Acceptable voltage discrepancy, Voltage at dash vs. voltage at battery |
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Acceptable voltage discrepancy, Voltage at dash vs. voltage at battery |
98101 |
Nov 24 2017, 06:26 PM
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#1
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Michael in Seattle Group: Members Posts: 373 Joined: 7-October 17 From: Seattle, WA Member No.: 21,495 Region Association: Pacific Northwest |
I started my car after sitting a few days and noticed the dash voltage meter went up over 15V. In Tech Tips 700 I read that overvoltage could lead to battery acid spills, so I quickly shut it off.
Prior to that, I'd noticed the dash gauge reads lower than I'd like when all the lights are on. I checked the voltage at the battery under different circumstances and they weren't so extreme in either direction. So now I'm wondering what the acceptable differences would be before you'd start to expect a poor (ground?) connection somewhere? https://www.youtube.com/watch?v=S6BcQC-cjXo |
Spoke |
Nov 24 2017, 07:20 PM
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#2
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Jerry Group: Members Posts: 6,978 Joined: 29-October 04 From: Allentown, PA Member No.: 3,031 Region Association: None |
There is a lot of resistance in the 40+ year old wiring and connectors in the 914. Measuring the voltage in the cabin with lights on could easily yield 2-3V lower than at the battery.
The voltage at the battery is the only voltage worth measuring WRT the voltage regulator and alternator. |
98101 |
Nov 24 2017, 08:07 PM
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#3
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Michael in Seattle Group: Members Posts: 373 Joined: 7-October 17 From: Seattle, WA Member No.: 21,495 Region Association: Pacific Northwest |
Thanks Mike and Spoke.
I was also confused by the 15+V reading I saw on the dash gauge when I first started the car. I didn’t catch that on video unfortunately. |
Mike Bellis |
Nov 24 2017, 08:49 PM
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#4
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Resident Electrician Group: Members Posts: 8,345 Joined: 22-June 09 From: Midlothian TX Member No.: 10,496 Region Association: None |
Thanks Mike and Spoke. I was also confused by the 15+V reading I saw on the dash gauge when I first started the car. I didn’t catch that on video unfortunately. I see -15 Amps and +11 Volts when you start it. The Amp gauge is bogus installed in the cabin unless there are two very large wires running all the way back to the alternator. If there is, make sure they are fused or you may burn the car down. Otherwise, throw the amp gauge away. There is no place to correctly connect this inside the cabin due to the way the factory wired everything. At most you will only be measuring one of 4 circuit paths. The low voltage on the gauge is mostly due to age of the wiring. Age of the ground plane (chassis) and the fact that the gauge is analog and your meter is digital. Both units process RMS voltage differently and will never read the same. There is also substantial voltage drop inherent in the factory wiring. |
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