Yet another dumb capacitor question

[Butcher]

When I test some caps on a DMM they go to a value and stay there but on some caps the value does not stabilize and just keeps climbing.
Why does this happen?

Thanks,
Dave

[armdnrdy]

It sounds like you are testing them in circuit.

You have to de-solder one leg to get an accurate measurement.

Same with resistors.

[Butcher]

Sorry I should have stated that these are new unused caps but good info for the future, Thanks.

[GibsonGM]

Would ESR (effective series resistance; a phenomena of caps that is unavoidable due to their construction/physics) account for a changing value when measuring?

I get this too; mainly on larger values (over 1u), which leads me to think the DMM is being 'fooled' by the changing charge due to RC time constant created by the ESR...

[armdnrdy]

I just tested a variety of large value caps from 100µf to 3300µf.....all gave constant readings.

My meter is a Fluke 87.

[GibsonGM]

Well...it's a Fluke    Mine is a $40 "Extech"...what are you using, Butcher?

[Butcher]

 Mastercraft on sale $40
http://www.canadiantire.ca/en/pdp/autoranging-digital-multimeter-0520052p.html#.VWtu4ksbTnc

perhaps a new DMM is in the future.

[Butcher]

Fluke is a little outta my price range though.

[armdnrdy]

Do either of you have one of the Atmega328 based component testers?

http://www.ebay.com/itm/Mega328-Transistor-Tester-Diode-Triode-Capacitance-ESR-Meter-MOS-PNP-NPN-L-C-R-/351049269845

I know that quite a few people purchased them (especially at that price) when there was a thread rolling around here.

If you have one...check the caps with this tester....see if there is a difference.

The caps I tested are general purpose...no low ESR types.

[Butcher]

Do either of you have one of the Atmega328 based component testers?

http://www.ebay.com/itm/Mega328-Transistor-Tester-Diode-Triode-Capacitance-ESR-Meter-MOS-PNP-NPN-L-C-R-/351049269845

I know that quite a few people purchased them (especially at that price) when there was a thread rolling around here.

If you have one...check the caps with this tester....see if there is a difference.

The caps I tested are general purpose...no low ESR types.

Might be worth getting. Do they have good reviews?

[armdnrdy]

Here's the thread:

http://www.diystompboxes.com/smfforum/index.php?topic=108076.0

Read through it....there's reviews and opinions throughout.

[Butcher]

Here's the thread:

http://www.diystompboxes.com/smfforum/index.php?topic=108076.0

Read through it....there's reviews and opinions throughout.

Thanks for the link,
I ordered 2 of 'em. One in the box with leads $29 and one no box $13 all with free shipping.
They look interesting for sure.

[armdnrdy]

Okay...maybe I should have disclosed this earlier.

I work for the company that reps this line of testers. I just made $15 dollars commission off of your purchase! 

[Butcher]

I feel like you have been withholding information.

[armdnrdy]

Just a bit of humor to lighten up the day! 

[GibsonGM]

My Extech meter is actually quite nice!  For the price, a good buy.  MiniTec 26, has served me well from electronics to auto and home wiring for 7 years.   It walks a bit on capacitance, but not much; most lower-end meters seem to.  I only 'test' low value caps anyway, since electros have a label you can easily see    

I think it's faster to toss poly's on the little tester (mentioned above) since it has a rack to plug them into!  For $15, I won't complain, and it gives a nice ESR readout on-screen!       

Mounted mine on a small piece of ultraply with a home-made battery clip.

[duck_arse]

butcher - are you cap testing on the ohms range, or a dedicated capacitance range (I hear new-fangled meters with numbers have them ....)?

[Butcher]

Dedicated cap range. Auto ranging.