Digital timer outlet loses program

AS Avi-tech said, specifically EMC issues, spikes resulting from switching inductive loads can easilly cause microcontrollers to reset or set them into unwanted modes where they write to memeory.

Try some suppression on the leads to the load, a nice chunky ferrite like you see in power supplies for laptops, a capacitor (suitably rated) across live and neutral will help too. If you are not into electronics then you can buy a filter. Make sure the incomming supply to the timers is filtered too.

You could always run a test by using the timers on a more passive load (say a table lamp) and see if the still fail...that would indicate that the problem is the incomming power...not the load.

Del

As AT & Del said the timer may not be able to handle load. You could purchase a motor starter that could handle the pump motor load and have the timer switch it.

Thanks for the helpful explanations. The inductive load explanation is really helpful. The aquarium pump is very small so I don't think it's a load issue. I'll look for a better built timer designed for both resistive and inductive loads. Thanks again.

Don't know if you can do this or not but one thing that can help you is just remove operating replay from inside and fix it somewhere outside.

Also put a spike suppressor at the VCC of timer.

Timer,

I had a problem with a PLC output controlling a buzzer. It would time and then unpredictably reset when the buzzer was on. Turned out that the buzzer was putting electronic noise back into the PLC through the output. When I changed it so the output was controlling a relay coil and the buzzer was wired through the relay, the problem disappeared.

Therefore, you can look at the type of load the pump represents. It is possible that it is introducing noise back to the timer. Another possibility is that the inrush current for the pump is momentarily causing a voltage sag, which is causing the timer to lose its memory.

I think that the external relay is the best approach to solving the problem. Inexpensive digital timers can easily have a design which leaves them susceptible to noise, voltage sags, or similar woes.

--JMM