Home » GMC » GMCnet » [GMCnet] Oh, did I mess up!
| Re: [GMCnet] Oh, did I mess up! [message #167529 is a reply to message #167458 ] |
Wed, 25 April 2012 07:23   |
 Richard Denney
Messages: 308
Registered: April 2010 |
Senior Member |
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On Tue, Apr 24, 2012 at 6:10 PM, Matt Colie <matt7323tze@gmail.com> wrote:
>
> As you didn't power anything up, the damage may well be limited to the
> alternator and the isolator. Alternator may well have survived if the
> isolator blew out first (most common) I am surprised that the combiner
> locked in. There must be something in its logic I don't understand. It
> should be protected from this.
>
No isolator. I think the combiner combined when I plugged in the power to
the coach. The combiner seems to be working now. It's current protection is
provided by the long leads, which had gotten quite warm, so they were
absolutely passing current. Reverse power was applied to the chassis side
of the boost solenoid. That side is also connected to the main 12-volt
power terminal, which supplied the fuse block in the dash, through a
fusible link. It's also the connection point for the alternator and many
other things that have been added, including the vacuum pump, the direct
power for the air compressor load-reduction relay, the electric wipers, the
ham radio, and maybe one or two things that I've forgotten. The two AC
relays also get their main power from that point.
The connection to the house circuits is on the house side of the boost
solenoid, so it's only connection to the chassis side is through the
combiner. There seems to be no damage on the house side--all the house
circuits work and neither of my protection breakers (a 60-amp thermal
breaker and a 40-amp magnetic breaker) had tripped. The output fuses on the
converter are there specifically for disaster protection, and I need to
check them. But as I recall, the converter is protected against incorrect
battery polarity.
I studied the connections to the main 12-volt terminal on the firewall
yesterday during my lunch break, using the picture that I linked. The
electric wipers were switched off, and are protected by a thermal
breaker--no path to ground. The vacuum pump relay only runs on the ignition
circuit; likewise the air compressor. Again, no path to ground. The
alternator I have not tested, but will, but it should have been protected
from reverse voltage by the alternator protection cable. The fusible link
was hot (but I caught it in time), so there was a path to ground somewhere
in there. The ham radio does find ground through the antenna
connection--the fuse on the ground power lead was blown. It's a 15-amp
fuse--it would have blown early in the scenario. Once I replaced those
fuses, the ham radio worked fine. All those other accessory circuits are
also fuse-protected and the fuses were undamaged.
The only fuse-block circuit that seems to be powered when the ignition is
off is the brake light/turn signal circuit. The dash radio, which in my
coach is probably not powered from the official source, is not getting
power and my suspicion is that it now gets its power from that brake light
circuit. It has an external power switch, however, and that switch does not
affect the dead short to ground I find the load side of that fuse. So far,
the only thing I can find that does not work is that circuit, though I have
not yet measured the voltage with the engine running to check the
alternator.
There was a slight odor of fried wiring in the hatch area for a minute or
two, but I detected none of that in the coach by the time I worked my way
around to the interior.
I have a "loud-click" electronic flasher for the turn signals. The front
side lights are powered through two 30-amp bridge rectifiers at the lamps
because they are LED and the turn signals and running lights feed power to
them at opposite pole (so that the turn signal will cancel the voltage to
extinguish the light when the running lights are on and power the light
when the running lights are off). The rectifiers have a higher current
rating than the fuse on the circuit, so I expect they rode out the event.
The running lights work as they should in any case. I'd hate to have to dig
down to those rectifiers behind the interior panels. The brake lights, turn
signals, and hazard lights are each powered by a physical switch that
should have prevented a path to ground, but I need to study the wiring
diagram.
Assuming the alternator survived, the only apparent victim is something on
that brake light circuit.
As to the terminals on the battery, yes, for some reason, I got it into my
head that the terminals were reversed from the old battery, which was a
side/top battery bought by the OP right before I bought the coach (that's
also when the alternator was replaced--which I did--the OP was my father in
law).
Rick "hoping to get a chance to look at it a bit more tonight" Denney
--
'73 230 "Jaws"
Northern Virginia
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| Re: [GMCnet] Oh, did I mess up! [message #167531 is a reply to message #167458 ] |
Wed, 25 April 2012 07:38 |
Richard Denney
Messages: 308
Registered: April 2010 |
Senior Member |
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On Tue, Apr 24, 2012 at 6:10 PM, Matt Colie <matt7323tze@gmail.com> wrote:
> ...I am surprised that the combiner locked in. There must be something in
> its logic I don't understand. It should be protected from this.
>
>
Forgot to mention that my combiner ground reference goes to the negative
terminal on the house battery, just because that battery has a convenient
wing-nut connection point for it. With the converter on, it would have put
out charging voltage, and the combiner would have seen 14 volts (or
whatever) on the house side reference against the house ground. The engine
side voltage would have been at -12 volts, right? It would have combined.
The combiner is designed for a high inrush current to allow batteries at
different voltages to equalize. The current model allows up to 400 amps for
up to two seconds. That should obviously have pulled the voltage down below
the trigger for the combiner, but the combiner has a delay to prevent
chattering. I had the chassis battery switched off before much more than
that went by, but I have the combiner connecting to the engine battery on
the battery side of the switch so that the converter will charge it even if
the main switch is off. So, until the combiner uncombined, it would have
left the batteries connected, using its long wires as the current limiter.
That would have left the converter connected, but again the converter is on
the other side of two different kinds of circuit protection breakers,
neither of which tripped, so I'm sure that the combiner was taking the
brunt of current flow and the converter wasn't drawing more than 40 amps.
The magnetic breaker would be pretty fast acting. That tells me the
converter is protected against polarity errors, even without inspecting it
(though I will still inspect it). I do have another Intellipower converter
(an ebay deal bought when I was more flush than I am now) if need be.
The only wires that were hot to the touch (though I'm not sure what all I
checked) was the wire to the main 12-Volt terminal and the leads on the
combiner.
Rick "noting that reconstructions sometimes bring insights to other related
issues" Denney
--
'73 230 "Jaws"
Northern Virginia
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| Re: [GMCnet] Oh, did I mess up! [message #167534 is a reply to message #167395 ] |
Wed, 25 April 2012 08:02 |
LNelson
Messages: 160
Registered: December 2008
Location: Springfield, MO |
Senior Member |
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Ken's story reminded me of a bonehead move on my part in my "busnut" years (the years between the palm beach and the Eleganza)....Anyway, I was somewhere with the bus, don't remember where, might have even been my driveway. I started the bus without airing it up first. On a bus, without air, you don't have anything, no brakes, no nuthin....but in this case, I realized I had no brakes, the bus was moving, slowly, and I could not shut down the engine because you need 65# of air just to do that. I remember moving backwards with the Jeep hooked up. My only course was to hold position with the clutch until I got enough air to set the ICC brake. Dumb......
Springfield, MO
Ex GMC'er, then GM Busnut
now '77 Eleganza ARS WB0JOT
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| Re: [GMCnet] Oh, did I mess up! [message #167568 is a reply to message #167529 ] |
Wed, 25 April 2012 20:01 |
Richard Denney
Messages: 308
Registered: April 2010 |
Senior Member |
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On Wed, Apr 25, 2012 at 8:23 AM, Richard Denney <rwdenney@gmail.com> wrote:
>
> The only fuse-block circuit that seems to be powered when the ignition is
> off is the brake light/turn signal circuit. The dash radio, which in my
> coach is probably not powered from the official source, is not getting
> power and my suspicion is that it now gets its power from that brake light
> circuit. It has an external power switch, however, and that switch does not
> affect the dead short to ground I find the load side of that fuse. So far,
> the only thing I can find that does not work is that circuit, though I have
> not yet measured the voltage with the engine running to check the
> alternator.
>
Mystery solved on what caused the short to ground as a result of the
polarity error. I don't think I could have done it very easily without Ken
Henderson's oversized wiring diagram. Disassembling the fuse block, I
discovered that all the wires fed by the left-side bus are orange, and they
all disappeared together into the dashboard wiring harness, so tracing by
color was not going to be a good thing. The diagram indicated that the next
stop for the orange wire on the stop lamp/turn signal/hazard circuit was
the brake switch. The powered side of the brake switch was a tie point for
a blue wire that went into the steering column to the turn-signal and
hazard switches. The unpowered side went to the brake lights. Attached to
that blue wire was one of those taps that I have a lot of and that I
despise. Tracing the wire that came off of that led me to the remains of
the cruise control that had been installed by the PO--he'd gotten power for
the cruise control from that always-on circuit. I removed that wire (and
those remains) and the short to ground went with it. There was no fuse in
the line (another mistake, of course) and the electronics in that cruise
unit apparently could not take the full 20 amps allowed by the main circuit
fuse. A short to ground remained.
I also found a blown fuse in the dash radio, which is mounted near the
glove box on Jaws and operated by a remote in the absence of red-headed
radio authority. Of course, it's a different size than any on hand so I'll
have to pick up a replacement tomorrow. I did confirm that even in its new
position, it is wired from the original (and correct) radio circuit.
Both combiners still work as does the converter. There's nothing left that
doesn't work, but I still need to start up the engine and check the voltage
on the alternator. If I fried the alternator, it just won't put out
charging voltage, right? And the APC should have protected the voltage
regulator, right?
Rick "almost caught back up to where he was Monday afternoon" Denney
--
'73 230 "Jaws"
Northern Virginia
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| Re: [GMCnet] Oh, did I mess up! [message #167582 is a reply to message #167568 ] |
Wed, 25 April 2012 21:19 |
Ken Henderson
Messages: 4140
Registered: March 2004
Location: Americus, GA |
Senior Member |
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Rick,
Congratulations -- good troubleshooting!
I'll be surprised if the alternator's fried: As you've mentioned, the
combiner limits the current -- and to much less than the alternator's
rating (which is determined by the stator's wire sizes). The regulator's
probably OK too.
Ken H.
On Wed, Apr 25, 2012 at 9:01 PM, Richard Denney <rwdenney@gmail.com> wrote:
> On Wed, Apr 25, 2012 at 8:23 AM, Richard Denney <rwdenney@gmail.com>
> wrote:
> ...
>
Both combiners still work as does the converter. There's nothing left that
> doesn't work, but I still need to start up the engine and check the voltage
> on the alternator. If I fried the alternator, it just won't put out
> charging voltage, right? And the APC should have protected the voltage
> regulator, right?
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Oh, did I mess up! [message #168401 is a reply to message #167395 ] |
Thu, 03 May 2012 19:52 |
thorndike
Messages: 185
Registered: January 2011
Location: Northern Virginia |
Senior Member |
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Richard,
Where in NoVa are you? I am in Sterling and would love to connect to another GMCer in the area.
Bob
571-235-3564
Robert Peesel
1976 Royale 26'
Side Dry Bath
Sterling, Va
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| Re: [GMCnet] Oh, did I mess up! [message #168406 is a reply to message #167395 ] |
Thu, 03 May 2012 20:31 |
JohnL455
Messages: 1198
Registered: October 2006
Location: CHICAGO |
Senior Member |
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I'll bet the APC should work for stoping reverse voltage to the regulator in this scenario, but not to the main OP terminal. As Ken H said we can hope the alt bridge and fied is tougher than what the long combiner wires can deliver. Let us know.
John Lebetski
Chicago, IL
77 Eleganza II
Source America First
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| Re: [GMCnet] Oh, did I mess up! [message #168845 is a reply to message #168401 ] |
Mon, 07 May 2012 22:34 |
Richard Denney
Messages: 308
Registered: April 2010 |
Senior Member |
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On Thu, May 3, 2012 at 8:52 PM, Robert Peesel <thorndike@pldsllc.com> wrote:
> Richard,
> Where in NoVa are you? I am in Sterling and would love to connect to another GMCer in the area.
Northern Loudoun County, between Waterford and Lovettsville. But good
luck finding me there these days. When I'm home, I'm hammered with
Stuff To Do, and in between those assignments, I'm adding to my store
of frequent-flier miles, or in the middle of a commute to Baltimore.
There are several GMC owners in the area, but I've had a heck of a
time connecting with them routinely except at rallies. I have to
travel all the way to Bean Station to say hello to Eric Tanner, who
lives in McLean, as I recall. That's just not right.
Rick "call me Rick" Denney
--
'73 230 "Jaws"
Northern Virginia
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| Re: [GMCnet] Oh, did I mess up! [message #168854 is a reply to message #168406 ] |
Mon, 07 May 2012 23:57 |
Richard Denney
Messages: 308
Registered: April 2010 |
Senior Member |
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On Thu, May 3, 2012 at 9:31 PM, John R. Lebetski <gransport@aol.com> wrote:
> I'll bet the APC should work for stoping reverse voltage to the regulator in this scenario, but not to
>the main OP terminal. As Ken H said we can hope the alt bridge and fied is tougher than what the
>long combiner wires can deliver. Let us know.
Okay, there is MUCH more to the story. Find a comfy chair, and settle in.
Part 1.
First, let's review what the wires on the alternator do. Pin 1 is the
initial excitation circuit. This is powered by a circuit that starts
at the ignition switch ACC position, goes to a connection that
supplies the ACC-powered bus in the fuse block, the air conditioner,
and the upstream end of the nicrome wire. The nicrome wire then
connects to a crimp in the fuse block that feeds the GEN tell-tale
light and Pin 1 on the alternator. When the key is turned to "ON", the
ACC circuit is powered, which supplies the nicrome wire and
subsequently Pin 1 on the alternator.
Pin 1 in the alternator is connected to the output of the stator--what
provides charging voltage to the battery and everything else. The
nicrhome wire therefore has current running through it if the voltage
at ACC is higher than the voltage at the alternator output. That will
be the case before the engine is started. That current goes through
the field wiring, which will magnetize it, which, in turn, generates
voltage in the stator. That "starts" the alternator. When it is
started, the voltage output of the stator is now supplying voltage to
all parts of the electrical system, including the ACC position of the
ignition switch that feeds Pin 1. Both ends of the nicrome wire
resistance have the same potential, so no current flows.
I can't tell from the wiring diagram where the other side of the GEN
tell-tale is connected, but it seems to me it must be connected to the
ignition circuit, which is the power source for the printed circuit
board on the instrument cluster. When the alternator is putting out no
voltage, the GEN light will light, but when it's putting out voltage,
the potential on both sides of the bulb will be the same and it won't
light.
If something happens to the alternator output, current will flow again
through the GEN bulb, notifying you of the problem.
Thus, the purpose of the nicrome wire is to act as a current limiter
to keep that fat field wiring from pulling too much current out of the
ACC position of the ignition switch. There is no problem with the GEN
bulb--it provides its own current limiting. Any reasonable
high-wattage resistor will work, as long as the voltage that gets
through it is high enough to excite the field wiring to start the
alternator. That means a low resistor value.
I did not understand all this before this weekend. It finally sunk in
about the 400th time Ken Henderson explained it to me, while he was
helping me figure out why I wasn't getting any charging voltage.
Rick "End of Part 1" Denney
--
'73 230 "Jaws"
Northern Virginia
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| Re: [GMCnet] Oh, did I mess up! [message #168855 is a reply to message #168854 ] |
Tue, 08 May 2012 00:08 |
Richard Denney
Messages: 308
Registered: April 2010 |
Senior Member |
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Part 2.
The coach ran fine down to Bean Station. I have a real voltmeter on
the dash, and it read 13.9 volts the whole way. Life was good. The
first official night of the rally, JR Slaten asked me if I wanted to
do any pit work--the pit was open and nobody needed it. So, I pulled
the coach into the pit to install the speed transducer for my Rostra
cruise control that I bought several years ago and never put in.
When I backed back out into my spot, which was right across from the
garage, I was backing into complete darkness and was focused on not
hitting anything. So, I wasn't looking at gauges. After John
Richardson guided me into place, I put it into park and then noticed
the gauges--11.5 volts. Huh?
So, the next morning, we started pondering it. There was much
measuring of this and that with voltmeters, and much testing with
weird results. Thank God Dr. Henderson was there--he doesn't need that
big wiring diagram he prints up--it's all in his head. And he
understands it. We discovered that the combiner was showing "combine",
but wasn't moving current. So, the combiner died as a result of wiring
the battery backwards last week. And the 200-amp contactor I'm using
as a boost solenoid moves some voltage at very low current, at least
for a while, when it is in disconnect mode--possibly the effects of an
anti-arcing circuit. Test lamps are often more useful than
high-impedance DVMs. The contactor worked intermittently during one
test period, but I think that's because in some cases we'd separated
its coil from its source.
But the result was inescapable--no charging voltage. The conclusion
was a dead alternator, presumably also a delayed victim of the
reversal.
So, after a couple of trips to town, I brought back and installed a
remanufactured alternator from Autozone.
And it didn't providing charging voltage either. Much study of the
wiring diagram (on my iPhone), much dreaming about wiring, much
discussion the next morning, led to the conclusion that Autozone had
provided me a dud. So, I yanked it and we took it back. They put it on
their tester, which has a pass/fail reading only, but with Ken, me,
and Larry Dilk standing there being stern, they only complained mildly
when Ken jammed the leads of my DVM under the alligator clips on their
tester. The result: 15.5 volts. The alternator was good.
So, back it went into the coach. But no luck--still no charging voltage.
(And then we made another little mistake. In trying to recreate the
Autozone test on the coach, we mistakenly left the alternator output
divorced from the field sense wire. The alternator--at idle--put out
close to 60 volts. Burned out the bulb in Larry's test light, too. And
maybe it was the cause of What Happened Later.)
The Fickle Finger of Fate now pointed to the initial excitation
circuit. We put a load and a meter on it, and there was no voltage at
Pin 1 with the Ignition Switch set to ON. We figured there must be an
open in the nicrome wire. We found that wire (which looked good,
actually), after some fiddling (and pulling apart the fuse block), and
just bypassed it with a wire from the Cruise circuit to a light bulb
(the best we could do for a current-limiting resistor--and good enough
as we will see) to the wire coming from the GEN tell-tale and Pin 1.
The light bulb glowed when the key was ON, and then went off as soon
as the engine started. 14 volts issued forth and everyone started
giggling. After two days, I sat in a chair and just talked--which had
been my intention for the whole rally.
But the story is not yet over.
On Sunday, I headed home, and made it as far as Abingdon, VA--about 85
miles--when the GEN light suddenly glowed like an aircraft landing
light and the voltmeter pegged to the right (something over its
maximum reading of 18 volts). I exited into a gas station lot and shut
it down post haste.
The Black List had Ken's cell phone listed, and he suggested that I
disable the alternator by pulling the Pin 1-2 connector so that it
would never start. I drove home with no further issue on the battery
and ran the genset to keep it charged.
But while I was shutting down the engine at the gas station, a funny
thing happened:
*The engine didn't stop running with the key in the OFF position.*
A couple of attempts at turning it off had no effect. What?!?!? For no
apparent reason, I reached down and wiggled the big connector on the
steering column, and the engine immediately shut down.
And then came to my mind: The engine refused to fire when I first
tried to start it in the pit--it just cranked and cranked. My engine
usually started immediately. But then it started right up and I didn't
think further about it.
A-HA!!!!!
And NOW you know the REST of the story, and Paul Harvey used to say.
MUCH is now explained--why the exciter circuit had lost its function
even though the nicrome wire was not burned, why the fault occurred
after messing with the cruise control stuff which meant doing some
wire tugging in that general vicinity, why the ignition didn't seem to
fire when attempting to start the engine after doing that tugging, and
why we saw the unexplained weirdnesses that we saw. And it explains
why we fixed the initial excitation circuit--we sourced the voltage
from the Cruise circuit--a different wire through that plug--rather
than from the connection that feeds ACC to the nicrome wire.
I took apart the connector, burnished the contacts, and put it back
together, but it will get much more attention before I take the coach
out again. Maybe the ignition switch, too.
Was this a result of the battery reversal? Maybe, but I doubt it.
(By the way, I discovered an interesting document this evening. It's
the Remy application wiring diagram for the 27SI alternator--which is
the factory 100-amp version of the alternator in our coaches. The
recommended circuit in that document is:
-Battery to Pin 2--the field sense wire
-Battery to Main Alternator Output
-ACC to GEN tell-tale lamp to Pin 1.
So, Remy thinks the GEN lamp in the instrument panel ought to be the
current-limiting resistor for the initial excitation circuit. The GMC
design is similar, but it uses a more reliable current-limiting
resistor--a couple of feet of nicrome wire. It will still work even if
the GEN lamp is burned out.)
Rick "who didn't intend to be a problem child at Bean Station, but who
profoundly benefitted from the best diagnostic minds in our community"
Denney
--
'73 230 "Jaws"
Northern Virginia
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| Re: [GMCnet] Oh, did I mess up! [message #168876 is a reply to message #167395 ] |
Tue, 08 May 2012 06:25 |
Luvn737s
Messages: 877
Registered: June 2007 |
Senior Member |
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I was 15 and thought I was ready to become a line boy at the airport, so after getting impatient with waiting for my dad (like all 15 yr-olds) I decide to "help him out" and tow the Twin Comanche to the hangar - alone. I jump on the Ford 8N we used as a tug and quickly hooked up the towbar and begin towing the airplane toward the T-hangar that was at he bottom of a small incline. (Who sees where this is going?) I take the 8N out of gear so as to not ride the clutch as I've been admonished and down the hill we go. Then suddenly CLANK! which is the sound of the towbar coming off the nosewheel of my dad'd pride and joy! Rolling backwards, I am unable to engage the tractor into reverse and the airplane quickly catches up finally impaling the Ford emblem from the hood into the nose and cowling of the airplane.
The drive home was 45 minutes of absolute silence with my mouth hanging open the whole time in stunned disbelief.
To this day when I see a 50 million dollar jet being towed from the hangar with mechanics on the flight deck as brake riders, I know why they are there.
Randy
1973 26' Painted Desert
Ahwatukee (Phoenix) AZ
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| Re: [GMCnet] Oh, did I mess up! [message #168882 is a reply to message #168855 ] |
Tue, 08 May 2012 06:57 |
Ken Henderson
Messages: 4140
Registered: March 2004
Location: Americus, GA |
Senior Member |
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Man! I'm sure glad you finally found something to make sense of some of
those strange symptoms! :-)
It was great seeing you again even if all the head-scratching did cost me
most of my few remaining hairs.
Ken H.
On Tue, May 8, 2012 at 1:08 AM, Richard Denney wrote:
> Part 2.
> ...
> *The engine didn't stop running with the key in the OFF position.*
> ...
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Oh, did I mess up! [message #168896 is a reply to message #168876 ] |
Tue, 08 May 2012 09:49 |
Robert Mueller
Messages: 9031
Registered: July 2007
Location: Sydney, Australia |
Senior Member |
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G'day,
This reminds me of a funny story. I was based at Westover AFB in Chicopee
Falls, MA in the 1960's.
Organizational Maintenance Squadron (OMS) was pushing a KC-135 into the
hanger where the Mechanical Accessories Shop and other Field Maintenance
shops were located.
There was an Airman 1st class (3 stripes) on the headset communicating with
the tug driver and the guys in the cockpit. There was an Airman 2nd Class on
one wing and an Airman 3rd class on the other and I can't remember what rank
was on the tail. As they pushed it in they ran the left wing tip into the
hanger. They pulled it back out, the Airman 1st was replaced by a Staff Sgt
and they tried again. Since they needed to fix the banged up wing they moved
over to a bay on the other side of the hanger. As they backed it in again
they ran the other wingtip into the hanger! They pulled it out and the Staff
Sgt was replaced by the Maintenance Officer; IIRC a First Lt. Since they had
to repair BOTH wingtips they pulled it into the middle of the hanger. They
got it into the hanger without hitting either wingtip, however, the roof
supports in the middle of the hanger were different from either side and
they ran the top of the vertical stabilizer into the hanger! Naturally after
the first crunch all the Field Maintenance Squadron shop guys were watching
this comedy and we cracked up watching this fiasco unfold.
Regards,
Rob M.
-----Original Message-----
From: Randy
I was 15 and thought I was ready to become a line boy at the airport, so
after getting impatient with waiting for my dad (like all 15 yr-olds) I
decide to "help him out" and tow the Twin Comanche to the hangar - alone. I
jump on the Ford 8N we used as a tug and quickly hooked up the towbar and
begin towing the airplane toward the T-hangar that was at he bottom of a
small incline. (Who sees where this is going?) I take the 8N out of gear so
as to not ride the clutch as I've been admonished and down the hill we go.
Then suddenly CLANK! which is the sound of the towbar coming off the
nosewheel of my dad'd pride and joy! Rolling backwards, I am unable to
engage the tractor into reverse and the airplane quickly catches up finally
impaling the Ford emblem from the hood into the nose and cowling of the
airplane.
The drive home was 45 minutes of absolute silence with my mouth hanging open
the whole time in stunned disbelief.
To this day when I see a 50 million dollar jet being towed from the hangar
with mechanics on the flight deck as brake riders, I know why they are
there.
--
Randy
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Rob Mueller
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Oh, did I mess up! [message #168937 is a reply to message #168855 ] |
Tue, 08 May 2012 10:52 |
ljdavick
Messages: 2305
Registered: March 2007
Location: Fremont, CA |
Senior Member |
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It’s like reading a Dashiell Hammett novel - Now we know that the Butler did it!
Larry (who likes a good read) Davick
On May 7, 2012, at 10:08 PM, Richard Denney wrote:
> Part 2.
>
> The coach ran fine down to Bean Station. I have a real voltmeter on
> the dash, and it read 13.9 volts the whole way. Life was good. The
> first official night of the rally, JR Slaten asked me if I wanted to
> do any pit work--the pit was open and nobody needed it. So, I pulled
> the coach into the pit to install the speed transducer for my Rostra
> cruise control that I bought several years ago and never put in.
>
> When I backed back out into my spot, which was right across from the
> garage, I was backing into complete darkness and was focused on not
> hitting anything. So, I wasn't looking at gauges. After John
> Richardson guided me into place, I put it into park and then noticed
> the gauges--11.5 volts. Huh?
>
> So, the next morning, we started pondering it. There was much
> measuring of this and that with voltmeters, and much testing with
> weird results. Thank God Dr. Henderson was there--he doesn't need that
> big wiring diagram he prints up--it's all in his head. And he
> understands it. We discovered that the combiner was showing "combine",
> but wasn't moving current. So, the combiner died as a result of wiring
> the battery backwards last week. And the 200-amp contactor I'm using
> as a boost solenoid moves some voltage at very low current, at least
> for a while, when it is in disconnect mode--possibly the effects of an
> anti-arcing circuit. Test lamps are often more useful than
> high-impedance DVMs. The contactor worked intermittently during one
> test period, but I think that's because in some cases we'd separated
> its coil from its source.
>
> But the result was inescapable--no charging voltage. The conclusion
> was a dead alternator, presumably also a delayed victim of the
> reversal.
>
> So, after a couple of trips to town, I brought back and installed a
> remanufactured alternator from Autozone.
>
> And it didn't providing charging voltage either. Much study of the
> wiring diagram (on my iPhone), much dreaming about wiring, much
> discussion the next morning, led to the conclusion that Autozone had
> provided me a dud. So, I yanked it and we took it back. They put it on
> their tester, which has a pass/fail reading only, but with Ken, me,
> and Larry Dilk standing there being stern, they only complained mildly
> when Ken jammed the leads of my DVM under the alligator clips on their
> tester. The result: 15.5 volts. The alternator was good.
>
> So, back it went into the coach. But no luck--still no charging voltage.
>
> (And then we made another little mistake. In trying to recreate the
> Autozone test on the coach, we mistakenly left the alternator output
> divorced from the field sense wire. The alternator--at idle--put out
> close to 60 volts. Burned out the bulb in Larry's test light, too. And
> maybe it was the cause of What Happened Later.)
>
> The Fickle Finger of Fate now pointed to the initial excitation
> circuit. We put a load and a meter on it, and there was no voltage at
> Pin 1 with the Ignition Switch set to ON. We figured there must be an
> open in the nicrome wire. We found that wire (which looked good,
> actually), after some fiddling (and pulling apart the fuse block), and
> just bypassed it with a wire from the Cruise circuit to a light bulb
> (the best we could do for a current-limiting resistor--and good enough
> as we will see) to the wire coming from the GEN tell-tale and Pin 1.
> The light bulb glowed when the key was ON, and then went off as soon
> as the engine started. 14 volts issued forth and everyone started
> giggling. After two days, I sat in a chair and just talked--which had
> been my intention for the whole rally.
>
> But the story is not yet over.
>
> On Sunday, I headed home, and made it as far as Abingdon, VA--about 85
> miles--when the GEN light suddenly glowed like an aircraft landing
> light and the voltmeter pegged to the right (something over its
> maximum reading of 18 volts). I exited into a gas station lot and shut
> it down post haste.
>
> The Black List had Ken's cell phone listed, and he suggested that I
> disable the alternator by pulling the Pin 1-2 connector so that it
> would never start. I drove home with no further issue on the battery
> and ran the genset to keep it charged.
>
> But while I was shutting down the engine at the gas station, a funny
> thing happened:
>
> *The engine didn't stop running with the key in the OFF position.*
>
> A couple of attempts at turning it off had no effect. What?!?!? For no
> apparent reason, I reached down and wiggled the big connector on the
> steering column, and the engine immediately shut down.
>
> And then came to my mind: The engine refused to fire when I first
> tried to start it in the pit--it just cranked and cranked. My engine
> usually started immediately. But then it started right up and I didn't
> think further about it.
>
> A-HA!!!!!
>
> And NOW you know the REST of the story, and Paul Harvey used to say.
>
> MUCH is now explained--why the exciter circuit had lost its function
> even though the nicrome wire was not burned, why the fault occurred
> after messing with the cruise control stuff which meant doing some
> wire tugging in that general vicinity, why the ignition didn't seem to
> fire when attempting to start the engine after doing that tugging, and
> why we saw the unexplained weirdnesses that we saw. And it explains
> why we fixed the initial excitation circuit--we sourced the voltage
> from the Cruise circuit--a different wire through that plug--rather
> than from the connection that feeds ACC to the nicrome wire.
>
> I took apart the connector, burnished the contacts, and put it back
> together, but it will get much more attention before I take the coach
> out again. Maybe the ignition switch, too.
>
> Was this a result of the battery reversal? Maybe, but I doubt it.
>
> (By the way, I discovered an interesting document this evening. It's
> the Remy application wiring diagram for the 27SI alternator--which is
> the factory 100-amp version of the alternator in our coaches. The
> recommended circuit in that document is:
>
> -Battery to Pin 2--the field sense wire
> -Battery to Main Alternator Output
> -ACC to GEN tell-tale lamp to Pin 1.
>
> So, Remy thinks the GEN lamp in the instrument panel ought to be the
> current-limiting resistor for the initial excitation circuit. The GMC
> design is similar, but it uses a more reliable current-limiting
> resistor--a couple of feet of nicrome wire. It will still work even if
> the GEN lamp is burned out.)
>
> Rick "who didn't intend to be a problem child at Bean Station, but who
> profoundly benefitted from the best diagnostic minds in our community"
> Denney
>
> --
> '73 230 "Jaws"
> Northern Virginia
>
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Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, Ca
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| Re: [GMCnet] Oh, did I mess up! [message #169019 is a reply to message #168876 ] |
Wed, 09 May 2012 07:52 |
Johnny Bridges
Messages: 2323
Registered: May 2011
Location: Braselton ga |
Senior Member |
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Did I tell you about the line boyy who got too frisky with the mower/tractor, and turned too fast? Slid it into the prop of a Twin Commanche, which drove the plane back in the T hangar and rumpled the trailing edge up to the spar on a support pole. We reskinned the wing from the spar back, replaced the control surfaces (her got them both), put a enw prop on it, and painted it. Not an inexpensive bit of foolishness. All thjis at the Wetumpka International Airplane
patch, in the early 70s. I still like Twin Commanches though - lovely little transport for two or three up to about 40 miles. Nasty idea for a twin trainer though.
--johnny
'76 23' transmode norris
'76 Palm Beach
From: Randy <Acrosport2@hotmail.com>
To: gmclist@temp.gmcnet.org
Sent: Tuesday, May 8, 2012 7:25 AM
Subject: Re: [GMCnet] Oh, did I mess up!
I was 15 and thought I was ready to become a line boy at the airport, so after getting impatient with waiting for my dad (like all 15 yr-olds) I decide to "help him out" and tow the Twin Comanche to the hangar - alone. I jump on the Ford 8N we used as a tug and quickly hooked up the towbar and begin towing the airplane toward the T-hangar that was at he bottom of a small incline. (Who sees where this is going?) I take the 8N out of gear so as to not ride the clutch as I've been admonished and down the hill we go. Then suddenly CLANK! which is the sound of the towbar coming off the nosewheel of my dad'd pride and joy! Rolling backwards, I am unable to engage the tractor into reverse and the airplane quickly catches up finally impaling the Ford emblem from the hood into the nose and cowling of the airplane.
The drive home was 45 minutes of absolute silence with my mouth hanging open the whole time in stunned disbelief.
To this day when I see a 50 million dollar jet being towed from the hangar with mechanics on the flight deck as brake riders, I know why they are there.
--
Randy
1973 26' Painted Desert
Ahwatukee (Phoenix) AZ
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"Sometimes I wonder what tomorrow's gonna bring when I think about my dirty life and times" --Warren Zevon
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| Re: [GMCnet] Oh, did I mess up! [message #172122 is a reply to message #168867 ] |
Tue, 05 June 2012 10:05 |
Richard Denney
Messages: 308
Registered: April 2010 |
Senior Member |
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On Tue, May 8, 2012 at 3:44 AM, Ken Burton <n9cv@comcast.net> wrote:
>
> I'm not sure what Rick's failure was on the way home but I'm sure he will get it resolved given enough time.
>
Me, neither. But just to close out the story (I hope), here's what
I've done since.
The Autozone alternator went back to Autozone, and grandly failed
their tests, as expected. They replaced it. This one came from a
different rebuilder, perhaps, or at least some of the parts came out
of a different pile, because the pulley was painted a different color
and other details were different. This one, unlike the other one, had
an SAE thread on the back and a metric thread on the main tensioner
ear. I made them supply the screws for these threads, which they did.
I had it tested there and it passed, and I installed it on the coach
and at least in the driveway it works.
I also replaced the dodgy old connector for pins 1 and 2, where it
plugs into my APC, which is now reinstalled on the coach. I spliced
that connector using high-quality crimps with a heat-shrink,
thermal-glue-filled jacket. That makes a good waterproof and hopefully
oxidation-proof connection--probably better even than solder.
I also checked each pin on the steering column harness plug and
reattached it in the clips that hold it (it was inexplicably loose
from those clips). And I reseated the connections to the ignition
switch. Everything seems quite predictable now, but I probably should
have just replaced the ignition switch altogether. I'm operating under
the assumption that the alternator that failed was weak, and that the
little mistake we made when trying to test it didn't help. It does
make me want to carry a spare alternator, despite that I don't really
have room for that bowling-ball-sized hunk of weight.
Taking it out on the highway again tomorrow, so it will get a road test.
Rick "trying not to take shortcuts" Denney
--
'73 230 "Jaws"
Northern Virginia
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