How to… make a 12V power supply
Do you need extra electricity to drive a pump or run emergency lighting? Construct this simple unit, says Sam Coles, and you’ll have 12V wherever you want it
This simple DIY project will give you extra 12V power wherever you need it
CARAVANS HAVE TWO electrical power systems: mains (230V AC, usually from a hook-up point) and 12V DC, which powers lights, pumps and so on. The latter is usually supplied from the leisure battery. There are times when it is useful to have access to a 12V DC supply remote from the vehicle (for example, powering extra lighting units, running portable cooling fans, or charging up a phone or tablet computer while you’re sitting outside the van). This project details the construction of a rechargeable power supply that has a capacity of 2.5Ah with a single bank of 10 AA batteries, rising to 10Ah capacity with the four-bank battery configuration. It also offers the convenience of two USB 5V sockets, suitable for charging phones and tablets. A CREE LED light is built into the case body, providing a handy torch function. The power supply can be charged with a smart electronic charger from a mains supply, via an adaptor or 12V DC source, such as a dashboard lighter socket. The charger ensures batteries are not overcharged, by switching off at the fully charged point. It can also supply a trickle charge to keep the batteries topped up, if this is needed. The charge state of the power pack can be monitored using the in-built digital voltmeter to avoid a potentially damaging fully discharged state. The capacity of the supply is 2.5Ah with one bank of 10 AA cells connected in series, increasing to 10Ah with four banks that are connected in parallel. Each bank can supply 2A. The fuse should be 5A for the single bank, 6A for two banks and 10A for three or four. The batteries used here are Duracell AA Duralock NIMH, with a capacity of 2500mah (2.5Ah), which do not suffer ‘charge drain’ when not being used. This means the power supply can be charged and stored in the knowledge that it will perform when required. It is absolutely essential not to mix manufacturers and battery capacities.