Hi, I’m new here (never used this entire platform before, but as the askElectronics reddit is down I thought i’d follow the trail to lemmy and see what’s what). Hopefully this works!

Ok so I have the following -

A variable boost converter This - set to 12v output.

Two sets of 2x 18650 batteries

A 12v LED strip.

The two circuits I’m sanity checking -

  1. Two 18650s in series, outputting about 8v, going to the boost (which ups it to 12v) and lighting up the 12v LEDS.

  2. Two 18650s in parallel, outputting about 4v, going to the same boost (which still ups it to 12v, so that’s working fine and seems to be within its working range), lighting up the 12v LEDs.

Question I wanted to check - Far as I am aware, both of these circuits should be fine and do the job. And I’m aware of how series vs parallel usually works (eg. double the voltage, vs double the capacity). However I’ve never used them with a voltage booster that sets things to a fixed output voltage.

I am assuming that the way the voltage booster works, means it will ‘drain’ the parallel circuit twice as fast as the series circuit. And so both will end up running the LEDs for the same amount of time. This sounds right in my head but wanted to confirm before I soldered all my connections.

Also wondered if, in this scenario, the general recommendation is to go with the parallel or the series circuit. I wonder if the series might have less losses through the boost circuit through heating etc, but I was just guessing.

Thanks! Long first lemmy post haha. > Unfortunately after posting this I discovered the TP4056 board won’t charge 18650s in series, only in parallel!

Edit: While it seems that running the cells in series would be more efficient, I have the issue that I recharge them using a TP4056 board, and they are only compatible with charging cells in parallel and not in series!

  • Susan_B_Good@discuss.tchncs.deEnglish
    5·
    1 year ago

    The standard countryside yokel reply when asked for directions applies, " Arrh, If you need to get to there, I wouldn’t be starting from here".

    For battery powered LED lighting - you shouldn’t be using 12v LED strips. You should be using bare LEDs and a constant current supply. Converting cell voltage to 12v, only to use (probably) resistors to limit LED current isn’t the way to go.

    You will lose far more, efficiency wise, starting from there, than you are worrying about losing in the series or parallel considerations.

    But then, you’d design the required power source and then the charger associated with it - not start with a charger, which then constrains your battery pack topology.

  • grasib@lemmy.worldEnglish
    4·
    1 year ago

    In general, what I remember from step up converters, is that they work more efficient the less they have to step-up. So a conversion from 4 to 12V is less efficient than a conversion from 8 to 12V.

    But I also remember that after a certain input voltage the change in efficiency is only minimal. According to the datasheet of the MT3608 this seems to be around 4V.

    Therefore I’d connect them in series, but I’m looking forward to other peoples input on this.

    Welcome to Lemmy!

    • nirurin@discuss.tchncs.deOPEnglish
      2·
      1 year ago

      Unfortunately after posting this I discovered the TP4056 board won’t charge 18650s in series, only in parallel!

  • JCreazy@midwest.socialEnglish
    2·
    1 year ago

    Hello. I believe you are correct because power in=power out. Series would be more efficient as there would be less voltage to boost.

    • nirurin@discuss.tchncs.deOPEnglish
      3·
      1 year ago

      Since writing this though I realised something important I had forgotten - these are rechargeable cells. And if they are wired in series, it means I need a much more complicated charging circuit (I currently use TP4056 boards to charge cells).

      So even though series might be more efficient, I think I’ll need to use parallel as a single TP4056 can charge two cells in parallel.

      Thanks for the answer though!

      • wizzor@sopuli.xyzEnglish
        2·
        1 year ago

        Funnily enough I have exactly the same set up on my healing bench right now, and was wondering about the same thing. Thanks for posting the question and your realization.