[Diy_efi] Starting and Charging CS Vs. SI

Tue Nov 1 16:23:46 UTC 2005

  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

----- Original Message ----- 
From: "Dustin Lof" <bubblesjrtwo at yahoo.com>
To: <diy_efi at diy-efi.org>
Sent: Monday, October 31, 2005 7:22 PM
Subject: Re: [Diy_efi] Starting and Charging

>
> If it is The original alternator to the 86 it should
> have a two wire connector, fairly large flat terminals
> side by side, plus a large insulated stud on the back
> of the alternator.  It is called the output circuit.
> The insulated stud goes to the battery, one of the
> terminals in the two wire connector should go to key
> on power, if you dont use a light bulb and have it on
> the same circuit as your ignition then you need to
> install a diode inline, without the diode the
> regulator will feed current back to the switch and the
> engine will not shut off.(It is grouned internally
> through a resistor in the regulator until the
> alternator begins to produce current then it switches
> to current, to shut the light off) My projects use a
> diode because they use a single pole toggle switch for
> an ignition switch. This is called the exciter
> circuit.  Most regulators function fine without any
> resistor whatsoever.  The second wire needs to go to
> the large stud on the back of the alternator, some
> factory harnesses run this wire to the stud on the
> firewall this is where the regulator senses the output
> voltage, if this wire is not there the regulator is
> unable to sense the output voltage and regulate said
> voltage.  This is called the sense circut. I am not
> sure off the top of my head which one is what,
> tomorrow in the light I can go look, and draw a
> scematic if you need. I hope this helps   Dustin Lof
>
>
> --- Milosz Kardasinski <miloszk at gmail.com> wrote:
>
> > I don't remember what value of resistor I used but
> > 50ish sounds about right. Perhaps this will help...
> >
> > CS manual on my site...
> >
> > http://www.no-bling.com/techdocs/CS-130.PDF
> >
> > Cheers,
> > M.
> >   ----- Original Message ----- 
> >   From: WopOnTour
> >   To: diy_efi at diy-efi.org
> >   Sent: Monday, October 31, 2005 7:43 PM
> >   Subject: Re: [Diy_efi] Starting and Charging
> >
> >
> >   Clayton
> >   I believe the field input terminal to the older CS
> > alternator is meant to be loaded by the BATT lamp.On
> > trucks that used a gauge with no bulb this circuit
> > utilized a resistor wire. So if you have it wired
> > directly you could either put a 194 bulb into the
> > circuit, utilize the BATT lamp in the exiting
> > cluster or maybe add a 40- 50 ohm resistor.
> >   HTH
> >   WopOnTour  >
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