Product category:
Batteries and Chargers
News Release from: Astrosyn International Technology | Subject: Lawtronics open card chargers
Edited by the Electronicstalk Editorial
Team on 21 August 2007
Open card chargers provide
uninterruptible power
The Lawtronics range of current limited open PCB chargers is available for 6V, 12V and 24V batteries.
The Lawtronics range of open card chargers from Astrosyn can be used as low-voltage DC power supplies for sealed lead acid batteries in uninterruptible power supplies Although these chargers can be used for other battery types, such as NiCad, NiMH, Li-Ion and Li polymer, the issues involved are more complicated and will not be covered here
This article was originally published on Electronicstalk on 22 Oct 2007 at 8.00am (UK)
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Many applications require a DC power source derived from mains AC power using a power supply or power adapter to step down the voltage and rectify the AC power to DC.
This is fine until there is a mains power failure, ranging from a momentary glitch through to a long-term outage.
The application may be required to remain on during this power failure to support systems like alarms, monitors or remote communications equipment.
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It might only need to keep running for a matter of seconds or it may have to operate for many hours.
In this situation a battery backed supply is required, where the battery (commonly a sealed lead acid type) supplies power to the application during periods of mains failure.
The length of time that power can be sustained therefore depends on the amount of power that can be stored by the battery.
Sealed lead acid (SLA) batteries, including gel batteries, are commonly supplied in 6, 12 or 24V versions.
The particular application will dictate the main requirements of the battery backed supply, namely the operating voltage range, current drain and the time for which supply has to be maintained.
As an example, assume that an application circuit can be powered by 12V DC.
The output voltage of a typical 12V SLA battery ranges from around 13.8V fully charged, dropping to around 10V when discharged.
While the mains supply is present, the charger circuit should be capable of supplying enough current to power the application and keep the battery topped up.
The amount of power that a battery can provide is rated by its ampere hour capacity (C).
It is always advisable to over specify the battery capacity to provide sufficient leeway for inefficiencies in power storage and life expectancy of the battery.
All good battery suppliers can provide information on the best way of choosing a battery with sufficient capacity for the application.
As a rule of thumb, allowing an extra 50% of battery capacity is a good starting point, for example, if you are expecting to draw 1A for one hour then the battery capacity should be at least 1.5Ah.
Generally speaking an SLA battery should not be charged at greater than C/4.
Conversely, even a very small trickle charger can keep a relatively large ampere hour capacity battery fully charged, depending on the duty cycle of power drawn by the application.
For example, an application that only draws current from the battery when the mains power fails might only require a very small trickle charger that can compensate for the self discharge of the battery used.
The Lawtronics range of current limited open PCB chargers is available for 6V, 12V and 24V batteries.
They should only be used when suitably enclosed, and are ideal for integration into OEM equipment.
When charging more than one battery at a time, in series or parallel, only batteries of the same manufacturer, capacity, age and weight should be combined and they should also be in a similar state of charge.
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