt axial flux wind turbines...) Mr. Piggot's book is more like a "college course in wind turbine technology".
Homebrew Wind Power by Dan Bartmann and Dan Fink (known as "The Two Dans" in the wind turbine community) The Two Dans' book is very practical, very hands-on. They give you enough information to loft your own wind turbine from pretty much nothing.
I got my copies of these books off Amazon, great prices.

Second:
An Axial Flux machine is a better choice for a wind turbine than a car alternator. In the words of Mr. Piggot:

"Car alternators are a very popular choice for newcomers to wind power. The are readily available, they have the right sort of power rating and they are designed for charging batteries. Nevertheless, they are not ideal when building windmills(sic). The part-load efficiency (when producing less than full output) is very poor, because the constant current in the field coil becomes a larger fraction of the reduced total. Modern car alternators are built for cheapness, light weight and high rpm."

What this means is that it takes energy to keep the field coil energized, and that energy is a large fraction of the generated power when the RPM's are low. However, ever the resourceful bloke, in his book he spends some time talking about how to modify an alternator to work better for a low-rpm device like a wind turbine.

On page 72 of "Homebrew Wind Power", the Two Dans say similar things about a car alternator vs. an axial flux machine.

You are on the right track going with an Axial Flux machine. They are single- or three-phase machines designed to work efficiently at the low RPMs and low torque conditions of gentle breezes.

Third:
Would you, please sir, give some thought to building a three phase axial flux machine vs. a single phase? I say that because a three phase machine loads the blade more continuously across each turn of the blades and you may find it to be a more stable, quieter, less-vibrating machine at three phase.

I get around 6 V out of one coil having resistance of 0.6 Ohm. When I short it, I get 10 Amp. This output is just for one coil.
I want to supply 30 V, 120 Amp to a load whose resistance is 0.05 Ohm. I'm wondering what could be best way to achieve this?

Any comments?

A machine that can maintain 30 volts across .05 ohm will push 600 amps through that microscopic resistance. Maintaining 6 volts across .05 ohm will give you your 120A into the .05 ohms. That's about 720 watts. If you built a 1000 watt machine, that would give you plenty of room to handle inefficiencies and deliver that 720 watts into the .05 ohm.

Page 162 of The Two Dans has a small table in it that describes number of turns in a coil, size of wire and expected output. I'll repro that little chart here:

Volts #AWG #Turns
12 2 strands #14 36
24 1 strand #14 70
48 2 strand #17 140

They go into amazing detail on how to wind your coils and how to fabricate the stator-full-of-coils. Particularly nice is the coil winding machine they show you how to build, which, incidentally, builds a coil the right size to give you a really nice stator.

A little instructables on the subject: http://www.instructables.com/id/7-Foot-Axial-Flux-Wind-Turbine/
If you'd like to BUY a kit: http://www.mikeswindmillshop.com/kits.html
And finally: http://www.otherpower.com

JKB

 

[jkbrigman]

BTW: I just re-read the thread and realized you want to drive a couple motors with a wind turbine.

Don't stop with the visualization of merely connecting the wind turbine to the motors. That visualization is not going to work, because motors require very high currents at startup, possibly higher than you can deliver with your wind turbine. Electrical behavior at startup of a generator and of a motor are quite different, especially if they are all AC machines.

What you are going to want to do is devise an energy storage device - a battery bank with a properly designed controller for your wind turbine - and feed energy into that energy storage device with the wind turbine. Then, that same energy storage device feeds the motors you desire to drive.

Get The Two Dans book. It's going to answer ALL of your questions and give you the long view you are seeking.

JKB

 

[LockH]

Subscribed.

 

[jkbrigman]

Thanks for your comment Major.
V = I * R : If this was so true or simple in case of Generators, I would not have started this thread at all
And maybe use an automotive or truck alternator : I'm building my own, I know I could get one in market for $ 10 or less from junk yard, but I've spent way more than I imagined initially for this Generator.

Wait a minute, wait a minute. I turns out I made another assumption: you are only saying "Generator", you aren't saying "wind turbine". I assumed, since you are interested in an axial flux machine that you were making a wind turbine (and my comments back to you reflect that).

Hey Generator....when you say you are making a "Generator"...what do you mean? What's the source of mechanical power?

Are you making one of THESE: http://theepicenter.com/tow02077.html

 

[LockH]

While perhaps some wait breathly for the "BIG REVEAL", I'm kinda hoping the device will suck energy from air (wind) and optionally (for extra bonus point), from "hydro" (aka water). Sadly, I kinda doubt there are any geothermal sources ready at hand.

 

[jkbrigman]

While perhaps some wait breathly for the "BIG REVEAL", I'm kinda hoping the device will suck energy from air (wind) and optionally (for extra bonus point), from "hydro" (aka water). Sadly, I kinda doubt there are any geothermal sources ready at hand.

+1 man, +1. Both of those being places where an axial flux alternator makes sense.
ON the other hand, we might never find out. I tend to kill threads when I comment.

While we wait, here's a well-documented build from Italy with an interesting slip-ring arrangement so the turbine can pivot to follow the wind and never kink-up a cord......
http://www.thebackshed.com/windmill/articles/SpitsFire.asp

 

[jkbrigman]

Witness my massive thread-killing ability in action....

 

[LockH]

"Generator" has been M.I.A. for maybe two weeks now. Still no word on watt his single phase axial flux generator output is to be used for (one might assume for battery charging), or watt options he might have for spinning the thing.
:?

 

[major]

Still no word on watt his single phase axial flux generator output is to be used for (one might assume for battery charging), or watt options he might have for spinning the thing.
:?

The generator was to power his motors.

I know but the load I have are 2 Motors .....

He never did mention the primary power source.

 

[Generator]

All- my apologies for not being active in last few weeks. I was caught in some high priority work.
Anyways, As of now, the mechanical power to generator is muscle power. I have gears, which can rotate the rotor for 1600-2000 rpm. I initially had only one coil, but now I have 3 coils in total, all hand wound with lot of pain.

My original intention was running motor directly but looks like that is impossible [thanks JKBrigman], but via battery it is still possible.

Also, please note that this is my experimental Generator. My intention is to run a motor out of the o/p of this Generator via Battery [for start up].

 

[Generator]

A machine that can maintain 30 volts across .05 ohm will push 600 amps through that microscopic resistance. Maintaining 6 volts across .05 ohm will give you your 120A into the .05 ohms. That's about 720 watts. If you built a 1000 watt machine, that would give you plenty of room to handle inefficiencies and deliver that 720 watts into the .05 ohm.
JKB

Thanks JKBrigMan for your comments. I have seen one of the Soft copy book online and have gone through it. I chose the handle as "Generator" because we all can improve the efficiency of this, so it should be generic name and every one can treat this thread as their own instead of mine .

In your above calculations, you missed to consider the internal resistance of the generator coil, which is 0.6 ohm. So if I use load of 0.05 ohm across the coil, it becomes 0.6 + 0.05 = 0.65. So the current flowing through load is 6/0.65 = 9.24 amp and then power consumed by load is 9.24*9.24*0.05 = 4.26888 watt. But the internal loss in this scenario is about 52 watt.

So I'll have to reduce the internal resistance of the generator by using parallel coils. If I use 12 parallel coils, then internal resistance of generator coils becomes 0.05 ohm and then I we can get maximum power transferred to the load of 0.05 ohm. Even in this case the load can consume only 180 Watt.

Whereas if we do short circuit test on these parallel coils and see how much maximum but useless power is being generated by generator internally, then we get something like this :
120 * 120 * 0.05 = 720 watt

This shows that the Generator virtually generates 720 Watt but only 180 Watt is what a load can consume in ideal situation.

This leads to one conclusion : Generators are 1/4 times efficient [or Deficient?] unless I'm doing something wrong

 

[Generator]

While perhaps some wait breathly for the "BIG REVEAL", I'm kinda hoping the device will suck energy from air (wind) and optionally (for extra bonus point), from "hydro" (aka water). Sadly, I kinda doubt there are any geothermal sources ready at hand.

As I already mentioned, this is experimental generic "Generator" not tied with Wind or Hydro power as of now, nor it is intended to be used in that way. Purpose is to learn more about the Generators.