How would I turn the PV panel to charge battery

Discussion in 'General Electronics Chat' started by Exjay, Jul 7, 2018.

  1. Exjay

    Thread Starter Member

    Nov 19, 2015
    I bought a lamp that has a PV panel to charge the battery. Later, the lamp got spoiled so I'm left with the PV panel and I don't think wanna dispose it. The wattage of the panel is 1.5W and voltage is 5.5v. Down here, power utilities is a problem, I wanna have a battery backup (power bank) for my phone. I want a circuit that will be charged by the PV panel and voltage will be stored to charge my phone.
  2. -live wire-

    Active Member

    Dec 22, 2017
    There are some complications, but it is certainly doable.

    Even with a 100% efficient circuit (no losses anywhere), it will charge a battery very slowly. Let's do the math for if you just want a few charges. That means 3 charges * 3.7V * 2.5Ah = 27WH (I am assuming the battery is a typical phone battery). 27WH/1.5W is about 18 hours. Realistically, it will be 24-36 hours in the sun to charge it up (2-3 days). There will be losses in charging, and it may not be fully bright. Additionally, there will be losses when charging the phone battery too. If you have an 80% efficient charging circuit for your pack and an 80% efficient circuit for charging your phone, there is an overall efficiency of 64%. This means if you really want a few charges you will have to get a larger battery than you may think (almost twice the capacity).

    But since it sounds like it is only going to be used occasionally, hopefully this will not be too big a deal. You will first need to get a battery pack (or salvage the one that came with it). Then you need a charge/protect/boost circuit (or multiple circuits). It is really not recommended that you make your own because lithium batteries explode when misused. I recommend something like this. It allows you to set the charge current. The one issue is that it will not work well if the pannel is obstructed. You also need a protection and boost board. I recommend something like this.

    You can, for the pack, combine multiply 18650s in parallel. Just make sure they are from the same batch and at the same voltage. The one issue is this might get a little expensive. You can also always go with a commercial option like this. Just know their pannels are also not too high power.

    And if you really need to be able to power things in an emergency, consider investing in a UPS. You could even try making one, with a sealed lead acid battery and some boards. Or at least try not to rely on a solar power that will take such a long time to charge a battery.