DC Generators

For an expert yes its easy but for armature its not.

Inefficiency causes problems not the problem causes inefficiency. There can be dozens of design parameters those can be responsible for poor and inefficient design.

Inside out design can work properly if made properly but level of intricacy is much higher.

It all depends on how big a generator (Voltage/Current delivery) what is driving the generator, Petrol/diesel/steam/hydro/wind/gerbils, and the distance from the generator to the user point.

The inefficiencies are not restricted to the generator itself but also to the delivery system from it. Things like voltage drop over cable lengths etc.

The automotive industry went from DC generators to Alternators because they delivered greater current from a given size of unit, and they were lighter to boot.

Its easier to create/control an alternating current from a rotating field and then rectify it than it is to create/control a DC current from a rotating field.

What is the desired result for your project or is it just a hypotheticle question?

Assuming that we are not talking about megawatt machines (you haven't told us the anticipated size!), the best way to generate DC is using an alternator and rectifying the result.

Assuming for a moment that you are NOT building this as a class project or university project, then don't build yourself, there are millions of them, sitting in scrapyards around the world, in a fully working condition......and at a very low price......

Most of the modern ones also have the diodes and control circuitry needed to keep either 12 or 24 volt (truck alternators) batteries correctly charged.....

These units have slip rings, not commutators (most DC generators have commutators, quite difficult to fabricate yourself to stay together at 1000s of RPMs), which are far better mechanically and will handle higher RPMs with less brush wear.

As its not clear from your minimal information what the aim is, I certainly think its time that you filled us in completely.....or we cannot help further......

"how about doing an article for CR4 on generator design?"

That sounds like an awesome idea, Andy. I in particular would be very interested in such an article.

Hi RHABE, I'm emailing privately as I don't want to get too far off subject. Eventually I will want to construct an alternator for a wind turbine. Your thoughts and "rough sketch" would be a great help. Also, what is the best way to cut the magnets? Thanks, Bob

PLEASE SHOW US HOW TO BUILD HOME MADE 3 PHASE GENERATOR!

I am going to start to do this soon for my wind turbine.

i start to understand the concepts but have a couple of questions. i have my magnets cut to form a ring, 16 per side make a ring on a brake rotor. ive seen design with solid ring of magnets and one with gap using 12 magnets per side.

(q1) wich is better? why? (endq1)

I understand that different coils turns and different gauge wire will give different volts.

(q2) could you provide a chart or scale that gives us a choice. At what rpms are these choices maximised for output?(end q2)

(q3) does the direction of rotation matter in these type of devises?(endq3)

In regard for connection to the grid for net metering.

Most wind sytems seem to generate a/c rectify to d/c to charge batterys. for of solar wich creates d/c there are inveters for grid connection.

(q4) how do you connect a/c generating wind turbine to grid for net metering, please name all devices needed.is some sort of isolation needed? what about the variable out put, how wil that effect the system ? (endq4)

thanks im starting the turbine this weekend ill send pics when im done

Will have to reclassify the privacy bit :). Are your designs similar to the units designed by Hugh Piggott? http://www.scoraigwind.com/

I have give you a GA, should have done it before, sorry.

It looks as though my idea that you do a CR4 article as a DIY Alternator is creating great interest......please think it over.

To the rest of CR4, please comment on the idea as soon as possible please....

Sounds like an excellent idea! I gave Rhabe a GA for his post, and you one for the suggestion.

I agree! 2 GA's from myself as well.

Hello RHABE,

sounds like you opened a can on worms.

I would also be interested.

I would like to make a suggestion, start simple with the how and the why, then add complexity, go into as much detail as you like. Some will be able to follow farther than others. (and some of us are just plain rusty due to school being years ago )

This is all in hope of your taking on the project. I am also planning a windmill

Brad

Why do you need DC and not AC ? For energy storage (batteries ) ?

What do you mean by rotor movable in and out of the stator ? Demagnetizing electromagnets ?

Is it easy to build an efficient DC generator?

What are the problems that could make them inefficient?

Can it work properly with the rotor movealbe in, and out of the stator?

There are many different different web sites devoted to generating low scale power for home use.

As Einstein reflected, its all relative.That is so far as ease is concerned, for me with my knowledge, availability of parts and the necessary tools, yes very easy. Without the appropriate ingredients not so easy.

People have a sliding scale for acceptable efficiency as well, based on available resources and the necessity of the outcome.

Thinking through the OP's question, if you used a bar magnet passing through a coil of wire then yes you will create a dc current of sorts. It will for the duration of one pass of the magnet, generate DC, it will fluctuate in voltage and current delivery during that pass dependent on the magnetic field of the bar magnet. It will present that voltage in one polarity across the coil in that one pass. When the magnet is then passed back through, the same effect will occur however the polarity of the power will now be reversed. If the magnet is passed back and forth at regular intervals, this will provide Alternating Current. By the addition of two diodes wired as a full wave rectifier and a filtering capacitor you will have DC.

As for efficiency, if you scaled up this basic generator so as to provide significant power. Then it would become very unwieldy and create significant structural loads and vibrations. Hence why it is better to rotate the magnetic field in the coil windings to generate the power, as one can balance the various kinetic forces accordingly. Also its easier to couple a rotating motive force to a rotating demand than a recipricating one.

I suspect the OP was "bench racing" rather than looking for an actual solution.

Is it easy to build an efficient DC generator?

Yes, building small toy airplanes is much more difficult. Magnets, steel, glue, wire and winding mechanism, axis and bearings, if running fast then balancing.

I am preparing a tutorial to be posted here (this will take some time), look on the post above at the coil I did. This is the most complicated part of such a generator.

Can it work properly with the rotor moveable in, and out of the stator?

You are thinking about a cylindrical construction and ALNiCo-magnets.

I am thinking about a flat (pancake) construction and either FeNdB-magnets or SmCo-Magnets. These magnets allow for opening the magnetic circuit without demagnetisation. AlNiCo-magnets need a spacer (iron or steel parts to avoid demagnetisation.

Flat is easy to build. If you need cylindrical then this is possible too - principles are the same.

As Einstein reflected, its all relative.

Scaling for power is possible without difficulty. But think about using an existing one, this will be cheapest and fastest.

AC one, two or three phase is possible and not very different. DC only by rectifying to avoid slip-rings or a commutator.

This needs rotating magnet-assembly and stationary coils, bringing some difficulties with the magnet assembly and its bearings, but not really bad.

I do not agree with your statement about scaling up and significant structural loads. Any structure and its weight and maybe unbalance has to be supported properly.

Reciprocating is not a good idea. Rotation is better.

RHABE