0
\$\begingroup\$

I design some plastic models, and I would like to include a small light (LED or similar). I am looking for a solution with a long battery lifetime. I'm not a electrical engineer but I read that, for example, 1 Red LED consumes around 20 mA, so with 2x AA batteries it lasts around 210 hours.

Does any solution exist for long life, e.g. for months? I don't need high brightness, it is only decoration for a diorama - for example, as a light in a small model of a house etc.

Thank you for any help.

\$\endgroup\$
  • 6
    \$\begingroup\$ You might get away with 1 or 2 mA if you use the right LED. \$\endgroup\$ – Andy aka Feb 6 at 18:20
  • 3
    \$\begingroup\$ the question is how much brightness you need. Generally, a pair of batteries, and a switching step-down converter can get you pretty far, but of course, the brighter, the higher the power consumption. Does your diorama really need to be on continuously for months? \$\endgroup\$ – Marcus Müller Feb 6 at 18:27
  • \$\begingroup\$ Thank you! I don`t need a lot of brightness, it is only for "visual effects" in small models. Diorama doesnt need continuously, but if there is a switch, I do not remember turn on/off it. So I look at for solution. 1-2mA LED are great - I do not know that exists. \$\endgroup\$ – frosty22 Feb 6 at 18:57
  • \$\begingroup\$ Have a look at the "tritiled" project. \$\endgroup\$ – pjc50 Feb 6 at 23:56
1
\$\begingroup\$

Some LED's are very efficient, and the eye is extremely sensitive. In a moderately lit room, a white or blue LED should be clearly visible, though not bright, with just 100 microamps. Two CR-2032 Li cells. Rated at ~200 mA/hr, this should last >2,000 hours, ~3 months. Put a 30 kilohm (kΩ) resistor in series (or even a higher resistance for a dimmer, but longer lived light). You could also use AA or AAA "penlight" cells (you'll need three or four for a white LED), and they should last a year or more.

The eye is less sensitive to red light, but a red LED can operate from a single Li coin cell. Try 15 kΩ with one Li cell.

A larger resistor decreases current, at the expense of brightness. Try a few different ones for your particular application to find a compromise that looks good on the model and lasts long enough. You might add a switch, but with very large resistors, the battery will last almost as long as if left on the shelf (5-20 years for Li-ion cells).

BTW, in a dark room, one microampere creates enough light to be seen easily.

| improve this answer | |
\$\endgroup\$
  • \$\begingroup\$ If I understand that resistor decrease consumption? Or it is require a "special" low consumption diod? I try "google it" and I found only diods with 2mA as lowest. \$\endgroup\$ – frosty22 Feb 6 at 19:16
  • 3
    \$\begingroup\$ @frosty22 You can run LEDs well below their rated current. You don't need a special LED to do it. The resistor controls the current. \$\endgroup\$ – Simon B Feb 6 at 20:06
0
\$\begingroup\$

You should consider using 2 D size batteries in place of the AAs. I have run a red flashing LED for well over a year hooked straight up to a pair of Ds, no resistor used.

| improve this answer | |
\$\endgroup\$
0
\$\begingroup\$

You could take the solar panel from a solar garden light and solder an LED to it. When light hits the panel the LED lights up. No batteries, no switches, it will run a very long time. Or just replace the white LED with a red one.

| improve this answer | |
\$\endgroup\$

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.