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John-Del[_2_] John-Del[_2_] is offline
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Default Disconnecting CFL bulb from powered circuit can cause damage?

On Friday, March 15, 2019 at 9:54:38 PM UTC-4, Jeroni Paul wrote:
I have a mosquito trap with a circline 10W UV fluorescent bulb and a fan, the bulb went bad and it proved difficult to get a replacement. Now I would like to run the bulb only at night to extend its life and I tought to add an LDR, some transistors and a relay to run the bulb only at night.

Problem is the same inverter runs the bulb (CFL like circuit) and the fan, and the fan must never stop. The inverter has separate transformers for the bulb and fan but the drive circuit seems shared.

My concern is if I can place the relay in series with one of the four bulb wires to turn it on and off safely. The inverter ran for several months with a blown bulb so it has no problem to run without a load. But can it be damaged if the bulb is disconnected while powered?



Is there room to add a supply just to power the fan? If so, you can arrange to power down the CFL inverter (even directly at the processing chip which usually has an enable line) when not needed instead of suddenly disconnecting the load. This way, you would probably not even need the relay; use your photocell and transistor to shut down the inverter directly.

I don't know if mechanically switching your lamp on and off will damage the lamp or supply, but my gut instinct is no.

Switching power at the processor IC will be safe for both.