I went with the de-solder, less destructive than cutting a tiny trace. However, reading more topics online, I found out that you can disable the charging circuit just by de-soldering a specific SMD resistor. The RTC modules are the infamous ZS-042 DS3231 which need a trace being cut otherwise they keep on trying to charge a normal (non rechargeable) CR2032 battery. Or what if there is a bug in the router, I’m not home to reset it, and then the lights are out until I can intervene ? Thus, the control module should be as independent as possible and very rarely to need WIFI. ESP8266 boots much faster than the WIFI router, and then it would need to keep trying to fetch the time. I decided from the beginning to go with an RTC module, mainly as redundancy. I had few Nodemcu V2 CP2102 available (ESP8266), some RTC modules and a bunch of IRLZ44N MOSFETs.
Hardware choices Schematic of the control module Since I didn’t want to dismantle the power plugs, the only remaining thing was to try things out – maybe Dennerle build something that has no problems being driven with PWM ? LEDs are best driven by constant current source and if Dennerle built it like this, then there could be drawbacks in using PWM to alter the brightness (see Is It OK to PWM a current source?). The standard way of controlling the brightness of an incandescent light bulb is using Pulse Width Modulation (resistive load, voltage source). I wondered if I can build something similar for the 3 other LED lamps I own, a Dennerle PowerLed 5.0 and two Dennerle Style Led L.
The AI Sol Nano LED light fixture installed over my mini reef has one very nice feature – “fade in” to a set brightness in the morning and “fade out” to Moon light in the evening.