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Can supercapacitors be used conventio...

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741
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Post Number: 40
Registered: 08-2005

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Posted on Wednesday, 11 October, 2006 - 10:54 pm:   Edit Post Delete Post Print Post

If I first discharge a supercapacitor from it's as-bought charged state, then does it behave as a normal capacitor ? For example, if I pass a sine wave through it, will the voltage lag the current by 90 Degrees etc ?

I ask because I suspect that there may be a catch.
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Obiwan
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Post Number: 833
Registered: 12-2005

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Posted on Thursday, 12 October, 2006 - 02:00 am:   Edit Post Delete Post Print Post

I don't know about the sine wave, never tried it.

But in general, no, you can't.

They're really more like a rechargeable battery than a "real" capacitor.

I took one apart and it had a damp, impregnated felt pad, very much like a battery. Either way, it's more of a chemical thing I suspect than an actual capacitance thing (as in with plates).

I suspect it will not work with the sine wave, because their charge and discharge rate is just WAY too slow. So maybe if the freqeuncy was sub, sub, sub-sonic you'd see something, but you're talking about a wavelength of days, not hours.

And they don't work well for filter caps in power supplies.

Strictly speaking, they're more for temp power storage, like memory, that sort of thing. Low current, long holding time, low discharge rate, low charge rate (long time to charge up), low discharge current, even low charging current.

Good question though!
Do Not Hit The Fly That Lands On The Tigers Head.
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Zeitghost
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Post Number: 429
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Posted on Thursday, 12 October, 2006 - 08:40 am:   Edit Post Delete Post Print Post

Caution!

The "dampness" is sulphuric acid!!!!
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Thomas
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Post Number: 139
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Posted on Friday, 13 October, 2006 - 08:39 pm:   Edit Post Delete Post Print Post

There is a catch, sort-of. The ESR (equivalent series resistance) is much higher. This means, simply, that they need much longer to charge and discharge than the average capacitor. By comparison with a battery, they charge practically instantly -- yet by comparison with an average capacitor, they are very slow. So, for instance, I used them to power some wind-up torch/flashlight designs. I needed to wire a "normal" capacitor in parallel to pick up the slack. Thomas.
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Thomas
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Post Number: 140
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Posted on Friday, 13 October, 2006 - 09:50 pm:   Edit Post Delete Post Print Post

Here we go.

Typical 1 Farad ESR = 30 Ohms.
Typical 10 microfarad ESR = 0.5 Ohms.

So if t=CR (rule of thumb), that's half a minute to charge the supercap, 5 microseconds for the 10 microfarad! So, your sine wave might need a period of one minute!

Thomas.
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Cpemma
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Post Number: 12
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Posted on Monday, 16 October, 2006 - 01:26 pm:   Edit Post Delete Post Print Post

"Typical 1 Farad ESR = 30 Ohms."

Supercaps are coming out with very much lower ESR, though a standard aluminium electrolytic will still beat them, and I believe paralleling standard electrolytics to get a high uF value reduces ESR still further?

One snag is the low working voltage; it's only 2.5V per 'cell' so to get higher values the caps are made up of 2 or more connected internally in series.

See http://my.execpc.com/~endlr/electrolytic.html
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Obiwan
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Post Number: 874
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Posted on Monday, 16 October, 2006 - 08:13 pm:   Edit Post Delete Post Print Post

Still have missing threads out here. Because I replied to this thread and it's not there.

And believe me, there was no reason to delete it.
Do Not Hit The Fly That Lands On The Tigers Head.
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Arw
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Post Number: 327
Registered: 04-2005


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Posted on Tuesday, 17 October, 2006 - 10:34 am:   Edit Post Delete Post Print Post

(Obiwan)

'Something is missing' doesn't really help to pin down any possible problems. Do you mean missing thread or missing article?

Please note, the preferred place to post problems is in Forum Help where everyone can see it, and I will pick it up. Unfortunately I can't guarantee to mine down every thread to pick up reports of forum problems.


-- ARW
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Obiwan
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Post Number: 879
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Posted on Tuesday, 17 October, 2006 - 06:27 pm:   Edit Post Delete Post Print Post

Sorry, I wasn't aware of a Forum Help.

What I had meant was that I had made a simple reply to Thomas, right after he posted or very shortly afterwares. Just a regular post in this thread.

I didn't give it a second thought until Cpemma posted, and I expected it to be under my post. Now my post isn't there at all.
Do Not Hit The Fly That Lands On The Tigers Head.
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Thomas
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Post Number: 141
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Posted on Wednesday, 18 October, 2006 - 02:24 pm:   Edit Post Delete Post Print Post

Hello Obiwan, from an Internet Cafe overlooking the Indian Ocean (I have some days off, and am let loose on my big single cylinder motorbike). Sorry I missed your post. At any rate, your last ones have come up. Thomas.
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Obiwan
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Post Number: 885
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Posted on Wednesday, 18 October, 2006 - 04:18 pm:   Edit Post Delete Post Print Post

Lucky you!!! I'd love to be there.

Yeah, it works most of the time. That's why you don't check to make sure your post is still there, they normally are.

Just once in a while, it gets a wild hair where the sun doesn't shine (even on the ocean) and it drops a couple.

(Message edited by obiwan on 18 October, 2006)
Do Not Hit The Fly That Lands On The Tigers Head.
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Thomas
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Post Number: 142
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Posted on Thursday, 19 October, 2006 - 02:26 pm:   Edit Post Delete Post Print Post

Off topic, this, Obiwan. I submitted, online, a substantial assignment for my M.A. While I wasn't watching, the system vanished it! No, said the system folks, it can't happen, it's impossible -- and yours truly was graded zero. Sure enough, it happened again -- but then I was watching closely. Thomas.
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Obiwan
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Post Number: 901
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Posted on Thursday, 19 October, 2006 - 08:32 pm:   Edit Post Delete Post Print Post

Yeah, I worked in IT for a while with plenty of servers, and even have my own internet server here at home on one of my servers. And people think that computers are infailable, I know for a fact otherwise.

I think they even have feelings. They have good times, they have bad times.

For a long time, that other forum would swear that posts were not indeed missing, and that it had to be something the user did wrong (that's what they always do). But sure enough, after it got really bad, several posts in several threads every single day, they finally admitted that it was the software and an upgrade was "on the way".
Do Not Hit The Fly That Lands On The Tigers Head.
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Arw
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Post Number: 333
Registered: 04-2005


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Posted on Thursday, 19 October, 2006 - 11:07 pm:   Edit Post Delete Post Print Post

Hopefully the matter of 'missing posts' can be closed if I say that EPE has certainly not deleted any such messages, it can only have been either an isolated network or server fault at that time. I am intrigued to read that a 'database error' was seen at one point.

The database-driven software is proving to be very robust and I am generally extremely pleased with the Discusware forum program.

The main reason for some earlier missing posts was reckoned to be related to using a flat file on a server, but the current MySQL database is proving much more efficient and the performance has improved a lot (and the ISP agrees). I see no trend regarding posts consistently going astray.

-- ARW
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Obiwan
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Post Number: 903
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Posted on Thursday, 19 October, 2006 - 11:15 pm:   Edit Post Delete Post Print Post

I didn't think that EPE was deleting them. But there has got to be a bug in the software. Hate to say it, but it's true.

I mean, if I reply to a post in a thread, and after I post it, it shows up at the bottom, then it "should" be locked in the database right?

Then it should show up later.

If it does not, and somebody didn't delete it, then that leaves a bug, no?

It's not like it's a new thing, other forums have these issues also. That was my point in the previous post, that servers do have faults from time to time. No server, no software is perfect. Ever.

Maybe due to several postings at the same time, on post is only getting displayed, but not actually added to the database, something like that.

It's not that big of a thing. But I have to say, that there are posts that go missing from time to time. Remember, I'm not the only one that has seen this.

Relax.
Do Not Hit The Fly That Lands On The Tigers Head.

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