Switchmode power supplies is much lighter and more compact, whilst Linear technology has been designed around using a 50Hz transformer and a regulation system, based on wasting energy in order to maintain output voltage regulation.  The SMPS is very efficient and wastes very little energy.

Charge given to a battery to correct voltage imbalance between individual cells and to restore the battery to fully charged state.

No, the metal case of the power supply should be connected to a secure earth as this ensures compliance with safety and EMC standards.  The DC output may be left floating depending on the system requirements.

As previously detailed, the energy stored within a battery cell is the result of an electrochemical reaction, so any change in the electrolyte temperature has an effect on the rate of reaction provided all other factors (charge voltage and current) relating to the reaction remain constant.

The simplest way of maintaining the rate of reaction within design parameters is to alter the charge voltage at a rate proportional to the change in temperature, i.e. decrease the charge voltage with an increase in temperature above 20-25°C and increase the charge voltage with a decrease in temperature below 20-25°C. The typical change in charge voltage is 3 mV / °C. Contact our engineers for further information, our battery chargers have temperature compensation options.

Temperature compensated charging ensures that batteries are charged to maximum capacity in cool environments and protected from overcharging in warm environments.  Temperature compensation should always be used when the batteries are going to be exposed to cold, hot or fluctuating temperatures.

End of discharge voltage is the level to which the battery string voltage or cell voltage is allowed to fall to before affecting the load i.e. 1.75V or 21V a nominal 24V system.

Programmable power supplies (CVCC variable DC power supplies, DC power supplies) are power supplies that can be operated in constant voltage (CV) mode or in constant current (CC) mode automatically depending on load conditions within the range of voltage values and current values that have been set ahead of time. Check out our range of programmable power supplies HERE.

The Helios Power Solutions Smartchargers senses the charging current into the battery and when it reaches a pre-determined level it enters the “float” mode.  Low cost chargers usually remain in boost mode for a preset time so a fully charged battery may be overcharged if connected to one of this type.

It is a type of plug-in connector with screw terminals, made by Phoenix and other manufacturers.  We use the one rated at 20A per terminal on our SR range, except where higher currents dictate the use of stud connectors.

Conformal coating will offer some degree of protection from moisture.  Direct contact with water or other fluids should always be avoided.

Many Helios Power Solutions power supplies do not actually have equivalents due to their custom design. Many of the cheaper alternatives can not be serviced or repaired and most must simply be replaced by another low cost device and the failed unit disposed of, which is to the detriment of the planet.

The SR range (except SR100) comes complete with removable mounting feet, which allow for a variety of mounting positions.  All our products may be fitted into our optional 19″ (euro) sub-racks.

Yes, it is not necessary to use the centre terminal.

It depends on the current rating of the power supply.  Stud connectors provide a more secure connection for higher currents and are generally used when the rating exceeds 20A per screw terminal on Helios Power Solutions power supplies.

All electrical equipment produces waste heat during operation due to internal losses.  This heat must be removed or the equipment will overheat and subsequently fail.  With low power equipment heat sinking and normal convection are adequate to dissipate this heat but with higher power equipment the most cost effective method for removing heat is by using a fan.

There will be no problem with VHF and UHF radios. Switchmode is not recommended for HF radios (20 – 30MHz, old citizen Band).

We manufacture two designs of meters;  one using a  ‘Hall effect’ current transformer to convert the current to a voltage signal, and one which utilises a current shunt.  The ‘Hall effect’ transducers have an inherent problem in that they tend to retain some residual magnetism after a large current has passed through them.   It is this residual magnetism which causes the false readings. The shunt versions have a much reduced zero point offset.

The two readings are obtained via different transducers and microprocessors.   The SNMP reading is obtained from an internal shunt , transducer and A/D converter in the power supply while the LCD meter has its own transducer, etc.   Each one of these components has a margin of error and sometimes the cumulative errors are at the opposite variance to each other.

The No-Break ™ DC UPS  has many features which a normal float charger does not, these including:

• Precise alarm indication for mains or DC faults
• Overcurrent protection on the battery circuit
• Battery presence checking
• Temperature compensated charging
• Low voltage disconnect circuitry to prevent deep discharge of the battery
• Independent charge current limit
• Automatic battery condition testing

Normally it is not necessary to have a boost on the No-Break ™ unit, as the power is on the system continuously and it is not that critical to restoring 100% of charge rapidly, as in the case of cyclic applications.  A boost charge voltage may damage the equipment which is permanently connected to a standby system.

No, the No-Break ™DC UPS is designed to operate with a battery connected and instability may result if there is no battery connected.  If you wanted to do this then it is advisable to use a standard two terminal DC power supply.

This is done to implement two of the features of the No-Break ™ UPS/charger.  There is an “electronic circuit breaker” fitted between the battery negative and load negative terminals to provide the battery overcurrent protection.  The separate battery circuit also allows for independent control of the charging current when required.

No, it would nullify all the features of using the No-Break ™DC design and provide false alarm signals from the relays.  If you wanted to do this, then it is advisable to use a standard two terminal float charger, with or without alarms.

At approximately 1.67 volts per 2V (nominal) cell, so for a 12V system the disconnect voltage is set at 10V.

Having an underground supply reduces the chance of lightning transients from direct (galvanic) strikes to the line. However, you are still at risk from all the other transient sources such as magnetically and capacitively induced lightning strikes, conducted transients generated by neighboring industry, switching of power factor correction equipment, utility substation switching and fault clearing on transmission lines. Therefore, yes, you do need surge protection.

Surge Protection Devices (SPDs) are like pressure safety valves on a boiler, which release dangerous excess pressure from the system. SPDs are installed across the AC power supply in parallel with the equipment to be protected. At normal operating voltages the SPDs are in a high impedance state and do not affect the system. When a transient voltage occurs on the supply, the SPD moves into a state of conduction (a low impedance) and diverts the transient energy/current back to its source or ground. This limits (clamps) the voltage amplitude to a safer level. After the transient is diverted the SPD will automatically reset back to its high impedance state.

• Maximum Continuous Operating Voltage (MCOV) – aim for a figure of at least 25% above the nominal supply voltage.
• Suppression Voltage – for 120V systems an SVR of <400V for electronic equipment and <600V for electrical equipment is recommended. This may be provided by cascading two SPDs.
• Surge Rating – approximately 100kA 8/20µs for service entrance and 40kA for branch circuits is recommended.
• Indication Status – a progressive life status indication from 100% down to 0% in various stages is preferable to a simple Go/No-Go indicator.

There is no one correct answer to this question. For a small facility, a single SPD installed at the service entrance panel can be sufficient, while for a bigger facility it is usually necessary to adopt a distributed protection philosophy where primary protection is installed at the service entrance panel, and secondary protection at branch panels. It can even be necessary to include additional point-of-use SPDs if this equipment is located some distance (100 ft or more) from the supplying panel. In addition to providing protection to the power panels, the installation of additional “multiservice SPDs” is particularly recommended. Such devices provide their greatest benefit by ensuring multiple services entering the facility (such as telephone, cable and power) are all tied to the same ground reference.

Many manufacturers attempt to highlight the importance of response time of an SPD. While important, one must not lose sight of the fact that response time is not an end in itself. An SPD offering a fast response time generally implies that a lower clamping voltage will result, however, this cannot always be assumed. The equipment under protection is not affected by the SPD’s response time, but by the residual peak voltage and waveshape reaching it. The magnitude of this residual voltage reaching the equipment is a result of many aspects of the SPD design including the surge & voltage ratings, the internal wire size, shape and loop area, the technology used and its speed of response.

Metal Oxide Varistors (MOVs) are ideally suited as voltage limiting devices due to their economical cost and effective surge capacities. They do, however exhibit an operational life which is proportional to the number and amplitude of the applied impulse. This life is non-linear, so doubling the surge rating provides a far greater length of life (typically 3-5 times) for the same size surge.

Most SPDs designed for service entrance or branch panel protection provide sufficient MOV material to give life expectations in excess of 10 years. Indication and alarm circuits should be provided by such devices to signal when their protection status has reduced to a level at which replacement maintenance is required. It is preferable that such indication occur prior to total depletion of the protection to allow a replacement module or device to be installed without the equipment being left unprotected.

This is a difficult question and depends on many aspects including – site exposure, regional isokeraunic levels and utility supply. A statistical study of lightning strike probability reveals that the average lightning discharge is between 30 and 40kA, while only 10% of lightning discharges exceed 100kA. Given that a strike to a transmission feeder is likely to share the total current received into a number of distribution paths, the reality of the surge current entering a facility can be very much less than that of the lightning strike which precipitate it.

ANSI/IEEE c62.41.2 standard seeks to characterize the electrical environment at different locations throughout a facility. It defines the service entrance location as between a B and C environment, meaning that surge currents up to 10kA 8/20 can be experienced in such locations. This said, SPDs located in such environments are often rated above such levels to provide a suitable operating life expectancy, 100kA/phase being typical. Recent changes to the IEEE have introduced a new scenario (known as Scenario II) which covers the situation of a facility sustaining a direct or near-by strike. Under such conditions, a very large ground potential rise can result and significant surge current flow on the G-N and N-L protective modes. Under such conditions, 100kA 8/20 or 10kA 10/350 energy levels can be expected.

We recommend the following products for service entrance protection:

• Main Switchboard High Risk
• Main Switchboard Medium Risk

Lightning induced surge currents are characterized as having very rapid rising “front edges” and long decaying “tails”. To a first approximation, the first number in each example of the above surge waveforms signifies the time taken for the surge to reach 90% of its peak value, and the second number, the time taken for this surge to decay from its peak to its half way value.

These times are measured in microseconds, although convention Phone 800-248-9353 Fax 800-677-8131 www.erico.com does not require that this unit appear after the wave shape. The ratio between these different waveforms is a complicated function based on the integration of the energy content. As a rule of thumb, a 10/350 surge rating is equivalent to about ten times the surge rating at 8/20. Put simply, 10 kA 10/350 is about the same as 100kA 8/20. Most MOV (metal oxide varistor) based SPDs are surge rated using the 8/20 wave shape, while air gap devices are rated using the 10/350 wave shape. SAD (silicon avalanche diode) based SPDs are usually rated using the 10/1000 wave shape.

Switching pulses and subsequent re-strikes in multistroke lightning, can produce very fast transients, with rise times in the fraction of microseconds. These can capacitively and inductively couple to equipment and cause induced over-voltages. The eliminate such fast spikes, it is usual to incorporate a level of filtering in the SPD device. This can simply be a capacitor connected in parallel across the SPD’s output, or it might be a true series LC filter – often called a two port SPD where there are distinct sets of input and output terminals. SPDs incorporating series LC filters generally provide superior filtering performance, however they are more expensive and need to be sized for the continuous load current. It should be point out that SPDs with so called “filters” would more accurately be described as waveshaping devices as the filter’s prime role is to slow the very fast rate of voltage rise dv/dt rather than to “filter”. Check out our range of  Surge Reduction Filters HERE

This is a patented technology where an SPD is able to discriminate between on the one hand the relatively low 50/60Hz frequency of long duration abnormal over voltages, such as occur when the utility power is poorly regulated or a “lost neutral” condition occurs, and on the other hand the faster transient activity of surges. Read More 

Protection of equipment connected to DC sources or power supplies generally involves installing protection at the AC input to the power supply. In some cases, protection might also be required on the DC side of such power supplies, particularly if long cable lengths are involved. Most SPDs will indicate if they are suitable for DC use and the maximum operating voltage to which they are designed for use on. Check out our range of DN Rail DC Power Surge Protection HERE

These are all forms are over-voltages and confused by the often loose and interchangeable use of terminology. The significance of the terms usually relates to their understood duration. For example, a transient is generally considered of very short duration (<10us) and relatively low energy content. Such electrical activity is often characterized by voltage switching spikes, which in themselves contain relatively little energy content, but are sufficient in voltage to cause junction breakdown in the substrates of semiconductors and failure.

Surges (>10us & <1ms) on the other hand, have a greater energy component and it is generally this which causes the damage and charring of electronic components and appliances. SPDs are designed against surges and transients.

Temporary overvoltages (TOVs) are created by faults on the utility power distribution system and can cause extensive damage since their time domain is much longer (ms to s or several cycles). Note that while UL 1449 Edition 2 ensures that the SPD will not created a fire or safety hazard under these conditions, SPDs are not designed to protect against TOVs.

Ideally, protection should be installed at the main service entrance as close to the N-G bond as possible. This will ensure that surge energies are routed to earth by the most direct part. In larger facilities where distances between this primary protection and the equipment being protected are long, it is also good practice to provide point-of-use protection as close to the terminals of the equipment as possible.

Yes and No! The ability of an SPD or surge component to respond to a voltage which exceeds its “turn-on” threshold, will govern the residual clamping voltage which the downstream equipment will be required to withstand. If the device is too slow, the clamping voltage will be high and the equipment may not be adequately protected. This said, too much is often made of manufacturers of “speed-of-response”. What is more important is the “clamping or residual voltage” performance of the SPD. It is also worth noting that nanosecond transients cannot travel far on power wiring, thereby limiting their occurrence in practice.

There are many aspects which affect the choice of module. Totally single phase units are rarely available beyond 20 kVA, above this size it is usually necessary to use a three phase input for the rectifier, even where the inverter output is single phase. When feeding this type of system via a generator it is important to remember that the bypass line will be single phase, demanding a higher current on one phase only. Larger units with three phase input/output are more easily distributed across generators and can also be used to feed single phase loads, and with good load balancing, need not be oversized.

Off-line (VFD) systems are usually low-cost products designed for a simple one or two user PC installations, they offer little or no protection against most supply problems and really only give support for short-term power loss. The load is fed from the mains during normal operation, hence ‘off-line’. On-line (VFI) UPS systems are regarded as ‘high-end’ and employ more sophisticated technology which uses a rectifier and inverter, hence ‘double-conversion’. This effectively isolates the load from virtually all types of power supply problems.

Power factor (pf) is the difference between actual energy consumed (Watts) and the apparent power (Volts multiplied by Amps) in an AC circuit. It is calculated as a decimal or percentage between 0-1 pf and 0-100% i.e. 0.9 pF = 90%.Traditionally, UPS systems were designed to support loads with unity or lagging power factors. However, modern uninterruptible power supplies can also now handle leading power factors. It does require careful planning during installation though, as leading power factors can place an overload on the UPS that it may not recognise.

Blade servers are the best example of a load with a leading power factor. They are capable of greater processing power within less rack space than traditional file servers and have been widely adopted in the telecoms and data centre sectors because of advantages such as simplified cabling and reduced power consumption.

There are several ways to try and reduce the impact of leading power factors, including increasing the size of the UPS, but the most common approach is to use active harmonic filters with power factor correction on the output.

This delivers a more acceptable load to the UPS, but it does reduce efficiency, take up more floor space and increase capital costs.

Transformer based Traditional technology, typically available from 10 kVA, suitable for industrial applications, galvanic isolation with inverter output transformer, typically standard technology from 100 kVA upwards
Transformer-less Typical technology from the smallest ratings up to 120 kVA, more compact footprints, lower weights, more suited to IT applications and environments, high efficiency across the load range, generally more cost effective.

UPS efficiency is based on how much of the original incoming power is needed to operate the UPS. For example, an uninterruptible power supply with a 95% efficiency rating will have 95% of the original input powering the load and connected systems, with the remaining 5% energy “wasted” running the UPS.

For a UPS, higher efficiency equates to lower losses of electrical energy in terms of heat output – low-efficiency UPS often require more air conditioning to help keep ambient temperatures safe.

Even a 1% or 2% improvement in operating efficiency can add to up substantial energy costs over the full-service life of a UPS (i.e. approximately 10 years), particularly for larger systems with higher power ratings. However, in any discussion about UPS efficiency, it’s worth keeping two things in mind:

• Different UPS systems have different efficiencies
• The same UPS has different efficiency depending on the load level.

The efficiency ratings that UPS manufacturers publish are based on running in online operating mode with a 100% fully-rated load. But as the load reduces, so too does UPS efficiency. As an example, a UPS running at 20-25% load may only be capable of 85% efficiency.

Efficiency is particularly important with parallel-redundant installations, as any inefficiencies arising from individual UPS’s that are under-loaded will be exacerbated at scale. This can be a major issue with many legacy installations, where UPS often run at less than 50% of their rated capacity.

In general, UPS efficiency has improved significantly over recent years thanks to a series of technological advances, principally the development of transformerless UPS systems.The difference in operating efficiency between modern transformer-free UPS and the older transformer-based UPS designs can be as much as 5-6%, although this divergence is less for the latest transformer-based models. Transformerless UPS have a flatter efficiency curve too, meaning that many versions can achieve high efficiency (>95%) at 25% load all the way through to full load.

Rectifier Converts AC voltage to DC voltage, recharges the batteries and maintains float voltage, handles overloads and buffers surges, can accept wide input voltage fluctuations.
Inverter Converts DC voltage to AC voltage, regulates and filters AC voltage.
Static Bypass Automatically connects load to mains supply if overload or fault occurs.
Battery Provides emergency power source when mains supply fails.

In terms of a UPS system, a warranty provides ‘best endeavour’ protection against mechanical faults or failures for a set period of time, typically 1 or 2 years from initial purchase, while UPS maintenance contracts offer ongoing support with the additional peace of mind of guaranteed emergency response times for engineer call-outs.

Uninterruptible power supplies are complex devices containing parts that can fail and consumables, such as fans and capacitors, that need regularly replacing. Warranties and ongoing maintenance contracts both help to reduce unnecessary downtime caused by UPS failure.

Warranties are valuable but can only ever offer ‘best endeavours’. Ongoing UPS maintenance plans provide more comprehensive cover including guaranteed emergency response times defined in either working or clock hours. These response times are clearly spelled out in a Service Level Agreement (SLA).

A typical maintenance plan can cover parts, labour and carriage costs. Most exclude battery replacement unless it is specifically requested, although some contracts will include battery labour.

Another key service provided in the majority of UPS maintenance plans is provision for an annual (or even biannual) Preventive Maintenance Visit (PMV), where a certified service engineer will undertake a detailed inspection and test of the UPS. This enables early detection of potential issues and gives the engineer the opportunity to install the latest software and firmware updates.  UPS maintenance plans can cover uninterruptible power supplies under or outside of warranty.

Static Bypass switches are used to bypass the UPS normal operation, in cases of high inrush or fault conditions. Manual bypass switches are an added benefit to allow service and isolation for safety purposes. Correctly designed systems should enable these operations to be performed without loss of power to the load. External maintenance bypass switches add the facility to remove the UPS from site, offers local isolation capabilities and enables all ac cabling to be completed prior to the UPS delivery.

Battery quality can be determined by the ‘design life’, typically between 5-12 years for VRLA batteries. The ‘design life’ is not and never will be a guaranteed life expectancy and relies on several factors including environment, temperature, maintenance, number of discharge cycles, charging regime etc. From experience, we generally expect a good quality 9-10-year design life product to need replacement in approx 6-8 years.

Capacitors in an uninterruptible power supply help to smooth, filter and store energy. A UPS includes dozens of different capacitors in both the power section and the printed circuit board level (PCB).

Capacitors contain a pair of conducting surfaces, usually electrodes or metallic plates, enclosed in aluminium or chromium-plated cylinders ranging in size from a miniature drink can through to a tube of Pringles. A third element – the dielectric medium – separates the conducting surfaces.

The charge a capacitor can store is measured in farads – after the famous physicist Michael Faraday – which is determined by the thinness of the dielectric layer and the surface area of the aluminium.

In the main power section of a UPS system, the capacitors are divided into the following categories:

AC input capacitors: form part of the UPS input filter and/or the power factor correction stage. These capacitors smooth out input transients and reduce harmonic distortion

AC output capacitors: form part of the UPS’s output filter. These connect to the critical load output, controlling the waveform of the UPS output voltage

DC capacitors: form part of the rectification system and energy storage, smoothing out any voltage fluctuations (also known as supply voltage filtering).

As well as batteries, capacitors are the UPS components most prone to failure. They age over time, with the electrolyte, paper and aluminium foil inside degrading over time. Factors such as excessive heat or current can speed up the rate of deterioration.

Depending on the manufacturer rating, capacitors can deliver up to 10 years of service life with the most favourable operating conditions. However, generally accepted industry best practice recommends capacitors are proactively replaced between years 4-8 of service life to reduce the risk of serious failure.

A single failure may not have too much of an impact as the remainder will be able to pick up the slack, although this places them under increased strain.

Ultimately, capacitor failure does have a negative bearing on a UPS’s performance. Filtering ability will suffer and there will be more issues with harmonics and electrical noise. In addition, energy storage volume will decrease, and it can even damage battery strings.

The worst-case scenario of a serious capacitor failure will trigger the UPS to bypass mode, leaving the critical load unprotected.

Indeed! Separate “grounds” or “ground references” can result in damage to equipment during lightning activity. A cloud-to-ground discharge can deposit extensive charge very quickly into the local ground mass of the earth causing the ground at the injection point to rise up in voltage with respect to more remote grounds. The resultant potential gradient established in the ground means that separate grounds could rise to different potentials resulting in a loop current and possible damage to equipment referenced to these two different points. This phenomenon can present itself in a more subtle way when equipment is connected to multiple services. An example of this can be a PC with modem where connections are made to utility power and telecom line. If these two services are not referenced together to create a common, equipotential, ground plane, damage can result. In fact, this is one of the more common causes of equipment damage. A well-designed multi-port protector will ensure such equalization between services at the equipment.

It is important to ensure that ground potential differences are not derived across equipment within a facility during ground potential rises. One way to ensure this is to adopt a single point approach to grounding of the equipment and services in the facility. This usually entails referencing all equipment in the facility to a single ground bar (or a number of ground bars that are solidly electrically bonded together), and ensuring that this internal bonded system is connected to the external ground system. “Single point grounding” refers to the single connection between the internal facility ground system and the external ground network. The external ground network can utilize multiple grounding elements such as ground rods and/or counterpoises.

There are a number of techniques for measuring ground resistance, the more popular being the “fall of potential method”. Measurements require a ground resistance testing instrument and qualified personnel. With larger facilities, it is important to take ground resistance readings by placing the injection and reference electrodes in the “far field” – essentially some few hundred feet from the inspection ground point. This will ensure that false or misleading results are not obtained by having electrodes too close to buried parts of the overall ground system. Clamp-on type instruments are not preferred in such situations due to the possibility of large errors in results.

This is probably one of the most often asked questions of grounding experts. Again there is no one answer. As a rule of thumb, an effective ground for lightning and surge protection purposes should be somewhere around 10 ohms. Obviously this can be difficult to reach in poor soil conditions and a cost benefit relationship comes into play. It is also important to stress that no definitive applies to grounding values. As an example, it is pointless insisting that a contractor achieve a ground resistance of precisely 10 ohms or less, when the testing method can be subject to as much as 2 ohms variation depending on how the test rods are laid. It is also worth keeping in mind that, the soil water content can vary as much as 50%, depending on the season of the year. There are “ground enhancing materials” which can be used to improve (decrease) the local ground resistivity.

More important than the absolute value of the ground resistance, is to ensure that all the equipment in the facility is referenced to an equi-potential ground plane through adequate bonding. By ensuring this, all separate pieces of equipment will raise to the same potential during a surge condition. This statement can be illustrated by considering the Space Shuttle, it is not “grounded” however all the equipment onboard will be referenced to an internal equi-potential ground plane.

The lightning surge event is characterized by having very fast changes in current and voltage, sometimes called the dv/dt and di/dt. In essence it is a high frequency event and as such the ground system is better considered as an AC impedance rather than DC resistance. The subject is complicated and requires knowledge of transmission line theory and special techniques to measure the effective impedance of the grounding system under impulse condition. Enough said!