The Batteries – PART 5: Disposable Batteries – Continue
Today’s Topic will be continuing with the explanation of disposable Batteries.
Our focus will be to the dry cells, more precisely, the Zink/Carbon and Alkaline batteries and more specific at their internal characteristics and parameters.
What is The Disposable Battery in its basis – The source of the electrical energy.
Let we see the parameters of one general battery : As every Source, and the battery has the lot of parameters:
Nominal Voltage, Internal resistance, Capacity, Nominal current, Maximal – Rated Current , Rated power.
Well, let’s see the real Battery: Bat.real#1 and theoretically ideal Battery Bat.ideal#2 :
What do they have both?
The main part or the Basis of the battery is its Power Source E: E = Uemf[V]
E = Uemf[V] ; for Dry cell Uemf = 1.5 … 1.55V
There is a resistor RInt, which is Serially connected to the Power Source E, representing the power losses into the battery, when the user is connecting the load, which consuming the energy. obviously, the power losses are linear proportionally to the output current, they representing a kind of thermal dissipation
In parallel , there is another resistor Rleak, representing the losses as current leakage – self-discharging the battery and minimizing its idle or shelf life.
These Two resistors are characterizing the manner of work in almost any kind of battery.
Example #1: The ideal Battery #1 : also has such resistors inside the body, but their values are as follow:
- Rint = 0 OHM ! – it means the ultra conductivity, and
- Rleak is equal to infinity >> there isn’t a leakage or self-discharge current.
When is applying Resistor Rload = 1, 2, 5, 10 ohms the output Voltage is staying unchangeable. The Battery Capacity doesn’t depend o the Output current.
There aren’t any losses into the internal Resistance – The battery has the ultra conductivity.
Example #2: The real Battery #2 : Zink/Carbon cell,
- Rint ~ 5 OHM – it means the low conductivity, and
- Rleak is equal to few megaohms>> there is a small leakage or self-discharge current.
When is applying Resistor Rload = 1, 2, 5, 10 ohms, the output Voltage is a visually changing. The Battery Capacity is strongly depending on the Output current.
The losses into internal Resistance are linearly proportional to the output current and they are significant with increasing of the current.
Example #3: The real Battery #3 : Alkaline battery cell.
- Rint ~ 0.1 OHM – it means the best conductivity, and
- Rleak is almost equal to limitless >> there are smaller leakage or self-discharge current.
When is applying Resistor Rload = 1, 2, 5, 10 ohms, the output Voltage is a weak changing. The Battery Capacity is virtually independent the Output current.
The Delivered to Output Load Battery Capacity is depending very weak in relation the Output current.
O.K. , let we suppose the real battery #2 and #3 and the ideal battery#1 have the same capacity.
Example: all listed above Batteries have Capacity : 1000 mA/h or 1A/h.
The Starting Value or Unominal = 1.5V.
On all batteries, we are applying the same resistive loads – for Example: 1 ohms.
Measuring the time, we are waiting, until each battery Voltage drops to ~ 0.8V ( the level, where the battery is empty ).
The results will be as following:
Ideal Battery :
Capacity or Power Delivered: = 100%
Real Zink/Carbon Battery:
Capacity or power Delivered: = 20%
Real Alkaline Battery:
Capacity or Power Delivered := 85%
It is Very revealing and teaching us the following: When We need a significant output current, we could choose the alkaline battery as the part of our design requirements. Choosing the Zink/Carbon Battery is well done in applications without any high current requirements. The high current will exhaust and perforate the negative Zink electrode – causing the ammonium chloride leaking and destroying the PCB traces, wires or metal details near the leakage. Always use the proper battery type.
Any LIGHT TORCH Manufacturers rely on high internal impedance batteries, and they don’t insert a necessary equalizing resistor in each current ring – The 4.5V Battery source : 3x AAA batteries are directly connected to equivalent White LED for example.
SCH. 1 Schematic of simple light torch
Resistors R1…Rn are inserted for the easiest explanation – they may not exist (their value is equal to zero) in the cheaper light torch versions
For the easiest explanation, we will use the example schematic (see SCH.1). In “bad designs”, the equalizing resistors (R1..Rn =0 Ohm) don’t exist.
They are represented as zero ohm copper tracks.
Does not wonder, the firstly included batteries in such cheap light torch are Zink/Carbon – the significant internal impedance proof the LEDs from damaging.
Using for powering the such “Bad design with zero Ohm equalizing resistors” the 3x Alkaline batteries set, will cause the LED defective.
Low Impedance 4.5 Volt alkaline pack will keep the voltage on each of LEDs will be too high (More than Normal UForward of White LED equal to ~ 3V) and the current carrying through them will be much than the manufacturer required rated current.
Next Time When You choose the battery for your Light Torch, sure how the LEDs are connected, is there any equalizing resistors or current limiting LED Driver before you are using the “Good and Long Lasting Alkaline Batteries.
Don’t Forget to use in a practice the things, you have learned today:
The battery doesn’t an ideal – it has the Internal Resistance!
Don’t Stop To Reinvent Yourself, Dear Explorers!
New zinc composition resulting in 10-years anti-leakage shelf life.