[Diy_efi] CS Failure

[Tom Visel]

I own a repair shop specializing in electrical and driveability 
diagnosis and repair.  If my shop had no overhead, I could probably 
retire on the income I make from alternators which other shops (or 
customers) installed and had die on them due to high resistance in the 
output circuit.   Intermittent or poor lamp circuit (L terminal) 
connections will cause intermittent no-charge problems.  Poor or no 
connection at the sense (S terminal, the big one in the regulator 
connector) may cause the alternator to undercharge, but rarely to 
overcharge or burn out.  What burns out CS-series (and indeed, all) 
alternators is heat.  Internal heat, cause by overwork because the alt 
can't charge the battery properly and/or can't monitor the battery's 
state of charge.  To diagnose your vehicle:

With a fresh known good alternator and a fully charged battery (12.66 V 
or better) installed, check the voltage drop on the positive and 
negative sides of the charging circuit.  To do this, get the alternator 
under a good load: engine running, lights on, heater blower and A/C 
running, cooling fans going if you have them.  If you have an ammeter, 
clamp type or no, measure the current flow through the system.  Positive 
or negative side will be the same, and be sure to include all of the 
wires at the battery in your measurement if using a clamp-type probe.  
Note the reading.

While the engine is still running, using your DVOM, measure the voltage 
between the alternator case (the case thru-screws are good candidates) 
and the battery negative terminals.  Note the reading.  Now measure the 
voltage between the battery positive terminal and the alternator output 
stud.  Note the reading.  If you got negative readings, ignore the 
sign.  It's the number that counts.

Total your two voltage readings.  This is the "voltage drop" in the 
charging circuit.  It is a reflection of the resistance in the circuit - 
resistance which will put a long-term strain on your alternator's diodes 
and overheat and kill them.  If you get a total of greater than 0.1 Volt 
per 10 Amps of alternator output, that is too much voltage drop and the 
connections and/or wires and cables will need to be improved.  For a 
standard 105 amp CS130, 10 gauge wire straight to the battery, with a 14 
gauge fusible link, is sufficient.  For a "high output" alternator, 8 
gauge with a 12 gauge fusible link is recommended.  Also, you can't have 
too many grounds.  Besides keeping your alternator alive, quality 
grounds (less than .050 volts drop) will help stave off computer 
stupidity.  You would be astonished at the number of vehicles that leave 
my shop with a sub-$150 repair (diagnosis, labor, parts, tax) when other 
shops told the customer that s/he needed a new ECM or a stack of new 
sensors.

TomV

Clayton Martiniuk wrote:

> Hello, I have an 1994 Chevy 350 that Keeps eating alternators for some 
> reason. They seem to work for about two days and then shit out. I have 
> a cs series alternator powered with one exciter/indicator wire at the 
> F terminal. Looking at the indicator bulb, I'll start the truck, the 
> light will go off for a while but turn back on intermittently. I heard 
> that these years of trucks seem to have a problem. Some say to ground 
> the back of the case to the batt but I dont see how on mine. I am 
> probably close to duty cycle but no major power drains. It gets very 
> cold here around -20 to -50. I am running an electric fuel pump. I am 
> running an red top optima with 800 cca. Does this Battery require 
> special needs? Is the answer an larger amperage generator or am I 
> doing something wrong?
> I am sick of buying alternators and no one can seem to figure out 
> whats happening.
>                                                 Thank you for your time
>                                 Clayton Martiniuk
>
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