alternator overcharge

[dingo]

OK, my latest test was to disconnect VReg and try the 12V light bulb between DF and B+....then i watched the Alt output simultaneously with Voltage at DF terminal where it connects to the bulb.

at idle..the Alt puts out 12.7- 12.9 and DF reads 6.6

at higher rpm Alt goes way up to 16 V and DF reads 7...7.4 etc

Ratwell.com says it should read 14V and 5 V


checking resistance at the harness DF to D- 5 ohms
D+ to D- 46 ohms
D+ to DF 51 ohms approx

DF to B+ no cont.

[Hippie]

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 ???

On a B system, negative to the field terminal on the alternator, positive to the regulator.

[Hippie]

at idle..the Alt puts out 12.7- 12.9 and DF reads 6.6

at higher rpm Alt goes way up to 16 V and DF reads 7...7.4 etc-----> I bet at 2K RPM and 5 volts of DF, it would be close to 14V

Ratwell.com says it should read 14V and 5 V ----> but at 2000 RPM, IIRC, not idle

To me, this is pointing away from a defective alternator. I'm still thinking about the wiring harness resistances. I don't know what's on there. Remember I have no diagram and a generator on my Bus. I have never had the opportunity to troubleshoot a Bosch/VW alt. system. I need to think a bit.

[dingo]

some other stuff i found...

High field current may produce uncontrolled alternator output and probable damage to the voltage regulator.
[....testing procedure complicated..with rheostats etc...] Generally, this is approximately 2.0 to 2.5 amperes at battery voltage (12.0-12.6v).

I already tested the isolation diodes internally..but still, this a test that can be done on running engine

This test will determine if the isolation diode is conducting alternator energy, from the rectifier diode assembly, to the output stud. If the isolation diode
is open, alternator energy would not travel beyond the rectifier diodes. A high voltage may develop in the alternator that could damage the voltage regulator.

(c) With the engine running at fast idle, connect voltmeter, negative lead to ground, positive lead to the auxiliary terminal, (D+). Note voltmeter read-ing
(d) Move voltmeter positive lead to the alternator output terminal. Note voltmeter read- ing.
(e) The voltage indicated at the output (positive) terminal should be 0.8 to 1.2 volts lower than
voltage noted at the auxiliary terminal. (D+) If voltmeter reading at the output (positive) terminal is battery voltage
(12.0-12.6 volts) the isolation diode is "open".

[dingo]

for your perusal..heres a schematic: http://www.vintagebus.com/wiring/bus-76.jpg

C and C1, on the left, are alt and reg...click to enlarge


also: The alt-dash light is effectively connected *between* battery (+) and alternator output, so it indicates when either side is low, though not both(!).

[dingo]

..pulled the alt. again...cracked it open...removed rotor and stator...checked for grounds on both ...nothing out of order.
Stator windings read correct resistance...and NO grounded field...

so much for thaT...

Ok wait...Haynes says stator wires should read 0.13 ohms between each pair (+-0.013)and when i measure mine its 0.4 ohms

but when i measure the pairs on my spare alt. i get the same 0.4 ohms

so either bot stators are out by the exact same amount (?) or my cheap meter is inaccurate

[dingo]

only funky thing i can see..is that worn out insulation on braided copper wire is possibly shorting against the plate that holds the 3 diodes at the very back of the alt., when i shove the plate back on to put the two nuts on the back of B+_ terminal

it only a 'possible'...but im clutching at straws now

[dingo]

OK my dad measured some Bosch stators at 0.3 and 0.2 ohms....so maybe that haynes book is outdated

i have glued in an insulation protection on diode plate to avoid shorting out when bolted down

not exactly expecting much

[dingo]

Alt. back in..fired up...same story...16V

[Hippie]

Darn. Try Regulator #4? I'm out of ideas.

[dingo]

yeah im stumped too...anyways i have some spare parts on the way to complete the spare Alt...and as a backup plan i found a nice Nippon Denso alt with piggyback reg that fits fairly well...tested, works fine...only small amount of improvisation needed...only question remaining is what to do with 85Amp ? espresso machine would be bueno !!

[Hippie]

bueno!

[dingo]

Infor for Hippie: i just realized that these early Bosch alts with external VR have the brush combo of DF and D-...whereas all subsequent Bosch alts with piggyback VR have the brush combo DF and D+...

[Amskeptic]

Infor for Hippie: i just realized that these early Bosch alts with external VR have the brush combo of DF and D-...whereas all subsequent Bosch alts with piggyback VR have the brush combo DF and D+...

Hippie asked if it was an "A" system before I deleted his post (how rude).
Hippie, check General Chat for "Here Hippie" (you can retitle it as you see fit) where you can let us know more about bottling plant programming.
Colin

[Hippie]

Sorry dingo, I'm too mentally tired and busy to help solve this or even remember what kind of a system it is.
Maybe Colin can figure it out. I shouldn't have gotten into this in the first place.
Good luck to ya, bro.