VOLTMETER CALIBRATION


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hondac200
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VOLTMETER CALIBRATION

Post by hondac200 »

Does anyone have a procedure to calibrate a 79 voltmeter? Mine shows 12.8 volts at 2,000 rpm but when checked with my multimeter it is actually 14.3 volts. Battery stays up, no charging issue, just seems to be calibrated incorrectly.

daves79x
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Re: VOLTMETER CALIBRATION

Post by daves79x »

It is likely not calibration, but very possible that's all the voltage you are getting to the voltmeter. Very common and leads to all sorts of starting and other problems. The path the battery voltage takes to the voltmeter is quite circuitous and has many connections, which get dirty and loosen over time. I'd trace all that out, clean and tighten every connection and then see what you have.

Dave

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Re: VOLTMETER CALIBRATION

Post by divan »

Hi, Hondac200 -- If you want to trace the volt drop to the meter (which is likely the cause of your low readings, as Dave points out) there is a good prior post by Aris Hadjiaslonis, aka Kool_Biker, on this subject. Search for the topic "In Defense of the original CBX alternator", Dec 22, 2012. Aris pretty well covers the problem and includes a photo of the shop manual wiring diagram with the wire path to the meter, connectors involved, etc. He also includes a pretty detailed discussion of his fix for the problem, which involves installing a simple relay circuit that feeds +12v directly to the meter, bypassing the wires and connectors that are likely causing the drop. It's a neat little mod and very easy to do. Or, you could just ignore the low reading, as many of us have done for years; but as Aris notes, seeing that low reading, say, on a long ride, can really worry the hell out of you. My meter always tended to hop around with vibrations, etc, sometimes giving an accurate reading, sometimes dropping as low as 11 volts. Installing the relay fixes the problem, so long as the meter is OK (and they tend to be pretty good instruments when properly fed). Finally, you may also want to just clean up the connectors involved anyway, just to be sure the drop the meter is getting isn't also affecting something else besides some of the instrument lights, which share the circuit.

Hope this helps
Dick Sullivan

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Re: VOLTMETER CALIBRATION

Post by Larry Zimmer »

Similar to Divan: You can 'calibrate' your meter using an external meter at the battery. Mine reads 13.1 when the battery reads 14.7 at somewhere around 2500 rpm. Or, as Aris did: use a small relay to connect the volt meter directly across the battery.
Larry Zimmer
cbxlarry@sbcglobal.net

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