Electrical Measurements

You need some special tools to measure voltage, current and resistance of your motor. The best simple and inexpensive device that can do all these tasks and even more is a digital multimeter. You may already have one or you can buy either basic or advanced digital multimeter at this site.

This is how you can measure voltage (basic multimeter shown):

Make sure that the test leads are connected to common (marked “COM”) and “V” terminals. Turn the switch so it points to 20 DC Volts (only if your voltage does not exceed this; in this range you can measure 0-20 Volts). Turn it on and take the measurements.

If you use advanced multimeter from our site you need to connect the test leads to “COM” and “V” and turn the main switch to “V=”. This is auto ranging multimeter so it will select automatically the best range for the most accurate measurements.

As you may notice for voltage measurements you do not need to disconnect any wires in the motor – the multimeter is connected in parallel to measured circuit. Very small current goes through multimeter in this mode as its resistance is really high.

To measure the current you need to disconnect your circuit and connect the multimeter in series so the current goes through the multimeter. Very low voltage drop is on the multimeter as its resistance in current measuring mode is low and could be ignored.

This is the typical connection for measuring the consumed current (basic multimeter shown):

For the consumed current measurement we recommend using the highest current range (10 A). The peak current for our motors may easily exceed 1 A even though at optimal speed the average current may be below 100 mA (0.1 A).

Make sure that your test leads are connected to “COM” and “10A”; turn the switch to “10A” for basic multimeter or to “A” for advanced.

If you need to measure the resistance (for example, of your electromagnet), just connect the multimeter to the coil ends. Please note that at least one end of the coil should be disconnected from the circuit in the motor!

For resistance measurements the multimeter test leads should be connected to “COM” and “Ω”. Turn the main switch to “Ω” for advanced multimeter; for basic model we recommend measuring the coil resistance on lowest setting (0-200 Ohms).

Before measuring the resistance connect the test leads together – your multimeter should display 0.0 resistance. If it shows a small resistance (basic multimeter may show 0.1-0.4 Ohm) it is probably the resistance of the test leads. Technically you need to subtract this number from your reading but in most circumstances you may just ignore it. Advanced multimeter usually compensates for test leads resistance automatically.

See Calculations section for useful formulas to help you calculate motor parameters based on your measurements.