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battery misconceptions

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user9253

Joined: 28 Mar 2008
Posts: 1944
Location: Riley TWP Michigan

Posted: Thu Sep 15, 2016 3:46 pm Post subject: battery misconceptions

Below is quote from another forum.  Are the statements true or false? Or part true and part false?

 	  Quote: 	
		   . . . .batteries (in parallel) need to be the same; same type, same brand, same model, same age. . . . I think parallel batteries should have diodes between them on the charging leg to prevent one draining the other.

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_________________
Joe Gores

lyleapgmc

Joined: 19 Feb 2014
Posts: 57

Posted: Thu Sep 15, 2016 5:20 pm Post subject: battery misconceptions

A couple on interesting concepts are revealed there. Theoretically the 

batteries should be identical in all the factors mentioned.  In reality, 

I doubt you will find that situation in the wild.  There may be two that 

are close enough for government work but not identical



The diodes mentioned would be to permit two slightly dissimilar 

batteries to be connected in parallel and function well.



Why the need or desire for batteries in parallel?  The output voltage is 

not increased.  The capacity is increased but a better plan would be one 

battery of sufficient capacity for the task at hand.



If higher voltage is needed, but by using two batteries in series, the 

same concept the writer mentions should be applied or use one higher 

voltage battery.  Even then you have a series of batteries, or cells, in 

series each operating on its own.



Regular cell checks would help to reduce differences in the cells thus 

the performance of the whole battery package.



On 9/15/2016 6:46 PM, user9253 wrote:

 	  Quote: 	
		   



 Below is quote from another forum.  Are the statements true or false? Or part true and part false?



>   . . . .batteries (in parallel) need to be the same; same type, same brand, same model, same age. . . . I think parallel batteries should have diodes between them on the charging leg to prevent one draining the other.



 --------

 Joe Gores





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=460501#460501




	




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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Sep 15, 2016 7:05 pm Post subject: battery misconceptions

At 06:46 PM 9/15/2016, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>



 Below is quote from another forum.  Are the statements true or false? Or part true and part false?



 >  . . . .batteries (in parallel) need to be the same; same type, same brand, same model, same age. . . . I think parallel batteries should have diodes between them on the charging leg to prevent one draining the other. 	


    There is no foundation in physics for having

    paralleled batteries 'match' . . .



    When you charge a battery from a constant

    voltage bus, there is no way that one battery

    feels the effects of any other batteries

    irrespective of their numbers, size or

    condition. 



    Further, when discharging paralleled batteries,

    each battery will deliver what ever energy

    it contains . . . again, there is no exchange

    of performance between batteries beyond each

    battery's ability to deliver energy.



    I have never understood the diodes for preventing

    one battery from 'discharging' another. Unless

    the discharged battery suffers badly trashed

    chemistry or shorted cells, the exchange of

    energy between a fully discharged battery and

    a fully charged battery is minuscule. 



    I think it was about 2005 when Paul M. mounted a

    ambitious effort to illustrate design flaws in

    the crowbar ov protection system. I think it was

    that same series of threads where he cited "sparks"

    that occur when you jumper-cable connect a 'dead'

    battery with a charged battery . . . perhaps

    sustained at 14+ volts by the rescue vehicle.



    Yes, connect a battery with less that 5% capacity

    to a fully charged battery, you do indeed see

    some sparks. But plot a curve of the energy exchanged

    between the two and you'll find that it is

    insignificant.  A battery delivers significant

    energy at 12.5 volts and down. But it takes

    a sustained application of 13.5 volts or more

    to push significant energy into a battery. That's

    why we call them 14-volt systems.



    Which explains the sparking observed when

    the dead battery is being connected to a running

    rescue vehicle. NOW . . . we're hooking our

    dead patient to a !4-Volt source . . . that's

    a different situation.



    But the idea that diodes are useful for mitigation

    of energy exchange between two good batteries

    in different states of charge is simply unsupported

    by the physics.

   



 

   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Sep 16, 2016 6:36 am Post subject: battery misconceptions

At 08:18 PM 9/15/2016, you wrote:

  	  Quote: 	
		  AeroElectric-List message posted by: Lyle Peterson <lyleap(at)centurylink.net>



 A couple on interesting concepts are revealed there. Theoretically the batteries should be identical in all the factors mentioned.  In reality, I doubt you will find that situation in the wild.  There may be two that are close enough for government work but not identical



 Why the need or desire for batteries in parallel?  The output voltage is not increased.  The capacity is increased but a better plan would be one battery of sufficient capacity for the task at hand. 	


    Paralleled batteries have been proposed in numerous

    AEC architectures over the years . . . but paralleled

    only for the purpose of (1) improved cranking performance

    (Z-14) or (2) offering a means for separating two batteries

    into separate tasks during battery-only endurance

    operations. In these cased, the batteries were only

    CHARGED in parallel . . . a situation were differences

    in size and condition of the battery is transparent

    to functionality of all batteries.



    During battery-only ops, individual batteries are

    partitioned into separate tasks. Again, the capacity

    and condition of any one battery has no influence on

    performance of other battery(ies). 



 

  	  Quote: 	
		  If higher voltage is needed, but by using two batteries in series, the same concept the writer mentions should be applied or use one higher voltage battery.  Even then you have a series of batteries, or cells, in series each operating on its own. 	


    This is what happens when a battery is crafted to

    meet system design goals. Earliest cars were 6v

    (3 lead-acid cells in battery). Later cars were

    12v (6 cells), some vehicles are 24v (12 cells),

    many electric vehicles are 36v (18 cells). Now,

    wether that array of cells is crafted in one device

    of necessary cells or multiple devices with smaller

    numbers of cells in series is driven by design goals.

    

  	  Quote: 	
		  Regular cell checks would help to reduce differences in the cells thus the performance of the whole battery package. 	


    Exactly. Cells connected series are no more capable

    than the weakest cell in the string.



    Back in the days when I shot a lot of film professionally,

    I used Vivitar 283 flashguns with 4xAA battery paks. I

    tried using NiCd . . . for a time . . . but they proved

    labor intensive to mitigate risk of a poor shoot. If

    only one cell of the 4 was weak, it would fall out of

    bed before the other three cells . . . but the whole

    array became useless. For a time, I would check the cells

    for capacity and build 'teams' of cells with similar

    capacity but it took too much time. Clients were paying

    all expenses of the job and a hand-full of batteries

    for radios, cameras, telemetry and data acquisition

    systems was perhaps 0.1% of the mission costs. I quit

    fiddling with NiCd and loaded fresh alkaline cells

    into all electro-whizzies at the start of the day.



    Cell matching becomes important for the case of

    building a large array battery from a series

    connected array of smaller batteries, . . . not just

    within any one battery but the whole string.



    This is the condition that prompts cap checks with

    benchmarks that call for replacement of the whole

    array at some established value . . . usually 80%

    of new. This benchmark is picked to meet battery

    only endurance goals while insuring that no single

    cell gets so far ahead in the down-hill run to

    failure that it puts all other cells at risk.



 

 

   Bob . . .

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