I only have access to electrical power via a generator for now, and need to continue to power the wireless router & cable modem even when the generator is out for a good part of the day or night.

Since the cable signal is still there, it only needs the modem & router on so that I can use the laptop on battery to work without the generator. I hope to be able to make a battery source for this setup to run for about 8 hours before recharging is needed.

The wireless router adapter is 19v 1.75a, and the cable modem is 12v 2.5a. The difference in voltage on these seem challenging. I wonder if I can just wire directly to these units from the correct batteries (what types?) because they're DC. Maybe even use a small solar panel to keep the batteries recharged and don't have to resort to the generator for most days.

Since I'm clueless on these matters, please help design this setup and explain what I'd need to do/buy to make it work. Safety is certainly a concern. I can put the battery outside if needed & wire it in, but it needs to be fire safe. Thank you!


closed as too broad by brhans, Eugene Sh., Chris Stratton, Warren Hill, Voltage Spike Feb 22 at 17:38

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ People are using UPS for this purpose. \$\endgroup\$ – Eugene Sh. Feb 20 at 14:40
  • \$\begingroup\$ 33 W is quite a bit for a WIFI router (I'm assuming it's WIFI, perhaps it's not), you may want to shop around for a lower power router. \$\endgroup\$ – sstobbe Feb 20 at 15:04
  • \$\begingroup\$ Could you please point out a UPS model or two that would meet this need or close to it? I'm not sure how to tell which will be enough. On the WIFI router, yes, it's an older version but works well & I like it. What should a normal wattage for a unit nowadays should be? \$\endgroup\$ – người Sàigòn Feb 22 at 4:31

If you want to buy rather than make, consider a UPS: Battery-backed, automatic battery management, and the AC output can drive any and all wall warts. You have 64 W of load. Assume the AC/DC converters you have are 75% efficient. That raises the total load to 85 W. Times 8 h equals 680 Wh. For a 12 V battery device, you need one rated for 57 Ah; 29 Ah for a 24 V battery.

  • \$\begingroup\$ That is not a "small" UPS, and a typical small UPS is not designed for extended operation anyway. \$\endgroup\$ – Chris Stratton Feb 20 at 16:07
  • \$\begingroup\$ Thanks @AnalogKid. It seems most UPS units are designed for a short time use. Could you please help point out one that would last a few hours? I looked but most don't specify Wh. I need to get work done for at least 5-6 hours at a time before resorting to generator.. If there isn't one, perhaps I can put together car batteries or Li cells? \$\endgroup\$ – người Sàigòn Feb 22 at 4:28
  • \$\begingroup\$ As a first-order approximation, battery voltage times battery Amp-hour rating, minus about 20% for efficiency, equals the Watt-hour capacity. There is nothing in a UPS design that limits it to short-term use. The short term, high power performance is detailed because that is the most often used criteria for an application. My UPS has two 12 hour, 7 Ah batteries, for about 134 Wh. \$\endgroup\$ – AnalogKid Feb 22 at 5:04

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