be all that as it may, it is simpler to remember that the mgb alternator has
a built in regulator. this internal regulator determines if the dc voltage
at it's output terminal is higher than what it is producing and sources a
voltage to the indicator light terminal if this is so. there are 3
terminals, a gnd, a large connector to the battery, and a connector to the
indicator light, which is mislabeled 'ignition'. I think the moss catalog
actually has a picture of the alternator connector
(do carefully check the fanbelt btw). any pulsing is usually a shorted or
leaky diode. These are replaced in a pack. This can occur at higher
electrical loads btw.
I find these alternators very sensitive to jump starts and any other arcing
on the frame of the car. I have had the car jump started or used it to jump
start someone and occasionally found the alt. whacked directly after. the
diode pack is available from Moss as well as the regulator. There should be
no voltage at all on a properly operating alternator regardless of make on
the indicator light terminal, and I believe regardless of the actual dc
voltage. I suppose that if someone had been radically altering your wiring
right before this, or your battery developed a strange high impedance cell,
(your electrical system would be working very very strangely), you might
produce some results like this, but if that were the case usually the car
wouldn't start in the first place. I really dislike that wimpy ground
connection at the battery location myself.
there is a lot of text in various places on putting a higher output bosch or
GM alternator in it's place, (either would outlast the car). then again I
have seen ads for used Lucas alternators for 35-50$ US. you could simply
take it out and take it to any decent auto parts store and ask them to hook
it up to the test jig and they'll tell you the results, it is a very
classical type of system.
-----Original Message-----
From: REwald9535@aol.com <REwald9535@aol.com>
To: wizardz@amdyne.net <wizardz@amdyne.net>; mgs@autox.team.net
<mgs@autox.team.net>
Date: Saturday, December 26, 1998 10:20 PM
Subject: Re: Alternator Light - Pulses?
>Paul,
>Before you go tearing too many thing apart let's go over your test results.
>
> >> The Volt Meter easily rises to +14 - 14.5 volts, when the car is
>first started from it's initial 12 volts. While the light is off, the Amp
>Meter will show a charge rate or roughly 3 - 5 amps. When the battery gets
>to 14 volts, ( a minute or two) the light comes on, and I'll see no
current
>flow on the amp meter.
>A fully charged battery is 12.72 V (excluding surface charge) there is a
>certain amount of resistance in each cell of a battery about .2V. To fully
>charge a battery you must have a voltage above 12.72 + (.2 X 6) = 12.92 V.
If
>a battery is discharged it requires less voltage to charge it, as the
battery
>reaches a fully charged state more voltage is required to keep charging it.
>The reason you are seeing no current when the alternator gets to 14 volts
is
>that the battery is fully charged. No more current is required to charge
the
>battery. Normal voltage from an alternator is considered to be in the
range
>of 13.5-14.5 volts.
>
>>>Conditions: Starts quick and easily. All ace. turned on, only drops the
>voltage a max. of 1 volt. (with the idiot light on or off)
>Doesn't sound like a bad battery or alternator to me. <G>
>
>>>QUESTION #1: Do I suspect the battery, alternator, or something on the
WHT
>ckt. that is loading down the line.
>>From you test results the battery is OK, and the alternator is putting
out.
>There may be problems in the circuit for the warning light.
>
>>>QUESTION #2: If it's the alternator, would it be the brushes? regulator?,
>diode array?
>Brushes I don't think so. Regulator possible, I'm not that familiar with
how
>B alternator systems are wired (hey mine has a C40 on it). Diode array is
a
>possible. Here is a simple test for bad diodes. Put an A/C (yes A/C)
>voltmeter across the battery terminals start the engine, headlights and
heater
>fan on. rev the engine to about 2000 RPM. Read the voltmeter. If you
>reading is less than four-tenths of one volt your diodes are OK. In your
case
>I would repeat the test when the warning light is on.
>
>>>QUESTION #3: Could the battery being at 14.5+ volts, make the alternator
>think it's not charging, so the light comes on, since the alternator output
>voltage is the same as the battery voltage?
>Assuming no voltage drops in the circuit, alternator output is the same as
>battery voltage. Now before you hit the flame on button let me explain.
>Let's say your alternator has an output voltage of 14.0 volts, measured at
the
>back of the alternator. Then when you measure the voltage at the battery
you
>will see 14.0 volts, assuming no voltage drops (resistance) in the circuit.
>If the system is at 14-14.5 volts the alternator is charging what the
battery
>needs. If the battery is fully charged, a system voltage of 14.5 and zero
>current into the battery would be normal.
>
>Another way to check the state of charge of you battery is to let the car
sit
>over night after driving with all electrical systems off. Then in the
>morning, before turning anything electrical on, measure the voltage across
>the battery terminals.
>12.6 Volts or above indicates a fully charged battery.
>12.4 volts is 3/4 charged
>12.2 volts is 1/2 charged
>12.0 volts is 1/4 charged
>If you measure you battery tomorrow morning at 12.6 you do not have a
charging
>system problem, you have a problem with the indicator light circuit.
>I hope this helps,
>Rick Ewald
>
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