Breaking the circuit

Oct 3, 2012 | Electrical & electronics

When designing a new high power DC uninterruptible power supply for use by the military in aggressive terrains, Advanced Technological Systems International selected high-performance circuit breakers from E-T-A Circuit Breakers, and a ruggedised armoured aluminium housing

Advanced Technological Systems International (ATSI) specialises in the design and production of some of the most advanced power supply systems, particularly for use in very rugged conditions and extremes of temperature. The ATSI RMHCPU-20 mains/battery critical power supply, a high power DC uninterruptible power supply (UPS), is one example. Designed for use by the military in aggressive terrains, the UPS is contained within a 25mm ruggedised armoured aluminium housing.

When specifying high-performance circuit breakers suitable for the conditions in which the units would be operating, ATSI approached E-T-A Circuit Breakers.

Mission critical equipment

Typically, in the field, the mission critical equipment being powered via the RMHCPU-20 UPS would use a 28V DC generator. Alternatively the power can come from a 110/230V AC power source via the UPS which converts it to 28V DC. Indeed both inputs can be connected at the same time, one acting as a back-up for the other. Providing ultimate back up are one or two pairs of ATSI ‘HAWK’ batteries, also connected to the UPS. The ATSI ‘HAWK’ is a NiMH battery providing 10A DC at 24V, capable of withstanding extremes of temperature – from the Arctic to the Tropics.

Operation of the UPS is very user friendly – once one or two pairs of batteries are connected, the main power switch can simply be turned to the ‘ON’ position.

Protecting the UPS

The RMHCPU-20 is designed to provide seamless switching between the power sources in the event of one failing, so that to the load the switch over is undetectable. A series of LEDs indicates which power source is being used, and an audible alarm warns of the switch over in the event of a power failure. With four ‘HAWK’ batteries fitted, up to ten hours of continuous use at 20A can be achieved – one pair is used at a time, so a drained pair can be substituted with fresh ones to provide continuous operation.

To protect the UPS – and the mission critical equipment it is powering – from power surges, the AC input, the DC

generated input and the DC output are each protected by proven, reliable circuit breakers for equipment (CBEs) from E-T-A Circuit Breakers. The inputs are each protected by an E-T-A 482 CBE: the DC input uses a 50A version and the AC input a special order 15A AC version. The DC output is protected by a 20A E-T-A type 4120 CBE.

The Type 482 is a compact, high-performance, single pole thermal circuit breaker with a tease-free, trip-free, snap action mechanism. With a threadneck for panel mounting, it has push/pull on/off actuation with an indicator band on the push button clearly showing the tripped/off position. Its design features ensure it will provide effective and reliable circuit protection in the most severe operating conditions – it can withstand acceleration, shock, vibration, salt spray, altitude and fluid contamination among others.

Type 4120 is a miniaturised thermal CBE with a trip-free mechanism and similar threadneck mounting and push/pull on/off manual actuation. While designed for aeronautical usage, the type 482 and 4120 are also suitable for many other application areas such as marine, automotive and industrial. In the RMHCPU-20 design, the CBE actuators are further protected by a plastic sheath.

An internal charging system on the ATSI UPS maintains the batteries at full charge while mains power is being supplied. Various indicator lamps and digital meters indicate the state of operation and current loading. Preconditioning also takes place if the batteries are left in circuit for over two months.

ATSI also designs and produces some of the most advanced surveillance and counter-surveillance equipment available on the market. Established in 1999, it is frequently called upon to provide bespoke design solutions to support the increasingly complex operational requirements of military and law enforcement agencies in their fight to counter the heightened terrorist threat and manage homeland security.

E-T-A Circuit Breakers

T: 01296 745154


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