ersinaytac

1. What is a battery?

A battery is essentially a can full of chemicals that produce electrons. Chemical reactions that produce electrons are called electrochemical reactions. In a battery stored chemical energy is converted into electrical energy in a previously mentioned electrochemical reaction. Electrons collect on the negative terminal of the battery, and moves to the positive terminal of the battery. This creates the current flow from positive terminal to negative terminal. Electron flow and current flow is in the reverse directions.

2. Basic Terms

Cathode: is an electrode through which electric current flows out, polarity is always (-)
Anode: is an electrode through which electric current flows into, polarity is always (+)
Resistance: is a measure of opposition to the passage of a steady electric current
Internal Resistance: is a concept that helps model the electrical consequences of the complex chemical reactions inside a battery
Current: a flow of electric charge or the rate of flow of electric charge (electrons)
Voltage: is the electrical force that would drive an electrical current between two points
Ohm's Law: V=IR


3. Usage Areas?

There are two different types of power supply that we can use in our robots. Since most of the robots are autonomeous we don't want any power cables around them, so the AC power is not an option for us. If we need high amount of voltage we should use AC power. All of the components use DC so we need a converter to use AC power. DC power is what we need to use if we don't need high amount of voltage in our robots. Since the power supply is in DC and all of the components work in DC, we don't need any kind of converter while using a DC power supply.

4. How to calculate what you need?

You should list all of the components in your system. The voltage and current requirements for every single component that you are going to use.

5. Types

There are a couple of different battery types, the most suitable battery type for robots is dry cell batteries.

5.1 Dry Cell

A dry cell battery has the electrolyte paste, with only enough moisture in the paste to allow current flow. Since the paste is only moist, the battery can be placed in any position. The dry cell batteries will not leak.

5.1.1 Disposable Batteries

Disposable batteries are the ones that we cannot charge and use it over and over. The most common ones are Zinc-Carbon and Alkaline batteries. We use this kind of batteries in everyday life, they are very easy to find and cheap. There are 4 different sizes. AAA, AA, C, and D. They all produce 1.5V with different amount of current. The batteries get heavier in this order; AAA, AA, C, D. Besides cylinderical shape also 9V prismatic shaped batteries are present. There are different types of disposable batteries available also.


+++++ Pros

Very cheap
Easy to find

----- Cons

Low current
You will need to buy a lot

5.1.1.2 Alkaline

The anode is made of Zn (zinc) powder and the cathode is composed of MnO_2 (manganese dioxide). The electrolyte in the battery is KOH (potassium hydroxide). An alkaline cell can provide between three and five times as much operating time than ZnC batteries.



+++++ Pros

High current
Easy to find
Cheap

----- Cons

You will need to buy a lot

5.1.2 Rechargable Batteries

Although the first investment cost is more than a disposable battery, in long term, using rechargable batteries are cheap. They have their own cycle life though. You have got to check your battery charged every single time while using it.

5.1.2.1 Alkaline

You can also use rechargable alkaline batteries. They are pratically the same with disposable alkaline batteries.



+++++ Pros

Cheap
Easy to find
Long cycle life (~5 years)

----- Cons

Heavy weight

5.1.2.2 NiMH & NiCd

A nickel-metal hydride battery uses a hydrogen-absorbing alloy for the negative electrode. Which is the main difference in between NiMH and NiCd batteries. NiCd batteries use cadmium instead of a hydrogen-absorbing alloy. NiMH batteries have nominal charge capacity 1100mAh - 2900mAh at 1.2V.





+++++ Pros

Long cycle life

----- Cons

Low capacity (1.2V)
Effected from temperature easily

5.1.2.3 Li-Po

The electrolyte in the battery is polyethylene oxide or polyacrylonitrile. There is no rigid metal case that covers the battery thats why the battery is light. Most of the radio controlled cars and aircrafts use LiPo batteries because of the low weight and long running time. Using LiPo batteries in our robots are most convenient. Cathode of the battery is LiCoO_2 or LiMnO_4 and the anode of the battery is Li or some kind of C-Li compound. LiPo batterues must be charged carefully, if they are overcharged they will easily become unusable.





+++++ Pros

Light
High current

----- Cons

Expensive
Short cycle life

5.2 Wet Cell

A wet cell battery has a liquid electrolyte. They work with pretty much the same idea as dry cell batteries. Leaks are biggest concerns in wet cell batteries. Because of the heavy weight and leakage risk we don't use wet cell batteries in our robots unless we need high amount of voltage and current.

6. Battery Chargers

All rechargable batteries have their own unique chargers. Also there are some computer controlled all in one chargers in the market. If you use same type of batteries all the time, you don't need to buy different chargers. After a while you might need to charge a couple of batteries at the same time, that's why buying a charger which can charge 2 or 3 batteries simultaneously will ease your life.