Previous in Forum: Differences between a Non auto MCCB and Isoaltor   Next in Forum: Smoke Detector Compliance with NFPA
Close

Comments Format:






Change Mode
Close

Subscribe to Discussion:

CR4 allows you to "subscribe" to a discussion
so that you can be notified of new comments to
the discussion via email.

Close

Rating Vote:







Add Vote
11 comments
Rate Comments: Nested
TommyTech
Commentator

Join Date: Dec 2006
Posts: 64
Good Answers: 3

How to directly measure large caps ESR?

08/09/2007 7:57 AM

I have a box of 96,000uF 10 VDC capacitors and I need to measure their ESR at 120 Hz. None of the LCR or cap meters in my lab are calibrated for ESR due to a technical problem with the procedure (long story, don't ask). The manufacturer uses a meter to measure ESR and may be derived from DF hence the 120 Hz parameter. I turned the web inside out looking for information on how to directly measure ESR and the only 2 methods that provide actual values are DC based or only work on small value caps. With all the giant brains reading this list someone has done this already.

Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.
Anonymous Poster
#1

Re: How to directly measure large caps ESR?

08/09/2007 9:13 AM

Please define http://en.wikipedia.org/wiki/ESR.
Register to Reply
Electroman
Guru
United Kingdom - Member - Olde Member!! Engineering Fields - Instrumentation Engineering - New Member

Join Date: Jul 2006
Location: Dunstable, England
Posts: 2821
Good Answers: 45
#2
In reply to #1

Re: How to directly measure large caps ESR?

08/09/2007 9:59 AM

As the dissipation factor is directly related to the ESR for these large electrolytics, you know the test frequency so you can calibrate or draw a chart up which will show the ESR against dissipation factor.

On any LCR bridge the disspation factor D=ESR/Xc = ESR x 2xpi x 120 x C = ESR x 750 x C =

ESR x 72.3 so ESR = D / 72.3 ohms - done!

John.

__________________
 A little knowledge is a dangerous thing - Googling is far worse!
Register to Reply
Electroman
Guru
United Kingdom - Member - Olde Member!! Engineering Fields - Instrumentation Engineering - New Member

Join Date: Jul 2006
Location: Dunstable, England
Posts: 2821
Good Answers: 45
#3
In reply to #2

Re: How to directly measure large caps ESR?

08/09/2007 10:06 AM

Hmmmmmm that looks a bit odd, so remember that at 120 Hz for a D =1 the ESR is going to equal the impedance of the capacitor...

at 120 Hz a 96000 uF is going to have an impedance of 72.3 ohms, so if the ESR is 72.3 ohms the dissipation factor is going to be one!

roughly!

__________________
 A little knowledge is a dangerous thing - Googling is far worse!
Register to Reply
Electroman
Guru
United Kingdom - Member - Olde Member!! Engineering Fields - Instrumentation Engineering - New Member

Join Date: Jul 2006
Location: Dunstable, England
Posts: 2821
Good Answers: 45
#4
In reply to #3

Re: How to directly measure large caps ESR?

08/09/2007 10:11 AM

Why do I have a sneaking suspicion I've made a pig's ear of that...

__________________
 A little knowledge is a dangerous thing - Googling is far worse!
Register to Reply
Electroman
Guru
United Kingdom - Member - Olde Member!! Engineering Fields - Instrumentation Engineering - New Member

Join Date: Jul 2006
Location: Dunstable, England
Posts: 2821
Good Answers: 45
#5
In reply to #4

Re: How to directly measure large caps ESR?

08/10/2007 8:49 AM

Nope I'm right, the above is correct!

I was getting confused remembering the design we did at Marconi Instruments in the early 70s for a customer who wanted to have the loss factor dial calibrated in resistance for measuring inductors...

It was quite straightforward really... John.

__________________
 A little knowledge is a dangerous thing - Googling is far worse!
Register to Reply
taejonkwando
Power-User

Join Date: Dec 2006
Posts: 441
Good Answers: 20
#6

Re: How to directly measure large caps ESR?

08/10/2007 11:11 AM

TommyTech, take a look at this site http://ludens.cl/Electron/esr/esr.html .

__________________
 intellectuals solve problems, geniuses prevent them ~ Einstein
Register to Reply
Electroman
Guru
United Kingdom - Member - Olde Member!! Engineering Fields - Instrumentation Engineering - New Member

Join Date: Jul 2006
Location: Dunstable, England
Posts: 2821
Good Answers: 45
#7
In reply to #6

Re: How to directly measure large caps ESR?

08/10/2007 12:22 PM

No that's a cheap and cheerful indicator, it doesn't actually do any measuring...

Just use an LCR bridge as I described for accurate measurements.

__________________
 A little knowledge is a dangerous thing - Googling is far worse!
Register to Reply
Anonymous Poster
#8
In reply to #7

Re: How to directly measure large caps ESR?

08/10/2007 2:52 PM

Thanks for all the input! Now I'll have to see if metrology has a LCR bridge they can part with. The typical ESR is rated at .007 Ohms so I'm looking at a DF in the ballpark of 1*10-4 . Really little and really big numbers seem to lead to no good in the end…………….
Register to Reply
Electroman
Guru
United Kingdom - Member - Olde Member!! Engineering Fields - Instrumentation Engineering - New Member

Join Date: Jul 2006
Location: Dunstable, England
Posts: 2821
Good Answers: 45
#9
In reply to #8

Re: How to directly measure large caps ESR?

08/11/2007 8:32 AM

Eh? how do you work that out Guest?

D= ESR x 72.3 = 0.007 x 72.3 = 0.5

That should be easy to read on any LCR bridge...

John.

__________________
 A little knowledge is a dangerous thing - Googling is far worse!
Register to Reply
TommyTech
Commentator

Join Date: Dec 2006
Posts: 64
Good Answers: 3
#10
In reply to #9

Re: How to directly measure large caps ESR?

08/13/2007 7:03 AM

OK that's what I get for rushing to finish up before I go home for the weekend! Didn't even notice I wasn't logged on. I'm looking at my notes and I had it right then mucked it up on the way to my desk. Still thanks for the information and the peer check! I have an old general radio bridge on its way over (checked our inventory for a Marconi first) and will be happy to have this job finished.
Register to Reply
Electroman
Guru
United Kingdom - Member - Olde Member!! Engineering Fields - Instrumentation Engineering - New Member

Join Date: Jul 2006
Location: Dunstable, England
Posts: 2821
Good Answers: 45
#11
In reply to #10

Re: How to directly measure large caps ESR?

08/13/2007 7:33 AM

There you go Tommytech, I've restored three of these wonderful instruments over the last few weeks, as well as improved the spec and calibrated them - look on ebay.co.uk soon

John.

__________________
 A little knowledge is a dangerous thing - Googling is far worse!
Register to Reply
Register to Reply
Have a Different Question?
11 comments
Copy to Clipboard

Users who posted comments:

Anonymous Poster (2); Electroman (7); taejonkwando (1); TommyTech (1)

Previous in Forum: Differences between a Non auto MCCB and Isoaltor   Next in Forum: Smoke Detector Compliance with NFPA

Advertisement

Got Something to Say?
Ask a Question
Start a Discussion

Search this Forum
Electrical Engineering:
Go

CR4 Sections
Aerospace
BioMech & BioMed
Chemical & Material Science
Civil Engineering
Communications & Electronics
Education and Engineering Careers
Electrical Engineering
General Discussion
Instrumentation
Manufacturing
Mechanical Engineering
New Technologies & Research
Software & Programming
Sustainable Engineering
Transportation

Site Directories
Forum Directory
Blog Directory
User Group Directory
RSS Feeds

CR4 Rules of Conduct
CR4 FAQ
Site Glossary

Who's Online (56 right now)
Show Members
Advertisement