Testing non polar Caps w/ simple multimeter?

[quaternotetriplet]

hi im wondering how to test mylar capacitor..

Im having no problem with electolytics using the resistance test... but tried mylar and not even a reading...

my question is any other way of testing the mylar capacitors?

[mictester]

hi im wondering how to test mylar capacitor..

Im having no problem with electolytics using the resistance test... but tried mylar and not even a reading...

my question is any other way of testing the mylar capacitors?

You won't be able to do it with a multimeter! Your mylar caps will just read open circuit on an ohms test - unless they're faulty! You need a proper capacitance tester. There are lots of circuits on the interweb. You feed a known AC (usually audio) signal into the capacitor, and measure what comes out of the other end.

[quaternotetriplet]

hi im wondering how to test mylar capacitor..

Im having no problem with electolytics using the resistance test... but tried mylar and not even a reading...

my question is any other way of testing the mylar capacitors?

You won't be able to do it with a multimeter! Your mylar caps will just read open circuit on an ohms test - unless they're faulty! You need a proper capacitance tester. There are lots of circuits on the interweb. You feed a known AC (usually audio) signal into the capacitor, and measure what comes out of the other end.

wow thanks.

[Grendahl]

First let me say that you cannot, unequivocally, test a capacitor and know that it is good with just a multimeter. If anyone tells you that you can, they’re simply wrong.

That being said, you can tell if it is bad, and you can get an idea if it’s good, but you won’t know for certain. Why? A multimeter is designed to measure Voltage, Current and Resistance. A capacitor stores charge. The charge that it stores is represented by current and time. Furthermore a capacitor has limits as to how high of a voltage it will work with.

To tell if a capacitor is bad, here are some tests you can do with a multimeter: 1st before you even break out the multimeter, do a visual inspection. Does it bulge or is it symmetrical? Is it discolored or does it look “nice”, is it leaking anything? If you answered yest to those questions don’t even waste your time with a meter, just get a replacement capacitor with the same specifications. If you can’t get exactly the same specs on a replacement capacitor you can instead get one with a higher working voltage. Difference in capacitance is dependent on the circuit that it is in and beyond the scope of this post.

For small value capacitors (around 0.01uF and less) about all you can do with a multimeter is check for a short or open. Either condition indicates it is bad, but lack of both does not guarantee “good”. Connect a voltmeter on the ohms range (x 10K) range to the capacitor. Make sure your meter is connected properly, the leads may or may not be positive or negative as you expect (check them with either another meter or a diode). If the capacitor is bad, the meter will either

* Stay at infinity (indicating that it is open) OR
* Drop to zero (indicating that it is shorted)

If you have an electrolytic capacitor of several uF or more, then you should be able to observe the following: It might be good if you see the needle jump towards zero and then slowly return to infinity. Note that if you have a DMM and it does not have a bar-graph display like a Fluke 7x/8x series you won’t be able to observe this. What you are actually seeing is the current from the meter charge the capacitor. Initially there is no charge and the current is high which makes the needle move towards 0. As the capacitor builds charge, the current becomes less and the needle returns to infinity.

To more completely test a capacitor, you need to test capacitance, leakage, equivalent series resistance (ESR), and maybe even the breakdown voltage. Each of these can be tested with specialized test equipment. Any testing you do should be done with the capacitor out of the circuit (at least one lead) as other components can (will ?) cause an erroneous reading.

If you want to test a cap to verify its value, you have to get fancier. Applying 60 Hz from a small transformer (less than the cap's rated voltage) and measuring the AC current will let you calculate the capacitance and show if the cap is still within its tolerance.

Here's a few links that contain info on how to do this:
http://www.hobby-hour.com/electronics/t ... uctors.php <- great info
http://www.repairfaq.org/sam/captest.htm
http://www.angelfire.com/electronic/fun ... _caps.html

Alternatively, there are a few digital multimeters on the market that can test capacitors and transistors, and have sockets to place them into.

[quaternotetriplet]

First let me say that you cannot, unequivocally, test a capacitor and know that it is good with just a multimeter. If anyone tells you that you can, they’re simply wrong.

That being said, you can tell if it is bad, and you can get an idea if it’s good, but you won’t know for certain. Why? A multimeter is designed to measure Voltage, Current and Resistance. A capacitor stores charge. The charge that it stores is represented by current and time. Furthermore a capacitor has limits as to how high of a voltage it will work with.

To tell if a capacitor is bad, here are some tests you can do with a multimeter: 1st before you even break out the multimeter, do a visual inspection. Does it bulge or is it symmetrical? Is it discolored or does it look “nice”, is it leaking anything? If you answered yest to those questions don’t even waste your time with a meter, just get a replacement capacitor with the same specifications. If you can’t get exactly the same specs on a replacement capacitor you can instead get one with a higher working voltage. Difference in capacitance is dependent on the circuit that it is in and beyond the scope of this post.

For small value capacitors (around 0.01uF and less) about all you can do with a multimeter is check for a short or open. Either condition indicates it is bad, but lack of both does not guarantee “good”. Connect a voltmeter on the ohms range (x 10K) range to the capacitor. Make sure your meter is connected properly, the leads may or may not be positive or negative as you expect (check them with either another meter or a diode). If the capacitor is bad, the meter will either

* Stay at infinity (indicating that it is open) OR
* Drop to zero (indicating that it is shorted)

If you have an electrolytic capacitor of several uF or more, then you should be able to observe the following: It might be good if you see the needle jump towards zero and then slowly return to infinity. Note that if you have a DMM and it does not have a bar-graph display like a Fluke 7x/8x series you won’t be able to observe this. What you are actually seeing is the current from the meter charge the capacitor. Initially there is no charge and the current is high which makes the needle move towards 0. As the capacitor builds charge, the current becomes less and the needle returns to infinity.

To more completely test a capacitor, you need to test capacitance, leakage, equivalent series resistance (ESR), and maybe even the breakdown voltage. Each of these can be tested with specialized test equipment. Any testing you do should be done with the capacitor out of the circuit (at least one lead) as other components can (will ?) cause an erroneous reading.

If you want to test a cap to verify its value, you have to get fancier. Applying 60 Hz from a small transformer (less than the cap's rated voltage) and measuring the AC current will let you calculate the capacitance and show if the cap is still within its tolerance.

Here's a few links that contain info on how to do this:
http://www.hobby-hour.com/electronics/t ... uctors.php <- great info
http://www.repairfaq.org/sam/captest.htm
http://www.angelfire.com/electronic/fun ... _caps.html

Alternatively, there are a few digital multimeters on the market that can test capacitors and transistors, and have sockets to place them into.

First let me say that you cannot, unequivocally, test a capacitor and know that it is good with just a multimeter. If anyone tells you that you can, they’re simply wrong.

That being said, you can tell if it is bad, and you can get an idea if it’s good, but you won’t know for certain. Why? A multimeter is designed to measure Voltage, Current and Resistance. A capacitor stores charge. The charge that it stores is represented by current and time. Furthermore a capacitor has limits as to how high of a voltage it will work with.

To tell if a capacitor is bad, here are some tests you can do with a multimeter: 1st before you even break out the multimeter, do a visual inspection. Does it bulge or is it symmetrical? Is it discolored or does it look “nice”, is it leaking anything? If you answered yest to those questions don’t even waste your time with a meter, just get a replacement capacitor with the same specifications. If you can’t get exactly the same specs on a replacement capacitor you can instead get one with a higher working voltage. Difference in capacitance is dependent on the circuit that it is in and beyond the scope of this post.

For small value capacitors (around 0.01uF and less) about all you can do with a multimeter is check for a short or open. Either condition indicates it is bad, but lack of both does not guarantee “good”. Connect a voltmeter on the ohms range (x 10K) range to the capacitor. Make sure your meter is connected properly, the leads may or may not be positive or negative as you expect (check them with either another meter or a diode). If the capacitor is bad, the meter will either

* Stay at infinity (indicating that it is open) OR
* Drop to zero (indicating that it is shorted)

If you have an electrolytic capacitor of several uF or more, then you should be able to observe the following: It might be good if you see the needle jump towards zero and then slowly return to infinity. Note that if you have a DMM and it does not have a bar-graph display like a Fluke 7x/8x series you won’t be able to observe this. What you are actually seeing is the current from the meter charge the capacitor. Initially there is no charge and the current is high which makes the needle move towards 0. As the capacitor builds charge, the current becomes less and the needle returns to infinity.

To more completely test a capacitor, you need to test capacitance, leakage, equivalent series resistance (ESR), and maybe even the breakdown voltage. Each of these can be tested with specialized test equipment. Any testing you do should be done with the capacitor out of the circuit (at least one lead) as other components can (will ?) cause an erroneous reading.

If you want to test a cap to verify its value, you have to get fancier. Applying 60 Hz from a small transformer (less than the cap's rated voltage) and measuring the AC current will let you calculate the capacitance and show if the cap is still within its tolerance.

Here's a few links that contain info on how to do this:
http://www.hobby-hour.com/electronics/t ... uctors.php <- great info
http://www.repairfaq.org/sam/captest.htm
http://www.angelfire.com/electronic/fun ... _caps.html

Alternatively, there are a few digital multimeters on the market that can test capacitors and transistors, and have sockets to place them into.

wow thanks.

[Grendahl]

LOL, yeah that was probably a bit more than you'd expected... but the answer is indeed in there!

[RnFR]

great answer! i think this should be moved over to the FAQs section.

[Grendahl]

great answer! i think this should be moved over to the FAQs section.

Thanks RnFR, but I have to admit that it's mostly plagiarized (albeit from several sources and not entirely a direct copy and paste).

When I have a question similar to the one answered above, I tend to open up both a document editor and a web browser at the same time. I search out the answers on the web, find the answers or parts of answers that in my opinion explain it the best, and then squash them all together in a word document that I can save for later reference. That's what the above is from.