Hi all,

Is this normal reading for a 150nf capacitor ? Please see the photo.

 

For F = 100kHz the 150nF capacitor reactance is equal to :

Xc ≈ 0.16/(C * F) ≈ 0.16/(150nF * 100kHz) ≈ 10.7Ω

And normally we do not check the ESR if the capacitance is smaller than 1μF.

 

I didn't think that ESR and capacitative reactance were the same thing. Am I mistaken?

 

I didn't think that ESR and capacitative reactance were the same thing. Am I mistaken?

You're right, they are not the same thing. ESR (effective/equivalent series resistance) is the amount of resistance you would need to put in series with an ideal capacitor (if you had such a thing) to duplicate the characteristics of the real-world capacitor you are dealing with.

 

I guess I would want to know more about this ESR meter and what it thinks it is actually measuring. BTW 10 ohms sounds like a pretty big ESR, by a couple of orders of magnitude.
It says it is an IN-CIRCUIT tester. Does that mean it will also test a component by itself?

 

Well, my Chinese cheap ESR metre show 1.7Ω for a 100nF film cap.

 

Is this normal reading for a 150nf capacitor ?

Sounds abnormal.
What do other capacitors in that size range test on your meter?

 

Is this normal reading for a 150nf capacitor ?

That doesn't look right to me; it's WAY higher than I'd expect.

It's hard to tell for sure, but that capacitor closely resembles a Panasonic ECWF-series metallized polypropylene film capacitor or one very similar. Looking at the ECWF spec sheet for 250V capacitors (I'm guessing on the voltage rating), the dissipation factor at 1 kHz looks to be around 0.01% which, for a 0.15μF capacitor, would imply an ESR of around 0.1Ω.

Also, the maximum permissible AC current rating for that part is shown as 2 amperes, which is not consistent with the result you measured; at that current, if the ESR were 10Ω the capacitor would overheat and be destroyed almost instantly.

So based on limited information, my semi-educated guess would be that your ESR reading is incorrect, and is indicating way too high.

 

That doesn't look right to me; it's WAY higher than I'd expect.

It's hard to tell for sure, but that capacitor closely resembles a Panasonic ECWF-series metallized polypropylene film capacitor or one very similar. Looking at the ECWF spec sheet for 250V capacitors (I'm guessing on the voltage rating), the dissipation factor at 1 kHz looks to be around 0.01% which, for a 0.15μF capacitor, would imply an ESR of around 0.1Ω.

Also, the maximum permissible AC current rating for that part is shown as 2 amperes, which is not consistent with the result you measured; at that current, if the ESR were 10Ω the capacitor would overheat and be destroyed almost instantly.

So based on limited information, my semi-educated guess would be that your ESR reading is incorrect, and is indicating way too high.

That's exactly what I thought, It was reading 10ohm in the circuit and 10.23ohm when removed.

 

Would this be a good replacement ? http://uk.rs-online.com/web/p/polypropylene-film-capacitors/7269984/

 

Would this be a good replacement ? http://uk.rs-online.com/web/p/polypropylene-film-capacitors/7269984/

That's exactly the part I was looking at to get the specs I cited; my guess (and it's only a guess) would be that it would, provided its voltage rating is adequate.

 

That's exactly the part I was looking at to get the specs I cited; my guess (and it's only a guess) would be that it would, provided its voltage rating is adequate.

Thanks for your helpful reply, the original cap is 154J400 I assume it's 400V ? While the Panasonic cap from RS is rated at 250V.

 

View attachment 116620

That attachment gives me an "attachment could not be found" error.

 

That attachment gives me an "attachment could not be found" error.

Apologies, its the same photo above with the 104K cap.

 

Thanks for your helpful reply, the original cap is 154J400 I assume it's 400V ?

Hard to tell without knowing the manufacturer's part numbering scheme. What's the highest voltage present in the circuit this capacitor came from?

 

Hard to tell without knowing the manufacturer's part numbering scheme. What's the highest voltage present in the circuit this capacitor came from?

Totally understandable since I couldn't fine the datasheet for this particular cap ! Do you mean I can measure voltage on the pins where I've removed the cap ? Is it safe to plug it in ? please excuse my little knowledge.

 

I don't have a similar size cap, but I have a slightly smaller one and that looks like a normal reading to me.

14.7Ω for 100nF cap is a normal reading for you ? Are you sure that yore ESR meter can properly measure such a small caps? Also what type of a circuit you are trying to fix?

 

Totally understandable since I couldn't fine the datasheet for this particular cap ! Do you mean I can measure voltage on the pins where I've removed the cap ? Is it safe to plug it in ? please excuse my little knowledge.

I wouldn't plug it in; definitely not. What is the voltage rating on those big electrolytic capacitors I see in the photo near where your mystery cap came out of? The rating should be shown right on the outside of the electrolytics, and might give us a hint.

 

I wouldn't plug it in; definitely not. What is the voltage rating on those big electrolytic capacitors I see in the photo near where your mystery cap came out of?.

They're 200v 390uf.

 

It's a class D amplifier.

Made by who ? And the model number is ? Also why do you think that this 150nF cap is broken in the first place, no supply voltage?