best way to measure capacitor and power contention issue

[titann]

1.What is the best way to measure a capacitor value? I refuse to use multimeter as it always show the same value for different capacitor.

2. What will happen if there are two source of power supplies supplying to an input? Eg, if i pump in 3V into 5V source, what does it impacts? Can you describe more details on power contention issues?

 

[rtarbell]

For your capacitance measurement, I would suggst using an LCR meter with four-wire capability (four wires as opposed to two wires, it is considered to be more accurate). Keep in mind that some capacitors (such as electrolytic) have a VERY large tolerance (for instance, +/- 20%). Getting two different measurements using the same meter is not uncommon.

If you put two voltage sources together as you describe, they will probably short out (and possibly blow up). In your example, the 3V source sees a direct short to ground when it looks at the 5V source. The 5V source sees a short to ground when it looks at the 3V source. Thus, there will be lots of current flow, and your two sources could start smoking.