Key--off current draw from 12SI alternator
Ed Treijs
Trans Am.
My new battery went completely dead in a week. A meter showed a
current draw of about 300mA with the key off. Removing the two-pin
connection from the alternator dropped the current draw to about 9mA.
This is a completely repeatable result.
The alternator appears to work fine, except maybe for being a bit weak
at idle with the backglass defrost on. However, something is obviously
wrong inside it.
The '78 Pontiac service manual refers to diagnosis using the "ALT"
light, but my T/A has rally gauges and no warning lights, so I can't
use the manual's procedure. Nevertheless, the manual says that "if the
ALT light is on with key off, remove the two-pin connector; if the
light goes out, replace the rectifier bridge." So I'm guessing that my
ALT light would be on with key off, assuming I had an ALT light?
The rest of the troubleshooting procedures involve disassembling the
alternator, which is more work in winter than leaving the two-pin
connector off when the car is parked!
So my four questions are:
1) Do the symptoms as described point to a bad rectifier bridge in my
alterntor?
2) For the short term, can I simply disconnect the two-pin connector
while not driving, and connect it when I am driving? (It's winter in
Ontoario!)
3) I have an overhauled/rebuilt 10SI with unknown components in it.
Can the diode trio and rectifier bridge be swapped between a fairly
high amperage 10SI and my 12SI?
4) Okay, I've studied the factory manual charging system pages and the
wiring diagrams. How on earth can a "ALT" light be on with the key
off? The light circuit is interrupted! Yet apparently it can happen?
Thanks
Ed
Scott Dorsey
>I have a 78 amp 12SI alternator, out of a mid-80s Riviera, in my '78
>Trans Am.
>
>My new battery went completely dead in a week. A meter showed a
>current draw of about 300mA with the key off. Removing the two-pin
>connection from the alternator dropped the current draw to about 9mA.
>This is a completely repeatable result.
You have a leaky diode.
>1) Do the symptoms as described point to a bad rectifier bridge in my
>alterntor?
Yes.
>2) For the short term, can I simply disconnect the two-pin connector
>while not driving, and connect it when I am driving? (It's winter in
>Ontoario!)
I suppose so, but it is just going to get worse.
>3) I have an overhauled/rebuilt 10SI with unknown components in it.
>Can the diode trio and rectifier bridge be swapped between a fairly
>high amperage 10SI and my 12SI?
I don't know, but you can look at it and see. Honestly high current
diodes should not be a difficult thing to find. Ask your local TV repair
shop.
>4) Okay, I've studied the factory manual charging system pages and the
>wiring diagrams. How on earth can a "ALT" light be on with the key
>off? The light circuit is interrupted! Yet apparently it can happen?
It wouldn't be the first time I have seen the factory manual wiring diagram
at odds with the actual vehicle. Just because the manuals say it's wired
in a particular way doesn't mean that it is.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
dsi1
> I have a 78 amp 12SI alternator, out of a mid-80s Riviera, in my '78
> Trans Am.
>
> My new battery went completely dead in a week. A meter showed a
> current draw of about 300mA with the key off. Removing the two-pin
> connection from the alternator dropped the current draw to about 9mA.
> This is a completely repeatable result.
A third of an amp drain doesn't seem like much although I suppose if you
didn't drive the car it could discharge the battery in a week or so. The
most basic test you could do is to measure the voltage across the
battery terminals with the engine running and with the engine off. A low
voltage with the engine running would probably mean your alternator was
the problem or that it's output wasn't enough for what you're running. A
low voltage with the engine off would probably mean a problem with your
battery or excessive drain. 300mA seems fine to me.
Ed Treijs
> Ed Treijs <ed.toro...@gmail.com> wrote:
> >2) For the short term, can I simply disconnect the two-pin connector
> >while not driving, and connect it when I am driving? (It's winter in
> >Ontoario!)
>
> I suppose so, but it is just going to get worse.
Okay, it's time to start doing a bit of alternator dissassembly.
> >3) I have an overhauled/rebuilt 10SI with unknown components in it.
> >Can the diode trio and rectifier bridge be swapped between a fairly
> >high amperage 10SI and my 12SI?
>
> I don't know, but you can look at it and see. Honestly high current
> diodes should not be a difficult thing to find. Ask your local TV repair
> shop.
May be easier to find a 12SI alternator in the junkyards than a TV
repair shop! I do have a decent AC/Delco parts place in my end of the
city.
....Ed
aarcuda69062
<ffe239c6-ec8f-4add...@k22g2000vbp.googlegroups.com>,
Ed Treijs <ed.to...@gmail.com> wrote:
> I have a 78 amp 12SI alternator, out of a mid-80s Riviera, in my '78
> Trans Am.
>
> My new battery went completely dead in a week. A meter showed a
> current draw of about 300mA with the key off. Removing the two-pin
> connection from the alternator dropped the current draw to about 9mA.
> This is a completely repeatable result.
>
> The alternator appears to work fine, except maybe for being a bit weak
> at idle with the backglass defrost on. However, something is obviously
> wrong inside it.
>
> The '78 Pontiac service manual refers to diagnosis using the "ALT"
> light, but my T/A has rally gauges and no warning lights, so I can't
> use the manual's procedure. Nevertheless, the manual says that "if the
> ALT light is on with key off, remove the two-pin connector; if the
> light goes out, replace the rectifier bridge." So I'm guessing that my
> ALT light would be on with key off, assuming I had an ALT light?
>
> The rest of the troubleshooting procedures involve disassembling the
> alternator, which is more work in winter than leaving the two-pin
> connector off when the car is parked!
>
> So my four questions are:
>
> 1) Do the symptoms as described point to a bad rectifier bridge in my
> alterntor?
Not necessarily.
> 2) For the short term, can I simply disconnect the two-pin connector
> while not driving, and connect it when I am driving? (It's winter in
> Ontoario!)
A problem is indicated, I'd want to know what it is before I assume that
just disconnecting the alternator connector is going to make life better.
> 3) I have an overhauled/rebuilt 10SI with unknown components in it.
> Can the diode trio and rectifier bridge be swapped between a fairly
> high amperage 10SI and my 12SI?
Doubt it. There are many different sizes and amp ratings of rectifier
bridges.
> 4) Okay, I've studied the factory manual charging system pages and the
> wiring diagrams. How on earth can a "ALT" light be on with the key
> off? The light circuit is interrupted! Yet apparently it can happen?
Because the circuit isn't interrupted?
Here's what I'd do; cull the tan wire from the 2 way connector, leave
the two way connector plugged into the alternator so that the red wire
is connected to where it normally is. Use your 12 volt test light to
see whether there is voltage at the tan wire coming from the ignition
switch or whether there is voltage coming out of the terminal on the
alternator where the tan wire was connected.
Which ever one has voltage dictates which direction you are going.
IOWs, you either have a short that is feeding voltage to the voltage
regulator (alternator) or you have a problem inside the alternator which
is feeding voltage back out to the ignition switch and (according to the
wiring diagram), the heater blower switch.
Ed Treijs
Alas, the advice was a little late, as I decided to "do something" and
the project just grew. But I do have more questions now.
> > 3) I have an overhauled/rebuilt 10SI with unknown components in it.
> > Can the diode trio and rectifier bridge be swapped between a fairly
> > high amperage 10SI and my 12SI?
>
> Doubt it. There are many different sizes and amp ratings of rectifier
> bridges.
I took both the 12SI and the 10SI apart. Once I got going, I decided
to treat it as an educational experience. If I break something, I will
learn from that. If I put something together that works, I learn from
that too.
I got puzzling readings from the 12SI bridge: it seemed to have no
conductivity either direction. I'd put it down to error or tool misuse
(I'm using a digital multimeter that has a diode check setting) but
the 10SI bridge checked out as I'd expect it (conductivity in one
direction). Additionally, the 10SI diode trio checked out fine, but
the 12SI trio again seemed to have no continuity either way!
Anyway, I didn't understand how the rectifier bridge was assembled,
and in learning how it's assembled I destroyed the 12SI bridge. The
10SI bridge fits, although the heat sink cooling fins aren't ideally
shaped for the 12SI end frame vents.
I presume that the SI-series rectifier bridges come preassembled on
the heat sinks, because the diodes appear to be bonded to the sinks (I
broke most of the diodes from the 12SI heat sink).
> IOWs, you either have a short that is feeding voltage to the voltage
> regulator (alternator) or you have a problem inside the alternator which
> is feeding voltage back out to the ignition switch and (according to the
> wiring diagram), the heater blower switch.
Aside: contrary to the 1978 factory service manual, my car does have a
blower off position. My '79 Firebird did indeed have a blower that ran
all the time, but my non-A/C '78 definitely has an off position.
Obviously, I should check if there's unwanted voltage on the tan/black
wire when the key is off. Would be annoying if I did all this teardown
stuff when it really was a wiring problem!
I put the 12SI back together with the 10SI bridge and diode trio. The
10SI did not have a resistor between the +12 brush connector and
ground--this is labelled as "Resistor (some models)" in my factory
manual, probably R5 in the circuit diagram GM provides. The 12SI does
have this resistor: it's about 48 ohms. I wonder why "some models"--
what causes it to be or not to be present? I might guess that the
resistor's presence is matched either with the regulator or the diode
trio, but which? Should I keep it?
Anyway, if the alternator works at all, I will have to get a proper
rectifier bridge, and also get the bearings replaced. 12SI stator is
noticeably heftier than 10SI stator; couldn't see significant
differences in the rotor.
So to summarize:
Didn't check tan (field) wire--need to check
12SI bridge and diode trio check out open; bridge is wrecked anyway
10SI bridge and diode trio check out fine--in use
12SI had resistor, and I kept it
Haven't reinstalled alternator to test
Certainly have learned a whole bunch about alternator innards, for
what use it is
....Ed
jim
Ed Treijs wrote:
>
> On Jan 11, 6:51 pm, aarcuda69062 <nonel...@sbcglobal.net> wrote:
>
> Alas, the advice was a little late, as I decided to "do something" and
> the project just grew. But I do have more questions now.
>
> > > 3) I have an overhauled/rebuilt 10SI with unknown components in it.
> > > Can the diode trio and rectifier bridge be swapped between a fairly
> > > high amperage 10SI and my 12SI?
> >
> > Doubt it. There are many different sizes and amp ratings of rectifier
> > bridges.
>
> I took both the 12SI and the 10SI apart. Once I got going, I decided
> to treat it as an educational experience. If I break something, I will
> learn from that. If I put something together that works, I learn from
> that too.
>
> I got puzzling readings from the 12SI bridge: it seemed to have no
> conductivity either direction. I'd put it down to error or tool misuse
> (I'm using a digital multimeter that has a diode check setting) but
> the 10SI bridge checked out as I'd expect it (conductivity in one
> direction). Additionally, the 10SI diode trio checked out fine, but
> the 12SI trio again seemed to have no continuity either way!
There should be 3 wires involved. There is a hot to the Battery and a
ground and a wire from the stator which is where the current being
rectified comes from. From Battery to ground.
But anyway the rectifier bridge shouldn't have anything to do with your
problem. If I understood your original posting correctly your current
leak is in the control circuit not the heavy gauge output to the
battery.
You also said you don't have a dash light. Normally the dash light is
part of what makes the alternator work. Usually when you disconnect the
wire to the dash light and it won't charge because that is where the
juice for the field comes from.
>
> Anyway, I didn't understand how the rectifier bridge was assembled,
> and in learning how it's assembled I destroyed the 12SI bridge. The
> 10SI bridge fits, although the heat sink cooling fins aren't ideally
> shaped for the 12SI end frame vents.
>
> I presume that the SI-series rectifier bridges come preassembled on
> the heat sinks, because the diodes appear to be bonded to the sinks (I
> broke most of the diodes from the 12SI heat sink).
If I remember correctly the diodes are pressed in. Here is a wiring
diagram and some trouble shooting tips:
http://www.autoelectricservice.net/images/Delco_10SI_Technical.pdf
-jim
aarcuda69062
<062d91c5-b347-42bb...@p24g2000yqm.googlegroups.com>,
Ed Treijs <ed.to...@gmail.com> wrote:
> On Jan 11, 6:51�pm, aarcuda69062 <nonel...@sbcglobal.net> wrote:
>
> Alas, the advice was a little late,
Sorry, I was replacing stepper motors in a 2003 Silverado instrument
cluster. (gotta eat)
> as I decided to "do something" and
> the project just grew. But I do have more questions now.
>
> > > 3) I have an overhauled/rebuilt 10SI with unknown components in it.
> > > Can the diode trio and rectifier bridge be swapped between a fairly
> > > high amperage 10SI and my 12SI?
> >
> > Doubt it. �There are many different sizes and amp ratings of rectifier
> > bridges.
>
> I took both the 12SI and the 10SI apart. Once I got going, I decided
> to treat it as an educational experience. If I break something, I will
> learn from that. If I put something together that works, I learn from
> that too.
>
> I got puzzling readings from the 12SI bridge: it seemed to have no
> conductivity either direction. I'd put it down to error or tool misuse
> (I'm using a digital multimeter that has a diode check setting) but
> the 10SI bridge checked out as I'd expect it (conductivity in one
> direction). Additionally, the 10SI diode trio checked out fine, but
> the 12SI trio again seemed to have no continuity either way!
That alternator shouldn't have worked at all if the entire rectifier
bridge was open.
You do realize that the diode test function on your DVM tests bias
voltage correct? You should be reading something like .7 at one
polarity and 0.0 when the test lead polarity is reversed.
The big old honkin Fox valley meters that were sold 30 years ago were
great for testing alternator internals, the ohmeter was powered by nine
volts which was more than enough to bias the PN junction to test the
diodes. I think the old Simpson 'tombstone" meters did as well.
> Anyway, I didn't understand how the rectifier bridge was assembled,
> and in learning how it's assembled I destroyed the 12SI bridge. The
> 10SI bridge fits, although the heat sink cooling fins aren't ideally
> shaped for the 12SI end frame vents.
They don't come apart, I used to bend the straps up from the studs to
totally isolate each individual diode from the rest of the assembly.
IIRC, I got bit in the ass by a bridge frame that was shorted between
positive and negative sides, time to re-invent the test.
> I presume that the SI-series rectifier bridges come preassembled on
> the heat sinks, because the diodes appear to be bonded to the sinks (I
> broke most of the diodes from the 12SI heat sink).
Yes, that is how they come.
> > IOWs, you either have a short that is feeding voltage to the voltage
> > regulator (alternator) or you have a problem inside the alternator which
> > is feeding voltage back out to the ignition switch and (according to the
> > wiring diagram), the heater blower switch.
>
> Aside: contrary to the 1978 factory service manual, my car does have a
> blower off position. My '79 Firebird did indeed have a blower that ran
> all the time, but my non-A/C '78 definitely has an off position.
>
> Obviously, I should check if there's unwanted voltage on the tan/black
> wire when the key is off. Would be annoying if I did all this teardown
> stuff when it really was a wiring problem!
Yup.
> I put the 12SI back together with the 10SI bridge and diode trio. The
> 10SI did not have a resistor between the +12 brush connector and
> ground--this is labelled as "Resistor (some models)" in my factory
> manual, probably R5 in the circuit diagram GM provides. The 12SI does
> have this resistor: it's about 48 ohms. I wonder why "some models"--
> what causes it to be or not to be present? I might guess that the
> resistor's presence is matched either with the regulator or the diode
> trio, but which? Should I keep it?
That resistor was needed on some applications with a warning light, its
purpose was to stop the warning light from glowing dimly at idle speeds.
With a no warning light application it wasn't needed, its presence or
lack there-of makes absolutely no difference in a vehicle with gauges
and no light.
> Anyway, if the alternator works at all, I will have to get a proper
> rectifier bridge, and also get the bearings replaced. 12SI stator is
> noticeably heftier than 10SI stator; couldn't see significant
> differences in the rotor.
Stator is bigger because the output rating is higher. At low amperage,
the 10SI bridge will probably work okay, at higher amperage it's gonna
smoke.
> So to summarize:
> Didn't check tan (field) wire--need to check
> 12SI bridge and diode trio check out open; bridge is wrecked anyway
> 10SI bridge and diode trio check out fine--in use
> 12SI had resistor, and I kept it
> Haven't reinstalled alternator to test
> Certainly have learned a whole bunch about alternator innards, for
> what use it is
Check the tan field wire for voltage with the key off BEFORE you
re-assemble with the new rectifier bridge, if there is no voltage there,
I'd recommend replacing the voltage regulator unless you don't mind
taking it all apart again.
Ed Treijs
> In article
> <062d91c5-b347-42bb-84d2-0a92011c2...@p24g2000yqm.googlegroups.com>,
> Ed Treijs <ed.toro...@gmail.com> wrote:
>
> > On Jan 11, 6:51 pm, aarcuda69062 <nonel...@sbcglobal.net> wrote:
>
> > Alas, the advice was a little late,
>
> Sorry, I was replacing stepper motors in a 2003 Silverado instrument
> cluster. (gotta eat)
That isn't even it; I have no internet at home and I was sitting
around yesterday afternoon, thinking "I gotta do something about that
alternator". I appreciate help, especially *accurate* help. Usenet is
getting a poor place to expect that, so sometimes I just go ahead on
my own.
> That alternator shouldn't have worked at all if the entire rectifier
> bridge was open.
Yeah, shouldn't, but it did, except big loads at idle would pull the
voltage way down after the car, and presumably alternator, warmed up.
I can't explain why the one diode trio didn't check out either.
> You do realize that the diode test function on your DVM tests bias
> voltage correct? You should be reading something like .7 at one
> polarity and 0.0 when the test lead polarity is reversed.
What I get is something like "568" in one direction and off-scale
flashing "3000" in the other direction. I think it reads resistance.
Alas, my DVM instruction book is.....somewhere, and I've never had to
check diodes in my 15 years of ownership. It may actually be .567;
kinda hard to see the decimal place on the meter.
> The big old honkin Fox valley meters that were sold 30 years ago were
> great for testing alternator internals, the ohmeter was powered by nine
> volts which was more than enough to bias the PN junction to test the
> diodes. I think the old Simpson 'tombstone" meters did as well.
To check the key-off draw, my father pulled out a real big (car-
battery-sized, and almost as heavy) made-in-England analogue meter
that was used by our local power company (Ontario Hydro) technicians.
Just in case my key-off draw was in the tens of amps. (My father was
an EE for Ontario Hydro, go figure.)
> They don't come apart, I used to bend the straps up from the studs to
> totally isolate each individual diode from the rest of the assembly.
> IIRC, I got bit in the ass by a bridge frame that was shorted between
> positive and negative sides, time to re-invent the test.
I drove out the pins/wedges staking/wedging each side of the plastic
middle piece. With those removed, the plastic piece slides out from
between the bridges (or vice-versa). At that point you wind up with
four major pieces: upper bridge, lower bridge, plastic holder/
insulator, and a three-post terminal strip to which the stator
windings attach. At that point, attacking each of the diodes
individually is no problem. Reassembly is inverse of disassembly.
I find it odd that the positive side of the bridge goes via a big nut
to the thick B+ stud, while the negative side of the bridge seems to
be grounded entirely by the wimpy hold-down screw. I think I want to
look at it again.
> That resistor was needed on some applications with a warning light, its
> purpose was to stop the warning light from glowing dimly at idle speeds.
> With a no warning light application it wasn't needed, its presence or
> lack there-of makes absolutely no difference in a vehicle with gauges
> and no light.
Hmm. The one thing it does do is to change my meter readings; on
continuity setting, suddenly the meter beeps for continuity in both
directions! It evidently assumes that a resistance of under 50 ohms is
as good as continuous. (Continuity beep works with ohm setting only.)
So removing the resistor makes it easier to check for proper diode
polarity and working.
> Stator is bigger because the output rating is higher. At low amperage,
> the 10SI bridge will probably work okay, at higher amperage it's gonna
> smoke.
Okay, I need to find a new 12SI bridge.
> Check the tan field wire for voltage with the key off BEFORE you
> re-assemble with the new rectifier bridge, if there is no voltage there,
> I'd recommend replacing the voltage regulator unless you don't mind
> taking it all apart again.
Hmm, 10SI and 12SI regulators look identical, but I don't have field
current specs for a 12SI. 10SI would be 2.5A, but this was a "higher
performance" rebuild by a reputable electrical shop. What new/upgraded
items they threw into this old 10SI (case part # makes it sound like
an early '70s build) I don't know.
Here's another question I'm pondering: why is the sense (#2 conector)
an external connection? The sensing lead is simply spliced into the
heavy main line coming from B+, and runs back to regulator. Surely it
could be jumped internally, say from the B+ stud, similar to the diode
trio. I'm guessing it's got something to do with troubleshooting
options, as otherwise why bother?
Anyway, thanks for all your info. I will soon be the alternator guru
on my block! (This summer I took apart my HEI distributor because the
mechanical advance had seized solid; yet another learning experience,
and the car started right up when I dropped the cleaned/greased unit
back in.)
....Ed
Scott Dorsey
>What I get is something like "568" in one direction and off-scale
>flashing "3000" in the other direction. I think it reads resistance.
>Alas, my DVM instruction book is.....somewhere, and I've never had to
>check diodes in my 15 years of ownership. It may actually be .567;
>kinda hard to see the decimal place on the meter.
This is correct. You have a .6V drop in one direction, and no current
flowing in the other direction. That's what a diode is supposed to show.
However, you can have diodes that measure OK at low voltages but break
down in actual service.
Nate Nagel
The voltage sense wire is extended so that the regulator is sampling
voltage at the battery not at the alternator. There *is* resistance
even in a 8AWG wire from the alternator through the ammeter and then
back to the battery (assuming you have an ammeter, that is.) For
troubleshooting purposes on a bench just connect it to the big stud.
I have been watching this thread; I have a 10SI with a Speedway diode
harness in my '55 Stude but have not had any issues with it yet (knock
on wood) save for low charge at idle, but I thin kthat is just because a
Stude 289 has a smaller crank pulley than a SBC
nate
--
replace "roosters" with "cox" to reply.
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