Intro - Primary cells - Secondary cells - Comparison tables
The following article is a review of the commonly available battery technologies for small battery powered electronic devices for which low weight and high battery capacity is an issue. It was written a while ago as a review of betteries for use in antweight fighting robots, a class of machine whose dimensions must not exceed 100mm and whose weight must not exceed 150g. However while it makes reference to antweights it contains information relevant to almost any home made small battery powered equipment. The article is split into four pages, please navigate using the links at the top and bottom of this page of text.
There are many ways to generate portable electric power. Sadly our application rules out most of the more obvious ones such as petrol powered generators as too heavy, while drawing more power than some of the other ones such as solar cells can supply. No doubt one day someone will build a miniature generator set using an internal combustion engine from a model aircraft driving a small electric motor but meanwhile an antweight robot builder is limited to using batteries.
In a 150g robot you can not afford to use too much weight on batteries. Every gram used in a battery is a gram you can't use somewhere else in the robot. As a guide, if you can keep your battery weight below 30g you should be getting it about right, though competitive robots have been made in the past with as much as 50g of battery weight
We will now take a look at a range of different types of battery that can be used in antweight robots. Some of the batteries we will be looking at, for instance AA cells, may be a bit big for antweight robots but they are included because they serve as a useful and familiar comparison between different battery types.
Batteries fall into two main categories, primary non rechargeable cells and secondary rechargeable cells. When considering a battery system, aside from the weight the other property we must look at is the capacity. This figure is a guide to just how much power is stored in the battery, and it is normally quoted in milliamp-hours (mAH) for the batteries we'll be considering. In theory a 100mAH battery will be able to deliver 100mA for an hour, but in practice this figure is best only used for comparison purposes. In general an antweight robot will struggle with a battery capacity of less than 100mAH. Why consider this figure and not the voltage? Batteries can come in all shapes and sizes with widely varying capacities, yet all with the same voltage. Consider the normal range of 1.5V batteries you can buy at your local supermarket. D cells have the same voltage as AAA cells but have way more power because they have a much higher capacity. Radio control systems are usually designed to work from a 5 volt supply so for safety's sake the battery voltage in an antweight robot is best kept between 4 and 6 volts anyway. If you decide to run a higher battery voltage than this you will have to fit a 5 volt regulator or BEC(Battery Eliminator Circuit) unit from your local model shop or a hobby electronics supplier. The alternative is to be prepared to watch your radio gear go up in smoke, so the extra cost is well worth it.
As well as the familiar range sold for consumer equipment, batteries are also manufactured in specialist sizes for industrial and commercial applications. Because antweight builders have the same interest in size and weight as the designers of these specialist batteries, some of the batteries we'll be looking at will only be available from electronics catalogues or other non retail suppliers.
Intro - Primary cells - Secondary cells - Comparison tables
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