Intuition would make you think so, but your intuition turns out to be
wrong in this case.
Reread Lee Hart's post on this subject. He has it correct.
All cells get/produce the same current because they are in series. The
cells all are charged and discharged at the identical rate. Thus, have
the identical state of charge. Any imbalance is caused by unequal
self-discharge, which is a strongly influenced by temperature.
The variations in temperature are indeed caused by variations in
internal resistance. You can visualize that resistance as a separate
resistor in series with the (ideal) cell. It does not influence the
state of charge because the current is the same in all cells.
It is the fact that the current is identical that is the key. All
electrons that enter one end of the string emerge on the other end. None
are lost. Each electron flips an ion in each cell. Whatever voltage is
needed is what there _will_ be, or electron flow will stop.
True fact.
Bill Dube'
On 6/17/2013 12:56 AM, [email protected] wrote:
Bingo
You got it.
The energy stored in cell has been reduced by losing some of the energy as
heat.
Mostly upon discharge because the loads are higher but also when charging.
Since resistance changes by the state of charge so does the amount of
energy lost.
Its why I recommend if possible to keep the SOC of the pack 40% to 80%.
If your charging above 90% there is higher resistance and more heat. The
cells that have the highest resistance lose more energy as heat which in turn
causes them to have a shorter service life.
If you deeply discharge a pack to where it is in a lower state of charge.
Resistance again increases as the state of charge drops. The energy lost as
heat is greater in cells with the highest resistance.
So both by charging or discharging. Your loses are greater when you push
cells to their limits as the resistance increases.
Since resistance varies cell to cell under best case conditions. When
pushed to their limits these differences between cells also increase and have a
greater impact.
Don Blazer
In a message dated 6/14/2013 9:59:43 P.M. Pacific Daylight Time,
[email protected] writes:
Date: Fri, 14 Jun 2013 22:57:43 -0400
From: "Al" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Subject: Re: [EVDL] Resistance Jack Rickard of EVTV.me
Message-ID: <00a701ce6974$1bcff760$4101a8c0@alkb2ayu>
Content-Type: text/plain; format=flowed; charset=iso-8859-1;
reply-type=original
That doesn't sound right.
Wouldn't the cell with the higer resistance lose some of the Ah as heat?
Al
----- Original Message -----
From: "Peter Gabrielsson" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: Friday, June 14, 2013 10:22 PM
Subject: Re: [EVDL] Resistance Jack Rickard of EVTV.me
While I agree that resistance is important you are unfortunately not
really
correct that it causes imbalance due to energy loss in series strings.
Batteries are primarily electron storage devices, that's why their
capacity
is measured in Ah (1Ah= 5767*10^19 electrons). In a series string the
amount of electrons you shove through each battery is always the same
regardless of resistance. If you put 5Ah into a string of two empty 10Ah
cells they will both end up at exactly 50% SOC even if one has 1000 times
the resistance of the other.
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