# Voltmeter

A voltmeter is an instrument for measuring electrical voltage. More precisely, what a voltmeter measures is the difference in the electrical potential of two points of an electric circuit. Voltmeters can be used to measure the capacity remaining in a battery so as to determine whether it needs to be recharged. (Sometimes the instrument is built into a device that uses a rechargeable battery so as to signal when it’s time to recharge.) Voltmeters can be used to measure any output of electrical power sources whether original or storage. Measuring voltage can give an indication of the efficiency of an electrical appliance. That’s especially true of devices that
are more efficient when designed to run at higher voltage, such as magnet motors. Voltmeters are also used to measure the output of a solar cell or solar panel, so as to determine whether the panel has lost capacity and needs to be replaced.

## Volts

There are three main ways to measure electricity: watts, amperes, and volts. A fourth unit, the ohm, isn’t a measure of electricity per se but of resistance to electric current; it’s an important factor in equations measuring the other quantities and functions analogously to inertia or mass in mechanics. Watts, amperes, and volts are related, interacting measures. Amperes measure the volume of current, and volts are a measure of the rate of flow. If you compare an electric current to a garden hose, amperes compare to how wide the hose is and so how much water can be moving through it at any moment, while volts compare to the pressure: how fast the water is moving through the hose. Watts put the two measures together to generate a figure for available power, and is the preferred measure of power used over time, while voltage and amperage are a measure of the intensity of an electricity source at any given moment, measured in two different ways.

## How To Connect A Voltmeter

To connect a voltmeter to a source of electricity, use the following procedure.

1) If possible, disconnect the power to the circuit you’re measuring.
2) Choose a point on the circuit where you want to measure the voltage (note that voltage can vary widely at different points of a circuit).
3) Using a length of wire properly rated for the circuit you’re working on, cut two lengths of it and strip the insulation from both ends of each wire about 1 inch wide.
4) Fasten one end of each wire to the voltmeter using the screw terminals and the other ends to the points on the circuit you want to measure. Connect the meter’s ground wire to any ground connector or ground wire.
5) Reconnect the power to the circuit.

This should verify that the circuit is functional and give a meter reading.

## Uses For Voltmeters

Although the measurement of voltage is very important, stand-alone voltmeters are not used that often. The preferred instrument is the multimeter, which is capable of measuring resistance in ohms and current in amperes as well as voltage. A multimeter will perform the functions of a voltmeter and those functions are quite important. It can be used to measure efficiency of any source of electricity and help determine when it requires replacement. That’s true of either battery sources or something like a solar panel.

As a general rule, the efficiency of an electric current goes up with voltage. A higher voltage allows a given current strength (measured in amperage) to do more work than the same current strength at a lower voltage. (Remember that voltage is analogous to water pressure; with high voltage a given amount of electric power is like a higher-pressure hose, so it can do more.) Measuring the voltage of an electricity source can tell us how efficiently it is applying the power that it’s able to generate.

## Voltmeter Use For Home Solar Systems

There are three reasons why a voltmeter (or the voltmeter function of a multimeter) is useful for purposes of a home solar system. One is quality control at the time the system is installed. It’s important to check the solar panels’ output to see whether any of them are defective, and measuring the voltage is a good way to do that. Whatever solar panels you are using will have a rating in terms of the expected voltage, and verifying this before installation is a good idea. This is really the most significant use. The second reason is to verify the peak output of the solar array in use. This will help you to evaluate your own energy use and budget accordingly.

The other reason to use a voltmeter for home solar systems is maintenance. Solar cells and solar panels lose some of their current as they get old. This is a slow process. Solar panels are usually warranted to lose no more than three percent of their power generation in the first year of use, and less than one percent per year thereafter; however, these figures are generally considered to be conservative and a good solar array should not lose that much. Measuring the decline over time can be a way of knowing whether a warranty claim needs to be made. It can also tell you when a panel has lost enough power generation that it needs to be replaced.