DC UPS Conclusion
The ability to really see exactly how a circuit performs before spending money on components and construction is quite an educational experience. The author has come from primarily a digital background with basic analog/passive component knowledge. B2 Spice enabled the simulation of a design concept and helped plan the next component purchases as the project rolled along.
A further improvement to the design would be to replace the LM317's with LM338 devices. This would enable higher loads and also facilitate faster charging. A relay in parallel with the battery diode D5 configured to switch when the main supply failed would remove the diode voltage loss. For situations of long power outage, a protection circuit would be needed to switch off the UPS. This would prevent a highly discharged battery and subsequent damage. Consult the battery manufacture's data sheet to obtain the minimum voltage recommendations.
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