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Types of Mobile Power Supplies

Why Mobile Power?

What is it that we can’t live without? Oxygen, water and food. Perhaps the next in order of urgency these days is electric power. At work, at home, travelling or camping, our cell phones, digital cameras and laptops are with us. These have now become essential parts of us. And God forbid, during a power outage, say during a hurricane, these can be our essential companions which can save our life or lives of others. All these need power. Without power they are dead weight and you become ineffective. That is why almost all models of these devices carry a rechargeable battery.

How Long Will It Last?
How long will that battery last if you start with a full charge? That depends on the battery capacity and the power consumption rate. Battery capacity is specified in Ampere Hours (AH). 1 AH means a battery will supply half ampere continuously for two hours. (2 x ½ =1). Perhaps for sales gimmicks, vendors tend to specify capacity of their batteries in milliampere hours. There is another reason. When dealing with small devices demanding a fraction of an ampere, the current is normally expressed in milliamps or hundreds of milliamps. Thus, smaller capacities are more understandably expressed in milliampere hours (mAH). Hence, knowing the capacity of the battery and the consumption rate, you can estimate how long the device will perform before crying for power. Under ideal conditions we should the product of discharge current and time to discharge to be equal to product of charging current with charging time. However, due to inefficiencies involved, the latter product will always be higher.

Energy capacity
The AH rating is good for defining capacity when the voltage is known and fixed. But another way of specifying capacity is the energy available. This expressed as watts (W-H). A 2 AH cell phone battery will provide a total of (3.6 V) x (2) Watt-Hour of useful energy.

Types of Mobile Power
Various types of mobile or portable power devices are available. To help you choose, a little description is in order. Broadly, these can be three types: built in, removable, or external.
Built-in power sources are a part of the equipment. Those can be removed, serviced and replaced by an expert. An example is the power supply in your desktop.
Removable supplies can be primary or secondary. Primary batteries are for one time use like the alkaline cells, whereas secondary supplies are rechargeable like the Lithium battery in your cell phone, camera or the laptop.
External supplies will normally be of a physically large size and be able to service more than one load simultaneously.
o Generators– An example is the old faithful the electromechanical generator. These can be bulky but powerful. For smaller applications generators are also losing ground to less noisy and lighter devices. But for larger loads, say above half a KW, and longer endurance, there is no match for the generator. Generators need a supply of fuel also. Parameters relevant to a generator are rated capacity, output voltage stability and quality, fuel tank capacity, ability to run on multiple fuels, electromechanical efficiency, wheel-mounting, remote start capability, noise level, and of course, the price. Find more here
o Inverters– Where AC power is required for a system, inverters of various sizes are available which can convert DC power eg, from the vehicle battery to AC. These devices are totally quiet except for the cooling fan. Find more here
o Power Banks– Large sized power banks are now available which could supply close to 500 watt-hours. These are normally made from supercapacitors which store energy with very little leakage. Built-in DC to DC converters can provide DC for charging various devices. An integral inverter can provide AC where required. Except for a possible cooling fan, such devices are absolutely noiseless.

Solar Mobile Power Supply
Depending on the application, portable solar devices can be used. Time will see virtually every caravan fitted with solar panels on the roof or walls. Quick-mount solar panels may be carried and installed when camping. Small devices with built-in solar cells, e.g., a solar lantern, are present in the market.
Price- The last but a very significant parameter is the price for the device. It is not necessary that a cheaper device will perform any lesser because it is cheaper. Some good designs may be sold cheaper than poorer ones. Marketing matters.

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