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I am considering building a 12v DC UPS for network equipment, and found this other question which contains a description of how one might build such a device. It suggests:

A Buck DC/DC converter handling charging, but a simple LM317 could also be used, especially if the battery is stored at a fixed temperature, (look up "SLA charger lm317).

The suggestion that a buck converter alone could be used for this purpose makes it sound like the battery would always be connected to the power source.

  • Will this damage the battery or create a safety hazard?
  • How would you determine the output voltage to set on the buck converter?
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A trickle charge "float voltage" in the range 13.5 to 13.8V is safe (and even healthy) to be continuously applied to a typical 12V lead acid battery.

Anything below that range won't effectively keep it charged, and above that range may cause long-term degradation.

Make sure the buck converter has adequate filtering - you might consider an extra LC filter stage on its output - so that the battery doesn't see ripple or switching transients that exceed 13.8V.

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