Ruggedisation Design Process

YEG Powerline is a specialist power supply and battery manufacturer and distributor with facilities to convert harsh design requirements into rugged solutions. With over twenty years of specialisation in this field the company provides solutions to meet almost any environmental or electrical demand and mechanical configuration.

YEG Powerline can provide cost-effective solutions for almost any electrical and mechanical configuration requirement, with output power ranging from a few watts to well over 30kW.

It has long been established that best practice is to develop rugged solutions where possible from COTS standard product to avoid delayed deployment of new equipment.
The YEG Powerline approach where possible is to adapt from standard designs or from several hundred field proven custom designs to meet clients most demanding design challenges. This keeps design costs lower and development time shorter. In other instances we start with a new design.

Environmental extremes in temperature, humidity, air pressure, mechanical shock and vibration are common problems when designing rugged equipment.

YEG Powerline has experience of many extremely rugged applications, including railways, industrial machinery, cranes, earth moving equipment, power utilities, oil exploration, airborne, military, marine, industrial PC and telecom with some products designed to give up to 30 years service. The company’s customers also have the benefit of complimentary use of a fully equipped EMC Testing facility at their High Wycombe head quarters.

Design considerations.
YEG Powerline highlights the main design considerations for ruggedising as follows.

Extended temperature range.
The operating temperature will have an effect on the life of the power supply. YEG Powerline have seen operating temperature ranges from minus 55 to plus 80 degree C.

The upper operating temperature has the greatest influence. Most power supplies (mainly AC/DC) operate up to 50 degree C with no degradation to components. Where it can operate at 70 degree C it will but with a shortened life unless it is given a lower (de-rated) power rating.

Typically for a power supply to operate at 70 degree C at 100W; a 200W power supply will be used.

Fan forced air cooling presents problems with the environmental integrity of the equipment. It is also a mechanical limiting factor when considering overall reliability. Enhanced cool wall conduction can be achieved with the addition of external heatsinks with milled radiation fins.

For external winter temperature operation (0 down to minus 40 degree C) the power supply will need to start up reliably or (in some applications) operate in specification. A good starting point is selecting a power supply that already has this rating. If not than the power supply components (e.g. semi conductors and output electrolytics) need to be upgraded. A more realistic expectation is for power supply to start up between minus 40 and 20 degrees C; the unit self heats when switched on through heat generated from internal components. When above minus 20 degree C; the power supply operates within specification.

No fail option.
Normally equipment uses a single power converter. Where no overall operational failure can be tolerated; a dual redundant type is used. In this case a power supply contains two identical AC/DC (or DC/DC) modules. If one fails the other takes over.

Environmental protection.
An example is where the power supply is in equipment which is open to outdoor elements. The unit may be subjected to water jets, sand or dust ingress. Enclosures with this type of protection use an IP code, e.g. IP67. If the power supply is embedded in full time enclosed equipment this can be less critical.

To minimize dust ingress when required; cooling methods will ideally be fan less; i.e. cooling by conduction. YEG Powerline has seen some applications where the customer equipment has been used near water (even worse salt water). In one or two cases a fan had to be used. In those instances internal components and PCB needed heavy protective coating. Such protection is a form of conformal coating.

Higher levels of IP protection, i.e. water proofing can be achieved by full encapsulation using thermally conductive potting compound and / or using an IP6x rated enclosure. The enclosure may need to be custom to fit certain form factors / footprint available in customer equipment.

External connectors also need to be considered; there are IP68 types for wet or immersion conditions.

Vibration and shock will also heavily influence the life of a power supply. The effect of vibration and shock on power supply internal components will cause displacement of components and potential open circuits.

A more rugged power supply may have to meet more stringent MIL-STD specifications. When considering the specifications, remember that how the power supply is mounted can cause mechanical resonance in the system. When the entire system is subjected to shock and vibration, a power shelf containing one or two supplies may start to vibrate at amplitudes greater than the system itself.

An embedded power supply may well have primary protection from shock and vibration from Ruggedisation of the equipment chassis and casing. The power supply itself will be more rugged if enclosed. The power supply internal components can be coated with ruggedising adhesive. For greater protection all components can be encapsulated with a thermally conducting compound.

Robust connections and cabling.
Particularly in equipment where standard cables would be prone to crushing or cutting because of associated enclosure lid. Such cables should be upgraded to cope with such crush damage. The other hazard for cables is in presence of aggressive chemicals or gases. An example YEG Powerline often encounter is battery acid fumes in traffic light chargers. Again cables need to be upgraded to deal with such corrosion.

EMC compliance is required to very demanding standards of emission and susceptibility.

YEG Powerline Ruggedisation Capabilities:

High output voltages - up to 800Vdc
AC or DC input
Single or multiple outputs
Single or dual redundant
Rugged PC power supplies
EMI filtering to meet any standard, typically EN55022 Class B
Alarms and other interface connections
Ruggedising and/or conformal coating, or full encapsulation
Rail-specific standards including EN50155, EN50121-3-2, EN 61000, IEC 61373 shock and vibration, and RIA 12, RIA 13 and RIA 20
UL508, EN60950 and equivalent standards for heavy industry
DO160 standards for airborne applications
MIL-STD-461 & MIL-STD-810 standards
Operating temperature ranges including -55°C to +80°C
Full electronic protection
Extended temperature range
High IP ratings, typically IP54 and above
Ruggedised for vibration and shock
Custom enclosures and racking

Compliance testing

To prove compliance to all required standards will involve some external test houses. However, we have at our disposal a substantial amount of power supply testing and proving equipment. All the following can be tested in house.

Conducted EMC testing
Radiated EMC testing
Harmonic Testing
Mains Bourne High Energy Surge testing
Mains Bourne Fast transients
Dip testing
Climatic Chamber covering the full temperature range down to minus 30 °C
High resolution photographic thermal imaging
ESD up to 15KV
Fully automated power supply test equipment
Transient response and Bode plot analysis to optimise power supply response
Isolation testing including type testing
Safety critical magnetic component isolation withstand