On by light - off by dark AC exhaust fan switch

[lopburi3]

Quick check of Lazada only shows on at night off at dawn type switch and most circuit box type are motion only.  Have bath where would prefer not to run wire and looking for way to use on/off wall box fan control to sense light on and off to turn fan on during time light is on.   Seems easy but all sensors appear to only operate on with dark.  Any ideas/source/laugh.  

[degrub]

If i remember my relay logic correctly, you just need an interposing relay with a normally closed contact to feed the power to the fan motor. The light detector module output provides the current to the relay coil. Match the current type (AC/DC) and voltage level provided by the light detector module. If the light detector output is too low, use another relay to switch a DC or AC power source that is fed to the interposing relay.

[lopburi3]

6 minutes ago, degrub said:

If i remember my relay logic correctly, you just need an interposing relay with a normally closed contact to feed the power to the fan motor. The light detector module output provides the current to the relay coil. Match the current type (AC/DC) and voltage level provided by the light detector module. If the light detector output is too low, use another relay to switch a DC or AC power source that is fed to the interposing relay.

That sounds right sensor power on (dark) will open contacts external relay cutting power fan.  Not pretty but should work.  Thanks.

[Crossy]

Alternatively, assuming you can get the dark switch apart, many of them have a change-over relay anyway, you should just be able to move the output wire to the normally closed contact.

 

[lopburi3]

3 minutes ago, Crossy said:

Alternatively, assuming you can get the dark switch apart, many of them have a change-over relay anyway, you should just be able to move the output wire to the normally closed contact.

 

Was thinking that - and had hope one might actually have an external wire to do so - but they all seem to be sealed box units and likely beyond my current eyesight/solder abilities.  ????‍????