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Wanting to design a cree led powered dock rechargeable torch running on 18650 cells Answered

Hi all, I had an idea the other day that it would be very useful to have a powerful torch in my van that is kept charging in a dock all the time (as required at least) when the engine is running.

I know I can get similar torches that charge via a USB cable, and that I could plug the cable into a cigarette lighter socket etc, but what I would like to do is as follows:

  • Power from a 12v (ignition switched) source in vehicle, to a charging dock.
  • Torch must be powered by 18650 lithium-ion cells (2 ideally).
  • Torch would run a cree (or cree style) powerful LED chip/diode (maybe up to 10w arbitrary power).
  • Torch does not need to have a wire plugged into it, but can be simply placed into the dock after use in order to resume charging. The connector for charging is not important but likely a jackplug type arrangement, or else spring terminals.
  • Housing will be 3D printed, and using a lens from an existing torch (probably).

So mostly I'm happy about making and designing this, except that I'm not certain about what setup (either the circuit design if bespoke or what off the shelf module etc) I should use for taking 12v to charge 2x 18650 cells in situ.
I have got small USB charging modules already, and I have things like voltage boosters/reducers, and tons of electronic components, but the USB charge module is no use for using with a 12v supply etc, so I'm not sure how to best address this part of the project.

If anyone has suggestions on good ways to accomplish this I'd be really grateful, thanks!


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2 years ago

Main problem with tasks like these is the batteries.
You will need a really decent charger!
There are a lot available that charge two cells at once and even by 12V if required.
However: Those are designed to charge two cells in parallel!
The charger needs to utilise the safety measures/chips that non-fake-batteries have and also be able to trickle charge.
The later means the charger keeps checking the full batteries and every now and then gives them a tiny amount of charge to compensate for the self discharge.
If two batteries in parallel with just 3.7V to work with are fine:

Include a switch with multiple terminals.
If set to ON or "light" it just connects the electronics for the LED to the batteries.
If set to "OFF" it disconnects the LED AND the charging capabilities.
Set to "Charge" and it will seperate both batteries to be charged by the salvaged charger.
The last step is vital unless you salvage a proper charger designed to charge parallel batteries.
In terms of requirements for a suitable switch to prevent more electronics:
A standard 1-0-1 switch won't do to seperate the cells.
In older audio equippment you could find switched with 2 or even three individual switches per position.
But of course those usually are rather long and bulky.
Since you mention 3D printing it should be possible to just use 2 or maybe even 3 1-0-2 switches that you "bridge" with a printed part to work in sync.
To be clear: 1-0-2 is the term for a standard 3-way switch that has 3 individual contacts, each position closes one contact while the other two open.
If you bridge them you can combine "ON" from one switch with "OFF" - or opening, from another switch ;)

Docking station....
Had a few but the only type that really worked for me (going bush and such things) is the pipe type.
Two rings on the device to provide contacts, two spring supported contact pins to get to the rings once inserted.
Although I have to say three contacts per rings at an angle of 120° would be best.