[DML] Re: alternator troubles

[Rob Hook <rob_hook@xxxx>]

I had some work done on my car locally which involved dismantling the rear 
suspension. A few months later (and it took several months to show 
itself), I started having strange alternator/battery problems. The 
alternator didn't seem to charge well at all but a test on my diagnostic 
machine showed it to be perfect. The battery would often die for no 
apparent reason and the car often wouldn't start. I eventually found the 
problem to be an improperly routed ground strap. The ground strap to the 
engine (the only one, as far as I can see) is hooked to the bolt that holds 
the lower suspension link on the driver side of the car. It should go 
from that bolt to a bolt on the transmission. It should NOT go to the 
motor mount. The mootor mount is made of rubber and won't provide a 
ground. This is why the strap is there in the first place. The mechanic 
had reconnected the strap in such a way that the engine was grounding to 
itself! I wasn't able to move it (stripped nut..maybe why he didn't put it 
back.) so I installed a second grounding strap running from the trailing 
arm bracket bolt where the negative battery cable connects to one of the 
starter motor bolts. Works like a charm!

--Rob Hook

-----Original Message-----
From:	Mike Substelny [SMTP:msubstel@xxxx]
Sent:	Monday, February 14, 2000 11:39 AM
To:	dmcnews@xxxxxxxxxxx
Subject:	[DML] Re: alternator troubles

DMC Joe said:

> If the battery is week the alternator will increase the output
> voltage. When the alternator sees no voltage from the
> battery (battery disconnected) it will run "full bore", this can
> cause serious and or permanent damage to the alternator and
> or other electronic components. If you have an auto trans this
> over voltage can damage the computer governor.

My expertise is miniscule compared to DMC Joe's, but I think the
situation is even worse than he describes. As I understand it, the
alternator does not put out nice, smooth DC current. It puts out a DC
wave pattern, and the car's electronics were designed with the
assumption that a battery would always be in the circuit to smooth out
that wave.

This should not harm motors (e.g. fuel pump), relays, or light bulbs, so
disconnecting that battery might have been a good diagnostic for cars in
the 60s. But if I am right, this test could seriously damage any solid
state components in the car, including the computer, the radio, any
'Zilla parts, etc.. If I am wrong someone please correct me.

I am pretty confident that running a DeLorean with the battery
disconnected is a BAD idea!

Donald, your messages have not mentioned the reading of your voltmeter
during this adventure. If your alternator is not working at all, then
"gunning the engine" as you described last Wednesday should not have
worked. Consider the possibility that you might have a more subtle
problem. Perhaps a bad ground wire somewhere is gobbling up just enough
current that your battery must discharge to keep the engine running any
time you are at low RPMs.

- Mike Substelny


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