Post-Mortem, Reverse Engineering: Tomzn TOQ7-125/2P Automatic Transfer Switch (& More)

The job of an automatic transfer switch (ATS), put simply, is to let a load be powered from two power sources, selecting the preferred input if it is available and the backup input if it is not. A good ATS will do this quickly enough such that the changeover time is short enough that a majority of appliances won’t even notice the interruption in power. Such switches are extremely useful where you want to have single-input devices be powered from multiple sources, or in my case, where you’d like to use a power station to run your appliances but want some continuity in case they fail unexpectedly or run out of charge mid-operation. I’ve taken a look at a few ATSes and liked the Tomzn Nightlight-series TOQ7-125/2P quite a bit. In testing, it was relatively consistently fast, while featuring an improved build quality compared to other units including additional insulation and arc-chute features. For switching the (usually much less than) 10A of a regular GPO, it was overkill, but I…