Jim; I appreciate this dissertation of the regulator circuitry which I
obviously never fully understod. I am saving it.
Blame it on the military. Unlike others who gained expertice in electronics
and such, I spend a lot of time on KB duty and in the brigg for being non
conforming, contrary and just a plain A-hole. I am learning now.
On 12/7/06, Jim Cathey <[EMAIL PROTECTED]> wrote:
> I cannot see how a bad diode/Rectifier, loose belt, bad fuse etc can
> keep
> the light on as you describe.
A bad diode can. The circuit has already been adequately described,
perhaps a bad ASCII schematic?
D1 D7 Winding A
D2 D8 Winding B
Terminal D D3 D9 Winding C
/----------------------------------+------|<|---------+-()()()()---+
| S1 | /------|<|----/
|
/----+--o-->o------+------+
+------|<|---------+-()()()()---+
| | | | |------|<|----/
|
=== | | ====
\------|<|---------+-()()()()---+
= ===== +-|Lamp|----------+-----|<|----/
=== Bat. |Misc.| ==== | Terminal B
= |Loads| =====
=== ===== |Volt.| Field
= | |
Reg.|----BR------()()()()---\
| | =====
|
\------------------+-------------------------+-------
BR-----------------/
|
Rest of Car <-- | ---> Inside alternator
|
Not shown are D4, D5, and D6, the other three heavy diodes that complete
the three-phase rectifier system. (They don't matter for the purposes
of
this discussion, and it was hard enough to draw the above and try to
make it clear.)
Normally, when everything is working right, battery current runs through
S1, the ignition switch, and powers various loads (ABS, radio, SRS,
ACC...), as well as running through the lamp to the voltage regulator,
thence through the brushes to the field winding and to ground. The lamp
is lit by this field current. No current goes through any of the
diodes.
Once the alternator is spinning, its generated current runs through
D1-D3
(and virtual ground is supplied through the not shown D4-D6) to charge
the battery. The voltage regulator monitors this voltage, and is
powered
by it too, through D7-D9, resulting in a net zero voltage across the
lamp
which remains dark.
Now, if any of D1-D3 are shorted, even when the key is off battery
current will flow through the offender, through the windings and
through D7-D9, to the voltage regulator which will power the field
winding, _and_ through the lamp to the other normally-switched loads.
There is obviously, in your case, enough current to light the lamp.
It only takes something like 100m-200mA to light the thing. It's
the alternator field winding that sucked the battery dry so quickly.
All clear?
-- Jim
_______________________________________
http://www.okiebenz.com
For new parts see official list sponsor: http://www.buymbparts.com/
For used parts email [EMAIL PROTECTED]
To Unsubscribe or change delivery options go to:
http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
--
Hans Neureiter, Houston, TX
'82 300SD, '95 E300D
