Designing a Solar and Li-ion Battery Powered Charger / Power Source Part 2

[@alysef21]

Great video! It looks like there is a small circuit board as part of the battery cell you are using (on the top near the wiring), what is that?

[@ForceTronics]

Good question, that tiny circuit on the battery cell is to cut off current flow once the battery becomes fully discharged. Most Li-ion / polymer battery cells are discharged around ~2.75V, if you were to continue to use them their voltage would drop quickly. Once they get to ~1.7V any further discharge you will damage the battery as well as possibly swell and over heat the battery. That circuit acts like an open once the battery gets to 1.7V (could differ depending on the battery). thanks for the question.

[@jaredharvey1511]

Have you considered something like 3x 18650 batteries in parallel? Basically 3x the capacity while maintaining a 3v pack.

[@ForceTronics]

I got a similar question on another one of my videos, maybe that was you too? No battery cell is the same and can have slightly different charge or discharge rates as well as capacities. And these differences can become more pronounced over time. To operate them in parallel you would have to come up with a sophisticated battery management system to properly balance them. Not sure what your application is, do you have a load that requires a large amount of current real fast and that is why they are in parallel? Otherwise I would just design a circuit that would operate one at a time. Once one is almost fully discharged, I would switch in the next one and switch out the discharged one. I would then repeat with the third one once the second one was discharged. This approach you don't have to worry about balancing them.

[@RoterFruchtZwerg]

cells in parallel don't require balancing and also their capacity doesn't need to be matched (but it's good practice). Almost all high power commercial batteries are paralleled cells. Like in powerbanks, laptops, vacuums, drills, ...

[@nmf5003]

You are absolutely correct about laptops using batteries in parallel, but they do use a balancing for their batteries in parallel. In fact Apple was the first to actively balance their parallel batteries in laptops in the 2000s and it had a noticeable increase in battery life. From their all other laptop makers followed. @@RoterFruchtZwerg

[@jaredharvey1511]

@@RoterFruchtZwerg cells in parallel will balance. Try putting a dead battery in parallel with a fresh new 18650 and see if the fire monster appears. It's important to make sure they don't feed each other and they only power the load. It's also important to charge proper. Internal resistance will create an imbalance if you attempt to change with one charger. I'm planning on one charger per cell.

[@jaredharvey1511]

​@@ForceTronics Lets try this again. Last 2 attempts failed to post. In my case the load is around 10mA to 100mA-ish. I'm chipping away at an opensource case for the TDeck I've put my files in onshape under "T-Deck_Case" I'm looking at 3 batteries to extend the life between charging. I intend for the device to sit in the window charging via solar or USB. It normally sits idle, charging batteries. I've been pondering that the 1st cell charges until it reaches full, full indicator then triggers the 2nd battery to charge, and then eventually the 3rd. Or perhaps I could charge the lowest V of the 3 cells first. I guess I need to decide if I want 3 batteries charged to 1/3 or do I want 1 charged battery and 2 empty batteries. I've been looking at the BQ24074 then add short circuit protection. Or perhaps go with the BQ25185 which includes the short circuit protection and works with a higher Vin. I like the JLC availability of the of the BQ24210DQCT.

[@thenextproblem8001]

Hi man, thanks for the other educational video. I have a question if you don't mind. I'm using esp32 with solar charging. İ can't use load share since panel charging 5v 100ma but Esp32 using 700ma. Good thing is Esp32 is waking every 15 min for 2 sec and goes to sleep. However, i don't want to charge my battery fully but 4.0V only. I'm using diode to drop voltage and its working great but sometimes diode is so hot to touch especially while battery is charging. Is there any other more appropriate way to do it? Buck converter didn't work as i wanted and limited the current

[@ForceTronics]

If the diode is hot to the touch you should probably go with a diode that has a higher current rating. You should be using a Schottky diode since they have a low forward voltage to help conserve power. You could replace the diode with a P Channel Mosfet or back to back p channel mosfets for better efficiency (I show this approach in my video). When you use mosfets you just have to make sure you have a signal to bias them at the right time. This could be a signal from another power bus like in my example or from a microcontroller.

[@lzyu5155]

can i know the ic u used for the circuit?

[@ForceTronics]

The model numbers for the charging IC and the regulator IC are shown in the video during the schematic review

[@amybanks7021]

P R O M O S M

[@ForceTronics]

If your implying I use any type of paid services to boost my views or likes. You are mistaken, I am way too cheap for that. All organic! And if you didn't care for me video content you are in the minority so it is probably a you problem 😋