6-9 V Interval Timer Commercial Availability

Thread Starter


Joined Nov 6, 2009
I got the circuit shown in the attched PDF (minus the relay) soldered up and when I apply power, the led comes on steady for a few seconds, then Capacitor C2 (100uF) blows up. I have checked and rechecked the circuit and don't find any errors. From looking at the wiring diagram, does anyone know where my potential error is based on C2 blowing up?



Joined Dec 19, 2007
Two reasons electrolytic capacitors blow up:
1: You exceed the maximum voltrage rating by a significant amount.
2: You install them backwards.
Correct polarity is an absolute requirement for electrolytic capacitors. And, my guess is that's what happened. I've seen this happen even in commercial products.



Joined Nov 12, 2008
I agree with Ken. Some questions:

1) What voltage are you using to power your circuit?

2) What is the voltage printed on the capacitor that blew? Also double-check the voltages of all of your capacitors.

3) If the capacitor is still in the board, is the polarity correct?

4) Check to be sure your power supply is connected correctly to your circuit, e.g., that + and - aren't reversed. Double-check with a voltmeter.

5) Take a good picture of the top and bottom of your circuit and post them - we may spot something else. This isn't to question your ability but to have a having a second (or third or twenty) set of eyes never hurts.