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stefuel
Joined: 07 Mar 2006
Posts: 3353
Location: Green Harbor MA USA
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| Posted: Mon Jul 04, 2011 1:18 pm Post subject: |
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| barclay66 wrote: | | stefuel wrote: | | Anyone care to comment on these readings??? |
Hi,
I think that measuring the ESR may not be an exact science. Depending on the meter type, the quality of the test leads and measurement methods the absolute values may vary. After all we're measuring in the range of miliohms. What can be determined (as you did) is an overall tendency and failure of single caps within a batch. What you can see in addition is that thicker caps provide less ESR than thin ones although they read the same capacitance/voltage specs.
In general I'd rather replace one more cap than waiting for its soon failure.
For your reference I've added an excerpt from my ESR meter's documentation which shows typical readings for different cap specs...
Regards,
barclay66 |
The "thicker" 13mm 16 volt caps that I have won't work where the original 10mm 10 volt ones came from. There is physically not enough room for them in a couple of spots. For those spots, even the 10mm ones are a bit tight for my taste as one if them is right up against a regulator and that one is right up against another cap of the same size.
I have found some 16v 2200 105c caps that are 10mm but a little bit taller. I think they will fit OK.
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stefuel
Joined: 07 Mar 2006
Posts: 3353
Location: Green Harbor MA USA
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| Posted: Mon Jul 04, 2011 2:04 pm Post subject: |
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Something else to consider when checking ESR on "in circuit" capacitors, especially what I'm looking at right now (power suppies).
"If measuring capacitors connected in parallel, the ESR reading will effectively be the value of ALL the ESR's in parallel not just the capacitor in contact with the probes". Per the ESR70's manual.
This is confusing as my "in circuit" ESR measurement of all the caps on the the rail with all the 10 volt caps was 0.04 which leads me to think that I was actually reading the best cap on the rail and ignoring the worst.
This is why I had to pull them all as I was getting the same exact reading on all the 10 volt ones even though I could only see physical damage and leaking on two of them.
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barclay66
Joined: 27 Jun 2011
Posts: 1304
Location: Germany
TV/Projector: Marquee 9500 Ultra
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| Posted: Mon Jul 04, 2011 2:31 pm Post subject: |
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| stefuel wrote: | | ...I was actually reading the best cap on the rail and ignoring the worst. |
Hi,
I don't think so. Resistors in parallel are calculated using this formula:
1/Rtot = 1/R1 + 1/R2 + ... + 1/Rn
Therefore each resistor lowers the total reading. I tend to believe that the test leads you're using might produce a reading error. Please try holding the tips directly together. You should get a reading of 0.00µF and an ESR of 0.00 Ohm. Any ESR Reading higher than 0.00 Ohm is the resistance of the leads themselves and should be taken into account when testing caps.
In the documentation of my ESR meter it is recommended using thick leads which should be as short as possible and routed close together for most of their length...
Regards,
barclay66
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stefuel
Joined: 07 Mar 2006
Posts: 3353
Location: Green Harbor MA USA
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| Posted: Mon Jul 04, 2011 4:53 pm Post subject: |
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OK, I've been off 0.01 on all my ESR readings. For some reason I am unable to calibrate to 0.00.
When I do the "test lead calibration" function the best I can do is 0.01 ohms.
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stefuel
Joined: 07 Mar 2006
Posts: 3353
Location: Green Harbor MA USA
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| Posted: Thu Jul 07, 2011 9:37 am Post subject: |
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| stefuel wrote: | OK, I've been off 0.01 on all my ESR readings. For some reason I am unable to calibrate to 0.00.
When I do the "test lead calibration" function the best I can do is 0.01 ohms. |
I emailed the manufacturer to ask about the inability to calibrate to 0.00 and this was their reply.
"Dear Mr. Stetson,
Thank you for your email concerning your ESR meter.
Don't worry, the offset of 1/100th of an ohm is a very small offset and it is normal for contact resistance to be more significant than that. The measurement process and the probe compensation process can result in a small offset and this is usually much smaller than the offset that the unit is eliminating for you (probe resistance, lead resistance etc). The overall resistance of the probes and leads is around 0.2 ohms, and the majority of that is removed by the compensation process.
I hope that reassures you. If you are still concerned, then don't hesitate to send the unit to us and we'll check it out for you."
I guess you probably couldn't even see that (1/100th) on a analog meter so I'll be satisfied with what I've got.
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