BATTERY CHARGERS AS POWER SUPPLIES

There are situations where a battery charger may need to function as a power supply, as well as maintain batteries. This can be when designed into a UPS (Uninterruptible Power Supply), or when testing or operating a DC system powered by batteries. Not all chargers are suitable for power supply operation, and some that are, are subject to limitations in their use, particularly threshhold amperage passing through. Most 'smart' battery chargers have a 'switching point', where they drop into the final stage (usually 3rd stage) float mode. Most switch mode chargers will pass current at the float voltage under this level if they have a 100% duty cycle.

The point of keeping the current draw under the switching point, is keeping the charger out of the second,'boost stage', which has a higher voltage than float, and will overcharge if left in this mode very long. For the Japlar Schauer units we carry, the switching current is a little over an amp. One of the handy features of the Samlex units we carry, is a dip switch settable mode called 'battery with load'. This setting deactivates the boost stage, allowing the charger to pass up to its rated current load without overcharging batteries connected to it. A 30 amp charger can supply up to 30 amps continuously if the load demands it.

Situations calling for power supply operation

An application like a medical cart with sealed lead acid batteries that need charging, but has a small current drain from some device that is always on, may be a candidate for a switchmode charger like a Schauer unit of appropriate voltage and amps. The charger would go through the stages to charge the battery pack, and end up in the float mode, feeding the small drain until unplugged/disconnected.

For larger current drains, we always prefer the Samlex units. We have supplied these for aircraft applications and R&D, where technicians or engineers want to test the avionics without draining the battery system. We have supplied OEM auto manufacturers and equipment manufacturers (such as John Deere) with Samlex units to incorporate into a trade show, auto expo, or even SEMA show display, where vehicle or equipment electrical systems are run for hours on end for demonstration purposes. We also have supplied robotics engineers/students with these units for testing and refining a DC powered robotic device.

There are electronic/radio applications as well. A radio repeating station (smaller DC powered units) can be set up with a battery bank feeding through a charger. When power goes out, the batteries feed the system. When power returns, the charger recharges the batteries while supplying the system load. We have used these setups for wireless internet repeaters, ham radio repeaters, scientific monitoring stations, and others. Email us with your specific application, and we'll see what is appropriate to solve the requirements.

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