Down to earth
QI tried to buy a nonsmart battery charger and found it impossible. A friend’s offered me one from his shed. How do I know it’s safe to use?
John Blandfield, Neath Ed says:
AYou can still buy a traditional one, just about, but the ‘smart’ ones are cheaper to make - they don’t need a heavy and expensive transformer. Look out for a bulky casing, heavy weight and a conspicuous lack of boasting about the charger’s nearmiraculous abilities on the box. They hide their light under a bushel but they’re great for fully-charging a geriatric battery, derusting components in washing soda solution, testing bulbs, etc.
As with any secondhand purchase, inspect the mains lead carefully for damage and strain marks especially where the cable exits the casing. Open up the plug. Check its cord grip, that it’s correctly-and securelywired and that it has the right fuse – usually 3A or 5A. A charger with a plastic casing provides insurance against electric shock. Metalcased ones either have an earth wire to the plug or are double-insulated, in which case no earth is provided. Perform a rudimentary check as follows. Earthed casings: use a multimeter on its continuity setting – one probe to bare metal on casing, one to earth pin of plug. It should beep if the two are correctly connected. Doubleinsulated (indicated by a square-within-a-square symbol on the casing): use the meter to test continuity between the casing and each of the mains plug pins. There should be none. This tests for any direct touching of metal parts and wires. It doesn’t indicate aged insulation which could break down at high voltages. To be sure, get it PAT tested by an electrician. Always use it with an earth-trip (RCD) circuit breaker.