BATTERY TESTERS

Abstract: A battery tester (12) for connection to a battery (10) has means for assessing ambient temperature, D.C. voltage across the battery and capacity of the battery in amps per hour and means (24) displaying the results in sequence.

Description: TITLE: Battery Testers DESCRIPTION This invention concerns a battery tester, especially for battery testers for use in testing lead acid batteries. There is presently no means for assessing how much current is available in a lead acid battery, although its well known that such batteries lose capacity over a period of time and that capacity is temperature dependent. Typically after three year a lead acid battery will only have 90% of its capacity, after four years 60% and after five years 40%. Where lead acid batteries are used in critical situations it would be useful to be able to assess their capacity or amount of current available. A typical critical situation where a battery may be used would be as a back-up for powering an alarm system. An object of this invention is to provide a tester for use on batteries to assess available current. According to this invention there is provided a battery tester for connection to a battery and having means for assessing one or more of and preferably all of the following: a) ambient temperature; b) D.C. voltage across the battery; and c) capacity of the battery in amps per hour. The battery tester of the invention preferably has a display for showing the assessed values. Preferably when all three values are assessed, the tester is programmed to display the results in sequence for pre-determined time periods. The display will typically be a LCD display that may be backlit. The battery tester is preferably powered by the battery under test, to which it is connected obviously, if the battery under test has no power remaining, the tester will not operate. The battery tester of the invention is preferably controlled by a microprocessor programmed to convert test values obtained into desirable results for display. The preferred battery tester includes a temperature sensor and the battery tester is preferably programmed to display the temperature detected in °C for a pre-determined period of say two seconds. Measurement of ambient temperature is important because the ambient temperature can affect the power output of a battery. Lead acid batteries are usually rated at 25°C, so that testing the ambient temperature, allows sensible comparison between a battery's rating and its assessed capacity. It is proposed that the battery tester will have its software programmed to a calibrated battery to provide a benchmark. Typically, a calibrated Yuasa brand sealed lead acid 20 hour rate 12 volt battery will be used for that purpose. The battery tester preferably also includes means for measuring the open circuit DC voltage across the battery. The voltage measured is preferably displayed for a pre-determined period of time, typically two seconds. Thirdly, the preferred battery tester of the invention has means for assessing the capacity of the battery in amps per hour. Preferably the tester applies a load to the battery, typically by means of a resistor, say a 1 ohm resistor, for a short period of time, eg for a millisecond. The voltage across the battery with the load applied is sampled and the capacity calculated therefrom preferably using an algorithm. There may, of course, be other suitable ways of deriving the capacity of a battery from a measured value of the battery, which could be used in the present invention. In the preferred embodiment of the invention, the battery tester comprises a box containing the required circuitry, including a temperature sensor and with an LCD display and leads for connection to a battery. Once the tester is connected to the battery, the programming of the tester will produce on the display firstly an ambient temperature reading for about two seconds, secondly an open D.C. voltage across the battery for about two seconds and thirdly the capacity of the battery in amps per hour until the tester is disconnected. It is envisaged that the readings displayed will be marked down on a record card or sheet for that battery, so that it can be monitored at regular intervals and its performance checked, to enable timely replacement of the battery, and to ensure that the battery complies with British Standards, which is particularly important for batteries in critical application situations. This invention will now be further described, by way of example only, with reference to the accompanying drawing, which shows a battery tester according to the invention. Referring to the accompanying drawing, a 12 volt 1.2 A battery 10 is under test using a battery tester 12. The battery tester has leads 14 and 16 for making electrical connection between the battery and the tester. The leads 14 and 16 have jaw type clamps 18 for gripping terminals 20 and 22 of the battery. The tester has an LCD display 24 on which are displayed in sequence ambient temperature, open circuit DC voltage across the battery and the battery capacity in amps. The circuitry of the tester comprises a PCB containing: a) a 5 volt regulated power supply; b) an analogue to digital converter; c) an 8/16 bit microprocessor; d) a battery monitor device which incorporates temperature sensing; e) a 1 ohm wire-wound power resistor; and f) a back-lit LCD display. Power for the tester is provided by the battery under test. When powered up by the battery under test, the programmed microprocessor sends a command instruction to the battery monitor device to take a temperature reading, which is analysed and displayed in °C on the LCD for approximately two seconds. For some markets, the battery tester may be arranged to show the temperature in °Fahrenheit. Alternatively, the battery tester may have means for selecting the scale of the temperature measurement, e.g. between °Celcius and "Fahrenheit. Once completed a second command instruction asks the battery monitor to take a voltage reading across the battery, which is again displayed for about two seconds. Finally, a third command instruction asks the battery monitor to place a momentary 1 ohm load across the battery under test whilst measuring the voltage. This voltage sample is analysed in real time and converted into an available current reading, which is displayed on the LCD and maintained until disconnected from the battery. The various displayed readings can be recorded on a record sheet or on any other suitable recording medium for regular monitoring of the battery under test.

Claims: CLAIMS 1. A battery tester for connection to a battery and having means for assessing at least one of the following values: a) ambient temperature; b) D.C. voltage across the battery; and c) capacity of the battery in amps per hour. 2. A battery tester for connection to a battery and having means for assessing the following values: a) ambient temperature; b) D.C. voltage across the battery; and c) capacity of the battery in amps per hour. 3. A battery tester as claimed in claim 1 or 2, having a display for showing assessed values. 4. A battery tester as claimed in claim 3 capable of assessing all three values and programmed to display the values in sequence for predetermined time periods. 5. A battery tester as claimed in claim 3 or 4, wherein the display is an LCD display. 6. A battery tester as claimed in claim 5, wherein the display is backlit. 7. A battery tester as claimed in any one of claims 1 to 6 powered by the battery under test. 8. A battery tester as claimed in any one of claims 4 to 7, wherein the predetermined time period for display of ambient temperature is two seconds. 9. A battery tester as claimed in any one of claims 4 to 8, wherein the predetermined time period for display of D.C. voltage across the battery under test is two seconds. 10. A battery tester as claimed in any one of claims 1 to 9, wherein the tester is programmed to apply a load to the battery for a short time, to sample the voltage across the battery with the load applied and to calculate the capacity therefrom using an algorithm.

Inventors: JONES ADRIAN, WALTON NIGEL, JONES, ADRIAN, WALTON, NIGEL
Applicants: ACT METERS LTD, JONES ADRIAN, WALTON NIGEL, ACT METERS LIMITED, JONES, ADRIAN, WALTON, NIGEL
Application year: 2000
Main classification: G01R31
IPC codes: G01R31