Kenwood L-1000T , 1990

If there's only 1/4 volt across the supercap, what's the cause? Is the charging voltage low, or is the cap leaky/shorted?

For testing, I'd try charging the cap through 100 ohms or so. That should give a time constant in a range suitable for following along on your DVM.

Unless you have zero vertical clearance, a replacement cap can be mounted just about anywhere. The lead length doesn't matter.

You should know that these types of capacitors have an extremely high internal series resistance so the internal resistance would swamp out 100 ohms and make the measurement useless. Low ESR is not needed since they only need to supply micro-amps when called to duty.

David

I once replaced a nicad battery in a tuner with a supercap, fed through about 5K. The capacitor charges up quickly, which does not suggest an extremely high series internal resistance. (I can check this, if you like. The tuner is in my bedroom.)

The Wikipedia article says that EDLCs have a very high /power/ density -- that is, they can deliver their stored energy very quickly. This is inconsistent with an extremely high series internal resistance. In fact, the article lists the following advantage...

"Extremely low internal resistance (ESR) and consequent high cycle efficiency (95% or more) and extremely low heating levels."

Wiring across from the cavernous central space makes sense. The very squat form factor of the original may well have precipitated its failure. I was forgetting about all the diodes along the power rail route so only one nearby standard electro (assuming the diodes are ok)

I may be wrong, but I think that we're confusing 'high internal resistance' and 'leakage resistance'. Internal resistance would be in series with the capacitor. Leakage resistance would be across the capacitor, causing it to discharge.

The Wikipedia article says that EDLCs have a very high /power/ density -- that is, they can deliver their stored energy very quickly. This is inconsistent with an extremely high series internal resistance. In fact, the article lists the following advantage...

"Extremely low internal resistance (ESR) and consequent high cycle efficiency (95% or more) and extremely low heating levels."

Note that we are not talking about super-caps here but memory backup capacitors that are very small considering their capacitance and CV^2 value. Super capacitors are a very different chemistry and for a different purpose entirely.

David

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I was not aware of the promising automotive use of supercaps, safe ultra-fast charge etc

Are you certain? A "conventional" cap would not be able to retain the memory very long. You need something 0.1F or larger -- and conventional caps rarely come in that size.

I installed a supercap in my Lux tuner, and it holds the memory two or three days.

William Sommerwerck Inscribed thus:

I would concur with William. I have a 0.22F @ 5v on my desk at the moment, it holds its charge for many days.

William Sommerwerck Inscribed thus:

I would concur with William. I have a 0.22F @ 5v on my desk at the moment, it holds its charge for many days.

David Inscribed thus:

Thanks for your note. Yes the cap I have is intended for memory retention service. I do have an ESR meter but it hadn't occurred to me to actually measure it, though I do take your point about discharging it first. I did discharge it some time ago and was surprised by how much the voltage had recovered the following day.

I'm not sure what the "typical" memory capacitor is. With respect to my Lux

William Sommerwerck Inscribed thus:

Hi William, I found references to "Super Cap" on EPCOS website.

This is an AC starter cap -- dubbed a Super Motor Cap. Not the same thing.

Old 0.047F , 5.5V dropped from about 5V to 1V in about 1 sec with DVM load. Replacement .2F one , connected to 5V ps via 220R took 35 sec to rise from

Baron Inscribed thus:

Just and update: I got the marked value wrong, its 2.2F @ 5v. There is no indication of the manufacturer. I've currently got a 4.5v 60ma torch bulb connected across it to discharge it. It took a few seconds for the bulb to stop glowing. Anyway I'm going to leave it overnight and check its ESR tomorrow. It should be well and truly discharged by then.

for something like that from 1990, it would most likely be a cap made by Elna (quite likely dark blue) NEC (possibly green) or Panasonic (all sorts of colors). Standard Oil was even making them at the time.

Also, they didn't have 'low' ESR supercaps like they do now, so ignore any crap off wikipedia or comparisons to modern datasheets for products that look the same.

Try 1980. I don't remember the brand, but I don't think it was any of these.

Regardless of what you do or don't think, IT WORKS. The storage time -- when the tuner is turned off and left off -- is about 40% of the original tiny nicad battery the supercap replaced (3 days versus a week). This seems reasonable, and is consistent with the information given in the Wikipedia article.

I don't think anyone here knows what they're talking about. I'm certainly aware of my own ignorance.

Lux

I discharged overnight an NEC U6 265 green, 0.2F, 5.5V and got an ESR of