I am fairly new to electronics. I am learning and I love it and all you wizards of the electrons. I will be your student for years to come I am sure. With that I could use a little lesson in coils.....

I want to make some manual powered small devices. I want to give the kids a hand crank power maker to charge cell phones and a couple of AA batteries for game controllers. At least I know they will burn some calories once I make these devices. I know I can buy similar items and well if it was all about that I would just buy a boat load of rechargeable batts. and chargers but hey that is not the goal. The goal is for me to learn and them to earn some power for their devices.

With that I would like to know how to judge the shape/size/number of turns, etc. about coils. Later when I feel much more comfortable I plan to make some coils for a homemade wind generator. So you can see why I am here asking. Being that I don't know what I don't know I may not ask the proper questions during this thread but maybe this will be the first of some basic lessons and knowledge for those who will follow.

With that let me start this thread with coil winding, and lets chat about the basics of how to size one up! I think the initial questions to ask will be....

1. What is a coil
2. What is inductance
3. How to figure out the size / number you may need
4. Selecting materials
5. Methods to wind the coil
6. Wiring the coil AC/DC
7. What to do with the output - rectifying etc.

I hope this thread isn't misplaced and I do look forward to learning and then making some more threads on other subjects like this!

Thanks in advance everyone!
~Coog

 

For the purposes of designing 'electric machines' - electro-mechanical power generating devices - coils plays a small but vital role.
More importantly, you need to understand magnetic design, magnetic flux, magnetic materials and magnetic circuits.

A typical generator has coil(s) that are placed within ferromagnetic structures designed to optimize the production of electricity.
Of course you can spin a magnet inside a coil and it will generate some voltage, but it will be hopeless as a practical generator.

 

For the purposes of designing 'electric machines' - electro-mechanical power generating devices - coils plays a small but vital role.
More importantly, you need to understand magnetic design, magnetic flux, magnetic materials and magnetic circuits.

A typical generator has coil(s) that are placed within ferromagnetic structures designed to optimize the production of electricity.
Of course you can spin a magnet inside a coil and it will generate some voltage, but it will be hopeless as a practical generator.

Sensa - Firstly thank you for the quick response!
I understand there is much to learn but is there an easy way to know that 20awg wire on a 1in core with 0.5in lenght and 100 turns would produce? Without learning everything about magnetism, I as a motor builder would want to size my 12 coils and get the right sized magnets to attach to the right size stator to produce 1500watts - which in the US is a typical 120vAC 15amp circuit, something most of us can use as a common amount of power. From there we can talk about smaller or large I suppose. So is there an easy way to get close - not exact - with a formula like 12awg * 100 turns on a 1in air core with 60 magetic pulses per second = XX watts? I would say our conversation could make assumptions like the magnets are on a spinning axle that has 12 magnets and revolves at 500rpm. that means 6000 magnets will pass over each 1 coil each minute = 100 pulses/passes per second. Now if there are 100 pulses due to the magnet passing over this air coil and it was <----> this big, fill in the blank, it would produce "x VDC" at "y AMPs". This times 12 gives me an estimated vDC and Amp output. I can then use that as is or convert it to AC.

With that information - how can we make this a discussion for the layman = me. I can wind the coil perfectly and I can use 16/18/20/24awg wire. I can make sure it is on a 1 or 1.25 or 1.3487 inch core. I can make a stator plate exactly 12.243 inch diameter as well or any size for that matter. BUT what I dont know is which gauge and how many turns to make each coil. I also dont know what each coil would produce for V or A. But knowing these things would help me decide what size I want to make for various projects. The coils for the wind turbine generator would be drastically different than the hand winding unit for the kids but in principle operate exactly the same just, the kids unit would be many time smaller and DC only instead of AC like the wind unit. The point of this thread is to give basic knowledge not just the answer flat out. So telling me to use xyz parts is good - but I want to learn so I can experiment with varying sizes etc and do some math prior to wasting materials building each unit at various sizes.

Mentoring/Thoughts anyone?

AFTERTHOUGHT - EDIT - If I have 12 - 1in x 1/8th inch Neo magnets and a spool of 23 awg wire and some more info from all you electro-mages, I could estimate how I might use these parts to make various generators for other projects as well.
~Coog

 

The problem with your idea is that air has very low magnetic permeability, which means it sucks as a conduit for magnetic flux.
This is why generators are heavy hunks of metal, an air-core coil presents a huge resistance to the magnetic flux necessary for efficient operation.
Designers of rotating magnetic machines are obsessed with reducing efficiency robbing air gaps in their designs, you want to make a generator that is all about air gaps?

It's like trying to make a car engine out of wood, just not the way to go.

 

no expert on the subject here, though have been through similar scenario. many factors to take into consideration. extract from here - https://answers.yahoo.com/question/index?qid=20090917224652AARSaXU

There is no straight or simple answer. The voltage depends on the strength of the magnetic field that cuts the coils, the rate that it cuts the coils and the number of turns it cuts. However the design of the generator influences all these things, and there are a lot of tradeoffs..

The strength of the field is affected by the layout, the gap between rotor and stator, and how the field is created, including what control is used. The rate of field cutting through the coils is affected by the diameter and the RPM. The number of turns is affected by the available space and the wire size. The wire has to be big enough to carry the desired current. Some sort of cooling has to be provided.

Having said that there is for a given layout and design a simple relationship between RPM and turns, that can be called volts per RPM per turn at some level of magnetic field excitation (before the cores saturate). So volts is proportional to the number of turns, and a higher voltage for a given speed is good with wind generators because they need to run at lower speeds.

The output power depends on the torque available at the operating speed, and the load that draws the power. This means there is a particular current for a particular voltage as power = Volts x Amps and the wires must be large enough, have sufficient cooling, and be able to fit in the space. The heating of the wires is due to the voltage dropped across the wires with the current through them, not the output voltage.

As you can see everything has an effect on everything else. You start with the power that the turbine can produce in a strong wind, and then everything follows from that.

One of the popular approaches is to obtain a suitable motor, and perhaps rewind it for a more suitable voltage and current. The motor wattage will be similar to the generator wattage. Thus a 200W motor that runs at 2000 RPM on 40V has a turns factor of 50 RPM per volt. It will generate 12V at 600 RPM. The voltage will vary from these simplified theoretical numbers according to the efficiency of the machine, so it will need additional RPM when under load, or a controlled increase to the magnetic field. This machine will be rated at approximately 6 Amps allowing for efficiency (because 200W is the mechanical output). That is the wire size.

If you have a 200W motor and want to charge a 12V battery, you probably want about 15V so 750 RPM, not 600 RPM, and a bit more for losses. The current for 12V (when the battery is drawing a lot of current) and 200W is 16.6A, so lets say you put as many turns of something like 20/25A wires (considering they will be hotter inside the generator). It will no longer be a 40V machine, as the wire is bigger, and so will need more RPM. There is therefore a trade-off between RPM and volts and even power.

hope that puts a little insight into your questions and 23 gauge wire's about 0.75a? capacity off memory. the magnets also seem a little small though you still need to be careful with them AND any metal objects moved to a safe distance.

 

you can teach yourself some basics much quicker than we could. Google "magneto-electric generator". Better still do that search at books.google.com, where several dozen old tomes can be found which will describe basic practices and give formulas you can use to calculate voltage and current. these old books are public domain and pdf copies can be downloaded for free.
One word of free advise about human powered electric generation. We cannot produce anywhere near a single "horsepwer". Most humans are capable of generating between .1 and .05 hp for long periods. Athletes can do more for short periods but not even they can approach the 1 horsepower generation goalpost.
Just be prepared to be underwhelmed by any human powered generator capability

 

Probably the easiest way to approach this is to use a small DC hobby motor and attach a crank to it. That way the coils, magnets and bearings are all worked out for you. You can probably find like a 6 volt 1 amp motor on e-bay for a few dollars.

 

Get an old battery dril and use the motor from that. Attach crank or some form of drive and generate away to hearts content. Maybe even attach it to a exercise bike!