Automotive alternator windings & rectifier

[Mike Cook]

http://www.autoshop101.com/forms/alt_bwoh.pdf

has photos of an alternator with 4 connections for windings (each of 3 phases
+ common), and the 8 diode rectifier. But wiring diagrams show only 3
connections and 6 diodes.

Where does the common winding terminal connect (there is a connection on the
rectifier plate)? Where do the other 2 diodes connect?

I handled one of these disassembled units but didn't have time to ohm out the
connections.

Thanks.

 

[amdx]

http://www.autoshop101.com/forms/alt_bwoh.pdf

has photos of an alternator with 4 connections for windings (each of 3 phases
+ common),

Not one of the pages shows four connections brought out from the
windings.

and the 8 diode rectifier.

I don't see any 8 diode rectifier.

But wiring diagrams show only 3
connections and 6 diodes.

Yup.

Where does the common winding terminal connect (there is a connection on the
rectifier plate)? Where do the other 2 diodes connect?

Common is created by the way the diodes are connected. >THAT< common is
connected to the auto frame.

I handled one of these disassembled units but didn't have time to ohm out the
connections.
Hmm.


Thanks.

Wo uld you ask your question again and maybe clarify the situation?

 

[Spehro Pefhany]

http://www.autoshop101.com/forms/alt_bwoh.pdf

has photos of an alternator with 4 connections for windings (each of 3 phases
+ common), and the 8 diode rectifier. But wiring diagrams show only 3
connections and 6 diodes.

Where does the common winding terminal connect (there is a connection on the
rectifier plate)? Where do the other 2 diodes connect?

The common in the Wye connection (called "Neutral Junction" in the
photo on page 18) goes to the 4th pair of diodes (and typically the
regulator). The other three pairs of winding ends ("Stator Lead Ends")
go to the other three pairs of diodes.

 

[Cydrome Leader]

The common point is sometimes used for fault detection.

When I was at Motorola SPD in the '60's I developed a circuit that
could detect just about any fault, shorted or open diodes and shorted
or open windings, by viewing that node. That node, BTW, is often
labeled "S". Old GM alternators brought that out as a post on the
back of the alternator (before regulators were internal... that's what
some of my patents are all about... integrating the regulator).

That was before CAD ;-) If I can find my hand drawing, I'll post it.

...Jim Thompson

dumb question.

what EXACTLY does the charge lamp indicate?

what triggers it to go on and off?

can it simply be removed and ignored?

 

[tm]

In sci.electronics.basics Jim Thompson


dumb question.

what EXACTLY does the charge lamp indicate?

what triggers it to go on and off?

can it simply be removed and ignored?

One cause that can light the lamp is a broken belt. You would like to know
as soon as that happens.

 

[David Lesher]

That pictured alternator is one used on Hondas. ISTM it's a
Nippon-Densi or such.

I have too much experience with same. I went through 3-4
boneyard ones before I bought a rebuilt one from Retarded Auto
Parts. That brand/model alternator is nice because the diode
array unscrews easily. No unsoldering needed.

That particular alternator has 4 pairs of power diodes; the
center point of the wye has a pair from there as well.... and I
have no idea why... Jim??

That said, all recent alternators also have a diode trio of tiny
diodes. Their function is to rectify enough power to excite the
rotor. It takes a few amps to drive it. Until it's up to speed,
that excitation comes from the battery, through the red idiot
light. When the alternator is up to speed, there is 12V on the
battery side of the lamp, and 12v on the load side....and it
goes out.

 

[Spehro Pefhany]

Not the alternators I've taken apart. The star point is typically a
crimp, and serves no other useful purpose.

Those were alternators with only six power rectifiers, right?

The field, and regulator power, are normally taken from an additional set of
diodes, usually 3, ie one per phase, such that the regulator is
effectively isolated from the battery when the engine is not turning.

The power rectifiers connected to the Wye common are used to extract
3rd harmonic power- yielding up to 10% additional current capacity-
when operating at high speed.



Best regards,
Spehro Pefhany

 

[Mike Cook]

Not the alternators I've taken apart. The star point is typically a

crimp, and serves no other useful purpose.

The field, and regulator power, are normally taken from an additional set of
diodes, usually 3, ie one per phase, such that the regulator is
effectively isolated from the battery when the engine is not turning.

But THAT'S why I'm asking here: this Denso alternator (used in MANY Hondas,
Toyotas, and myriad other makes) does have a common terminal connection to
the rectifier. The rectifier has EIGHT diodes.

Yes I agree that common configuration is 6 diodes. That's why I'm confused.
The system is quite populous and apparently functions. I just don't
understand how.

 

[Fester Bestertester]

One problem with this arrangement... if the red idiot light burns out

or a wiring fault opens the circuit, the alternator won't "bootstrap"
the next time you start the car, and you won't (of course) get any
red-light warning. Dead battery, here we come.

Ask me how I know :-(

That's why you LOOK at the Idiot Light when you turn the ignition switch on,
just before you start the engine. A lit ALT bulb means it is present and
functioning.

 

[Jasen Betts]

dumb question.

what EXACTLY does the charge lamp indicate?

current into the regulator not supplied by the altenator.

what triggers it to go on and off?

basically a working altenator.

can it simply be removed and ignored?

you could replace it with a short circuit

 

[Cydrome Leader]

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.

http://static.schneider-electric.us...ormers/Harmonic Mitigating/0104ED9501R896.pdf

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.
5,000 rpm.

http://youronlinemechanic.com/alternator-with-neutral-point-voltage/

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

http://autonopedia.org/renewable-energy/generators/alternator-secrets/

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.

 

[Don Kelly]

The power rectifiers connected to the Wye common are used to extract
3rd harmonic power- yielding up to 10% additional current capacity-
when operating at high speed.

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.

 

[Spehro Pefhany]

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.

Some more info:-

http://tinyurl.com/kdcsayk

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



Best regards,
Spehro Pefhany

 

[Don Kelly]

Some more info:-

http://tinyurl.com/kdcsayk

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
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