Need Help with a Timing Circuit

[gb043]

I need a controler for a solenoid with a variable ON time of 20 seconds to 2 min. or so, and an OFF time of 30 seconds to 5 min. The supply voltage can be 5 to 24 volts AC or DC. The load is a relay, less than .5 watts. The simpler the better! Thanks

 

[hotwaterwizard]

a 555 wil do the trick.

 

[gb043]

Thanks so much! I'll have to do some studying, but I think it will work out well.
Thanks again, Gary

 

[hotwaterwizard]

My simple Code practice oscillator may work too.

https://www.electro-tech-online.com/threads/float-recharging-what-does-it-mean.11316/[/url]

 

[Oznog]

I wouldn't take a 555 to such huge time periods! Not that the 555 won't work, but you're depending on the capacitance and leakage of an electrolytic for accuracy.

To charge a 220uF from 1/3 Vdd to 2/3 Vdd over 2 min with Vdd=5V means the charging current averages around 3 uA, if I got the calc correct. But, pulling an electrolytic cap spec randomly off of digikey shows a leakage of 8.8 uA. Since the cap's leakage is unpredictable, varying by lot, voltage, age, and temperature, reliable operation seems quite dicey. The timing period could vary a lot, and it's possible that charging current could equal leakage and the time period is infinite.

For time periods like this, you can use a 555 with a more reasonable (shorter) time period going through a counter. But really, a PIC may seem to be complicated but realistically it's probably the best solution and is physically quite simple, although learning to use them has a considerable learning effort.