ESR Value for Electrolytic Capacitor question

[AndyA]

I'm fixing a SMPS supply from my sound bar. I have discharged all the caps safely.

If I measure the ESR with my DER EE-5000 on a Sam Young NHA 1000uF 35V I get 0.03. I can't find the ESR for any of the Sam Young caps online. So far as I can tell this one is OK.

When I measure 2 of the Sam Young NHA 470uF 10V I get an ESR of 3.7 and 4.2. Is this within spec or are they bad? 

Can I test the ESR of a capacitor in circuit when in parallel or series and still get the correct reading?


Thanks

[Shock]

Can I test the ESR of a capacitor in circuit when in parallel or series and still get the correct reading?

If you check on google images for ESR charts it will tell you even 10/20 years ago whenever those charts were made ESR for a 470uF 10V should be around 0.2 ohm or less, so yes that reading is quite high.

If there are other capacitors or resistances in parallel it can throw off the reading, remove them from circuit and double check. Check capacitance as well.

If the electrolytic capacitor has brown gunk leaking out, a raised or domed top, a blown bung or any discoloration below it on the PCB it's venting and needs to be replaced. For SMD caps sometimes you will see faded printing which points to leaking electrolyte.

[wraper]

When I measure 2 of the Sam Young NHA 470uF 10V I get an ESR of 3.7 and 4.2. Is this within spec or are they bad? 

Certainly bad. BTW you should measure ESR at 100kHz, just in case.

[kripton2035]

+1 for bad caps. first to try to sap with a good one.
how old is the soundbar ?

[AndyA]

Do you mean 100Hz or 100kHz?

The sound bar is at least 8 years old.

[wraper]

120 or 100 Hz is used to measure capacitance, 100kHz is frequency ESR is usually specified at except some rare cases.

[wraper]

Although DER EE-5000 may refuse to measure ESR at 100 kHz if you connect large capacitance. In such case you can measure it as Rs. It's just that ESR at 120 and 100 kHz are quite different figures and the most difference will be with small capacitance like below 100uF.

[AndyA]

Although DER EE-5000 may refuse to measure ESR at 100 kHz if you connect large capacitance. In such case you can measure it as Rs. It's just that ESR at 120 and 100 kHz are quite different figures and the most difference will be with small capacitance like below 100uF.

Rs mode is working great. 

I have a cap here that is 33uF 450V but its not on any chart that I can find. Do you know the worst ESR for this cap?

Thanks

[wraper]

Although DER EE-5000 may refuse to measure ESR at 100 kHz if you connect large capacitance. In such case you can measure it as Rs. It's just that ESR at 120 and 100 kHz are quite different figures and the most difference will be with small capacitance like below 100uF.

Rs mode is working great. 

I have a cap here that is 33uF 450V but its not on any chart that I can find. Do you know the worst ESR for this cap?

Thanks

If it's lower than few ohms, should be fine. Depends on series a lot, I'd say if more than 10 ohms, you can be pretty sure it's going bad.