Converting 3 x 1.5v led lamps to 18650 batteries

Thread Starter

hroldan

Joined Oct 12, 2016
13
Hi, I have a bunch of diverse LED lamps using 3 x 1.5v = 4.5v, some are remote controlled (IR) and work pretty well, no noticeable heat after prolonged use.

  • Is there an easy and practical way to convert these into 18650 battery operated?
  • Is there a simple module or circuit that you would advice to use?

A single 18650 battery is rated around 3.7v but reaches 4.2v fully charge (depending on your charger it can be 4.2v or more), the difference in volts doesn't really matter: the problem is these can deliver more and faster amps than any set of 3xAA or 3xAAA batteries due differences on their internal resistance. It's really rare to find cheap lamps with an specialized circuitry, instead they rely on a resistance and the speed AAA batteries work. You could easily argue about details and specifics around this but in general this is the big picture, long story short just using 18650 causes the LEDs to overheat, or whatever sort of cheap regulator is used inside the circuit. Besides it is far from efficient.

I have used different current limit resistors, but it's not efficient and energy is wasted. Also tried the old LM317 as current regulator but only works on certain cases, as it's operation will also steal some volts reducing the power output. The old 555 needs some adjustments and anyway none of this would feature any undervolt/discharge protection.

I'm looking for a better and cheap way to do this. Any recommendation? perhaps there is an already integrated IC to do this. I'm a fan of electronics but due to little practice I'm a little rusty at present time.
 

Thread Starter

hroldan

Joined Oct 12, 2016
13
I have a bunch of these. Remote controlled (IR) using 3xAAA batteries. Tested using one 18650 and the light is great BUT... the components (circuitry) overheats. I could add a heatsink but the temperature means it's not being efficient and burning energy, the ideal thing is to avoid the overheating. The led is not suffering in this case but I know eventually the circuitry will die.

It doesn't overheats in waiting mode (off, waiting for ON remote signal), just heats up when the lamp is on.





There are adapters you can buy on eBay that extend the metal housing of the flashlight so a 18650 can be used. Been doing this for years, works great.

https://www.ebay.com/itm/332040477937?hash=item4d4f279cf1:g:fEQAAOSw9PNbmMM~
Cool, didn't know about these, thanks.
 

dl324

Joined Mar 30, 2015
13,535
Cool, didn't know about these, thanks.
If you have flashlights that user the 3 AAA holders, use extenders that will hold an 18650 battery centered in the tube. Also be aware that the extenders aren't universal. I bought some and of three types of flashlights I tried, they only marginal for one. The extender mates with the body well, but the cap end is too large and I need to use aluminum foil to take up the space.

Another option is to use 18500 batteries with a spacer to hold them centered. I've used 3/4" CVPC pipe with the center drilled out to accommodate the battery. You only need it to be half an inch or so in length. I've used them without spacers, but always worry about the battery getting shorted. 3/4" PVC won't work; the OD is too large.
 
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