[Diy_efi] Starting and Charging CS Vs. SI

[Don Sauman]

David

Last year I fitted a 10Si alternator to my Jeep Wagon and had to work 
out those solutions.

Thanks for a very clear and informative description.

Don

David Allen wrote:

>  If he's got an SI series alternator (the one described- with the 2-wire
>flat plug - like an 85 model would probably have) there's one more thing to
>consider with the resistor or light bulb.
>  When the alternator is running, the current to power the field (the rotor
>winding) only comes from the current produced by the alternator windings,
>through the diode trio.  When the alternator is not turning, the rectifier
>diodes prevent battery power from reaching the field winding. At this point,
>the supply voltage for the field will fall off and provide a "ground" for
>the warning lamp.  This small current will flow through the field winding
>and will excite the alternator when the engine is started.
>  Here's where the fun starts. If there is full battery power on the field
>circuit without the engine running (because a non-resistive circuit is
>connected between the warning lamp terminal and switched power) the voltage
>regulator will try to regulate the field as during normal operation.  It
>will put as much current through the field winding as possible trying to
>maintain the system voltage.  All the field current is flowing in the
>warning lamp terminal, through the rotor winding, and grounding through the
>regulator output stage. This is not, in and of its self, bad.  BUT when this
>happens without the engine running there is no cooling airflow from the
>alternator fan, and in several minutes the regulator will overheat.
>  There are several regulator manufcturers out there.  A good one will
>probably survive like this no problem.  But in years past, this hookup has
>burned out alternators.  If you always crank the engine immediately, it will
>most likely not happen.  But it is a risk and can cause problems down the
>road.
>  One of the easiest ways is to solder together a 50R high-watt resistor,
>and a large diode (like one of the Radio Shack 6 amp jobs) and seal it up in
>heat-shrink. Connect it between the ignition switched power circuit and the
>alternator's warning lamp terminal.  You have a setup that will provide
>protecton against backflow of current (engine not stopping) and regulator
>overheating with stopped engine and key on.
>  The off-highway equipment I work on uses SI alternators on certain older
>models.  They use the exact setup described above.
>  The way I know this to be a fact is an interesting story.  We had a call
>on an off-highway truck with an SI alternator issue.  The complaint was that
>alternators keep failing.  The customer had been installing alternators from
>AutoZone, NAPA and Advance Auto.  All would fail in short time.  All this
>started after the original one (which had lasted years and) failed from a
>bad bearing.
>  This machine had the resistor/ diode assy described above.  At some point
>in the past this had been removed and bypassed.  The original Delco
>regulator withstood this without problems but the aftermarket units would
>not. The failure mode for the alternators was severe overcharging (over 16
>V) for 2 or 3 minutes followed by rectifier burn-out. It might charge
>normally for days or weeks before this would happen.
>  Installation of a resistor/ diode and a new NAPA alternator fixed it.
>  BTW  I didn't see the original post. If he has the original alternator to
>the 1994 model engine, it will be a CS series unit and does not need any
>resistor.  Connect switched battery power to the terminal labelled I or F.
>This unit will have a 4 pin Metripack connector built into the alternator
>but the harness may only connect to one of the pins. (The connector pins are
>tiny and needle-like with one larger than the rest.) If this overcharges it
>needs repair, or there may be moisture in the connector putting a low but
>detectable voltage on the sensing "S" terminal. Just my two cents worth!
>David
>
>  
>

-- 
Don Sauman
Documentary Photography and Video

35 Asteroid Way
Carlisle 6101
Western Australia

P: 08 9361 0337
F: 08 9361 0581
M: 0413 746 695