UPS Design – Part One



UPS Image (APC)

Recently I was posed with a training dilemma facing sales staff at a national distributor of computer hardware as to why UPS sales were so poor. UPS pricing margins are relatively high compared to fast moving peripherals and components and is therefore more immune to forex fluctuations and should be always on the priority list of sales staff – the question raised then is why they move slowly until there is a catastrophe on the grid. A lot of the forums written about UPS are tainted by ignorance which is a pity considering that they play a very important role in protecting your computer or other sensitive electronic equipment.  I have been involved in the design and repair of UPS equipment for almost three decades so hopefully this article will debunk a lot of the theories out there.

First of all the UPS is not a safeguard against lightning strikes, it being the number one cause of most serious damage to the UPS and load.  UPS specification, usually in VA and input voltage range does not include the maximum energy that it can withstand on it’s input, neither the period it can withstand this energy burst. A UPS does have an RJ45 socket for a telephone plug – this being used to service the modem IN – OUT connectors which has passive protection. The modem is therefore safeguarded against voltage spikes, surges which may have been caused hundreds of meters or yards away from your incoming line. I have seen burnt protection devices on this  throughput and this is again caused by a spike of unknown but very high magnitude. It will not protect the modem. Secondly the UPS is designed to cover a specific input voltage range and often mains surges are higher than the recommendation – prolonged high voltages at the input WILL damage the UPS.  I have recorded AC input voltages as high as nearly 300V where the UPS input voltage swing has possibly been designed for between 195 and 260V for a 220V mains voltage. The UPS will boost low incoming voltages and ‘buck’ high incoming voltages to maintain a steady output voltage, often a sustained irregular voltage of a few seconds or more – but again this is dependent on design and safeguards in place.  With most line-interactive UPS users must still power down their equipment when the alarm is set off.  Listening to the alarm of most UPS is irritating, so why prolong the agony.  Are the users even aware that if the battery is faulty or going flat due to a lower than normal voltage that the UPS will shut down?  Often without warning.

With mission critical equipment however one does not have the liberty to power down – if you have purchased correctly the UPS is designed to run for lengthy periods of time, even days, whilst mains voltage is within the prescribed limits. In most cases the consumer will have purchased a double-conversion or Online UPS for mission critical work.  So why do I read so often about Online UPS not being as polished as the manufacturers claim?  Especially since Online UPs are very expensive,  often up to 6 times that of line-interactive and most certainly you pay for what you get. Design is very sophisticated,  switching circuitry is usually over-rated for the VA rating of the UPS as a whole and the storage cell amperage hour capacity is higher than that of the interactive equivalent. In 9 times out of 10 damaged UPS of this type (except APC) are not checked by the technical staff as to what caused the damage and they will be repaired or replaced at no cost to the user if under warranty. In 9 times out of 10 the UPS has been damaged because the user has inadequate knowledge of high energy circuits and either does not have a qualified professional check the input to the UPS or runs the UPS from a generator which has no AVR.  In one incidence I recall a user returned 9 1500VA online UPS over a period of 12 months. The ‘technical representative’ overseeing the replacement asked no questions – in every case the input circuitry had swollen reservoir capacitors, a sure sign that there was something seriously wrong with the input voltage.  High power UPS from APC (or any reputed company) cannot be utilised unless a qualified engineer has signed off the equipment for the designed usage and believe me – your input voltage and load current is going to be checked.

I cannot always blame the user though – there are manufacturers bringing out UPS which have been manufactured and sold without proper Q.C. and in one case, a UPS manufacturer designing a unit with standard outlets for the country of choice – while this may seem a good idea it certainly isn’t. This particular UPS had the earth wire running over the heat-sink and worse still the upper cover pinched this earth wire against the heat-sink.As sure as unscrupulous manufacturers make deadly switched mode power supplies, so to we can point fingers at UPS manufacturers.  Always buy a reputed brand and if not a reputed brand from a reputed distributor/dealer to ensure good and without frills warranty support. If the distribution channel does not have qualified engineers you may be sitting on a time bomb. Fortunately, this is not the norm as there are some excellent manufacturers out there, mostly Asian. I always look at the quality of the PCB, the quality of the manual and nowadays, the quality of the website.

Going back a few steps, why would you need a UPS to feed your notebook? Simply put, the SMPSU of your notebook is a simple power supply. Just like your PC, the SMPSU feeds all the circuitry but lacks the ability to monitor for severe surges or brownouts – the notebook has a backup battery to help out with blackouts but not surges. The PSU will still take the initial knock, your external hard drive will still take the knock and your peripherals, scanners, printers and whatever else will still take the knock.  Modern UPS are cheap and certainly protect your equipment from surges or brownouts. Don’t put them anywhere as most UPS has a modified AC voltage at it’s output and there is electronic equipment which doesn’t like it and make sure that you use a double-conversion UPS for mission critical equipment. I’ll further elaborate on this in the second part of the article when we look into the electronics used – please don’t blame the UPS when so often we find that the UPS is used incorrectly, especially out in the field, without grounding and after lightning strikes.

PART TWO – schematics, reasoning and sales facts.  Due Sunday 10th June 2012.

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