Hey everyone, I am trying to build a battery powered water valve, using a solenoid, which is 12V activated.
For powering it, I thought on using 4 18650 batteries connected in series and a step down to get always 12V. Now, the issue is on how can I recharge those 4 batteries...
My initial impulse (Primarily because I have tons of these) is using 4x 03962A modules (https://www.aliexpress.com/item/32993121231.html) and wire them in series, connecting each of them with one 18650 cell, so a basic diagram would look like this (Forgive me the bad quality drawing):
You could, instead, use a single cell and boost converter. Do you know how much current the solenoid draws at 12V? Do you know how long you need the solenoid to work on a charge?
Generally, a multi-cell charger uses a charging voltage of 4.2V per cell across all cells, and switch a resistor across cells that reach full charge early. A set of voltage dividers lets you check the voltage at each cell to get the voltage on each cell.
Depends on the model, but essentially this forms one big battery so P+/- are the input and output of the battery. Just think of them as the poles of a single battery cell. Check the specs of different models to find one with the correct inputs and output voltages.
Further, this steps up the voltage for you so all you should need is a 12V linear regulator with enough amps for the solenoid.
Well, I am planning on putting some solar panels to keep them charged, these are 5V 220ma cells. That's about 1.1Wh. If I step it up to 12V for the charger, I guess I should still be able to get 1Wh out of it, right? (with the loss due to the step up in the middle...)
So, 2 - 3 hrs of sun a day should be enough to keep them charged...