3
\$\begingroup\$

I need to power a 10 W device to operate 16 hours a day on a 50% use capacity. So 10 W device running 8 hours a day I guess. I need to run this device from a battery pack as no AC is available. How many days can I run on what size of battery? Ideal is 14 days before recharge, how big a battery will I need?

\$\endgroup\$
1
  • \$\begingroup\$ Do you have any access to sunlight, so solar can help top-up the battery across the daytime ? \$\endgroup\$
    – Criggie
    Dec 8, 2023 at 2:23

2 Answers 2

4
\$\begingroup\$

10 W * 8 hours/day * 14 days = 1120 Wh battery.

Do yourself a favor and get a larger one than you need. Especially lead-acid suffers from deep discharge so a two times overrating would be advisable. Lithium-ion is less sensitive, but ideally you would dimension to operate between 20-80 % SoC, implying a 1.4 overrating factor.

\$\endgroup\$
2
  • \$\begingroup\$ Definitely oversize your battery. Especially if it has to survive under less-than-ideal temperature conditions as well. In winter, it's not uncommon to see commercial-grade Lithium-ion solutions hold 30% less charge, which means you need to over-engineer your battery to hold at least 143% of what you think it should under ideal conditions. \$\endgroup\$
    – Mast
    Dec 7, 2023 at 20:45
  • 1
    \$\begingroup\$ Then there's durability of a battery. How many months/years should it survive? Depending on the battery you get, expect 5-15% degradation each year. \$\endgroup\$
    – Mast
    Dec 7, 2023 at 20:46
2
\$\begingroup\$

Simply multiply the numbers together.

10 W * 8 h * 14 = 1120 Wh.

\$\endgroup\$
1
  • \$\begingroup\$ And realize that a lead-acid or gel battery can deliver perhaps 50% of the nameplate rating. Lithium is better under ideal conditions, but suffers much more from cold (unless it has built-in heating, which also impact actual Ah delivered). \$\endgroup\$
    – Jon Custer
    Dec 7, 2023 at 22:34

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.