Uninterruptible Power Supply

Posted by PITHOCRATES - February 12th, 2014

Technology 101

The Battery in a Laptop is basically an Uninterruptible Power Supply (UPS)

When working on a personal computer (PC) you’ve probably learned to save your work.  Often.  So if something happens you won’t lose your data.  For there is nothing more frustrating than writing a report off the top of your head without notes only to suffer a power interruption.  And if you didn’t save your work often everything you typed after the last time you did save your work will be lost.  Forever.

Of course if you were working on a laptop you wouldn’t have to worry about losing your work.  Even if you didn’t save it.  Why?  Because of the battery.  Laptops are portable.  We use them often times where there are no power outlets.  Running them, instead, on the internal battery.  Some models even let you change a battery with a low charge to a freshly charged battery without shutting down your laptop.  Which extends the time you can work without being plugged in.

The battery in a laptop is basically an uninterruptible power supply (UPS).  You can work on a laptop while plugged into an AC outlet.  But if someone trips over the cord and pulls it out of the outlet the laptop will switch over to the battery.  And the only way you would know there was a power interruption is if it was yanked off your lap when the person tripped on the cord.  Because thanks to that battery the computer itself never knew there was a power interruption.

The Main Components of an Offline/Standby UPS are a Charger, a Battery and an Inverter

A PC doesn’t come with a built in battery like the laptop.  But we can add one externally.  Which a lot of people have done.  Not only to prevent the loss of data.  But to protect the electronics inside their PC and other sensitive electronic equipment.  Like a monitor.  A cable modem.  A router.  Even a big screen television.  As sensitive electronic equipment can only operate safely in a narrow band of voltages.  And really don’t like things like surges and spikes coming in on the electrical utility line from a lightning strike.  Or under-voltages on hot summer days when everyone in the neighborhood is running their air conditioners.

A UPS can provide a battery backup.  And it can protect your sensitive electronic equipment from surges, spikes and under-voltages.  Which can cause great harm.  Something those surge protected plug-strips can’t protect you from.  They may take a spike or two.  But they are passive devices.  And can do nothing to protect you from an under-voltage (i.e., a brownout).  Only a UPS can.  Of which there are three major types.  Offline/standby.  Line-interactive.  And Online/double-conversion.

An offline/standby UPS is the least expensive and simplest.  The main components inside the UPS are a charger, a battery and an inverter.  It plugs into an AC outlet.  And the devices you want to protect with it plug into the UPS.  If the input voltage (the voltage at the AC outlet) is within a safe range the AC outlet powers your devices.  Also, the UPS controls circuit will monitor the battery voltage.  If it is too low the controls will turn on the charger and it will charge the battery.  When the voltage on the battery is at the level it should be the controls disconnect the charger.  If the UPS controls detect an over-voltage, an under-voltage or a power loss an internal switch disconnects the AC outlet from your devices.  And connects them to the inverter.  A device that converts the DC voltage from the battery into an AC voltage for your equipment.  It will power your devices from a few minutes to up to a half hour (or more) depending on the power requirements of your devices and the battery size.  If the voltage at the AC outlet returns to normal the internal switch will disconnect the devices from the inverter.  And reconnect them to the AC outlet.  If there is a complete power loss you will have time to save your work and safely power down.

The Online/Double-Conversion provides the Best Power Protection for your most Sensitive Electronics

An offline/standby UPS is an efficient unit as it only consumes power when it charges or switches to the battery.  However, switching to the battery every time there is an over-voltage or under-voltage can shorten the battery life.  A problem the line-interactive UPS doesn’t have.  Because it doesn’t switch to the battery every time there is a power fluctuation in the input power.  The line-interactive UPS is basically an offline/standby UPS with an additional component.  An autotransformer.  Which is basically a transformer with a single winding and multiple secondary taps.  If the input power is within the safe range the voltage in equals the voltage out of the autotransformer.  If the input voltage is too high the controls will switch the output to a different secondary tap that will lower the voltage back to the safe range.  If there is an under-voltage the controls will switch the output to a tap that will raise the voltage back to a safe range.  So that these over and under voltages will be corrected by the autotransformer and not the battery.  Which will remain disconnect from the load devices during these autotransformer corrections.  Thus increasing battery life.

The offline/standby UPS is a little more costly but it will have a longer battery life.  And it will also be efficient as it will take minimum power for the controls to switch the taps on the autotransformer.  But if you want the best power protection for your most sensitive electronic equipment you will get that with the more costly and less efficient online/double-conversion UPS.  This UPS is different.  It takes the power from the AC outlet and converts it into DC voltage.  It then takes this DC voltage and produces a pure AC voltage from it.  Free from any voltage irregularities.  Completely isolating your sensitive electronic equipment from the dangers on the electric grid.  For the electrical loads are not normally connected directly to the AC outlet.  They are always connected to the AC output of the inverter.  Which makes this unit the least efficient of the three as it is always consuming power to power the connected loads.

The battery is always connected in the online/double-conversion UPS.  So in a blackout there is no switching required to transfer the loads to the battery. Making for a seamless transition to battery backup.  Of course, sometimes the electrical components inside the UPS malfunction or fail.  In that case the UPS can switch the loads directly to the AC outlet.  Should imperfect power be better than no power.  They will also have an isolation bypass switch.  So you can switch these units directly to the AC source to service the UPS components.  Which may be necessary due to one drawback of the online/double-conversion UPS.  Because the components are always consuming power they generate more heat than the other two types.  Requiring additional cooling to keep these units operating safely.  But they can overheat and breakdown.  Which makes an isolation bypass switch handy to service these while still powering the connected loads.

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