Page 36 - EngineerIt July 2021

ELECTRONICS

How to choose a backup power system

skom has made no secret of the Inverter with large battery pack
fact that is struggling to meet the An inverter is not a UPS. At best, it can be compared to an off-line UPS, provided it has
Ecountry’s power demands. Over- been fitted with an auto-switch that will transfer from mains power to inverter power should
loading and maintenance requirements there be a failure. In most cases the unit allows mains power to pass straight through
have resulted in power failures becoming and, when the power fails, switches to the inverter. Switching time is anything from 20
more frequent and longer lasting. As milliseconds upwards, but some inverters are actually designed to have a “dead time”,
an electricity user in SA today, you in other words there is a complete loss of power to the load before the inverter power is
should not be asking yourself if you will switched on. The battery pack will be sized according to the run time required.
experience a power failure but rather how The advantages of this solution are that it is quiet, emits no exhaust fumes and
often and for how long. requires minimal maintenance. Although the batteries need replacing every three to seven
Previously when purchasing a UPS, years (depending on battery type), which is expensive, the typical running expense of this
clients would look for units that would solution is usually cost effective.
merely give them enough time to shut down The disadvantages are that it offers little or no protection against mains fluctuations,
their computers, but as our businesses spikes, or surges. Moreover, if it is one of the systems that is designed to have a dead time
become more dependent on computers, before the inverter starts, computers will shut down and reboot.
this approach is no longer viable. Once battery power is exhausted, 8 to 12 hours are needed for recharging, during
Businesses today are more dependent which time there will be very little backup available until the batteries are fully charged.
than ever on their IT and find it difficult to
operate without this valuable tool. They Generator
need solutions that can keep them running A generator creates a 220/230V supply from either a diesel or petrol motor connected
and fully operational without interruption. to an alternator. The key advantage is that runtime is unlimited. As long as the unit is
The real decision now facing consumers is refuelled, the generator will keep running. However, the user should check the manual, as
not if they need power backup, but rather some generators have a recommended usage period, after which they need to be cooled
how much of their business do they need down before being restarted.
to keep running, and for how long. As A standalone generator has a number of disadvantages. Between the mains failure
a rule of thumb, in the absence of other and generator start-up is down time. Even if an auto-start is used, this down time will be
requirements, the runtime should be two to anything from 20 to 60 seconds. If a manual start is used, the delay will be far longer.
four hours. During this delay period all electronic equipment will go off, computers will have to be
re-started and there could be damage to data files. The same process applies when the
There are four options for backup mains returns.
systems with extended run times: A further disadvantage is, as loads switch on and off, the generator’s output may
• Inverter with large battery pack fluctuate up and down before stabilising. Depending on the generator, the output wave may
• Generator not be clean. Generators have the additional disadvantage of needing a suitable storage
• UPS with extended battery packs space, depending on size. Noise and generator fumes can be a problem. Generators
• UPS and generator combination must be run regularly even when there are no power failures, to make sure they are

Comparison Chart

UPS With Long Long Inverter With Long Long Generator Generator UPS Combination
Run Time Battery Pack Run Time Battery Pack

Improves incoming mains to protect
equipment – Protects against spikes 3 7 7 3
and surges

Zero switch over time between 3 7 7 3
mains fail and backup

Quiet operation 3 3 7 7

Run time can quickly be replenished 7 7 3 3

Low running cost once installed 3 3 7 7

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