How to Make a 12v Nimh Battery Charger from an Atx Power Supply

Unfortunately, a computer PSU (power supply unit) can not easily be converted to a battery charger by simply adding clips to the output and connecting to battery terminals. Doing so may cause burns, injury or explosion. Use of the correct charger will ensure a long, safe battery life. Read on for more battery information.


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    Car Booster Packs may be suited for recharging via the small tabletop type automotive battery chargers. These chargers are probably cheaper than many computer PSU's, and are designed specifically for automotive type batteries. Determine the cell or battery technology (if unable to transport) and consult a battery specialist (such as Battery Plus or Interstate Battery stores) for the suitability to task for this charger.


  • Rechargeable batteries generally accept and hold a charge better with long, low charging currents rather than quick, high current charges.
  • Single use (disposable) cells and batteries are "Primary" types and rechargeables are "Secondary" types.
  • What's the difference between a cell and a battery? A cell is one unit that is a voltage source (usually between as little as 1.2V for rechargeable Cadmium and as much as 3.8V for the single-use Lithium types). Common AAA, AA, C and D cells are often incorrectly referred to as "batteries". A battery is a group (hence the term "battery") of cells combined into a single package that can not easily be split apart into individual cells. Examples of a group of cells packaged together to form a battery are automobile batteries and 9V "transistor radio" batteries.


    1. Most PSU simply provide a regulated DC voltage output. Quality chargers on the other hand, are "intelligent" - they will limit charging current based on battery conditions. As a cell or battery charges, a quality charger monitors and continuously "ramps" its output down eventually to a "trickle" charge current once charging is complete. This prevents overcharging and leaking (or worse). The best chargers condition cells and batteries; many by safely discharging before attempting to charge, and others simply charge based on the amount of residual charge left in the cells. A cell or battery can be left on a trickle charge for a great length of time, so it will be ready when needed instead of dying "on the shelf". These methods help to maximize cell and battery life by minimizing "memory" effect of recharging only partially discharged cells and batteries.
    2. There are many different technologies for cells and batteries. NiMH (nickel metal hydride), NiCad (nickel cadmium), Alkaline and the "lead acid" (common for most automotive batteries) are just a few. While most people know not to charge Alkaline cells, many do not know that NiMH and NiCad cells and batteries use chargers specific to the technology / chemical makeup. NiMH chargers should only to be used on NiMH cells & batteries and NiCad chargers should only be used on NiCad cells and batteries.
    3. Improper handling, storage and charging of cells and batteries can at the very least shorten the life of the battery (reducing the number of charging cycles) and worst cases can cause chemical burns and explosions.
    4. Open any vent(s) on a cell or battery prior to recharging so that gases can not build up pressure in the casing.
    5. Never allow open flames in areas where cells and batteries are being or were recently charged.
    6. Always charge cells and batteries in well ventilated areas to allow flammable gases to escape.
    7. Protective glasses or face shield, clothing and gloves should be worn when working with cells and batteries - and with lead acid (and other "wet" types) in particular.

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