How to Install a Voltmeter on Your Boat

An Easy, Inexpensive Boat Improvement with Benefits

Voltmeter. Getty Images Credit: Rouzes

Here's a very simple do-it-yourself project with useful benefits such as detecting or preventing a power problem on your boat. Most boats have 12-volt electrical systems powered by one or more batteries that are recharged by the engine's alternator or other electrical sources such as solar panels or a wind generator. If you don't already have a voltmeter wired into your system to keep you informed of your batteries' charge and the charging voltage, you can add one for a minimal cost and start reaping the benefits within minutes. Read this article about the benefits and uses of a hard-wired voltmeter in your system.

Installing a Voltmeter

You can always use a standard multimeter to measure voltage right at the battery terminals, but it's very easy to install a permanent voltmeter at or near your main switch panel so that you don't have to access the battery every time.

As with all boating gear, you can buy an expensive marine meter or complicated boat system, or just get an inexpensive voltmeter and wire it in yourself. (You could have 20 of these fail over the next 30 years and still spend less than a top-of-the-line marine version.) Be sure to get a digital model rather than an analog voltmeter, because you want the accuracy and ease of measuring very small differences in voltage.

Wiring

The wiring is as simple as connecting the positive (red) and negative (black) leads of the meter to the primary power input in your switch panel - assuming a standard panel. If you have multiple batteries, then likely the battery selector switch is outside the panel, such that power flows into the panel from, for example, either battery A or battery B or both. Thus the meter shows the voltage of whichever battery is currently being input into the panel.

If you wire the meter to the power input, the meter will be on whenever the battery switch is on. In this case, note that whenever a load is put on the battery (by having any lights or anything else turned on), the voltage will naturally drop somewhat. For the most accurate reading, have nothing turned on when measuring the battery voltage level.

Alternatively, you could wire the voltmeter to another circuit inside the panel that does not directly consume power. For example, I wired mine to the circuit for an interior cigarette plug adaptor used for charging various handheld electronics, since that circuit was already fused and had its own on-off switch. In this way, I simply flip that switch on to activate the voltmeter.

Conclusion

Before installing this model about a year ago, I had simply hardwired in a very small, cheap multimeter in the same circuit. That one lasted me 10 years with no regrets. I could tell when my aging batteries were holding less charge and when they discharged more rapidly when using lights and electronics at anchor. I could tell that my alternator was continuing to put out the right voltage (in my case, about 14.5 volts charging). I could tell when it was safe to continue to use one battery to power my autopilot because the other was fully charged for starting the engine.

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