DE-5000 LCR Meter - Polyester film greencap ESR - Page 1
Forum section: electronics / beginners

author: LiftedTrace
author_rank: Regular Contributor
timestamp: August 17, 2025, 11:45:31 pm
content: I got this meter and was checking some electrolytic capacitors and it seemed to give accurate results from what I can tell, but then I pulled this cap out of an audio amplifier and checked it and it seem the ESR is quite high (See attached pic).Could this be accurate or am I doing something wrong, or is this meter not great for these types of capacitors?Thanks.

author: TimFox
author_rank: Super Contributor
timestamp: August 17, 2025, 11:50:14 pm
content: Quote from: LiftedTrace on August 17, 2025, 11:45:31 pmThat capacitor looks like polyester film, otherwise known as MylarTMor PET.At 100 kHz, ESR = 8.7 ohms impliesQ= 69, which is not unreasonable for that dielectric; polypropylene would have much higherQ.However, that is a relatively high test frequency: what did you measure at 1 kHz and 10 kHz, displayingQ, and did you do the CAL open and short circuit compensation before the measurement?

author: LiftedTrace
author_rank: Regular Contributor
timestamp: August 18, 2025, 12:21:02 am
content: Using the short clips, I ran the calibration with them open, and then closed.@1k - ESR=.25k ohms, Q=240@10k - ESR=55 ohms, Q=109

author: TimFox
author_rank: Super Contributor
timestamp: August 18, 2025, 12:48:10 am
content: Those are reasonableQvalues for polyester capacitors.The manufacturers usually specify theQat 1 kHz for those units.

author: LiftedTrace
author_rank: Regular Contributor
timestamp: August 18, 2025, 12:53:25 am
content: Ok. This is pretty new to me, so I am not really sure what Q is. What threw me was the ESR. Up until I got this meter I had never heard anything about Q in all my casual searching about caps, its been always about ESR, and the general idea I always seen was the lower the better.Now I got this meter and feel like a deer in head lights.Thanks for the help, looks like I got some learning to do.

author: TimFox
author_rank: Super Contributor
timestamp: August 18, 2025, 01:15:28 am
content: Qis the “quality factor” for a capacitor or inductor.A perfect capacitor, at a given frequencyf, has a reactanceXC= 1/(2 pif C) and a series resistance ESR = 0.For that series circuit,Q=X/ESR, which you normally want to be high, so you want ESR to be low, when compared with the value ofX, which depends onfandC.

author: LiftedTrace
author_rank: Regular Contributor
timestamp: August 18, 2025, 09:12:10 pm
content: OK, I think I understand. Thats why when I check a larger electrolytic, Its tested at a lower frequency, changing the value of X. For example I checked a 3900uF cap at 100Hz and had a Q factor of 26. The measured cap value divided by the Q value gave me a value of .016 ohms. When selecting ESR on the meter is just showed zero, which I guess .016 ohms is pretty close to zero.QuoteIs there a rule of thumb or anything for how much lower a value of ESR should be in relation to X?

author: TimFox
author_rank: Super Contributor
timestamp: August 18, 2025, 09:29:18 pm
content: Quote from: LiftedTrace on August 18, 2025, 09:12:10 pmNo rule of thumb, it depends on the application. For large electrolytics, the ripple from a rectifier depends on the ESR, which is why it is often specified for such capacitors.If you are testing a part to see if it meets specs, you can compare eitherQor ESR to the manufacturer's data sheet for that part at the frequency specified.Another parameter often quoted isD= 1/Q, the dissipation factor.At a given frequency, you can choose to measure the equivalent parallel valuesCPandRPinstead of the series values.TheQvalues are the same for the two cases, where for the parallel caseQ=RP/XP.For very highQvalues,XPis close toXS, but they are quite different for lowQ.In the parallel case, a good part has a high equivalent parallel resistance.Approximately,RPis aboutQ2xRS: feel free to check my algebra.