How to make a simple wattmeter

When repairing electronic devices or appliances, it is always a good idea to check the power consumption of the device to get an idea of the correct functioning of the circuit being repaired. Generally, an ammeter is used to check the alternating current consumption. Multiplying this consumption by the mains voltage gives the power consumption in watts. However, home multimeters usually do not have this option. In the following, we will look at how to make a simple wattmeter with a home multimeter.

Branded wattmeter


- Digital multimeter (Should measure AC voltage to the order of one thousandth of a volt).

- Two resistors (R1 and R2) of 0.47 ohm and 5 W.

- A resistor (R3) of 33 Kohm and ½ W.

- One resistor (R4) of 39 Kohm for 110 V or one of 33 Kohm for 120 V.

Setting up our simple wattmeter

To create our WattimeterWe will make a fairly simple circuit, which consists of connecting the multimeter's crocodiles to resistor 3 (R3) in such a way that both connectors are one on each side of the resistor.

Home wattmeter circuit

Then, from one side of the resistor we connect the resistor (R4), and from the output of this resistor and the free side of the resistor (R3) we connect in parallel the resistors (R1) and (R2). The free sides of the parallel arrangement will be connected to the mains and the other end to the device to which we are going to check the power consumption.

How to measure


Once we connect the newly created device to the mains and to the device we wish to measure the power consumption of, we switch on the multimeter on the lowest VAC scale and connect the multimeter terminals to the newly made arrangement.

Each of the millivolts registered by the multimeter will syndicate a consumption of 1 watt, so we can easily estimate the electricity consumption.

7 thoughts on “Cómo hacer un wattimetro simple”

  1. Hello, very good circuit. If my multimeter has the lowest scale of measurement 200v ac there is nothing to do, right?

  2. This is very good, except that they should have added the values for different voltages, not only 110v and 120v but also for 220v, 240v, and 380v, to order.....

      1. Components:
        R1 and R2 - Resistors 0.47 ohm, 5W
        R3 - Resistor 33 Kohm, 1/2W
        R4 - depending on the mains voltage * R4 - depending on the mains voltage * R4 - depending on the mains voltage
        * for 110V ... 39 Kohm
        * for 120V ... 33 Kohm
        * for 220V ... 2200 ohm

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