MK125 light sensitive switch hysteresis and supply voltage

I have constructed the kit and installed it in my yacht to control the anchor light which must, in accordance with maritime regulations, be displayed at night (when at anchor :smiley: ). The benefit is that I can be away from my yacht in the afternoon and be confident that the anchor light will come on in the evening if I am late back, and be switched off in the morning to save battery power when the sun comes up (but I don’t because I’ve been out late :wink: ).

Except that it doesn’t work at all as expected.

The light cycles many times at dusk, annoyingly flicking on then off then on again. This can be exacerbated if the yacht is rocking in any waves as the incident light is changing on the yacht all the time. I have read in some posts that increasing the value of one of the capacitors can solve the multiple on and offs. Which capacitor do I need to change and to what value?

The second problem is that the unit appears very sensitive to supply voltage; when the fridge switches on (or tries to) the light sensitive switch unit will trip and the anchor light will go out for a few seconds (of the hysteresis?). When the unit tries to switch back on again, it causes the fridge to switch off until the fridge hysteresis period expires. Both systems then cycle around this crazy loop again until I intervien :confused: Is the unit so sensitive to supply voltage? If so, is there a mod I can make to overcome this?

Thank you, CC

Hysteresys can be increased by increasing C3
As there is no on-board regulator, unit will respond to fluctuations in supply voltages, which is a problem with marine applications.
A possible solution is to run the the circuit from a regulated 5 or 9VDC source (except for the relay, which needs 12V).

Hello I am new here and might have a simmilar problem, but need to understand if the symptoms are the same. I use the MK125 to switch a 12V motor. At night there is no problem with the switching, it switches once, the motor runs and all fine. In the morning the relay flicks on and off several times within seconds, until either the battery is empty and it stops all together, or light conditions are changing to a bit brighter. Would increasing the capacitor C3 sort this out? I would need to find a way that once the electronic says on to the relay it stays on for several ideally minutes until ist flicks back? Is this possible?

It is possible that the switching of the motor causes unwanted transitions of the op-amp, especially if both are fed from the same supply.
Regulating the supply and/or increasing hysteresis might help.

Yes, the motor and the MK125 are fed from the same supply. It is a lead battery and I thought it would be very stable for this very reason. How can I stabilise a battery further? Is there a limit to which it makes sense to increase the capacitor C3 to increase the hysteresis (currently 100uF)? What about the 4700uF others in the forum have tried?

Hi did you find a solution to this? I’m having the same problem.