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 -
-
Two 18650s in series, outputting about 8v, going to the boost (which ups it to 12v) and lighting up the 12v LEDS.
-
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!
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.
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!
Unfortunately after posting this I discovered the TP4056 board won’t charge 18650s in series, only in parallel!
Hello. I believe you are correct because power in=power out. Series would be more efficient as there would be less voltage to boost.
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!
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.
If you haven’t considered this, it’s another option. You can make a USBC pd battery bank from 18650’s, or buy commerical ones.
Paired with a trigger board like this, it works well for projects. I’ve made a few from old laptop cells. https://youtu.be/DQLrZA5RMjQ
It’s great to see you exploring different platforms for your electronics inquiries! Regarding your setup with the variable boost converter, 18650 batteries, and the 12V LED strip, your analysis is on the right track.
The boost converter indeed stabilizes the output at 12V irrespective of the input voltage. In your scenarios, both setups - series and parallel configurations of the 18650 batteries - should effectively power the LEDs at 12V through the boost converter.
Your assumption about the parallel circuit draining faster than the series circuit due to the boost converter’s behavior is accurate. Since the parallel circuit offers half the voltage but doubles the current capacity, it will indeed discharge quicker compared to the series circuit.
Concerning the choice between parallel and series setups, there are trade-offs. The series circuit might experience fewer losses through the boost circuit due to its higher efficiency with higher input voltages, potentially reducing heating issues. However, as you mentioned, charging cells in series isn’t feasible with your TP4056 board, limiting your option to the parallel configuration.
Given your charging constraints, sticking to the parallel configuration seems more practical for recharging purposes. While it may drain faster, using the parallel setup is compatible with your charging board and allows for easier recharging.
I noticed your edit about the TP4056 board being compatible only with parallel charging, which aligns with your previous discovery. It’s a crucial factor to consider in maintaining the functionality and longevity of your battery setup.
If you want more insights on the efficiency differences or additional alternatives for charging in series, I have an informative post on converter types that delves into various setups and charging considerations, which might offer further clarification for your project.
Feel free to explore and let me know if there’s anything specific you’d like to dive deeper into!