Take Charge
Headset review
Take charge… Ian Fraser explains how to check and look after your battery, and what to consider when deciding to replace leadacid with lithium…
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atteries are one of those components that many of us take for granted and most of us are totally reliant upon them for starting our aircraft. But how do we know if they are up to the job? Manufacturers suggest life expectancy of a normal aircraft battery could be five to seven years, and although some users wait until the starter begins to falter before replacing the battery, others change them regularly as a matter of normal service routine. Some of us now permanently connect smart chargers, which the ‘charger’s champions’ say can double the life of a battery. I have heard reports of aircraft battery lives of between two and 20 years, but who really knows how long you can expect your battery to be reliable for? I don’t think anyone does. So, is there a practical, simple engineering means of deciding if and when your battery needs replacing? The short answer to that is, yes. However, if we do decide the battery needs to be replaced, do we really need another 12kg lead brick? That’s a fair chunk out of our useful load after all, and technology has improved such that a much smaller lithium battery can provide adequate current to start even a large engine. With the reducing electrical load for other electrical equipment, suitable batteries are
48 | LIGHT AVIATION | June 2021
Above The old Concorde lead-acid battery and the new EarthX lithium-Iron.
available today that weigh less than 20% of the original, which could be a saving of 10kg. Before we look at smaller, lighter batteries it is key to appreciate exactly what an aircraft battery needs to do and with how much power it needs to do it – and that is it must not only start the engine, it must also provide an adequate source of electricity in the event of an alternator failure.
Starting requirements
To explain starting and its battery requirements, I will split the process into two parts: getting the starter itself and the engine moving; and then the normal cranking of the engine. Getting the starter and engine moving, or ‘breakaway’ as the specialists refer to it, initially requires a massive burst of current, e.g., for a Lycoming O-320 some 200-300 amps. This current then reduces as the starter gets up to speed. Once it is moving at the normal turning or cranking speed (about 60 engine rpm or two blades per second), that current should drop to between 80-120 amps. If the engine is labouring during the starting process due to cold weather or a fault, it never gets to that sweet cranking speed and is actually placing a higher demand on the battery than if it were cranking normally.
