CHARGING DELAY

I have a 1970 Austin Mini that was originally fitted with a dynamo and have converted it to an alternator, which means that even on short journeys I don’t need to worry about depleting the battery.

The problem I have is that when initially starting the ignition light glows and the volt meter indicates that the battery is not charging. After revving the engine past the 2000rpm mark, the light is extinguished and the voltmeter shows a charge of around 14.5V.

After this point, the charge rate is continuous whatever the speed of the engine and the ignition light does not come on again. I’m assuming that this is due to some kind of switch in the alternator which once activated allows the alternator to charge at the correct rate until switched off again. Martin Malpass This is quite a simple problem to resolve and is due to the bulb in the ignition warning light. The original fitment of a dynamo required a very low wattage bulb to operate correctly. The dynamo is ‘ self- exciting’ which means it requires no battery voltage at all to begin to operate.

The alternator requires some current to activate it. Using a slightly higher wattage bulb in the ignition warning light will allow the current to flow easier, meaning that the alternator will get the required current to allow it to begin to charge sooner.

The original bulb should be a 987, which is a 2.2w screw fit bulb. Using a slightly larger wattage bulb should cure the charging delay. You may though need to adapt another bulb holder and ensure that the bulb is not too higher wattage, as this may become too hot and melt the surrounding area.