Automotive alternator windings & rectifier

Yes.

Thanks, I've learnt something today. I was aware that harmonic neutral currents are an issue with mains supplies but never thought they might be an advantage here.

I can find very little on the web regarding neutral point rectification for car (Lundell) alternators, but there is a lot about 3rd harmonic neutral currents. An example how these manifest in electrical systems for non-linear loads.

A conventional automotive alternator uses six diodes to rectify three-phase AC (Alternating Current) into DC (Direct Current). The average voltage of the neutral point is 1/2 of the output DC voltage. While a low output current flows, the voltage at the neutral point is mostly DC, but it also includes an AC portion. As current output increases, the AC portion increases.

When the alternator speed exceeds 2,000 to 3,000 rpm, the peak value of this AC portion exceeds the DC output voltage.

This means that, compared with the output characteristics of the alternator without neutral-point diodes, the output gradually increases from midway by 10 to 15% at a normal rated alternator speed of approx.

common to the chassis 3 big diodes to battery positive 3 small diodes to the altenator regulator another small diode between the regulator and the altenator light,

eigth diode, dunno.

current into the regulator not supplied by the altenator.

basically a working altenator.

you could replace it with a short circuit

They are a multitude of ways to implement the "idiot light" function, some used relays, some were a part of the regulator.

I'm in the midst of moving right now, old house sold faster than new one's construction, so I'm stuck in a snow-bird friend's loaner with no access to my (paper) file cabinets.

When I get back on the air I'll retrieve those drawings and post.

Keep in mind I did no automotive after about 1973, so I'm not up on any modern approaches.

Or, like many GM alternators, the rotor was mildly magnetized to provide "kick-start", minimum load requirement hidden by the "daylight-safety" headlamp BS ;-) ...Jim Thompson

Here's a diagram of what the above link failed to clearly explain

so somehow tapping neutral is good. I guess those two diodes bypass current flowing int coils the wrong way or something? As to how speed matters, I'm not following that.

If you consider that at any time 2 windings will be supplying one polarity of current and the remaining winding the other polarity, you can see the neutral point is going to move in the direction dictated by the two windings. At higher currents, and higher frequencies, the inductance of the winding causes an increasing voltage to appear at the neutral point.

That doesn't make sense to me. One advantage of 3 phase is the elimination of triplen harmonics. Now, with a 3 phase bridge-will there be a significant 3rd harmonic voltage? Certainly,if the wye neutral is not connected to the DC ground, there is no 3rd harmonic current and power. Generally this is a good thing. Somehow, I appear to be missing something-could you elucidate? A circuit diagram and analysis would help.

Some more info:-

http://ece.ubm.ro/cjece/web/CJECE_VOL5_2012/3_Barz.pdf

Best regards, Spehro Pefhany

Thank you for the information- also thanks to Mike Perkins-The references were useful my background is in power systems so I have a different view on 3rd harmonics.

Don Kelly remove the cross to reply

You are referring to the diagram on page 3 of the above document?

Those are not the individual windings brought out of the alternator. The 6 winding leads are connected internally through the diode bridge and brought out as two connections to the outside world. The B+ terminal and the alternator frame ground. This is shown on pages 23 and 24.

What isn't made clear in this document are the connections between the windings, field and internal regulator. The regulator connections are brought out as the IG, S, and L terminals (some alternators may have more or fewer of these connections).