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Thursday, June 26, 2014

Batteries

Batteries come in all kinds of shapes and sizes and are designed for a wide variety of uses. I'll explain a bit about some different types of batteries as well as their pros and cons.



There is some terminology to be clarified first:

  1. A battery is a collection of cells. 
    • A car battery requires multiple cells to work. 
    • Most of the things you think of as batteries (AA, C, D, etc) are actually single cells. The larger ones have the same voltage as the smaller ones, they just supply power for a longer period of time. 
    • 9V batteries, however, are the exception to this. 
  2. Since the voltage output of each cell is dependent on the chemistry of that cell, we stack cells together in series to add the voltage up in order to get workable levels of voltage out of a battery. 
  3. There are two kinds of cells, primary (disposable) and secondary (rechargeable). 
    • Most of what we call batteries are secondary, or storage, cells that store a fixed amount of electricity in chemical energy. Once a secondary cell is depleted, it may be rechargeable depending on the chemistry and physical design. 
    • In a primary cell, the chemistry is not as easily reversible, so recharging them is not feasible (or possible in the case of fuel cells).

Common types of cells/batteries

  • Lead-Acid: Your average car battery is a good example of a lead-acid battery. Heavy, durable, rechargeable, fairly inexpensive, and easily recyclable, this type of battery has been around for over a hundred years.  Deep-cycle lead-acid batteries are constructed to allow deep discharge and frequent recharging that will kill a typical automotive battery. Forklift batteries are deep-cycle batteries that can last 10-15 years with proper maintenance. Lead-acid cells generate about 2.0 V each. Modern car batteries use 6 cells, and therefore produce 12 V. 
  • Alkaline: The AA, AAA, C and D cells that you stuff into your flashlight are examples of alkaline cells.  Most of these are disposable (not rechargeable) for normal use but can be recharged if you're careful and pay attention to them. They generate about 1.5 V per cell.
  • Lithium-ion (Li-ion): The batteries used in newer electronics (cell phones, laptops, etc.) are usually Li-ion technology. While smaller and lighter than most of the other technologies for the same amount of storage, they are more expensive. They have a long shelf-life and are rechargeable roughly 500 times before they start to fail. The voltage produced stays fairly level until they are exhausted at which  point it drops to nothing very fast. Li-ion batteries  often use a flammable electrolyte and are under pressure, so they can be dangerous if damaged. Never short-circuit a Li-ion battery as it will overheat rapidly and may explode or catch fire. Li-ion cells produce between 3.0 and 3.7 V per cell. 
  • Not to be confused with Lithium cells, which are commonly found in the larger "button" sells used in watches and other small electronics. The standard CR2032, used in a lot of cheap red-dot sights, is a good example. The CR designates that it uses Lithium-Manganese Dioxide chemistry and is round, the 20 is the diameter in mm, and the 32 is the thickness in ┬Ám (actually 3.2 mm). Most Lithium batteries are not normally rechargeable. Lithium cells produce between 1.5 and 3.7 Volts per cell, depending upon the specific chemistry used.
  • Silver Oxide: Some of the "button" cells used in hearing aids, watches, and other small electronics use Silver Oxide chemistry. Good for low wattage applications, they have a long shelf-life and are expensive for the minute amount of power they can store. They are non-rechargeable and put out about 1.5 V per cell.
  • Nickel-Cadmium (Ni-Cad): Older cordless drills and other tools used Ni-Cad chemistry.  They tend to be larger and heavier than a Lithium battery that can hold the same amount of charge, and have a bad habit of developing a "memory" if they were  recharged from a partially discharged state. The voltage drop as they are discharged tends to taper off slowly, giving you warning that your battery is dying. Ni-Cads produce 1.2 V per cell.
  • Nickle-Iron: Thomas Edison got a few things right; he sold a lot of Nickle-Iron batteries. Big, heavy, and prone to overheating, they were used for back-up power in the early 20th Century. They were very simple to use and tolerant of abuse. They were best used in applications where they were under a constant charge and would discharge if there was any interruption of the incoming current (Uninterruptible Power Supply, aka UPS). They had low power density and they self-discharged faster than other types of cells, but they could last 20-50 years if maintained properly. 1.2 V per cell.
  • Nickle-Metal Hydride (NMH) cells were common in recent times as rechargeable replacements for the common alkaline cells, but only produced 1.2V instead of the 1.5V of an alkaline cell. This led to many of the newer electronic gadgets not running properly (or at all) due to the lower voltage. While they were able to come close to the Li-ion batteries in capacity, they would self-discharge as much as 4% per day. NMH rechargeable batteries have mostly replaced Ni-Cad batteries in cordless tool applications, but Li-ion batteries are taking over rapidly.


Uncommon cells

  • Fuel cells use a fuel - usually a hydrocarbon like methane or an alcohol - and oxygen from the air to produce electricity. Complicated, requires heat to start reaction, and bulky, they've never quite caught on.
  • Metal-Oxygen cells use a reactive metal like pure aluminum and air to generate electricity. Higher energy density than Li-ion cells, but not rechargeable and disposing of the waste became a problem before they hit the commercial market. There are designs for laptop and cell phone metal-air batteries out there, but they're not for beginners.
  • Thermal batteries use a molten salt as an electrolyte and have a shelf-life measured in decades. Once activated, they produce a huge burst of power that lasts for a few seconds to a few minutes. Developed for the German V1 and V2 missiles in WW2, they are still used today in artillery and missile systems. 


In the following weeks, I'll try to show how you can find and use some of these to make life a little easier in times of crisis.

The Fine Print


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