GB2354378A

GB2354378A - Non-interruptible power supply

Info

Publication number: GB2354378A
Application number: GB9921728A
Authority: GB
Inventors: Brian John Thompson; Graham Spencer Bestwick; William George Gates; Simon John Kerslake
Original assignee: Lucent Technologies Inc
Current assignee: Nokia of America Corp
Priority date: 1999-09-14
Filing date: 1999-09-14
Publication date: 2001-03-21
Anticipated expiration: 2019-09-14
Also published as: GB2354378B; GB9921728D0

Abstract

A non-interruptible power supply is disclosed. Its cabinet contain an AC to DC converter 6 providing a DC output to an input of a DC to AC inverter 6 for converting DC to AC. A battery 4 floats across the converter output/inverter input. An air conditioning unit 14 cools the interior of the cabinet. Control means is responsive to: the presence or absence of AC power at a mains input and to the temperature of air in the cabinet: <SL> <LI>a) in the presence of mains power, to cause the air conditioning unit to operate only when the air temperature is above a first predetermined threshold; and <LI>b) in the absence of mains power, to cause the air conditioning unit to operate only when the air temperature is above a second predetermined threshold, higher than the first. </SL> Normally, the air conditioning unit will switch on and off to maintain the internal temperature of the cabinet nominally at 20{C, for example. This is required in order to obtain a long battery life. When the mains supply fails, the back up time, in which the battery is effective to maintain the supply, is important. Operating the air conditioning unit to hold the internal cabinet temperature to 20{C will consume a significant amount of power reducing the possible back up time. Operating the battery at higher temperatures, e.g. 40{C, for short periods, e.g. one hour, will not have much effect on battery life.

Description

2354378 NON-INTERRUPTIBLE POWER SUPPLY This invention relates to

non-interruptible power supplies.

Non-interruptible power supplies have an AC to DC converter, e.g. a rectifier network and a DC to AC inverter for converting battery DC to AC. A battery is floated across the rectifier output/inverter input. The converter is connected to the AC mains supply in use. When the mains supply fails, the inverter continues to supply AC power until, hopefully, the mains supply is restored when the battery is recharged via the rectifiers. The battery is often in the form of a bank of separate multicell batteries. It is important that the battery bank is kept at an even temperature, in particular is not allowed to over heat, and that individual cells or batteries are all kept at the same temperature. To this end it is known to cool the equipment. If the power supply is intended for use outside, it would be conatined by an environmentally sealed cabinet and cooling would be affected by an air conditioning unit.

Air conditioning units are usually AC powered. It is possible to take the power supply for the air conditioning unit from either the. mains supply or from the inverter output. If the air conditioning unit is supplied from the mains, if that fails (the possibility for which the non-interruptible power supply is provided) the cooling also fails and the non-interruptible power supply soon becomes too hot.

The invention is based on the realisation that if the air conditioning unit is supplied from the output of the inverter, it will draw a significant amount of battery power which will shorten the back up period.

Against this background, in accordance with the invention, there is provided a non interruptible power supply, having a mains input for AC mains power and comprising a cabinet containing an AC to DC converter providing a DC output to an input of a DC to AC inverter for converting DC to AC, a battery floating across the converter output/inverter input, AC power driven cooling means for cooling the interior of the cabinet; and control means responsive to: the presence or absence of AC power at the mains input and to the temperature of air in the cabinet:

a) in the presence of mains power, to cause the air conditioning unit to operate only when the air temperature is above a first predetermined threshold; and b) in the absence of mains power, to cause the air conditioning unit to operate only when the air temperature is above a second predetermined threshold, higher than the first.

The cooling means may be a heat exchanger, for example, or most preferably an air conditioning unit. Normally, the air conditioning unit will switch on and off to maintain the internal temperature of the cabinet nominally at 20'C, for example. This is required in order to obtain a long battery life. When the mains supply fails, the back up time, in which the battery is effective to maintain the supply, is important. Operating the air conditioning unit to hold the internal cabinet temperature to 200C will consume a significant amount of power reducing the possible back up time. Operating the battery at higher temperatures, e.g. 400C, for short periods, e.g. one hour, will not have much effect on battery life.

The second threshold is preferably in the range 250C to 400C.

In one example, the air conditioning unit is supplied with AC power via a temperature sensitive change over switch from a mains supply when the temperature in the cabinet is at or below the second threshold, and from the output of the inverter when the temperature in the calbinet is above the second threshold.

One embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which:

Figure 1 is a schematic cross section of a non-interruptible power supply embodying the invention; and Figure 2 is a block circuit diagram of the power supply of Figure 1.

Referring to the drawings, the non-interruptible power supply has a bank 2 of batteries 4, e.g. 12 or 6 volt batteries, arranged to give a typical voltage of 48 volts. A rectifier network 6 receives AC at an input 7 from the mains and delivers a 48 volt DC output in parallel to an inverter 8 and the battery bank 2. The equipment is mounted in a rack 9 contained by an environmentally sealed cabinet 10 closed by a door 12, so that it may be used outside.

In order to cool the equipment, in particular the battery bank 2, the door 12 carries an air conditioning unit shown generally at 14. Inside the cabinet air is drawn in through inlet vents 16 cooled and returned through outlet vents 18. To dissipate the heat removed from the internal air, ambient air is drawn from outside the cabinet through inlet vents 20 passed through a heat exchanger, not shown, and returned via outlet vents 22.

The air conditioning unit is controlled so as to keep the air temperature in the cabinet at or below one of two thresholds.

As may be seen from Figure 2, the air conditioning unit is supplied with power by a temperature sensitive change over switch in the form of a thermostat 36. A temperature sensitive element 38, e.g. a bimetallic strip, operates a change over switch 40 so that when the temperature in the cabinet is below an upper threshold e.g. 400C, the air conditioning system is supplied from the mains. A second thermostat 23 is located in the inlet for internal air flow through the air conditioning system and controls the unit to limit the internal air temperature to about 20"C, switching the unit on above a lower threshold and off at or below the threshold (ignoring hysteresis). If the mains fails, the air conditioning system stops operating and the temperature in the cabinet rises to the 400C upper threshold. At that point the thermostat 36 operates to change the supply for the air conditioning unit to the inverter 8. Hysteresis in the operating cycle of the thermostat keeps the air conditioning unit operating until an intermediate threshold is crossed. If the temperature does cross the intermediate threshold, the air conditioning unit will not operate (unless the mains supply is restored) thus saving power until the upper threshold is reached. In some thermostats the difference between the two thresholds can be adjusted.

Claims

A non-interruptible power supply, having a mains input for AC mains power and comprising a cabinet containing an AC to DC converter providing a DC output to an input of a DC to AC inverter for converting DC to AC, a battery floating across the converter output/inverter input, AC power driven cooling means for cooling the interior of the cabinet; and control means responsive to: the presence or absence of AC power at the mains input and to the temperature of air in the cabinet:

a) in the presence of mains power, to cause the air conditioning unit to operate only when the air temperature is above a first predetermined threshold; and b) in the absence of mains power, to cause the air conditioning unit to operate only when the air temperature is above a second predetermined threshold, higher than the first.
2. A power supply as claimed in claim 1, wherein the second threshold is in the range 25C to 40'C.
3. A power supply as claimed in claim 1 or 2, wherein the first threshold is 200C or less.
4. A power supply as claimed in any preceding claim, wherein the cooling means is supplied with AC power via a temperature sensitive change over switch from a mains supply when the temperature in the cabinet is at or below the second threshold, and from the output of the inverter when the temperature in the cabinet is above the second threshold.
5. A power supply as claimed in any preceding claim, wherein the cooling means is an air conditioning unit or a heat exchanger.

5. A power supply as claimed in any preceding claim, wherein the cooling means is an air conditioning unit or a heat exchanger.

AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS:

CLAIMS 1 A non-interruptible power supply, having a mains input for AC mains power and comprising a cabinet containing an AC to DC converter providing a DC output to an input of a DC to AC inverter for converting DC to AC, a battery floating across the converter output/inverter input, AC power driven cooling means for cooling the interior of the cabinet; and control means responsive to: the presence or absence of AC power at the mains input and to the temperature of air in the cabinet:

a) in the presence of mains power, to cause the AC power driven cooling means to operate only when the air temperature is above a first predetermined threshold; and b) in the absence of mains power, to cause the AC power driven cooling means to operate only when the air temperature is above a second predetermined threshold, higher than the first.

2. A power supply as claimed in claim 1, wherein the second threshold is in the range 250C to 40"C.

3. A power supply as claimed in claim 1 or 2, wherein the first threshold is 20'C orless.

4. A power supply as claimed in any preceding claim, wherein the cooling means is supplied with AC power via a temperature sensitive change over switch from a mains supply when the temperature in the cabinet is at or below the second threshold, and from the output of the inverter when the temperature in the cabinet is above the second threshold.