Re: ESR Meter - Roll your own - ESRrev0.JPG

Mike Monett · 2007-07-09T05:23:47+00:00

> John Lark >> Something roughly like this, maybe. This is a 2-minute hack, so >> don't jump all over it right away; a real design would take more >> time. >> Basically, it's an oscillator that dumps current into the cap, >> and a synchronous detector to remove most of the orthogonal >> component. It ain't perfect, but should be a lot better than a >> scalar measurement. >> John > This was built along similar lines. The synchronous rectification > is not perfect due to phase shift in the forward signal path but > the arrangement is useful for reducing the annoying capacitive > quadrature component from Q's up to about 3 (at the 100kHz). It's > usable down to the milliohm area and proved the (cheap) 1000 off > 10uF cap's I bought, had an ESR of between 1 and 3 ohms!. Hi John, Do you mind if I make some comments? The 1 ohm resistor, R5, can be removed from the circuit. It is at a virtual ground node and has little or no voltage across it. So removing it has little effect on the circuit. With R5 gone, and the ESR range switch in the 1 ohm position, the 180 ohm resistor, R4, is effectively in series with the capacitor under test. The op amp merely changes the location of the ground node, and inverts the output signal polarity. Since R4 (180 ohms) is now in series with the capacitor, it completely swamps out the internal ESR (0.05 ohms.) This means the series combination of C, L, and R has negligible "Q", and there is no quadrature or orthogonal component in the circuit. However, as the ESR decreases, the corresponding voltage drop that we are trying to measure also decreases. We no are faced with the problem that the di/dt from the inductor is much larger than the I*R drop from the ESR. This means the leading and trailing edge of the square wave have large spikes. If you used a diode peak detector to measure the amplitude, it would respond as best it could to the leading...

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John Larkin 19 years ago

Since lots of single-chip uPs include decent adc's these days, why not just digitize the voltage drop across the cap? One could then note the cap charging slope and untangle it from the true esr. And measure capacitance, for free.

John

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SP 19 years ago

buck)

Sure,however I think the sensitivity of the typical 10 bit ADC in a cheap micro is about an order of magntitude too low, so you need a preamp anyway.

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Winfield Hill 19 years ago

Thanks, I'll try that if I can find a certifiably-bad cap. I have five different kinds of large impedance-measuring instruments that can measure milli-ohm esr, some in circuit. But the appeal of the little esr meter is its small size.

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John Larkin 19 years ago

buck)

That's about right, but it's still going to be simpler than most of the goofy and truly terrible "esr" meters we've seen here lately.

You may as well measure leakage and dielectric absorption while you're at it; code is cheap.

John

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Michael A. Terrell 19 years ago

Do you want some failed caps with high ESR? I can send you plenty. :(

I can even test them on the original design DSE meter and mark the ESR on each for you.

Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida

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Winfield Hill 19 years ago

Hey, that would be great! Here's my address.

Winfield Hill 617-497-4670 Rowland Institute at Harvard

100 Edwin H. Land Blvd Cambridge, MA 02142-1297

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Michael A. Terrell 19 years ago

I'll try to get them out, first of the week. I have a plastic gallon bottle that's about half full, right now. I think I still have some larger FP mount electrolytics that were rated for 60 Hz use. I'll have to go to the post office to pick up some flat rate boxs.

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is an example, if you've never seen this obsolete style.

Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida

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Fred Bloggs 19 years ago

All you're going to get is a bunch of this crap:

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i.e. any measurements you make will not be representative of anything. The last link on that page, Hillman-Helmold, goes into the physical chemistry of the failure, no detectable depolarizers to prevent the formation of H2. Also, anyone who cares to educate themselves on the reliability testing of e-caps will discover that failure is *defined* by a 2-3 increase in ESR:-) This is not really an independent discovery of some techie in a repair shop, sheesh. See Electrolytic Capacitor Life Testing and Prediction, by the Ford Research Lab guys, IEEE Industry Application Society, Annual Mtg, New Orleans, Louisiana, Oct 5-9, 1997, for a summary and refinement of life prediction models as a function of about half dozen major variables, for the last word on the subject....

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Fred Bloggs 19 years ago

Granted they are amateurish junk, but your designs and ideas are so

*ugly* they are borderline grotesque. When you have something artful to suggest that will be the day....

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John Larkin 19 years ago

You don't approve of my products? Show us some of yours.

John

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Fred Bloggs 19 years ago

As they say, I don't have to be a chef to know the food stinks...

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John Larkin 19 years ago

Show us something you've designed.

John

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John Tserkezis 19 years ago

Then by your reasoning, you should be able to gauge the relative stinkness of your own cooking?

Linux Registered User # 302622

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Michael A. Terrell 19 years ago

Gee Fred, is there anything you DO like about electronics?

Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida

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Michael A. Terrell 19 years ago

Maybe its not the food, but the diner?

Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida

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Fred Bloggs 19 years ago

You show us an esr meter that doesn't require a VMX crate.

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Winfield 19 years ago

I suggest we have an esr-meter design contest. However, to make it usenet friendly, and accessible to the readers, all entries must be made in ASCII drawings, annotated with text.

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