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Nov 16, 2023

Rocker switch turns itself off

Need to save stand-by power? How about a mains switch that turns itself

Need to save stand-by power?

How about a mains switch that turns itself completely off?

Omron has released such a thing: a manual mains switch with a coil inside that will flip it to the ‘off’ position following the application of 5V for 50ms. Unlike a latching relay, the coil cannot set it to the ‘on’ position.

There is also a more elaborate version, dubbed "delayed-off" (see below), for situations where power cannot be un-predictably removed – when data has to be stored first, or a machine has to be bought to rest, for example.

"The switch is a great asset in implementing systems that meet the requirements of the European Commission ErP Ecodesign directive," said Omron. "It specifies that the power consumption of equipment in any off-mode condition shall not exceed 0.5W. In stand-by, consumption should also not exceed 0.5W, unless the equipment has a status display in which case 1W is permissible."

Called A8GS, the switches look just like a normal mains rocker switches, and are rated for 16A at 125Vac and 10A at 250Vac (3mm contact gap, UL and cUL approved, EN conforming).

As contacts are silver alloy, there is a minimum load (5Vdc 200mA). For working below this, a gold alloy versions functions down to 3Vdc 1mA, and up to 5Vac 200mA.

This is not a great lump of a thing. It measures 30x17mm when seen from the front, and is 28.5mm deep from the mounting face to the end of its terminals.

Power contacts are SPST or DPST, and both power and coil connections are either all 4.8mm spades, or all solder terminals.

There are also versions where the coil is supplied through a 2pin connector (CT series from Tyco, or XR from JST). And there are all-manual versions without a coil.

The coil (11? 455mA) is rated for 4.5-5.5Vdc 50-100ms, with 5s minimum rest between operations. "In case of applying voltage within the range from 5.5 to 24Vdc to the coil, contact your sales representative," said the firm.

The so-called ‘delayed-off’ version, dubbed A8GS-T, does not actually have a delay built-in.

"It features a delayed off function to allow safe shut down of electrical equipment", said the firm. "With this switch, the power to the system is maintained when the switch is returned to the off position. The system is then powered down by an external signal after an interval determined by the designer. This prevents issues with data loss or circuit damage through forced power off by the user, and can help safer application design."

Put another way: It is a triple pole single-throw switch, with two poles allocated to power switching and called the ‘signal contact’. All three pairs close simultaneously when the switch is manually set to ‘on’.

While the signal contact follows the mechanical position of the rocker, the power contacts can only be turned on by the rocker, and off by the coil.

Manually selecting the off position closes the signals contact. Seeing this, the electronics can run an orderly shut-down procedure, then actuate the coil to cut mains power.

The data sheets (see links above) have clear operation diagrams.

A8GS-T shares other specifications with the standard A8GS.