Connect with us

Modifying 4.5 V (alkaline) lamp to run brighter with 3.6 V (NiMH)

Discussion in 'Power Electronics' started by seanspotatobusiness, Nov 26, 2018.

  1. seanspotatobusiness

    seanspotatobusiness

    181
    4
    Sep 11, 2012
    I have a lamp which takes three D-size batteries. It seems to have been designed to function best with alkaline batteries and is relatively dim (in fact the bright and dim settings both appear the same) using 1.2 V NiMH batteries. I was wondering what circuit I might use to increase the brightness of the lamp without draining the NiMH batteries below ~0.9 V to protect them from damage.
     
  2. kellys_eye

    kellys_eye

    4,289
    1,143
    Jun 25, 2010
    Fit a 2.5V bulb....
     
  3. seanspotatobusiness

    seanspotatobusiness

    181
    4
    Sep 11, 2012
    It doesn't use a bulb but three SMD LEDs which are connected in parallel.

    This is the circuit that feeds the LEDs (there are no other components on the board with the LEDs). I figured the simplest thing to do would be to add a circuit between the battery and the original circuit which would boost the voltage to 4.5 V but I need it to cut-out at ~2.7 V supply to protect the cells. Would such a circuit continue to use power whilst the lamp was off, though?

    [​IMG]
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    24,860
    2,571
    Jan 21, 2010
    Use 4 NiMH batteries.
     
  5. seanspotatobusiness

    seanspotatobusiness

    181
    4
    Sep 11, 2012
    The battery compartment is designed for three. A fourth cell would be an awkward thing to add to the outside of the case and I think would leave the cells vulnerable to reversing polarity during discharge, plus the voltage might be too high when freshly charged? It would also no longer be waterproof (I bought it for camping although it's probably seen more indoor use than outdoors).

    I have a voltage boosting module that will maintain 4.5 V output while input drops down to ~2 V but that's still risking reversing polarity if my cells aren't well balanced. I regret buying this lamp!
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    24,860
    2,571
    Jan 21, 2010
    Use a number of lithium cells in parallel with a buck regulator. Find one that has a low voltage cutout.
     
  7. Audioguru

    Audioguru

    2,345
    516
    Sep 24, 2016
    The thing was designed for only 4.5V. Why do you want to destroy it with a higher voltage?
    A higher voltage will cause a higher current which makes little electronic things smoke and burn.

    Right now I am modifying a similar product. It is a solar garden light that has a real IC and I have its datasheet. It uses a voltage stepup circuit with an inductor determining its peak output current. It was dim with its original 330uH inductor but I am using an 82uH inductor to make it nice and bright. The datasheet shows that the IC can survive an inductor that produces 3 times higher current than my modification. I replaced the cheap weak Chinese Ni-Cad battery cell with a much higher capacity Western Ni-MH cell.
     
    hevans1944 likes this.
Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.