DC-DC converter with build in battery charger!

Discussion in 'The Projects Forum' started by Tobbe, Jan 28, 2016.

  1. Tobbe

    Thread Starter New Member

    Jan 28, 2016
    Starting on my first usefull project, after building some beginner kits for fun on pcb.
    My English isn't too good, so I have to explain this simple.
    I have a LED headlight, that I want to connect to various 12v sockets in for example a snowmobile or a atv.
    The light function best with 16,8v.
    New sleds and atvs got a power saving automatic that shuts off the 12v cigarette outlet when the engine is on idle.
    So here is what I want to build:
    A DC(from vehicle typical 13.0-13.7v) to DC (16.8)converter/power supply. I will also have a battery pack 4x18650-14.8v in the same box. I do not want the voltage to be more than 14.8v on the batterys because the headlamp has a micro controller that sets the headlamp to 10% output when the voltage is less than about 15v to save battery, a energy saving mode (I will test where the exact limit for this is). I want the light to go into power saving mode when running it on the internal battery.
    So the circuit is easy enough on paper, using diodes the light will be on from the powersupply that gives 16.8v and when the powersupply gets disconnected it will run of the battery in 14.8v-energi saving mode.
    But I also want a safe battery charging circuit build in so that the batterys are fully (or almost) charged at all time. I guess the circuit will have to be build so that the maximum charge voltage is somewhere around 3v to protect the batterys from over charging, witch will give me about 12v, so maby I need to up the voltage to closers to 15v to get the light to work. Have not tested how low I can go on voltage before the light turns of. I do not need a circuit that limits the use of batterys to protect them, the headlamp has this function build in.

    Can anyone help on this? I find lots of kits on ebay for the powersupply, and I also found some kits for a charger circuit. But I need to get all of this in one, not to big box.

    Hope someone could walk me through this, and do not hesitate to treat me as a newbie. I am by all means a beginner in this type of projects.

    I have solderd a lot of engine management systems, so the soldering and that part of building is not a problem. The difference is, a EMS comes with all the parts in a kit and a detailed description on where everything goes!