Received a call from a member who'd bought a small 12/240 volt petrol-electric generator. It was bought to power her occasionally watched TV, but mainly to charge a battery for 12 volt lighting. Running the TV was fine, but after several hours charging the battery would only run a couple of 15 watt globes for an hour or two before expiring. Surmising that the battery was crook (which it may well have been) she bought a new one, but this would not charge either. The vendor established that the 12 volt output was within specifications (and this was confirmed independently), and told our caller that he could do nothing further about it.

Unfortunately for our buyer he was technically correct: she had fallen into a trap that has caught many a person before. Many small generators have a so-called '12 volt' output that provides around 12.4-12.6 volts on load. This is about the same as a charged 12 volt battery, and that's all this 12 volt output does. It simulates a 12 volt battery, not a battery charger. The output is intended for directly connecting (i.e. without a battery) devices such as 12 volt TVs, mobile phone chargers etc. With most generators this output will not effectively charge a 12 volt battery because that requires 14.1-14.4 volts - way beyond the voltage output of most of these generators, and high enough to damage some directly connected 12 volt devices.

This is rarely spelled out in promotional literature. Worse, several generator salespeople queried whilst writing this column assured me, wrongly, that their generators would fully charge a battery. The buyer has no legal redress. Had she been advised that the generator would charge her battery she would have had a clear case under the Statutory Warranty provisions of the Trade Practices Act. But she reasonably but wrongly assumed that it would, and did not query it. Happily there is a solution. This is to use a mains battery charger running from the 240 volt output. Unfortunately this involves spending another eighty or so dollars; worse, small generators are gas guzzlers anyway and adding a battery charger increases the losses. So it's not an elegant solution, but it works.