Project: Troubleshooting Low-order Harmonics Issue on an Air Conditioning Unit

Time scale: 1 working day

Scope of work: An air conditioning unit recently underwent testing at an accredited EMC test lab, only to fail the low-order harmonics test. In response, the manufacturer has approached us to conduct an in-house EMC pre-compliance check. Our goal is to identify the root cause of the issue and rectify it before sending the unit back for retesting at the lab.

Troubleshooting Process: Using both a differential voltage probe and a current probe, we managed to pinpoint the primary source of the noise. Our investigation revealed that a significant portion of the noise originates from the deck fan unit, which is powered by an electrically controlled (EC) motor to drive the fan. Upon analyzing the current waveform, it became evident that the mains current drawn from the power network lacks sinusoidal characteristics. Instead, this waveform comprises low-order harmonics that surpass the limits specified by industry standards.

The low-order harmonics test was then tested by using a low-cost analyser from TTI, HA1600A, together with a clean AC source. A clean AC source is essential for the harmonics test.

The solution to the problem is straightforward, adding a mH level inductor helped smooth the mains current and it is the most cost-effective way of solving this issue at this stage of the project.

Testing the deck fan by using a harmonics analyser
Testing the harmonics with an inductor
The mains current waveform has improved

We made a YouTube video to demonstrate how to test the low-order harmonics