AsocialSurvival
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What happens to capacities of batteries when connected in series or parallel?
For example I have two Li-ion batteries, and I connect them in series to increase voltage.
What's going to happen to capacity of the overall capacity?
Does it increase, decrease, or stays the same (like of one)?
BTW, I am electrotechnician, and still have never understood this, very complicated.
Also, good if you know what happens to voltage and maximum current?
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WGTR
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Energy (volts x ampere-hours x 3600) of each cell is added together to determine the total energy (in Joules).
Voltages add together when cells are in series, ampere-hour capacities of each cell add when cells are in parallel. Otherwise the overall voltage and
current ratings remain the same.
Energy (J) = voltage (V) x amperes (A) x time (seconds)
The internal resistance inside the cells add if cells are in series. This means that maximum current ratings remain the same in this case. If cells
are in parallel, the maximum current ratings of each cell add together.
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franklyn
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Since a battery is also a resistor , the best most efficient use of
their combined rating is to drain them connected in parallel.
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smokeup
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Agree with franklyn. technically the capacity is the same, but when you put them in series you raise the voltage and if the load is the same in both
cases you will drain the batteries down faster. On the other hand, if you want a brighter flashlight putting them in series is the way to go.
(assuming the bulb can handle it)
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unionised
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Quote: Originally posted by franklyn  | Since a battery is also a resistor , the best most efficient use of
their combined rating is to drain them connected in parallel.
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Unless it isn't.
http://en.wikipedia.org/wiki/Maximum_power_transfer_theorem
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Texium
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Thread Moved
21-11-2023 at 14:20 |
semiconductive
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?? The power theorem is about rate of energy transfer, not efficiency. ???
The less current going through each battery, the less voltage drop there is, and the more efficient the transfer will be. In my experience it is
usually the case that parallel hookups of batteries will run a device longer than a series connection will.
The reason is that parallel resistance lowers the *total* resistance and voltage drop being experienced. This makes minimum power loss in the
battery; though it may cause other kinds of power losses (depending on what you are running and how far away it is.)
But:
When making series connected battery packs, there are several risks that reduce the maximum capacity that can be exploited. One is that if you
discharge the whole pack completely, it's possible for one battery with slightly more energy capacity to reverse charge a battery next to it. This
usually results in damage or destruction of the second cell.
Toyota Prius traction batteries NiMH, are this way. If the voltage per prism battery is run below about 5V, one or more internal cells become
reverse biased; and the pack is immediately (and permanenetly) damaged. It will never fully charge again.
Note: I rebuilt a Toyota traction battery to better than factory new, and watched the **** computer assume it was still old, and charge it wrong.
Destroyed itself, immediately. If you don't replace the computer with the pack, you're screwed.
I think series hook up of batteries is only more efficient when it *reduces* both the current required from each battery *and* the power loss from
resistance in the wires of the load. This is sometimes the case:
eg: Higher voltage can be transmitted over longer wires with less power loss.
This is the major reason Toyota's battery pack is made; since at 200-240V D.C. the wires going to the front wheel electric motors can be an 1/8th inch
thick. Tesla car motors are the same way. etc. Alternatives designs using 3V D.C. motors are impractical, because would require all wires to be
extremely thick, heavy, and the motors do not produce the desired torque due to internal resistance. A practical 3V car motor is unlikely to be able
to produce highway speeds...
What happens to the voltage and current of a stacked pair of batteries depends on what you hook it up to. It is complicated.
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woelen
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Connecting batteries in parallel must be done with care. Especially if one battery is drained more than the other, its voltage may be lower and this
may lead to large currents from one battery to another.
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