DC UPS: How B2 Spice was used

Trivial examples: 3 front panel LED's were needed to monitor and confirm each of the regulated outputs were active. B2 Spice was used to calculate the current limiting resistor. The components were quickly dropped and wired. A parameter sweep on the current limiting resistor can be easily performed. The correct value can be obtained by checking the manufacturer's recommendation against the graph, at the intersection the resistance will be shown. Alternatively use the operating point mode and modify the resistor value directly. Hit simulate and you will obtain the results in the schematic.

LED circuit (Download circuit: A/D 2000 | A/D v4)

Setting the charge voltage:
Many charging circuits exist for gel batteries. The one presented here is no different. The LM317 voltage output is controlled by the R3 resistor in the diagram below. To obtain the correct value, the datasheet can be consulted and buttons pushed, or a parameter sweep can be performed. The transfer graph shows the point where the output voltage is 13.660V and resistance is just over 2.6K. In the real UPS a variable resistor has been used and the output adjusted with a fully charged battery and monitored until it reached 13.65V.

LM317 circuit (Download circuit: A/D 2000 | A/D v4)

But why a DC UPS?
The whole UPS under load draws 1.2Amps. A 7AH gel battery is sufficient to keep all the author's networking gear up and running for over 5 hours. The main computer UPS has long shutdown before this one runs out of juice, time to break out the laptop!