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voltage gauge accuracy?

Old 03-18-2019, 09:03 PM
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Default voltage gauge accuracy?

on my last boat and this boat both of them show 12-13 volts on the gauge. Now I haven't had a chance to put a volt meter on the battery to see what the actual voltage. Usually it should be 14-14.5 so what's up with these volt gauges?
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Old 03-18-2019, 10:56 PM
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14.4 when engine running, 12.6 engine off, no load, rested. So it depends on what and when you're measuring.
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Old 03-19-2019, 03:55 AM
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Hello, depends on from where the voltage reading is coming from, add to the mix some corroded terminals and any inaccuracies in the gauge and the readings can be erratic.
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Old 03-19-2019, 04:31 AM
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Temporarily connect a digital voltmeter to the battery posts and compare the readings with the dash-mounted voltmeter both stopped and running. That way you will know exactly what you need to know when you have to know it.
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Old 03-19-2019, 05:30 AM
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Originally Posted by fishmaster273 View Post
on my last boat and this boat both of them show 12-13 volts on the gauge. Now I haven't had a chance to put a volt meter on the battery to see what the actual voltage. Usually it should be 14-14.5 so what's up with these volt gauges?
12-13 volts is a very wide range

Google Images "state of charge chart"

personally, i only rely on real battery monitors that are either wired in-line using a shunt or have a computer that closely monitors (i.e. balmar)

i never rely on gauge on dash or MFD etc
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Old 03-19-2019, 06:08 AM
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Originally Posted by mystery View Post
12-13 volts is a very wide range

Google Images "state of charge chart"

personally, i only rely on real battery monitors that are either wired in-line using a shunt or have a computer that closely monitors (i.e. balmar)

i never rely on gauge on dash or MFD etc
Why have a gauge if it cannot be relied upon? Either fix the problem or toss the gauge if it lies.

Or follow the advice offered by seahorse and one will know precisely what the voltage is.
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Old 03-19-2019, 06:19 AM
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Originally Posted by fishmaster273 View Post
on my last boat and this boat both of them show 12-13 volts on the gauge. Now I haven't had a chance to put a volt meter on the battery to see what the actual voltage. Usually it should be 14-14.5 so what's up with these volt gauges?
What is up is that most voltmeters are built to sell at some low price point. Fidelity and accuracy are generally lacking. Then too there are voltage drop issues that will affect what is displayed on a volt meter.

In general if a voltmeter reads X with the motor not running, and then X plus Y with the motor running, that will tell the user that the electrical system is operating. Same with only a low voltage light being used.

Depending upon how much one cares and what they are willing to spend, one can have 100% accuracy or one can have no voltmeter (or a dead meter) at all installed.

As with fuel quantity gauges, it seems that most will curse the darkness of poor voltage indication rather than light the candle of acceptable accuracy.
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Old 03-19-2019, 06:23 AM
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Originally Posted by alloyboy View Post
Why have a gauge if it cannot be relied upon? Either fix the problem or toss the gauge if it lies.

Or follow the advice offered by seahorse and one will know precisely what the voltage is.
Why have it? Because the builder put it there. and they likely used undersized wiring and there is a voltage drop just from the battery to the gauge.

Last edited by mystery; 03-19-2019 at 06:34 AM.
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Old 03-19-2019, 06:27 AM
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Digital volt meters are inexpensive, easy to install on board and provide reliable information about status of charge(ing).
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Old 03-19-2019, 07:25 AM
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Originally Posted by mystery View Post
Why have it? Because the builder put it there. and they likely used undersized wiring and there is a voltage drop just from the battery to the gauge.
It would not be rocket science work to simply fix the wiring issue then. That is lighting the candle.
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Old 03-19-2019, 07:50 AM
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Most chartplotters and sounders have a voltmeter display on them. Do yours?
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Old 03-19-2019, 08:19 AM
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Originally Posted by alloyboy View Post
It would not be rocket science work to simply fix the wiring issue then. That is lighting the candle.
but that would not solve that most standard gauges are not that accurate
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Old 03-19-2019, 08:19 AM
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Originally Posted by Jus Teasin View Post
Most chartplotters and sounders have a voltmeter display on them. Do yours?
i would not ever rely on MFD voltage
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Old 03-19-2019, 08:41 AM
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Originally Posted by mystery View Post
but that would not solve that most standard gauges are not that accurate
It would not.

How accurate does a voltmeter need to be? 5%? 3%? What should the resolution be? To the tenth of a volt? To the hundredth of a volt?

How far should a voltmeter vary in voltage from battery voltage? A tenth of a volt? A hundreth of a volt? Half of a needle width?

Going digital can drive some folks wild. For instance "my port motor is indicating 147.8 degrees and my starboard motor is indicating 147.1 degrees. Something is wrong with my port motor. It is running hot. What is wrong with it?"
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Old 03-19-2019, 08:44 AM
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Originally Posted by Jus Teasin View Post
Most chartplotters and sounders have a voltmeter display on them. Do yours?
I suspect that most do have a volt meter function.

But they don't usually indicate battery voltage. Probably do not.

They indicate input voltage to the chart plotter. Maybe.
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Old 03-19-2019, 08:53 AM
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Digital gauges simply point out the difference between precision and accuracy. With a digital gauge you can have an inaccurate reading precise out to 3 decimal places.
We needed to have our Fluke digital meters recalibrated every few years before we were allowed to trust them. Who knows how good a Harbor Fright meter really is?
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Old 03-19-2019, 09:01 AM
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Even the Flukes are calibrated to X percentage of accuracy. No two might ever display the exact same voltage. Particularly out to 3 decimal places. Both may be perfectly acceptable.

Drives some people crazy.
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Old 03-19-2019, 10:01 AM
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This discussion explains why automobile manufacturers shy away from gauges that display numerical values which confuse drivers and lead to unfounded customer complaints. Much less customer contact when only "idiot lights" are provided.
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Old 03-19-2019, 10:09 AM
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Originally Posted by White Bear View Post
This discussion explains why automobile manufacturers shy away from gauges that display numerical values which confuse drivers and lead to unfounded customer complaints. Much less customer contact when only "idiot lights" are provided.
Customer to service advisor: "My voltmeter was reading 14.6 volts yesterday. Today it is reading only 14.5. I want a new charging system installed under warranty."

Actually, I installed a digital voltmeter in the power port of my 2016 Ford. With a "smart" charging system I suppose. The voltage is all over the place. From over 15 volts to down below 13 volts. Changes all of the time. Turn on the head lamps and it jumps up to about 15 volts no matter what it was before. Disconcerting to an old school guy until I got resigned to the fact that is the way that it is.
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Old 03-19-2019, 03:07 PM
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Originally Posted by alloyboy View Post
I suspect that most do have a volt meter function.

But they don't usually indicate battery voltage. Probably do not.

They indicate input voltage to the chart plotter. Maybe.
Where do you think that voltage comes from?
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