GB2269494A

GB2269494A - Mains operated smoke alarm with back-up power supply

Info

Publication number: GB2269494A
Application number: GB9318966A
Authority: GB
Inventors: Roy Clegg
Original assignee: DERBYSHIRE MAID Ltd
Current assignee: DERBYSHIRE MAID Ltd
Priority date: 1992-09-19
Filing date: 1993-09-14
Publication date: 1994-02-09
Anticipated expiration: 2013-09-14
Also published as: GB9219845D0; GB2269494B; GB9318966D0

Abstract

The smoke alarm incorporates a capacitor 6 as a back-up facility to provide automatically a secondary power supply which, when fitted to a normally operated mains voltage smoke alarm, powers the smoke alarm, in both the stand-by and alarm modes, in the event of a mains voltage failure. A 9.2 volt, 2.5 Farad capacitor 6 may be formed by four series-connected 2.3 volt, 10 Farad capacitor 7 charged from the mains power supply or via power supply unit which also normally powers the alarm and includes a transformer 3, rectifier 4 and resistor 5. <IMAGE>

Description

SMOKE ALARM This invention relates to a smoke alarm either of the mains operated kind, or the mains powered low voltage kind, particularly but not exclusively, for domestic use, incorporating a smoke detector and an associated control circuit having electrical power means to trigger an audible and/or visual alarm, upon a setting threshold of the smoke detector being exceeded by the presence of smoke within the effective vicinity of the detector.

Smoke alarms are in use throughout the world including some models which have a battery as a secondary power supply in the event of mains failure, interruption, isolation etc, (hereinafter referred to generally as "failure"). However, to ensure effective operation of the smoke alarm i.e., to ensure that it is always in an active, operational mode, trite battery (or battery pack) requires regular checking and/or exchange, and some require discharge, which activities a householder regards as tiresome and consequently it is frequently neglected, with the result that no battery checking is ever effected, or is effected so infrequently that - unknown to the householder - for long periods of time the alarm has no battery back-up.

According to the present invention there is provided a smoke alarm of the mains operated or mains low voltage types, incorporating a control circuit having a capacitor back-up facility to provide, immediately and automatically, a secondary power supply to power the smoke alarm, in both the stand-by and alarm modes, in the event of a mains failure, with restoration of mains power firstly commencing immediate and automatic re-charging of the capacitor back-up facility until maximum capacitance is reached, and secondly and simultaneously re-establishing mains power to the smoke alarm.

From the practical viewpoint, the capacitor back-up facility needs to be of sufficient electrical capacity that it can provide a secondary power supply sufficient to power the smoke alarm for say seven days under stand-by operation and fifteen minutes under alarm conditions.

The capacitor back-up facility comprises a system of collecting and storing electrical charge, for use as a power supply in the event of mains failure, from e.g. the normally operated mains voltage smoke alarm, utilising capacitors as the storage device.

The system of collecting and storing power within the capacitor back-up facility is by means of an electrical charge from mains power, via the existing control circuit of the smoke alarm into one or more capacitors, during the normal operation of the smoke alarm.

The system of utilising the stored power in the capacitor back-up facility is by means of an electrical discharge from the capacitor(s) to the control circuit of the smoke alarm during the period or periods of failure of the mains supply.

Amongst the advantages provided by the smoke alarm in accordance with the invention are: 1. the non-existance of an operational back-up facility, unknown to the householder, due to failure to check the battery condition, is totally avoided, as the use of backup batteries is similarly avoided, and hence the provision of an effective power back-up in the event of mains failure etc., is guaranteed.

2. after a mains failure the capacitor back-up facility has the capability of re-storing power supply in its capacitors sufficient to supply the smoke alarm in the event of further mains failure.

3. the capacitor back-up facility overcomes the costs of replacing batteries normally found in mains with battery back-up" smoke alarms in two ways: i) the cost of the battery ii) the cost of the labour to change the battery 4. environmental advantages arise in that the hazards normally associated with the disposal of spent batteries required in conventional, mains powered, battery back-up, smoke alarms is eliminated.

5. the smoke alarm is a safer unit because it does not rely on batteries and the subsequent replacement of batteries.

6. the smoke alarm is also safer because it will overcome the temptation of removing, for other use, a battery from e.g. a normally operated mains with battery back-up smoke alarm.

7. in the embodiment of a mains powered low voltage (e.g. 12-50V) smoke alarm - typically installed for instance in a standard communication system between tennant and warden in sheltered housing - the presence of the capacitor back-up facility in the alarm according to the invention enables the further back-up battery pack, which would be conventionally required exclusively for the smoke alarm(s), is unnecessary and need not be installed, whereby the smoke alarm(s) is capable of operation independently of system power supplies.

A smoke alarm in accordance with the invention will now be described in greater detail, by way of example, with reference to the accompanying drawing which is a part of a circuit diagram.

In the drawing, an industry-standard mains operated smoke alarm power supply (PSU) unit is illustrated diagrammatically by the dotted box 1, with an incoming mains supply to ' the PSU 1 being via a line 2, initially to a transformer 3, then via a diode 4 to a resistor 5 and then to a capacitor back-up facility 6. The latter may typically incorporate four 2.3 volt D.C., 10 Farad capacitors 7, connected in series to give a capacitor back-up facility of 9.2 volts DC x 2.5 Farad. For instance a suitable part to serve as the capacitor 7 is a 2.3 volt x 10 Farad capacitor manufactured by Panasonic under part number EECA2R3U106.

Between the resistor 5 and the capacitor back-up facility 6 is a power output lead 8 to an industry-standard control circuit (not shown) of a smoke alarm.

Thus, under normal operating conditions when mains power is available via line 2, power is supplied to the smoke alarm control circuit via transformer 3, diode 4, resistor 5 and lead 8, with the capacitor back-up facility 6 charged to full capacity by mains power, while in the event of mains power being absent for whatever reason e.g. failure, interruption, isolation etc., power is immediately available from the capacitor back-up facility 6 for a reasonable period - typically seven days in a stand-by mode, or fifteen minutes in an alarm mode.

Claims

1. A smoke alarm of the mains operated or mains low voltage types, incorporating a control circuit having a capacitor back-up facility to provide, immediately and automatically, a secondary power supply to power the smoke alarm, in both the stand-by and alarm modes, in the event of a mains failure, with restoration of mains power firstly commencing immediate and automatic re-charging of the capacitor back-up facility until maximum capacitance is reached, and secondly and simultaneously re-establishing mains power to the smoke alarm.

2. A smoke alarm as claimed in Claim 1, wherein the control circuit incorporates a transformer.

3. A smoke alarm as claimed in Claim 1 or Claim 2, wherein the control circuit incorporates a diode.

4. A smoke alarm as claimed in any preceding claim, wherein the control circuit incorporates a resistor.

5. A smoke alarm as claimed in any preceding claim, wherein mains power, to charge or re-charge the capacitor back-up facility is via the transformer, diode and resistor.

6. A smoke alarm as claimed in any preceding claim, wherein the capacitor back-up facility incorporates a plurality of capacitors connected in series.

7. A smoke alarm as claimed in Claim 4 and any claim appendant thereto, wherein, between the resistor and the capacitor back-up facility is a power output lead to the smoke alarm.

8. A smoke alarm substantially as hereinbefore described with reference to the accompanying drawing.