Schleifenbauer has been using bistable relays in its PDUs since 2008, in combination with switched outputs.

We hereby inform you of the advantages and durability of this approach!

What is the use of switched outlets in a PDU?

The usefulness of switched outlets in a PDU can be summarised in three advantages:

Remote management and monitoring possible

First of all, switched outlets make it possible to remotely control the power supply to connected equipment. For example, one can perform a hard reset without being physically on site by switching an outlet off and on again. 

Ease of management of the PDU

In addition, switched outlets can contribute to management. Think of the situation in which an administrator switches off all outlets by default. When a device has to be connected to a PDU, the administrator can indicate that, for example, outlet number 3 in server rack 5 will be switched on, so that the device can be placed there.

Useful in case of power failure

Finally, switched outlets can be useful in the event of a power failure. When voltage returns, connected devices will provide a momentary current surge. A device with 1 amp continuous consumption will generate a 10 amp current surge for a few milliseconds when switched on. Depending on the amount of connected equipment, this can cause the preceding fuse to blow, which is obviously an undesirable situation.

The advantages of a switched PDU in the event of a power failure.

PDUs with switched outlets can overcome the tripping of the preceding fuse by switching the outlets on one by one when the power returns, by means of a relay.

In this way, the height of the current peak is limited to the height of the starting current of one device, and an undesired situation is prevented.

The function of a relay at switched outputs in a PDU.

To supply power to the outlets in a PDU, the relays have to be closed. To do this, the relays have to be energised by means of a power supply.

We think this application has disadvantages; therefore Schleifenbauer has been using bistable relays in switched PDUs for years.

We would like to explain our motivation for choosing bistable relays in more detail, with more insight into the function and advantages.

What is a bistable relay?

A bistable relay can be compared to a set of points on a railway: A set of points is in a certain position; the position changes when a command is given. 

A bistable relay functions in the same way: The position of the output changes when a command is given. No permanent power supply is required.

The advantages of a bistable relay over a conventional relay.

There are three major advantages of using bistable relays in switched PDUs, compared to a conventional relay.

Minimal power consumption and lower energy costs

The power consumption of bistable relays in a PDU is almost zero; power is only consumed at the moment of switching. A conventional relay consumes approximately 1 Watt continuously when the output is switched on. Because of this, the difference in energy consumption between a PDU with bistable relays and a PDU with conventional relays can run up to tens of Euros on an annual basis.

No internal heating of the PDU

Because bistable relays do not consume power, no heat is generated, so there is no internal heating of the PDU.

No continuous voltage

The most important advantage is that bistable relays are not dependent on a power supply that is continuously active. Think of the example of the switch in a railway: when a position is selected, the relay will remain in this position, whereas a conventional relay has to be powered continuously.