1
\$\begingroup\$

Forgive me if this is a really basic question, but I'm still at the "consideration" stage of a basic LED project, thinking about lighting up one of those flexible LED strips from a microcontroller such as an Atmel AVR. But it'll be an outdoor gadget so it'll need to be run from batteries.

I've seen other questions specifically using car power and how to get a lower voltage from that, and other questions starting from a 3V supply and boosting it to 12V, but I'm not even sure which of those I want. Which would be better, starting from a 12V battery source (either 2*6V or even a real car battery?) and dropping it for the microprocessor, or starting from something lower (like AA batteries?) and boosting it for the lights?

The lights apparently need 12V, and the back of my envelope says they'll draw around 1A, which sounds a lot, multiplied by a few hours (say 3 or 4), so it seems that's far too much for AAs unless I connect a few handfuls of them. Also it would be nice if the batteries could be recharged easily (and I've no idea how to do that with a car battery!).

At the moment I'm assuming that getting the microprocessor to switch the strip(s) on and off is a separate problem, I'm just at the stage of thinking about the power, the two separate voltage levels, and whether the whole thing is feasible or not. Any help would be very welcome!

\$\endgroup\$
  • \$\begingroup\$ What LEDs are you considering? Do you have a spec? \$\endgroup\$ – Andy aka Apr 23 '13 at 10:51
  • \$\begingroup\$ Strips of red LEDs on a roll which is cuttable to various lengths. Voltage is 12V, and based on the strip lengths I think I need, I calculate a draw of about 1A. I need to check whether the strip can take a (little) bit of weather though. \$\endgroup\$ – PenguinPete Apr 23 '13 at 11:24
  • \$\begingroup\$ That's not a spec - how did you calculate 1A draw. You are interested in efficiency and life of the battery so this might be important when considering an answer. \$\endgroup\$ – Andy aka Apr 23 '13 at 11:36
  • \$\begingroup\$ The data sheet says "max forward current 4.4A" and "Power dissipation 52.8W" for the whole roll. I'm not going to be using the whole roll, and not all of my strips will be on at the same time, so I came down to roughly 1A. \$\endgroup\$ – PenguinPete Apr 23 '13 at 11:58
  • \$\begingroup\$ Maybe a link to the data sheet? \$\endgroup\$ – Andy aka Apr 23 '13 at 12:01
1
\$\begingroup\$

Using AA batteries is not practical if you need an ampere for several hours. Based on your level of experience (I'm guessing) a small 12-volt sealed lead-acid battery sounds like a good choice. There's no point in trying to develop a high-efficiency regulator for the microcontroller, so just use a linear voltage regulator. Keep in mind that the voltage from a 12V battery actually ranges up to about 14V so make sure your LEDs can handle that. Small chargers for 12V batteries are available at your local huge box store or automotive supply.

\$\endgroup\$
  • \$\begingroup\$ Thank you! I hadn't seen the "sealed lead-acid" batteries which aren't car batteries. They look just right. I'll look at "linear voltage regulators" too. \$\endgroup\$ – PenguinPete Apr 23 '13 at 11:31
  • \$\begingroup\$ I'm not sure what you're going to support your AVR uP (I suggest a pre-assembled board like an Arduino if you're new to this for your first project). But just look at the board's power supply requirements on the datasheet and drop the voltage to meet them. Chances are on a board (rather than the raw uP) there's probably some power regulation and conditioning, anyway and so something like a 7805 or whatever would be fine. \$\endgroup\$ – Dan Sheppard Jul 12 '15 at 0:55

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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