alternator overcharge

[Hippie]

When you spin the rotor, it generates residual magnetism electricity and fools the ohmeter.
I am suspecting a grounded rotor now. That could cause your wild outputs.
If a wire has broken and contacted the pole piece, that could explain the high resistance from slip ring to slip ring and still acount for a high field current and inability to be regulated.

Check this out:

http://books.google.com/books?id=keDwvn ... gh&f=false

[dingo]

thanks for the link...good stuff !!...should answer all my questions !

my old Haynes manual says that between sliprings, should measure 4ohms (+- 0.5)...so yes, 11 ohms is wayyyy out'

ok time to derust and crack that sucker open

[dingo]

alternator cracked open...slip rings had a silvery sheen covering them and showing high resistance...smoothed them out with fine sandpaper down to shiny copper...they now read 4.4 OHms. Much better ! hope that solves the issue.

Question: how the hell do you get the rabbit back in the hole...past the two brushes ?? Haynes cops out by saying 'it is the reverse of dismantling'

some special tool or technique ??



edit: ok, i figured it out...a welding rod with 4 or 5 specifically angled bends...you can snake it in thru the side slot and hold the 2nd brush down, then carefully remove once rotor is seated.

[dingo]

Ok, refreshed alternator re-installed in vehicle. Fired it up..but the overcharge is STILL there ! It is definately less wildly fluctuating..probably due to refreshed sliprings..but its way too high 15-17V....

whats left ? the dash light shorting out ? but it doesnt flicker...goes on and off exactly as it should...????

[Hippie]

Dash light? I don't think so. Did you check for grounds while you had it apart? Third regulator out?

[dingo]

no i didnt check for grounds....blech... All the diodes checked out...and i had convinced myself that the 4 ohms on the revived rings would solve everything

then i built a little regulator tester to test all my questionable regulators...got distracted.

[Hippie]

OK. Well a ground might not show up in an ohmeter test anyway. Often need a megger to find a coil ground as they put out a 1000 volts or so in pulses.
I would try to look up how to full field the alternator in this model, and see if you can manually regulate the field coil with it grounded or maybe with a reostat. Typically alternators draw up to about 2 amp at 12 volt through the field coil when the D+/B+ is trying to put out maximum voltage. Is there a way you can regulate field coil current manually to eliminate the regulator or its ground as a cause?

In other words, can you force the alternator to reduce its voltage output by manually controlling the field current at a given engine RPM with the regulator disconnected? Can you test the field current draw when it is running with the regulator?

Someone with a VW alternator set-up want to help us out by doing a field coil (DF) DC current draw test when it is working properly?

Regulator------------->open wire and Ammeter in series reads??? (mind polarity please)------------>DF terminal on Alternator

We need more info that I/we don't have to test.

[Hippie]

Also, I would like to see your regulator test jig you made. Cool.

[Hippie]

Is this a Bosch system? Does the warning light apply field current all the time thru the reg, or just excitation at start-up? Maybe you were on to something in that lamp circuit question.

http://www.alternatorparts.com/understa ... nators.htm

Do you have a Bentley schematic you could posts here?

[Hippie]

Here's another site: http://www.pelicanparts.com/techarticle ... eshoot.htm

The short of it is that some alternators and generators are self-exciting, meaning that the manufacturer built a little ferrous material into the field coil's core, so that there is a little residual magnetism already in it when the engine starts. That magnetic flux gives the rotor something to cut across at start up so an output voltage is produced...just a little bit. The output is fed back into the field coil through the regulator to continue building until it puts out full voltage at B+/D+ and there you go.

Apparently the Bosch is not self exciting and doesn't have any magnetism to get the whole system started unless there is a little trickle of current throught the alternator lamp on the dash. Once the alternator comes up to speed, the B+/D+ output is fed back to the field through the regulator and that greater current is now the running field coil, and is regulated to control alternator output (B+/D+) to the battery.

I wonder is something is not right there, where the field current is always coming from the lamp circuit from maybe another shorted diode somewhere so the the field current is bypassing the regulator and cannot be turned down by the regulator, leading to your high output voltage. Although, the lamp works you say, and it is the right wattage I assume.

It's just a thought. But now I am really interested in this problem and want to know what the heck is going on.

[chitwnvw]

But now I am really interested in this problem and want to know what the heck is going on.

Me too!

[dingo]

1. What is a TYPE B alternator system (This is the Bosch one we are talking about)

The “Type B” system has the VR connected between the alternator’s field and power. The VR regulates the BUS voltage by controlled powering of one side of the field (the other side of the field is grounded). A “Type B” alternator typically has one field terminal, or two terminals with one terminal connected to ground. Ford alternators are typical examples of “Type B” alternators. Even momentary grounding of the field (typically caused by wiring short, or failing alternator) will result in a field over-current condition damaging an unprotected VR. (maybe thats what keeps frying my VRegs ???)

What is a TYPE A alternator system

The “Type A” system has the VR connected between the alternator’s field and ground. The VR regulates the BUS voltage by controlled grounding of one side of the field (the other side of the field is powered). A “Type A” alternator typically has two field terminals. Prestolite alternators are typical examples of “Type A” alternators. Uncontrolled grounding of the field (typically caused by wiring short, or failing alternator) will result in an over-voltage condition, possibly damaging the VR and other electrical components.


2. From my old Haynes :

between slip-rings: 4 ohms (+- 0.4)
slipring to shaft...should be NO cont...else winding is grounded
between each pair of stator windings: 0.13 ohms (+-o.13)
stator to ground...should be NO. cont...low resist = grounded

3. 12V light bulb inserted between DF and any B+ should act as crude regulator (harness disconnected) It has worked for me before, but not this time.

[dingo]

bench testing voltage regulator...its not well written, but simple schematic


http://www.oocities.org/fwarner_au/mc_t ... g_test.htm


i dont have a variable power source..so my testing was inconclusive

[dingo]

My spare alternator: the rotor and stator windings all check out fine as far as resistance and no shorts...tho i can see insulation starting to flake off and some areas are green with corrosion....man these gizmos are getting old....i think my longterm goal is to find a more modern alternator that will fit in the hole...

[dingo]

Regulator------------->open wire and Ammeter in series reads??? (mind polarity please)------------>DF terminal on Alternator

what is the correct polarity for the in-series ammeter ???