Hi folks,
In a recent thread, I've been trying to find the answer to a question I've been asked about the difference between two FireAngel smoke alarms. However, not only have I not yet got an answer to that question, but my thread rapidly got sidetracked into a discussion about the merits (or otherwise) of FireAngel products in general.
Since no-one has yet been able to answer my question, it's probable that no-one my ever be able to(so I may try asking FireAngel). However, this exercise has caused me to look and think a fair bit about the issue of fire alarm batteries in general, which leaves me fairly confused. - so I wonder if anyone might be able to help to educate or un-confuse me! My comments/questions are as follows ...
1... There are plenty of battery-only fire alarms around which use a 9V non-rechargeable alkaline battery (typically about 550 mAh), which is expect to last for a year or more. That implies an average consumption of around 0.06 mA. The actually current draw may well be intermittent, such that it is much greater than that when current is being drawn, but it would nevertheless be surprising if the 'peak' current (whilst it was being drawn) were more than, at most, a small number of mA.
2... Mains-powered alarms are usually powered by the mains but have battery back-up. When the battery is rechargeable (usually lithium-ion), the situation is pretty straightforward - the alarm is usually powered by the mains, and the battery is kept charged so that it will always be more-or-less fully charged, and hence able to 'take over' should there ever be a mains power failure.
3... My confusion arises when the battery in not rechargeable - either alkaline (typically 550 mAh) or lithium metal (typically 1,200 mAh). Both usually have shelf lives of about 10 years, and are said by the alarm manufacturers to be able to last for at least 1 year and 10 years respectively.
4.... When a non-rechargeable battery is used as the backup, it is not literally 'doing absolutely nothing' in the absence of a mains failure. Whiilst it would be possible to monitor the 'no load' voltage of a battery with virtually no current drain from it, there is presumably a need to monitor its voltage when supplying the 'peak' current that may be needed to run the alarm - so, I would imagine, at most, 'a few mA for a few seconds', occasionally.
If an alkaline battery can, alone, actually run an alarm continuously for a year or more, I find it very hard to understand why it should not last a lot more than a year (potentially its entire shelf-life) when supplying only "at most, 'a few mA for a few seconds', occasionally". On the basis of what I've said, I would have expected an alkaline back-up battery to last for it's entire shelf-life (which could be 10 years), hence quite possibly rendering it unnecessary to consider a non-rechargeable lithium one. What am I missing?
Can anyone help me understand?
Kind Regards, John
In a recent thread, I've been trying to find the answer to a question I've been asked about the difference between two FireAngel smoke alarms. However, not only have I not yet got an answer to that question, but my thread rapidly got sidetracked into a discussion about the merits (or otherwise) of FireAngel products in general.
Since no-one has yet been able to answer my question, it's probable that no-one my ever be able to(so I may try asking FireAngel). However, this exercise has caused me to look and think a fair bit about the issue of fire alarm batteries in general, which leaves me fairly confused. - so I wonder if anyone might be able to help to educate or un-confuse me! My comments/questions are as follows ...
1... There are plenty of battery-only fire alarms around which use a 9V non-rechargeable alkaline battery (typically about 550 mAh), which is expect to last for a year or more. That implies an average consumption of around 0.06 mA. The actually current draw may well be intermittent, such that it is much greater than that when current is being drawn, but it would nevertheless be surprising if the 'peak' current (whilst it was being drawn) were more than, at most, a small number of mA.
2... Mains-powered alarms are usually powered by the mains but have battery back-up. When the battery is rechargeable (usually lithium-ion), the situation is pretty straightforward - the alarm is usually powered by the mains, and the battery is kept charged so that it will always be more-or-less fully charged, and hence able to 'take over' should there ever be a mains power failure.
3... My confusion arises when the battery in not rechargeable - either alkaline (typically 550 mAh) or lithium metal (typically 1,200 mAh). Both usually have shelf lives of about 10 years, and are said by the alarm manufacturers to be able to last for at least 1 year and 10 years respectively.
4.... When a non-rechargeable battery is used as the backup, it is not literally 'doing absolutely nothing' in the absence of a mains failure. Whiilst it would be possible to monitor the 'no load' voltage of a battery with virtually no current drain from it, there is presumably a need to monitor its voltage when supplying the 'peak' current that may be needed to run the alarm - so, I would imagine, at most, 'a few mA for a few seconds', occasionally.
If an alkaline battery can, alone, actually run an alarm continuously for a year or more, I find it very hard to understand why it should not last a lot more than a year (potentially its entire shelf-life) when supplying only "at most, 'a few mA for a few seconds', occasionally". On the basis of what I've said, I would have expected an alkaline back-up battery to last for it's entire shelf-life (which could be 10 years), hence quite possibly rendering it unnecessary to consider a non-rechargeable lithium one. What am I missing?
Can anyone help me understand?
Kind Regards, John
