Home » Public Forums » GMCnet » [GMCnet] Just a Short Trip
| [GMCnet] Just a Short Trip [message #166365] |
Sat, 14 April 2012 23:44  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma:
|
Senior Member |
|
|
Yesterday I got a call from Jerry Holloway. He and Audrey were taking a
short weekend trip from Griffin, GA to Warwick, GA to attend the "Grits
Festival" (another reason to visit us, JimK). He was seeing higher than
usual engine oil temperature, 250*F coming out of the oil pump. While sort
of high for a 70*F day on mostly flat roads, I assured him that it wasn't
anything to be overly concerned about.
Last night I got another call: "Everything's falling apart!: The
refigerator's quit. The generator runs but doesn't put out 120 vac. My
turn signals don't work. Can I come by there on our way home tomorrow?"
"Sure -- plan to spend the night here." "We'll be there about 4:30."
Just after noon today I got another call: "We'll be there in an hour or
so. Oh yeah, I just stopped for gas and had to use the boost switch to
start the engine. I turned on the dash air blower to Hi and it works, so
the alternator's putting out."
About 2 PM they pulled in behind my engine-less GMC and Jerry and I started
troubleshooting.
Sure 'nuff, the refrigerator wasn't working. He'd recently replaced the
control board with one of the great "Dinosaur" boards. It had a blown DC
supply fuse, which he'd replaced. I couldn't find anything wrong, so
advised him to exercise the 3 year warranty.
The generator, probably the cleanest 6kW Power Drawer I've ever seen,
started right up but wouldn't power anything. I checked the CB and it was
OK. We decided the generator wasn't essential to their trip home. I
pointed out to Jerry that the house battery in the rear compartment was
leaking and corroding the surrounding aluminum. When he touched it, he
found the case swelled and hot! Hmmm...
So we moved on to the starting problem. The engine wouldn't start. I
checked and found the battery at 10.5 VDC, and noticed the sticker on the
WalMart battery said "10/06". With no further discussion, Jerry said
"Let's go to WalMart", and we did. After he installed the new battery, the
engine fired right up. When I checked the voltage on the alternator
terminal of the isolator, it was 27.5 VDC so I immediately told him to shut
the engine down. He raised the hatch and reported that the alternator was
VERY hot. Assuming that the regulator had failed, we pulled the
alternator, an AutoZone 100A version installed 02/07 IIRC. They tested it
and despite good readings, immediately shut it down because of excessive
noise and vibration. Surprisingly they had one in stock.
After we got the alternator back in, I monitored its output while Jerry
started the engine. OOoops! 31 VDC!!! SHUT IT DOWN!
After disconnecting the leads to the alternator, I checked the diodes.
Sure 'nuff, the chassis battery side's diode was open. That deprived the
alternator of feedback voltage and allowed it to run "open loop". What I
do NOT understand is why the voltage went so high. It has always been my
understanding that shortly after GMC MH production began, they began to use
regulators with an internal voltage limit of about 18 VDC. I've never
before seen an alternator output voltage that high.
After re-attaching the isolator leads, with the chassis battery wire moved
to the alternator terminal, we again checked voltages with the engine
running: Chassis side @ 14.6 VDC and House side @ 13.7 VDC -- Exactly what
I expected.
Now we know pretty well what happened: The isolator failed some time over
the past year while they haven't used the coach. During the 100 mile trip
down I-75, the chassis battery was receiving no charge current and the
alternator was busy boiling the house battery with 27+ VDC. It also
damaged the refrigerator's Dinosaur board before its fuse blew. And the
oil temperature read high, tracking the high applied voltage. The miracle
is that more electronic components weren't damaged (there may be some we
haven't yet found).
If I'd checked the isolator first off (which was my first inclination)
Jerry could probably have gotten a little more use out of the 6 year old
chassis battery. And we might not have replaced the alternator (even
though AutoZone did so willingly). The house battery's only a year or so
old and will undoubtedly require warranty replacement soon, though it's
holding full+ charge at the moment.
We don't know what happened to the generator -- I suspect the bridge
rectifier blew all on its own. We'll check that tomorrow -- they're
sleeping in their coach tonight with full hookups 1/2 under my RV shelter.
SO, I learned something new today (as during each of the previous 27,454):
Not all alternators are internally limited to 18 VDC!!! BAD NEWS!
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI+ & EBL
www.gmcwipersetc.com
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
|
|
|
|
Current Time: Tue Oct 08 17:26:06 CDT 2024
Total time taken to generate the page: 0.01358 seconds
|
GMCforum
Search
Help
Register
Login
Home
