Capacitor Polarity: Which Edge is Negative?

In summary, if you're replacing capacitors on a board, it's best to measure the resistance across the leads to determine which is negative. If all else fails, you can try to determine which side is negative by looking for the stripe or bar on the cap.
  • #1
DaveC426913
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I'm an only somewhat-experienced electronics tinkerer. I'm working on a board from an older widescreen TV. It has these kinds of capacitors:
_NVCAP.JPG


I've looked everywhere online.

Which edge is negative? The black(purple) or the grey?
 
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  • #2
There is another way to determine which side is the + side and the - side. The + side's lead will be longer than the - side's lead.
 
  • #3
Considering that these are surface mount capacitors, I believe it will be quite difficult to determine which lead is longer. However, there is a standard for this (assuming these are compliant parts). The side with the stripe on top indicates the negative lead, and the side with the bevels indicates the positive one:

http://www.marketa.com/cht/pdf/ele/sc_series.pdf
 
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  • #4
If all else fails, measure the resistance across the leads. Then reverse the polarity and measure the resistance again. The polarity that gives the highest resistance is correct.
 
  • #5
Corneo said:
There is another way to determine which side is the + side and the - side. The + side's lead will be longer than the - side's lead.
Not if I'm examining an existing board!

skeptic2 said:
If all else fails, measure the resistance across the leads. Then reverse the polarity and measure the resistance again. The polarity that gives the highest resistance is correct.
How does that tell me which is the negative lead?

See, I'm replacing all these capacitors with newer ones of a different type. I don't know the circuit. I know what's negative on my existing caps, I just need to know which way to put them in.

Looks like the negative side of a cap is always indicatged by the "stripe" or "bar".

Good. That means I put them all in correctly and don't have to redo the whole thing!:-p
 
  • #6
Can you power up the circuit and measure which is negative on the caps? If not, usually circuits have a positive supply and a negative ground. Many times large caps have the negative side connected to ground.
 
  • #7
Alas, all my careful soldering seems to have been for naught. Now the TV gets no picture.

Most likely I've fried the board with my ham-fisted soldering iron technique.
Second most likely, I've broken some of the delicate traces when the capacitors came off.

Oh well, it cost me nothing.
 
  • #8
Use some 30ga wire to bridge the broken traces. Don't give up yet.
 
  • #9
dlgoff said:
Use some 30ga wire to bridge the broken traces. Don't give up yet.
Yeah but the trouble is, they're so fine and they're multi-layered on the PCB so it's virtually impossible to tell where they connect to.
 

Related to Capacitor Polarity: Which Edge is Negative?

1. What is capacitor polarity?

Capacitor polarity refers to the orientation of the positive and negative terminals of a capacitor. It is important to correctly identify the polarity in order to ensure proper functioning of the capacitor in a circuit.

2. How do I determine the polarity of a capacitor?

The polarity of a capacitor is usually indicated by markings on the body of the capacitor. The negative terminal is typically marked with a minus sign (-) and/or a shorter lead, while the positive terminal is marked with a plus sign (+) and/or a longer lead.

3. What happens if I connect a capacitor with the wrong polarity?

If a capacitor is connected with the wrong polarity, it can lead to malfunctioning or damage of the circuit. This is because the polarity determines the direction of the flow of current, and if it is reversed, it can disrupt the circuit's operation.

4. Is it possible for capacitors to have the same polarity on both ends?

Yes, there are types of capacitors, such as ceramic capacitors, that do not have a specific polarity and can be connected in either direction. However, it is still important to pay attention to the markings on the capacitor to ensure proper connection.

5. Can I reverse the polarity of a capacitor?

No, the polarity of a capacitor cannot be reversed. If you need to change the polarity, you will need to replace the capacitor with one that has the correct polarity for your circuit.

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