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I have a lead acid battery from an old broken ups.

And I have a WIFI router with power adapter.

Can I connect the battery directly in the middle between the power adapter and the wifi router like a capacitor, so wifi would still work when there's power cuts?

I assume my idea is too naive. What should I consider if I want it to work as I imagined?

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  • \$\begingroup\$ Is your current source a ture current source, a voltage source or a battery charger? Also, it's drawn upside down. \$\endgroup\$ – winny Jun 19 '17 at 19:11
  • \$\begingroup\$ The current source... It's the power adapter that belongs to WiFi router. :) \$\endgroup\$ – LPVOID Jun 19 '17 at 20:14
  • \$\begingroup\$ So a voltage source then. Will only work if the battery has almost exactly the same voltage as the source and a 12 V lead-acid battery will be ruined if kept at that low voltage. \$\endgroup\$ – winny Jun 19 '17 at 20:33
  • \$\begingroup\$ @winny Really? I didn't know that... The adapter gives 12V and the battery nominal is 14V. Will that ruin the battery? \$\endgroup\$ – LPVOID Jun 20 '17 at 3:56
  • \$\begingroup\$ Yes. Float to 13.6 V. Google it. \$\endgroup\$ – winny Jun 20 '17 at 5:05
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Well, sort of, but not really.

  1. The power supply would need to be adjusted to put out about 13.7 volts. This is the nominal float voltage for lead-acids, and is the point you should aim for.

  2. There would need to be some sort of isolation between the battery and the supply when power is off, or the battery may back-feed the power supply, and may well damage it.

  3. After a prolonged outage, a mostly-discharged battery requires something other than a simple voltage charge, and this would be complicated by the router current load. Go Google on battery charge algorithms.

  4. For a prolonged outage, it's a really good idea to have a way to cut off the router when the battery charge level gets low. It doesn't take a whole lot of complete discharges to permanently damage a lead-acid.

All of these problems can certainly be addressed, and routinely are. The result is called a UPS. Trying to roll your own without knowing what you're doing is a really good way to damage one or more of your components.

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