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Spockie-Tech
Site Admin
Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia
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Going back a couple of posts to where Jake and John were discussing self-discharge of a pack possibly driving some cells into reverse polarity..
At first glance, I'm on Jakes side, with no circuit from one end of the battery string to the other, I cant immediately see how any of the cells could be reverse charged..
The self-discharge-to-zero yes, since there is an obvious leakage path within the cell itself, but there is no current path for the electrons to flow from one end cell to the other end cell, so no way for a conventional current flow to be pushed backwards through the middle cell.
I presume john, that you mean that the presence of the left and right cells attached to the middle cell offers somewhere for the electrons to flow, even although those cells have no circuit on their other end either ?
Is it that the self-discharge reactions in the end cells somehow absorbs ions from the center cell as part of their self-discharge ? I still dont completely see it though.. wouldnt the polarity be wrong for that sort of flow to occur ?
I dont think we need the precise chemical reactions just yet until we understand where the current is going and why..
Heres a diagram of what I think you mean is happening, perhaps you can tell me if I'm on the wrong track here.
Blue is conventional current flow, red is self discharge flow, green is my guess at this not-understood across-the-cells discharge flow
_________________ Great minds discuss ideas. Average minds discuss events. Small minds discuss people
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Mon Oct 18, 2004 10:59 am |
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JohnMuchow
Joined: 25 Aug 2004
Posts: 21
Location: New York City, USA
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quote:
Originally posted by Spockie-Tech:
At first glance, I'm on Jakes side, with no circuit from one end of the battery string to the other, I cant immediately see how any of the cells could be reverse charged
Neither can we...cause we screwed up!
Having spent the weekend talking to two electro-chemists who know wayyyyyy more than I do about this stuff (and, I swear, caused smoke to come out of my ears with all the neuron damage they caused), I can now say that we were wrong and that you and Jake were right...
self-discharge cannot cause cell-reversal if no load is attached to the pack
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This is something that to us seemed quite obvious except that we misunderstood 2 items we read and didn't explain clearly enough what we were investigating when we asked for confirmation of this from someone we thought knew better than us. Since we couldn't test this very easily (it would take months), we accepted what we thought was right without confirming it ourselves. This isn't a good excuse, but it is the reason why it happened.
My apologies to you Jake and thank you for sticking up for what you felt was the right answer. As a small token of appreciation for helping us find this mistake in our Tech Tips, we'd like to offer you 50% off any of our products. Just order and pay normally and we'll immediately send you the money via PayPal (we get a copy of the invoice when any of our products are ordered).
We have updated our Tech Tips and removed this incorrect information and won't be recommending anything we can't test ourselves or triple confirm with the electro-chemical gurus. Sorry for any confusion our mistake has caused! _________________ John Muchow, CamLight Systems
http://www.camlight.com
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Mon Oct 18, 2004 1:35 pm |
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