Series vs Parallel batteries

JRTJRT

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How would a flashlight function differently when the batteries are hooked up in series, and then hooked up in parallel?
 

BB

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Unregulated flashlights (virtually all filament type, and many LED) require the voltage to be pretty closely controlled... Just look at a light with 1.5 volt AA battery--new, the light is bright. As the battery gets down to 1.0 volts, it is quite yellow and dim.

LEDs, will "keep their color" but will dim as the battery voltage falls. Simple LED circuits may have a series resistor to limit the current, or, with smaller batteries (and the "right LED"--depending on the LED's acceptable forward voltage "Vf"), may be direct drive.

Just placing two batteries in parallel will double the current at the same voltage. Placing the same two batteries in series will double the voltage and keep the same current capabilities.

Also, the batteries themselves have many differences too. Alkaline are good for moderate temperatures and lower current. NiMH/NiCads are good for higher currents (NiCads are also good for wider temperature ranges). Lithium primary cells normally have a higher 1 cell voltage and very low resistance (high current capability) and wide temperature ranges... And much more is out there.

The "lights" themselves have a designed voltage and current requirement. Usually, one would not expect to "rewire" the batteries and have the typical flashlight operate correctly... However, with "electronic" flashlights, one can be designed to take a wide variety of voltages and cell types.

With "electronic" lights, there are many types of converters--some that only drop voltage, others that only raise voltage, and some with feedback (regulation). And every regulator has its limits (min/max voltages, currents, temperatures).

In the end, there is really no simple one answer to your question other than "it depends"...

Do you have a specific question about a light and batteries?

-Bill
 

VidPro

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say you start with 2 cells that are 1.2V and 2000ma of capacity each.

if you run the Cells end to end (like in a long tube like flashlight) they are in series.
doing series increases the total voltage potential. 1.2V X 2cells =2.4V of voltage

if you put them side by side, and wire them together , then that is parellel, and is UNLIKE most standard flashlights. you dont increase the voltage but increase the total capacity of the battery.
2000ma X 2 Cells = 4000ma of capacity

of course that is rather simplistic, and doesnt anywhere near explain all the things, but it becomes easy to understand when you have some Analogy to real life as to what the word VOLTAGE is being used for in the language.
 

VidPro

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so lets see if i can do the voltage/current analogy similar to how they explained it to me.

voltage is how fast each car is driving down the freeway, double the voltage (speed), and the stuff will move down that path twice as fast.

Current is how many Lanes of the freeway they are moving down.
go from 1 to 2 lanes at that Same speed, and more power can go down that path.

the more batteries you stack up end to end, the faster stuff will come flowing out of it
the more batteries you put side to side, the more Capacity they have
Plus in parellel the more potential current you can get flowing at that voltage.

ok so they used little electron guys who ran though, but its almost there :whistle:

Capacity is how many cars are sitting in the parking lot , trying to get ONTO that freeway , depending on the Path they are allowed to travel.
 
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VidPro

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:wave: MR, Electron.
you realise there really is enough little guys here to try and demonstrate this, just for fun.

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:D - - :kiss: - - :p - - :naughty: - - :mad: - - :drool:- - :rolleyes: - - :p- - :naughty:
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ok there is your Electron SIMs, as you can see traveleing down the wire


with a higher voltage
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:bumpit::bumpit::bumpit::bumpit::bumpit::bumpit: :bumpit:
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Mr and mrs electrons move down the wire faster .
 
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VidPro

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Mr, Electron Says: :wave: with a higher current

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- :bumpit::bumpit::bumpit::bumpit::bumpit::bumpit: :bumpit:
:bumpit::bumpit::bumpit::bumpit::bumpit::bumpit: :bumpit:
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more electrons flow down that path.
 

VidPro

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Mr Electron says:
:wave: your battery has in it, stored potential energy

_________----_______
|:sweat: - - :sleepy: - - :tinfoil:- -:mecry:|
|:p - - :drool:- - :eek:hgeez:- - :duh2:- - :confused: |
| :sigh: - - :drool:- - :rolleyes:- -:green: - -:D :faint:|
|:sweat: - - :sleepy: - - :tinfoil:- -:mecry: |

|:p - - :drool:- - :eek:hgeez:- - :duh2:- - :confused: |
| :sigh: - - :drool:- - :rolleyes:- -:green: - -:D :faint:|
|:sweat: - - :sleepy: - - :tinfoil:- -:mecry: |
|:p - - :drool:- - :eek:hgeez:- - :duh2:- - :confused: |
| :sigh: - - :drool:- - :rolleyes:- -:green: - -:D :faint:|
-------------------------------

 

VidPro

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Mr Electron says:
:wave: the more potential energy in your battery, the more electrons want to move from the one side to the other.
so the more total capacity is there able to move.


_____-----____

|:duh2::confused::ironic::crackup::D:laughing: |
|:mecry::p:grin2::D:faint::green: |
|;):candle::tinfoil::):grouphug:|
|:shrug::thumbsdow:grouphug:;):laughing:|
|:popcorn::D:faint::tinfoil::shakehead:sigh: |
|:ironic::huh::eek:oo::eek::confused::sick::crazy: :faint: |
|:tinfoil::shakehead :devil::):whistle::sigh: |
|:thumbsdow:shrug::broke::eek::eek:oo::sick:|
--------------------

Mr Electron needs an Editor, so he says things right.
 
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JRTJRT

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Thanks for the explanations guys!

I'm having flashbacks from high school electonics class! :shakehead

So, let's say I took a simple incan bulb and one battery that gave 1 hour of light.

Adding a second battery in series: bulb twice as bright, light lasts 1 hour.

Adding a second battery in parallel: same brightness, but light lasts 2 hours.

Is that about right? :eek:hgeez:

... and do I get a prize for the thread with the most smilies? I was thinking a G2L :huh:
 

VidPro

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Mr electron says: :candle:
Resistance is ,The opposition of a body or substance to current passing through it, resulting in a change of electrical energy into heat or another form of energy.

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:bumpit::bumpit::banghead::touche::devil::bumpit: :bumpit:
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VidPro

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So, let's say I took a simple incan bulb and one battery that gave 1 hour of light.
Adding a second battery in series: bulb twice as bright, light lasts 1 hour.
Adding a second battery in parallel: same brightness, but light lasts 2 hours.
Is that about right? :eek:hgeez:

... and do I get a prize for the thread with the most smilies? I was thinking a G2L :huh:

yup that is about right, then all them other mitigating factors that keep it from being a exact 1-2 ratio. but close enough
 

VidPro

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Mr electron :rock: takes a crack at showing an electronic gate.

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:bumpit::bumpit::rant::hairpull: :toilet: :shakehead :) :scowl: :sleepy: :mecry: :thinking: :green:
-----------------------------/ :faint: / -----------------------------------
. . . . . . . . . . . . . . . . . . . / :faint: /
. . . . . . . . . . . . . . . . . . /:popcorn:/

like a Transister, of the many types mosfet, fet, scrs even , a small ammount of flow is used to control a larger ammount of flow.


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:bumpit::bumpit::bumpit: :twothumbs :bumpit::bumpit: :bumpit:
-----------------------------/ :clap:/ -----------------------------------
. . . . . . . . . . . . . . . . . . . / :clap:/
. . . . . . . . . . . . . . . . . . /:clap:/
 
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VidPro

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Mr. Electron says: :tinfoil:
a resistive wire filiment, like an incadescent bulb.

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:bumpit::bumpit::devil: :devil: :candle::devil: :candle: :devil: :bumpit::bumpit:
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. . . . . . . . . . The resistance causes it to heat up till its white hot
 
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half-watt

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T
So, let's say I took a simple incan bulb and one battery that gave 1 hour of light.

Adding a second battery in series: bulb twice as bright, light lasts 1 hour.


first off, you'll probably instaflash the bulb's filament (or, depending upon the specifics of the design, or the LED or supporting electronics in LED lights) . so, your batteries would last a real long time since your bulb won't be drawing any current!!! might want to get a different bulb rated for a higher voltage. best case though highly unlikely scenario, bulb glows brighter for less time before it burns out. how much less time? would depend upon a number of factors dealing with both the filament (e.g., max rated voltage) and the application or host (e.g., how much heat it can remove/dissipate), not to mention the increased power consumption.


Adding a second battery in parallel: same brightness, but light lasts 2 hours.

Is that about right?

'bout right!!



... and do I get a prize for the thread with the most smilies? I was thinking a G2L :huh:

no. you could get banned for that!!!

just kiddin'.

but, there is a theory that there are a limited number of smiley's available in the world and you might want to reconsider usin' more than your fair share.

also, i could be wrong and maybe it's just an untrue rumor, but i've heard CPF has a liftetime quota on smiley's and you may have just about used yours up.

ok. 'nuff of the bad jokes.

quite the smiley artiste to say the least
 
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BB

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Thanks for the explanations guys!

I'm having flashbacks from high school electonics class! :shakehead

So, let's say I took a simple incan bulb and one battery that gave 1 hour of light.

Adding a second battery in series: bulb twice as bright, light lasts 1 hour.

Adding a second battery in parallel: same brightness, but light lasts 2 hours.

Is that about right? :eek:hgeez:

... and do I get a prize for the thread with the most smilies? I was thinking a G2L :huh:

No, not really... (actually, I had to think a moment on how to describe this to get the numbers right).

First, remember your basic equations:
  • V=I*R
  • I=V/R
  • R=V/I
  • P=IV
  • P=I^2*R (power in Watts)
  • P=V^2/R (power in Watts)
A couple others to involve time:

  • P*T=Joules (Watt*Seconds, time=seconds, but many people use hours instead of seconds to get smaller numbers and reasonable numbers for day to day use)
  • P*T=Watt*Hours (time=hours--Handy for battery ratings)
  • P*T/1,000=KilloWattHours=kWh (1,000 Watt Hours--used on your home utility bill)
  • I*A=AmpHours (Ah--typically used for battery ratings, 100Ah=average car battery capacity--not missing volts--most people assume voltage is known based on discussion--1.2 volts for an Alkaline cell, 12 volts for a car/boat, etc.).
So, first we define the load... For a first approximation, lets assume that a filament bulb is a pure resistive load (fixed resistance value).

If you double the voltage, then from I=V/R, you double the current. So, your batteries will last 1/2 as long (not the same time)

Now, with 1/2 the burn time and twice the voltage, that would mean that the light was burning with 4x the amount of power (watts)--typically, if you double the rated voltage to any given bulb, it would "insta-flash"--Think of taking at 120 VAC bulb and connecting 240 VAC--not a happy camper.

From the equations:
  • I=V/R
  • P=V^2/r=I^2R
We can confirm that doubling the voltage (or current) when squared, gives us 4x the power with a fixed R value.

So, from your example, two batteries in parallel (with a fixed resistance filament bulb) will last four as long vs two batteries in series (but with 1/4 the ("wattage").
  • 1 battery = 1 hour (1 power unit from bulb)
  • 2 batteries in parallel = 2 hours (1 power unit from bulb, twice as long)
  • 2 batteries in series = 1/2 hour (4 power units from bulb, 1/2 as long)
Now, if we take a 220 VAC bulb and cut the voltage in 1/2... The bulb generates 1/4 of the power... But, since the brightness of a bulb is something like to the 6th power (IIRC--numbers below are just a guess for the sake of discussion here), that means when you cut the voltage in 1/2, you actually lose (1/2)^6=1/64 of the light. So, the light becomes much less efficient at generating light (1/4 the power, 1/64 the light, so ~1/16 as efficient). Pretty obvious when a light turns yellow/red/dark at lower voltages/currents.

For the real story, filament bulbs are not a fixed resistance, but their resistance varies with the filament temperature. And, in fact, their resistance drops substantially as the temperature drops. So, as they dim, the are actually drawing more current that a simple I=V/R equation would suggest.

A few years ago, I ran across the equations (voltage, current, light, life) for a typical filament bulb from a link here on CPF--perhaps somebody here has that bookmarked somewhere.

Now, with electronic regulators... A whole different kettle of fish...

There are linear regulators... and basically act like a variable resistor in series with the bulb (and give off waste heat to control the voltage/current to the bulb)... So adding voltage, the regulator drops more voltage, and gets warmer. 2 batteries in series, bulb stays the same brightness, current remains the same, and batteries last the same number of hours. However, you now have used two batteries where one battery was used before (1/2 the power was wasted to have a regulated light).

A series resistor with an LED is a "fixed resistance" regulator. Simple, cheap, wastes some power, and LED output changes with battery voltage (more of a "converter" rather than a "regulator").

A switch mode converter with negative feed back (flat output regulated light) is what most here would aspire too... Switch mode regulators are pretty efficient, can work over wide ranges in voltage/current, and can be made to be "adjustable" to set light levels according to needs (LED's are more efficient in this case as their efficiency vs current/voltage is much flatter than a filament bulb--and LED's, are typically most efficient at low currents--so when they dim, they get slightly more efficient--unlike a filament bulb which gets horribly inefficient at generating white light).

And, there are several common types of switch mode converters/regulators used in flashlights (using inductors to help convert energy)...
  • Buck (used to drop battery voltage--most efficient)
  • Boost (used to raise battery voltage--less efficient)
  • Buck/Boost (can drop or raise battery voltage--lesser efficiency)
Boost is typically used in 1 cell lights where the Vf (forward Voltage of LED, or even filament bulb too--but rarely used) is higher than the battery voltage. Many times just are converters (not regulated) in less expensive lights (original ARC AAA and CMG Infinities are examples of unregulated boost converters. The more expensive lights like Fenix single cell lights, and many others, use regulated boost converters). Somewhat less efficient than Buck, and becomes less efficient as input voltage falls (much below 1.0 volts, the internal voltage drops become too large). If the input voltage is over Vf, then there is no regulation and the current/voltage to the LED will rise with the input voltage until the LED fails with over voltage/current.

Buck is typically used in multi-cell lights where the battery voltage is always over the regulated output voltage, and where efficiency is important and size/cost (for example using a resistor) is less so. Buck converters/regulators can get over 85% efficiency. The Fenix P3D and many other 2 cell+ CR123 lights are Buck converters/regulators. When battery voltage falls below Vf (+~1 volt), then the voltage/current simply falls with the input voltage and the LED gets dimmer (with digital control, the LED can be made to flicker or other things happen when battery voltage falls).

Buck/Boost is just a combination of both regulators to allow any battery voltage to be used (within reason). Least efficient as it contains both converters to support the wide voltage range.

Now, down to your original question... Assuming that the series/parallel question, with a regulated light, and the battery voltages falling into the acceptable ranges for the regulator used--then adding a battery simply will extend runtime... If you have two in parallel, the current to each battery will fall by 1/2. If you add two in series, the input voltage will double, but the current will fall in 1/2.

In real life, there are more issues--component ratings, regulation type (voltage/current--although either regulation type is very similar in construction and design), and even other ways to control lighting levels (PWM--Pulse Width Modulation--Say 100 Hz cycle--100% on, 100% bright; 50% duty cycle, 50% bright; 1% on duty cycle, 1% bright; etc.).

And the loads themselves are not "linear" devices... I mentioned before that the filament bulb's resistance drops as it gets dimmer/cooler (there are some simple regulator circuits that use an incandescent bulb as current regulator just like this--as voltage drop, the light gets dimmer, more current to load). Also, LED's are highly non-linear devices. Diodes, instead of a straight line in an IV graph, they have a vary sharp knee... Below a certain voltage, they don't conduct. As the voltage raises, they begin to conduct more an more current in a non-linear fashion. That is why LED's usually need a resistor or regulator in series with them if the battery is any larger than a coin cell. A minor change in voltage can either give you no light, or a thermal run-a-way (as the current increases, the resistance decreases, causing more current to flow, more heat, then smoke).

I will stop here--and I should have probably stopped several pages ago--but I hope that this helped a bit.

-Bill
 

JRTJRT

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Holy Cow. Thanks for that post Bill. I need to read it again when I get home, but I'm getting the jist of it... :thumbsup:
 

Bougie

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Sorry for the necrobump, but I have a question related to this very subject : is there any difference between series and parallel when it comes to safety ?

Is one combination more prone than the other to encountering issues, whether during use on when stored in the flashlight ?
 

xxo

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Series is potentially more dangerous, particularly with lithium primaries or lithium-ion cells. if the cells don't have the same state of charge/capacity, one cell can over discharge and heat up/possibly explode.
 

DIWdiver

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If one cell has less capacity, it will be completely discharged before the other. If you continue to draw current from the two cells, one will continue to discharge, and the other will begin to reverse charge. In cells containing lithium, this can cause fire and/or explosion. The risk ranges from moderate to quite low depending on the exact chemistry that you are talking about. In non-lithium cells, this will simply damage or destroy the cell.

That is one of the reasons that protected LiIon cells and Battery Management Systems (BMS) or protection boards exist.

Battery protection circuits, under various names, and whether incorporated into the cell, the battery, or the device, mitigate some of the risks that lithium cells present. They can prevent some or all of the following: overcharge; over discharge (including reverse charge); charge at too high or low temperature; discharge at too high or too low temperature; high charge current; high discharge current. There are other risks, such as manufacturing defects and physical damage, that protection circuits cannot mitigate.

Over discharge and reverse charge are among the high risk factors. These are very possible (even likely) in series connected batteries, and are almost completely mitigated by protection circuits.

Reverse charging is among the highest risk factors, and is ONLY possible with series connected cells. This is why many people prefer no series connected cells. It completely eliminates one of the highest risks.

This is not to say that devices with series connected LiIon cells cannot be safe. I'd guess that a billion or more laptops and power tools have been sold with series connected LiIon cell power packs, and few if any fatalities.

Flashlights, however, present a special problem. Let's discuss that tomorrow.
 
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