Mobile phones lead way on waste power

Modern mobile phone chargers are leading the way on the green front by drawing zero or negligible or zero power when they are plugged in but not in use, according to reports on the web today.

The conclusion was confirmed by an impromptu test of chargers in the PCW office, none of which drew measurable power. But we found that adapters for heavier equipment have a long way to go.

A scanner adapter draw three watts when not in use, and one for a KVM switch drew two watts. Yet many users leave adapters and chargers plugged in, forgetting that they are themselves electronic devices that draw power.

Around six billion adapters of one sort or another are used worldwide, according to estimates on the Efficient Power Supplies site set up by California's Electrical Power Research Institute, which means a lot of power is being wasted.

There are two types of power adapter: linear, the oldest, which consists of a transformer to reduce the mains voltage to that required by the client device, plus a rectifier and smoothing to change the AC to DC; switched-mode uses solid-state circuitry to regulate the supply, though it also uses a smaller transformer.

A transformer will draw current even if it is not under load, which is why adapters get warm when you leave them in the socket. But larger switched-mode supplies can also draw power even when not in use.

The wastage is not confined to leaving adapters plugged int when not in use. Efficient Power Supplies says some power adapters are only 20 per cent efficient, which means 80 per cent of the power they draw is wasted as heat.