 Voltmeter, Accuracy? |
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| 1988Hawk |
 Sep 19 2010, 04:06 PM
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#1
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Newbie  Group: Members Posts: 41 Joined: 17-April 08 From: Chicago Member No.: 8,929 Region Association: None  |
I have a dash mounted combo gauge with a voltmeter as one of the components. It tends to read .5-.8 lower than when I take a reading at the battery. With the lights and heater blower on I get 12.0 on the gauge, 12.5-12.8 on the battery. Is this common?
Jim |
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| tradisrad |
Sep 19 2010, 04:11 PM
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#2
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Senior Member Group: Members Posts: 985 Joined: 11-September 06 From: San Mateo, CA Member No.: 6,815 Region Association: Northern California |
i think it is fairly normal to have a lower reading at the gauge; after all the gauge is not hooked to the battery.
I take my voltage from the coil. |
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| jt914-6 |
Sep 19 2010, 05:49 PM
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#3
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Driving & working on teeners 41 years Group: Members Posts: 1,786 Joined: 3-May 08 From: Bryant, Arkansas Member No.: 9,003 Region Association: South East States |
The volt meter really drops when you hit the brakes....mine is hooked up straight to the battery through an off-on switch so I can check the voltage when I want.
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| bmtrnavsky |
Sep 19 2010, 05:53 PM
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#4
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Member Group: Members Posts: 355 Joined: 20-October 07 From: Longview, TX Member No.: 8,245 Region Association: Southwest Region |
Mine does the same thing. Daytime it reads just under 13v. Night time with heater and lights it runs just under 12. It jumps all over the place if I use my blinker.
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| swl |
Sep 19 2010, 07:25 PM
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#5
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Senior Member Group: Members Posts: 1,409 Joined: 7-August 05 From: Kingston,On,Canada Member No.: 4,550 Region Association: Canada |
The console guage will never be as accurate as your volt meter. The only way to know for sure is to disconnect the guage and use your volt meter across the wires normally connected to the guage.
You hear a lot of talk about cleaning grounds. What is being described above is symptomatic of a path that has contact resistance - whether it be on the ground side or on the hot side. Each connection, even the wires themselves, has a bit of resistance. Voltage drops over the circuit proportional to the resistance of that part of the circuit. Your goal is to have the resistance of the load (headlights, blowers ...) large compared to the resistance of the wires and contacts. When the contacts are bad you see that noticable difference between the battery voltage and voltage across the load. If your voltage drops significantly when you turn you lights on you should probably search out the source. |
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| bmtrnavsky |
Sep 19 2010, 07:29 PM
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#6
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Member Group: Members Posts: 355 Joined: 20-October 07 From: Longview, TX Member No.: 8,245 Region Association: Southwest Region |
I guess I know what I'm doing next weekend... (IMG:style_emoticons/default/smash.gif)
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| jim_hoyland |
Sep 19 2010, 09:38 PM
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#7
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Get that VIN ? Group: Members Posts: 9,303 Joined: 1-May 03 From: Sunset Beach, CA Member No.: 643 Region Association: Southern California 
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I found all the above oddities as well. My solution was to install a relay;
Battery to relay 30, then relay 87 to voltmeter Fuse panel ( switched side ) to relay 85, and 86 to ground Mounted the relay under dash, brought the wire from battery through pass side firewall along door sill to relay ( fused !) |
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