Home » Public Forums » GMCnet » [GMCnet] Re: The Importance of a Voltmeter
| [GMCnet] Re: The Importance of a Voltmeter [message #368226] |
Thu, 30 December 2021 12:58  |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma:
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Thank you Ken for your input.
It only takes that one time issue to realize that having one one can be a
good thing to have,
On Thu, Dec 30, 2021 at 10:45 AM Ken Henderson
wrote:
> I just stumbled across this note from 2006; it's still applicable, so I'm
> posting it for everyone's consideration:
>
> Voltmeter to the Rescue
>
> Do you have a voltmeter monitoring your chassis battery voltage? You
> should. Here’s an example of why: We returned from Florida last night
> after a three week, two rally, two GMC alternator excursion. As we left
> Melbourne, FL enroute to Bowling Green, FL, Elaine and I both smelled
> something funny, so I stopped and tried unsuccessfully to find the
> source. When I restarted the engine, I noticed that my dash voltmeter was
> reading 16 VDC and sometimes jumping even higher. Knowing that much
> voltage would damage the batteries, we turned on the headlights, A/C
> blower, and every interior light we could find. That dropped the voltmeter
> reading to about 15 VDC, a marginally high voltage, but not terribly
> destructive, so we continued the trip. After about 15 minutes, the
> voltmeter reading dropped quickly to 12.5 VDC, which indicated that we were
> operating on the chassis battery alone, with no alternator contribution.
> With only 130 miles to travel, I decided to continue. Over the next 100
> miles, the voltmeter dropped steadily; at 10 VDC, the engine faltered so I
> switched on the house batteries using my non-momentary battery boost
> switch. The voltage quickly climbed back to 12.5 VDC, the engine ran fine,
> and we reached Bowling Green with no further difficulty.
>
> The next day, after failing to repair the dead alternator, I bought a
> rebuilt one and installed it. The voltmeter once again read 14.7 VDC, the
> exact voltage indicated on Advance Auto’s tester. I kept the old
> alternator so I can repair it for a spare and we continued our travels
> around Florida. About 100 miles before we got home, the voltmeter again
> jumped to over 16 VDC and the inverter I use to run my laptop computer
> kicked off because of the overvoltage condition. Even turning on all the
> lights would not bring the voltage back down and it would occasionally jump
> even higher, so I decided on a temporary repair. Reasoning that the
> just-replaced alternator was probably OK, the most likely reason for the
> voltage going high was that the voltage sense lead was not providing the
> battery voltage to the alternator, causing it to “think” it needed to
> produce more voltage. A jumper wire from the #2 lead on the alternator to
> the chassis battery corrected the problem and allowed us to continue to
> Americus without further difficulty.
>
> The voltmeter alerted me to the original alternator problem so I could take
> preventive action (by placing additional load on the alternator) before it
> damaged my batteries. Then when the second alternator began to act up, it
> enabled me to determine the probable cause of the problem and provide a
> temporary fix without damaging the batteries or the rebuilt alternator.
> Neither of those problems would have been indicated by the GEN light until
> the alternators actually failed. A voltmeter is money well spent.
>
>
> Ken H.
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--
Jim Kanomata ASE
Applied/GMC, Newark,CA
jimk@appliedairfilters.com
http://www.gmcrvparts.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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