Hello,

I have this old alternator, which I'm trying to setup for an exercise bike. Previously, I had worked with a kind of different alternator, although the operating principle is the same, it confuses me a little bit. Below you can see the alternator, its nameplate, and a 0.5 ohms/100 watts power resistor. In the yellow circle you can see the alternator's pins functions: B+, tach, GND, and FLD (field). When pedalling, I should expect a voltage between B+ and GND, right? Because I see nothing when I measure it. Also, the resistor should be connected between B+ and GND? And how can I vary the strenght of the field through the FLD pin? In other alternators, I've seen two pins for the field. In this case, should I vary the voltage between FLD pin and GND (ground) ?

 

If the field winding is brought out it looks to me as though the regulator is missing, you can make one with a LM311 or similar. Unless you can get the correct one from a wrecker, BTW typically you need a initial voltage as most auto alternators are not self exciting.
Max.

 

If the field winding is brought out it looks to me as though the regulator is missing, you can make one with a LM311 or similar. Unless you can get the correct one from a wrecker, BTW typically you need a initial voltage as most auto alternators are not self exiting.
Max.

My confusion is more about the wiring. This is what I think:

1- Power resistor between B+ and GND.
2- Regulator between FLD and GND
3- The tach signal might no be of interest

Am I right?

 

You need to apply 12v to the Field Terminal and gnd, to excite the alternator, then when peddaling you will get an output at the B+ and gnd.

You will need the regulator or have to make one, to maintain 14V output.

 

Ok. So, the power resistor is just to provide a path for the generated energy at B+, right? Can I PWM between Field and GND to vary the strength when pedalling?

 

The simplest is the comparitor with an input pot for the regulated output voltage as needed.
Max.

 

The simplest is the comparitor with an input pot for the regulated output voltage as needed.
Max.

If measure the field effective resistance, I get 5 ohms. At 12V, this is 2.4A. This means I need like a 3A supply for this setup?
I will check the LM311 that you suggest.

 

I actually made one for a 230vdc generator, you could adapt this version of it as needed.
You need an initial voltage after that it is self sustaining.
Max.

 

This is a Bosch altenator regulator circuit that will work with that altenator. Or ateratively buy a RE55 reg, or find one in the wreckers.