Rectifiers help

[Junkie]

I have this little Stirling generator that I made : http://www.youtube.com/watch?v=tN9ol5pdZ5Q

It's a stepper motor being used as an alternator, I have connected the rectifiers as the diagram below:



I've connected an LED in place of the battery pack. But I think there is some kind of fault in my circuit as the led flashes (I believe it should only strobe a little  )

Also when I connect to batteries the meter registers a current flowing into the battery (around 15-20ma) but how is this possible if
my battery pack is 3.6V but the alternator is only outputting 2V.  Is there a better way to get power out of this stepper motor ?

Can somebody confirm if it is acceptable to connect the two rectifiers in series ?
Also would it be better to use germanium diodes as they have a lower voltage drop?

Thanks for any suggestions ! 

[ghurd]

Need to see the pic.
Have a link?

The LED will flash hard if wired certain ways, especially at low RPM.  There are several ways to get around it.

The battery will charge during voltage spikes.  Just like the LED flashes during voltage spikes.
The 2V reading is because the LED limits the voltage.

G-

[ghurd]

I found the pic.
That series configuration is just wasting voltage.  And amps. 
The coil inductance will play havoc.

Rectify each coil and parallel the bridge outputs.
To minimize the flashing, hang a big fat cap (470uF?) on the bridge outputs, and put a 100 to 480 ohm resistor between the cap and LED.

Nothing I could do about the pic or link.  Found it here,
http://sites.google.com/site/reukpower/projects/coffee-cup-windmill

G-

[Junkie]

Yep thats the right pic, it's showing up here but could because of where it's hosted (sites.google can be iffy sometimes)

Do you think I could use 0A91 diodes or similar to rectify them because the current is tiny and
less voltage drop across the bridges would be a big help (I think?)

Thanks for your reply and going to the trouble of looking for the right image

[ghurd]

I would be a bit concerned about Vo or Vcap.
The voltage spikes are certainly over 10V.

1A Schottkys would be good, if you were sure the total LED current would keep the cap voltage under control.
I would probably just use 1A 40V Schottkys and not worry about it.

The pic is too big for the board.
I only see a double space empty spot where you see the pic.
The resize code did not work, and my wife's html code attempt at it did not work either.
40kb seems kind of silly for that line diagram anyway.  Save it as a gif.  Probably get it under 4kb.
The actual photo of the circuit is only 11kb.
G-

[Junkie]

That should work. I've just changed the bridges into parallel and it's a lot easier to turn under load so I might see more power
when I get it connected to my Stirling again!

Do Schottky diodes have a lower voltage drop than other diodes or is it about the same ?

Thanks again.

[ghurd]

Schottkys have a lower forward drop, and they are faster acting.
Problem is they tend to have a low max Vr.

You should not have much of a voltage problem.  The problem will be the amps plateau.

If you want pretty lights, use about a 500 ohm resistor for each LED, and add more LEDs.  Could probably do pretty good with even 10 or 20 LEDs.

G-

BTW- I would try it like this,