[DML] Re: Alternator problems

["David Teitelbaum" <jtrealty@xxxxxxxxxxx>]

I would agree that the alternator is bad. I suspect you have blown 1
or more of the diodes. That would cause a high ripple DC that the
voltage regulator cannot control. Changing the regulator won't help.
You need to replace the alternator or at least replace the bad diodes.
In most cases it is prudent to replace ALL of the diodes because even
though some may not have failed the others are probably on borrowed
time. The cheapest way is usually to just replace the alternator
rather than try to rebuild it. By time you do the brushes, bearings,
voltage regulator, and diode bridge, you can buy a reconditioned one
for less. Of course that is assuming you get one done by a reputable
shop. Many only replace the bad part, wash it (and wash out any
lubrication in the bearings) and spray paint it. This is not what I
would call "reconditioned". An ordinary dc voltmeter cannot read the
AC component in the DC voltage. Try reading on the AC scale. Anything
over around 1-2 volts AC is BAD. If you take the alternator out and
have it bench-tested they should be able to quickly see if the diodes
are popped. The diodes can be damaged by jump-starting and momentaraly
connecting the cables up wrong. It doesn't always happen immediatly
either. Overheating the alternator can also be the cause from
overloading it.
David Teitelbaum
vin 10757


--- In dmcnews@xxxxxxxxxxxxxxx, "Dave Swingle" <swingle@xxxx> wrote:
> Rich and I were working on an alternator issue today that I've never 
> run into. I know how to look for the usual stuff, but this one has me 
> stumped.
> 
> Start car - alternator light stays on, charging system at 12.1 volts 
> (DVM, not the dash gauge. Dash gauge looks to be about 9 volts). 
> 
> Rev Engine - charging system jumps to 13.9 volts, light stays on. 
> 





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