Today's Message Index:
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1. 04:49 PM - battery misconceptions (user9253)
2. 06:20 PM - Re: battery misconceptions (Lyle Peterson)
3. 08:05 PM - Re: battery misconceptions (Robert L. Nuckolls, III)
Message 1
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| Subject: | battery misconceptions |
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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| Subject: | Re: 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:
>
> 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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Message 3
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| Subject: | Re: battery misconceptions |
At 06:46 PM 9/15/2016, you wrote:
>
>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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