[Healeys] voltage drop was intermittent OD part 3

Richard Ewald richard.ewald at gmail.com
Thu Aug 19 11:21:23 MDT 2010


How do I interpret the results?
Just like golf a low score wins.  In a perfect world all voltage drop
reading would be zero, indicating no resistance in the circuit, but
guess what we dont live in that perfect world.  You will always get
some type of reading.  The object is getting the number as low as
possible.
Lets say you get a reading of 1 Volt.  That means if you put 11 Volts
into the cable at the battery (this is the voltage of a very healthy
12V battery while cranking) you will get 10 Volts out the other end as
1 Volts is being lost to resistance
If I got less than 1 Volt drop between the battery and the starter I
would probably be happy (particularly if you consider the length of
that one cable).  But for the sake of conversation lets say I get a
reading of 3 Volts.  This means that if I put 11 Volts into the cable
I am only getting 8 Volts out the other end.  This is staring to get
real marginal and might leave me stranded.  At this point I want to
pin point the exact cause of the resistance.

How to isolate the problem:
Test the circuit in sections.  In our LBC starter scenario you could test
Battery post to battery cable clamp (a might hard with the OE cap
style battery cable end I admit)
Battery end of the cable to solenoid end of cable
Across the solenoid itself
Cable from solenoid to stud sticking out of the starter.
Dont forget that current must be flowing for each and every test.
That means in this case you have to crank the car.
Lets say after all of these tests I find high voltage drops at the
following points
Battery post to cable end
Across solenoid
Solenoid to starter motor stud.
At this point I would pull the connections apart, clean them with
steel wool, apply dielectric grease and reassemble.  When I was all
done, I would retest.  If the voltage drop was now acceptable I am
done.  If say the drop across the solenoid was excessive I would hit
the catalog up for a new solenoid.
The trick here is to isolate the circuit into sections and test/
repair/ retest/ move to next problem until you have the voltage drop
under control.
More follows


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