# Efficiency test for motor drives

Hey I have a BLDC square wave controller. How to check the efficiency of the controller alone (not including the BLDC motor). Any suggestions ?

• I have checked with DC load test machine, but what I get was the efficiency of both motor and controller. But I want to efficiency of the controller only.

• Are two wattmeters suitable for this, which are designed for 3 phase power measurement?

• I think a power analyzer could be used but it is very costly and even we don't have one.

• I don't think you can measure the efficiency of the esc on its own. Apart from the quiescent current it draws. You will need a load (i.e. motor) in order to draw current and observe the input power vs the output power. For that a current probe on one phase and voltage probe between two phase of your motor that you can input on an oscilloscope (use differential voltage probe and clamp on current probe if possible to be safe with your test gear) and a DC power analysis at the input should get the job done. The rest is math. Mar 4, 2020 at 8:04
• The efficiency will be (has to be by definition) zero. Mar 4, 2020 at 11:01
• "I think a power analyzer could be used but it is very costly and even we don't have one." - do you have (or can hire/borrow) a digital oscilloscope? Mar 4, 2020 at 14:45
• A poor mans power loss tester would be an insulated box around the driver. Either a small one and measure the inside temperature after steady state has been reached or a very large one and measure the rise rate of the temperature. Reset and place a resistor inside it instead. Adjust power until you have the same temperature/rise rate as your motor driver. Voilá! Mar 4, 2020 at 16:27
• Yea i have an digital oscilloscope with normal two probes.... Could i use two clamp meter(AC current & voltage) in two phase in order to measure the output power. Mar 5, 2020 at 10:55

To determine efficiency, you need to load the controller appropriately and then measure the input and output power or the losses. Neither of those is easy to do accurately. Wattmeters that can measure the power accurately may be quite expensive. You may find it easier to enclose the controller in an insulated box and measure the temperature rise of air flowing through the box to remove the heat. You will need to control and measure the air flow. You will also need to know the humidity and barometric pressure.

You may be able to determine the losses by simulation as accurately as you can measure them.

You can measure the output of the controller with the two single phase wattmeter method, so if you've got a three channel power analyzer you can set it up so that one is measuring the input (assuming that you have a single phase AC, or DC supply), and two the output of the controller, and some analyzers, like the Yokogawa one I have, have the efficiency calculation built in (it's just (W1+W2)/W3 when the third channel is the input measurement).

What you need to be wary of is that, if there's PWM on the output, that the frequency response of the meters is adequate to capture the real time current-voltage product, most moving coil wattmeters will not be able to do so, even many digital ones .

• I dont have a power analyser. Though input power is easier I could able to calculate that one, but i need to calculate the output power. Could i use two clamp meter(AC current & voltage) in two phase in order to measure the output power. Mar 5, 2020 at 10:54