Help with timer construction

[ingemar]

Hi, I hoping someone electrically/electronically savvy can help me. I've just started running my ventilation system using solar power. (The plan is to go 100% solar when I can afford a solar panel capable of running my lights.) While this has been great and saves on electricity/money, I've lost the ability to use my fans on a timer.

What I need is (ideally) a pre-made on/off time for DC devices or alternatively, instructions on how to modify a digital timer designed for AC outlets to work with 12VDC.

Currently, the solar panels 12V 300mA charge a 12V battery. I plug in my fans when I want to use them (2 fans 12VDC 70mA each). I thought about using a photosentive switch or heat sensitive switch to synchronize the fans with the lights, but I'd like to be able to run the fans off and on throughout the day so I end up with a net gain from the solar panels. I.e., not turn on the fans until about 10AM, when it starts to get hot, so the battery is being charged in the morning light, and also run the fans 50min on and 10min off throughout the day in hopes that the input will be greater than the output or at least equal. The battery is necessary to maintain a steady voltage and current. Also, it gives me the option of running the fans at night if it is a particularly hot day/night.

Thanks.

[tkromer]

Lots of ways to do this, If you want something highly customizable for cheap (not to mention you could run 20+ devices) get a PIC chip and a programmer... At that point the possibilities are endless. There are plenty of premade stuff, but I suggest rather than wiring a timer, just program a PIC. If you leave it in a socket rather than hardwiring it, you can even reprogram it to control additional fans/lights/misters/etc and put it back in the socket when you're done.