micro teensey alternator power output problems

[myfacelackseyes]

Hi there, I've put together a very small alternator which I was planning to use as a rear-hub dynamo for a push bike (they don't seem to make rear wheel integrated dynamo hubs anymore and I'd like to be able to turn the bike over and spin the cranks by hand to charge batteries while relaxing in a park or on a camping trip)
Anyway, the unit I built is a 10cm radial alternator, the rotor consists of 24  3 x 3 x 3mm ndfeb magnets and the stator is wound with 3 sets of 6 coils each of 40 turns .0135mm enameled wire, wired in star and recitfied by a small diode array.
However when I hooked it up I was only generating 200mv, less than a tenth of the voltage I need.

I'm wondering whether this is just a case of having very undersized field magnets, too few turns of wire or something else?

I'd thought of rewiring the stator with a single coil (like this http://www.windstuffnow.com/main/mini-gen.htm) but I'm having trouble figuring out exactly how to?

The other option is rewind the stator with many more turns of wire per coil, I don't really want to spend much more money on this project so more powerful magnets are out.

[birdhouse]

I'd like to be able to turn the bike over and spin the cranks by hand to charge batteries while relaxing in a park or on a camping trip

i've never built a PMA from scratch, so don't have any info on that. 

i will tell you that there are folks here that use "ped gens" basically exercise bikes that produce electricity to charge a battery.  seems ~50w is about all an average human can sustain for a decent length of time. 

my point being, recharging a battery and relaxing in the park don't seem to fit in the same sentence, unless we're talking about a small cell phone battery.  even then, a small 10w solar panel would probably do a far better job. 

adam

[myfacelackseyes]

we're talking about a 3 - 5 w generator to charge small lithium cells for lights and a cell/ mp3 charging attachment, the advantage it has over solar is that the biggest drain on the system would be during night cycling.

[Bruce S]

When you built this did you test the output of each set of 6? It could be you have one of more of the sets either keeping the voltage down or something is amiss.
How do you have the sets wired star or delta?
Can you possibly post a picture of the unit?
While you might not get the full 3 -5 watts out you should be able to get the voltage up to a usable range.
Come back with a little more info.
Bruce S

[myfacelackseyes]

I tested the total output of all the coils wired in star and rectified with diodes.
I'm planning to wind a 400 turn coil and test the voltage output of that when I next get the chance.
Will the output voltage be higher using a single phase with alternating polarities of coil than using star or delta wired three phase?

[dave ames]

Hard to know what you are up to without a better description, Pictures or a diagram?

I suspect a geometry issue with the magnetic circuit, or the coils, maybe both.