alternator help- pedal power

[purvisgs]

Hi, We just put together a basic "pedal power" demonstration bike, using a belt on the rear wheel as a large pulley and a small pulley on the alternator mounted behind the seat...  we figure that with the current gearing, we have it spinning at around 3500 rpm....

somewhat similar design  to this site:

http://www.c-realevents.demon.co.uk/altgen/altpedgen.htm

anyways, the alternator we are using is off of an older watercooled vw, it has an attached voltage regulator....  We would like to charge a 12v battery with it for a stereo/ etc for demonstrations...  

The alternator + voltage regulator has 2 contacts (attached together, (+)), the casing is hooked to ground, and it has a 3rd wire that I believe is for a charge warning light...)  

When we pedal with just the + and - contacts hooked to a battery, it doesn't put out a charge, so we tried the internet and came across the above mentioned site, below is a direct link to their wiring diagram...

http://www.c-realevents.demon.co.uk/altgen/hrcircdiag.GIF

I could not completley understand what the circuit on the above mentioned link is doing, and tried to replicate it, but couldn't find any resistors that were even close to the ones they are using (or the right size light bulb)....  

Is my thinking correct that they are just using resistors to regulate the "difficulty" of pedaling?  

I understand that in order for the alternator to start charging, the field coil must be energized....  However, I am not quite shure how to go about that with the resources we have avaliable (scrounging parts, etc)...  I tried running a small power supply (12v) to the (+) contacts on the alternator, and this did not start charging at ~14v...  

I also tried using a light bulb (12v, 5w) in the same manner as the circuit above describes (from charge warning terminal through bulb to (+) terminal)... what difference would using the 24v 3w bulb they describe make?  (it seems to me this would just change the speed the alternator cuts in at...?

Well anyway, we would greatly appreciate any help in simplifying or explaining these concepts or any errors in our thinking....  By the way, the alternator was working when we pulled it from the car..

Thanks for your help!

[Nando]

Who are you ?.

Your name ?.

Unhappily you are using an alternator, too poor efficiency for starters.

You need to apply, to the field, sufficient current for the alternator to produce enough voltage to initiate charge current.

Start with about a 3 or 4 watts lamps ( at 12 volts) or a variable power resistor 25 ohms 25 watts or so.

Maximum power one may harvest is around 70 watts for about 2 hours or higher for very short times.

Nando

[Norm]

   Going to a lot of trouble  about $22 bucks

most of this shipping charge, put it to the back

tire like this....

http://www.fieldlines.com/story/2005/3/23/225230/317

   The flywheel has left hand threads so it should

be turned counter-clockwise or it will unscrew,

put the outside of the belt against the wheel of

a 10 speed select the most suitable gear connect

directly to a battery...pedal faster than the

battery is turning the PM motor and you'll charge

the battery the harder you pedal the higher the

rate of charge...a simple switch to turn it off

when not pedaling.

                   Have fun!

                     ( :>) Norm.

[kell]

One very important point:  alternators have the field wired in one of two possible configurations.  In one of them, you get field current by grounding the field; in the other, you get field current by supplying the field with current from a positive source.

The diagram in the second link you posted shows an alternator of the second type.  However, I think your VW alternator may be of the first type (I just took part in a discussion about old VW and GM alternators on another discussion board).  If that is indeed the case, then you have to connect the F terminal to ground instead of the way they have it in that diagram.  

You can vary the output by putting a resistance in the conductor that goes from field to ground.

[ghurd]

I think Norm and Nando have it right.

A car alternator is not just a good choice.

Norm's motor works quite well.

A simple diode will stop it from motoring

when it is not generating power.

(Norm, I'll send one up)

G-

[purvisgs]

Thank you for all the input-  I chose to use an alternator instead of a dc motor because we already had it, and we were really trying to minimize costs for this project that realistically won't be used to generate "usefull" power (only periodic power for demonstrations, etc-) I realize that it is not the most efficient way of generating dc power, but...

Well anyway, I went back and tried several more things with no sucess.. starting to think that the alternator might be bad after all...  

I tried running from the terminal that goes to the charge warning light to both + and ground to energize the field, but the alternator didn't ever start charging...  The only real voltage that I have been able to measure out of it is from this charge warning light terminal to ground- I record around 2.5 volts @ max speed...

The gearing (tire as pulley to alternator) gives us about 18:1, and the existing chain drive and gearing allows for aprox 3 rev's per second of the wheel * 60 seconds gives us aprox 3200 rpm, which I figure should be enough...

I am thinking that I might try it without the voltage regulator hooked up just to see if I can register any output at all..

Can you see any flaws in my thinking?  anything I should try before we go out and get another alternator?

Thanks for your help!

Greg

[ghurd]

Still not a good choice. At all.

Surplus Center, 2.25HP Treadmill motor. $9.99. (and then about $12 shipping).

No problem. It works.

G-

[electroshock]

I would like to wish you luck!!!!!

All the suggestions that I have read on my indever

were to use a PM motor They might be efficient but there is

no way to adjust the magnetic field in them....if there is

then I would like to know...

what youre doing with an alternator, I have a design simmilar

on my drawing board...chains sprockets and even a belt

I think you would have better luck if you gutted the voltage regulator

and built a simple one (any power supply would work up to 4 amps and

 I would put a pot on it to adjust the rotor field) LM317t voltage

regulator for starters... alternators are a dime a dozen its a matter

of how to throw it together for a power unit.

have fun I know I am.