SDG #153 Why does the Quick 861 cause lights to flicker??

After the Quick 861X review, the question remained why the station made the lights in the lab flicker. A power meter and oscilloscope were connected to examine the voltage and current waveforms, and the results were compared with the Best BST-863, Quick 857DW+ and Metcal HCT-900.

The two Quick stations switched the heater on a half cycle basis. The Best tended to draw current in wider blocks, while the Metcal used complete cycles and drew less power. The lights were sharing the same outlet strip as the stations, some distance from the consumer unit. The supply voltage could be seen dipping when the heater drew current, and the LED lights were responding to those short dips.

That explains the flicker observed in this setup. Adding a mains noise filter to the station would not fix the voltage drop caused by those current pulses. This is a follow-up to the 861X review, not a separate test of the 861DW, and it does not resolve the handpiece earth wire concern raised in the original teardown.