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Battery versus Plug-in Power
Plugs are, by design, meant to be easily unplugged. With an alarm system however that compromises their reliability because they can become unplugged so many ways:
- A annoyed operator can simply yank the plug out to silence the alarm, and forget to plug it back in.
- Sometimes an outlet is "borrowed for some emergency".
- Cords can get tripped on, or snagged, and come unplugged inadvertently.
- The circuit breaker for a branch power line can trip and not be noticed if nothing important is on that line.
- Power outages are a time when alarms are most needed because thats when pumps stop pumping and normal protections may not be there. Even when power returns, many systems need to be reset before operating again. This is the time when fuses often tend to blow because of the abrupt startup surge.
- Plug connections can oxidize in corrosive enviroments.
Battery power by comparison, is uninterruptible, and the alarm can only fail if someone willfully disconnects the battery. The downside is of course that batteries eventually discharge. Now though, battery technology has advanced to the point where some batteries can last for 20 years.
Other Considerations
Even when the level alarms have power available as with the relay output option, battery power still offers advantages: If power fails then there will be no need to control a pump, but there could still be a need for level monitoring.
The low battery alert will chirp and flash at the reduced rate of 5 seconds every 20 seconds to conserve power. Even on units without the low battery alert there is a sort-of built-in low battery warning system as the audio buzzer volume gets quieter as the battery voltage drops. Operators will have no trouble recognizing this. (Operators like the Drum Alarms and want them to keep working because they make their life easier.)
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Type of Battery?
Either type of Lithium battery will provide 50 hours of continuous alarming which in most situations will last for a few years. In cases where the alarm is not activated often, then the shelf-life determines the required battery-change frequency. The discharge rate of Lithium Manganese Dioxide (Ultralife) batteries is approximately 2% per year which means that after 10 year the self discharge will reduce the charge to 80% of a new battery. (80% is the common industry-accepted threshold to say when a battery is spent) Lithium Thionyl Chrloide batteries have a discharge rate of approximately only 1% which means the battery can last 20 years.
Lithium Thionyl Chloride batteries have the flattest discharge voltage curve, longest shelf life, widest operating temperature range, and lightest weight of any 9-volt battery. For these reasons Gizmo Engineering recommends this as the best choice.
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