Where are all the ESR meters?

Perhaps a better question is, how big is big?

Several designs we've been considering have a pair of diodes to discharge the test capacitor and limit the circuit voltages, but I've heard these can fail with large, charged capacitors.

I think the issue isn't necessarily how high the voltage (tube amplifiers get to hundreds of volts), or how high the current delivered, but how much energy is going to be dissipated in the protection components that discharge the guilty capacitor.

I'd say the answer is, the size of two fists. I think we're talking about ~ 100J of energy. Isn't that more than enough to blow out a common glass diode and/or a 1/4-watt resistor?

Should be enough to crank you over a few times ;-)

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
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What does your physical disability have to do with a complete absence of any constructive circuit contributions to SED?

WH is stalling... input protection has little to do with a basic measurement architecture. I had no idea this little project would be so difficult for everyone:-)

I know ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
         America: Land of the Free, Because of the Brave

If it's a 4-terminal gadget, all you need to do is current-limit three of the leads. My pfet current source does that inherently, with an added diode for the other direction. Or spring for a few of those Supertex depletion fets, or the protected SSRs.

I think the protections can be added once an architecture is settled on. Basic issues:

Analog/needle or digital/uP?

Simple scalar impedance, or tease out the resistive component, or resolve both real and imaginary parts?

Fixed or variable frequency?

Measure anything else? Capacitance? Resistance? Inductance?

Time or frequency domain?

John

Interesting that for a proposed "group design", hardly anybody is willing to make a first step. The psychology of group design is fascinating, and it turns out that an audience is a huge inhibition; people tend to not expose ideas if they fear they are imperfect, and might give some nit-picker grounds for public criticism.

Brainstorming is delicate because people are fragile. At my place, we scribble goofy ideas on a whiteboard, do a lot of stupid stuff (don't distinguish between circuit-as-proposal and circuit-as-joke), argue and laugh a lot, and sometimes come up with brilliance, with no way to tell who gets the credit. Some people just can't play at this game.

John

Hey, Fred, post an ESR circuit!

John

Protection is easy - read the voltage across the cap in question with a comparator, if it is more then a few volts, have a indicator displayed to discharge the cap first. If it is below a few volts, connect the cap to the metering circuitry with a couple of low RDS on FET's.

I think that the medium is more the problem than what the people involved can or cannot play at. Try using an archived text posting medium for your next brainstorming session and see how that works out.

We are using a poor tool for this job.

all...

Most definitely, and primarily to elicit critique from "Michael Terrell," a self described "I never claimed to be a circuit designer" type, who is always long on superficial opinion and woefully short of usefulness.

Well whatever...the task is straightforward and does not require a great amount of ingenuity. The ingenuity comes in deciding the functionality of the meter. In my opinion there is nothing to accomplish by going half way to an impedance analyzer, there are already plenty of compact and fully functional products in that niche. The key is to produce the simplest possible design that measures ESR, if something else comes free along with that without introducing one iota more of complexity then fine, but if it requires one speck of dedicated hardware not useful for determining ESR then it goes. This will require that you discover something inherent to ESR that allows for a very simple circuit architecture. That is all the help I am going to give you at this stage:-)

Thanks for the excellent illustration of my point. You are far more concerned about your ego than you are about the technology. Probably that explains why you don't design electronics.

There's a great irony here; that is all the help I am going to give you at this stage.

John

all...

Don't post it to elicit criticism. Post it to elicit suggestions, improvements, riffs, history, amazement.

John

Analogue, 0 to 1 ohm resistance (linear down to a few mohms), in series with

1uF and above. Discharge protection, Kelvin sensing etc, just added fluff. It's a core idea that will offer the interest and Laurels. Q's of even a 100 require a board full of bits. The ESR problem is up in the 1 part in a 1000 area. Fred seems to have something up his sleeve. I'm intrigued :)

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Not being a designer, I won't participate (and you wouldn't want me to!) in the process. But please consider that an ESR meter can -- if designed with it in mind -- be handy at measuring things such as resistance of battery cells, giving indication of relative age. With the dozens of rechargeable AA cells lying around, I want to know how they're getting on in years...

A small problem is that if you put in diode protection, measuring cells is out unless you decide to switch the protection on and off. Or come up with a more elegant solution...

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Right. I know, because I *have* been cranked, more than once. :-(

I'm not stalling; my paper sketches nicely handle the protection requirements I posted. Basically my design is a simplified version of the HP meters I have, based on the fact that 5% accuracy is good enough. I've been slowed down a bit by the need to evaluate single-supply instrumentation amplifiers, etc. And by my real projects: working on the book, home projects like my rust-infected Japanese Kerria, my Honeysuckle arbor, and of course, my Harvard job, with 1T generators, TEC drivers, -- things like that.

Just use a spring return spdt toggle. Toggle to test.

Ckt ---o o

Good idea for some applications, but how are you going to maintain contact resistance? We are talking about readings of hundreds or thousandth of an ohm.

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prove it.
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Michael A. Terrell
Central Florida