Replacing a DC Adapter with a Battery Pack, Design advice - Page 1
Forum section: electronics / beginners

author: Lukas52
author_rank: Contributor
timestamp: October 05, 2025, 09:30:54 am
content: Hi,I am currently trying to figure out a way to replace a super annoying and impractical AC to DC power adapter with a self made battery pack.I want to use a 4S LiFePo4 Battery 4Ah with its own PCB (commercial one, not self made). That gives me 14,6V - 10V of usable Voltage range as my power source.The device i want to power runs on 9V - 12V with 40 mA typical and 50 mA peak current. However 9V is cutting it a bit close, so i'd like to stay at least 200 mV above that, just to be save.I already built some very basic prototype using a DC to DC converter module of amazon, but its utter garbage. I tried 3 different Models and they all come with the worst type of adjustment pot imaginable... So setting anything remotely precise simply isn't possible. I don't see myself being able to design my own Step down block since i don't want to create my own PCB and i think this would get to complicated for a single layer Prototyping board. Also they don't come anywhere close to their 90+% efficiency claims... I could get a "proper" power module from mouser for example tho, haven't tried those yet.Given my relatively low current and the small amount of voltage i need to drop i started thinking if maybe simpler is better and i could simply use a LDO Regulator like the TL751L10CP. If i read the datasheet correct it should drop out somewhere between 10,2V and 10,6V which is fine with me, while providing a 10V output. What i can't seem to find out is how much power the regulator draws when no power is being drawn and if i can somehow disable it to save power during standby.That brings my to my next problem:I want a LED that turns on when the battery is getting low, without drawing to much power by itself. I also want another LED to turn on when the battery is full.Simplest way to do that i could come up with is a micro controller. Since i never had to program one myself i would want to use a Arduino nano R4. The good thing about that is i can power it straight from the battery, no regulator required. But i am worried about its power consumption and how to sense weather or not something is plugged into my power pack or not (to turn the regulator on for example).I am trying to get about a week or real world usage out of a single charge (45 hours powering my device, rest of the time sleeping).To charge the pack back up i want to use a simple LiFePo4 charger and just plug it in using a barrel jack charge port (that part i have figured out already).I could, theoretically, upgrade to a 6 Ah pack to get my desired runtime if necessary, but using a bigger battery just so i can get away with poor optimisation seems too lazy, even for meI take any advice i can get at this point

author: BILLPOD
author_rank: Frequent Contributor
timestamp: October 05, 2025, 01:22:31 pm
content: Good Morning Lukus52, if space isn't an issue, then one of these batteries would work for you.https://www.amazon.com/Mighty-Max-Battery-Replacement-Generators/dp/B07J1H3LLZ/ref=asc_df_B07J1H3LLZ?tag=bngsmtphsnus-20&linkCode=df0&hvadid=79920869053520&hvnetw=s&hvqmt=e&hvbmt=be&hvdev=c&hvlocint=&hvlocphy=105222&hvtargid=pla-4583520395535823&psc=1

author: Lukas52
author_rank: Contributor
timestamp: October 05, 2025, 06:50:14 pm
content: Size isn't that critical, but lead acid batteries bring their own problems (like short lifetimes if not used as per their design).A large battery like this would certainly fix my runtime concerns, but i would still need to somehow regulate the voltage down a bit and deal with a rough charge level indication.I do appreciate the suggestion, thank you