Re: help: 300sd alternator

jingyuanw@xxxxxxxxx wrote: 
Hi Folks,

Battery in a 1982 300SD died the other day, so I took a multi-meter to
check whether there was any short in the circut. It turned out that the
alternator was partially shortted: the resistance between the two
battery cable poles was in the teens with the battery disconnected and
alternator connected, the resistance with the alternator disconnected
was infinity.

So I took the alternator out and studied how it should work. The diode
pack seems to be OK(resistance around 7 ohms one way, infinity the
other way). The voltage regulator seemed to be working: when I applied
12 volts to the regulator, there was currect between the two brushes;
when I appied 14 volts to the regulator, there was no currect between
the two brushes.

The voltage regulator only has a over all resistance of 7 or 10 ohms,
since there is a resistor on the regulator that said 68 ohms on it, I
assume it should be this way.

The problem is, the positive pole of the battery is always connected to
the volgage regulator positive pole(resistance is zero), so there is
always a drain through the voltage regulator(resistance at most 68
ohms), if my assumptions are correct so far, there must be some switch
to shut off the voltage regulator, where is this switch then? Ignition
switch?

Help is greatly appreciated, thanks in advance!



batt-<Diode---| rotor ---------------O
 |            |
 |            |---Diode>-- regulator --- stator-0
 |                       |
  --Diode>lamp ----------


Hope my ascii is readable. The upper two sets of diodes are of course triple sets for three phase current.

--

Roland Franzius
.

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