Battery Power System - Page 1
Forum section: electronics / projects

author: chinneii
author_rank: Newbie
timestamp: August 12, 2025, 08:53:58 am
content: I am currently designing a battery powered system to power a load with a power consumption of up to 100W at 24VDC.I need my system to be powered by a wall outlet but when the outlet is unplugged, which to the battery.Is there any suggestions on how I can achieve this?I have thought of using BMS modules that can help power the load while simultaneously charge the battery, but am unable to figure out fundamentally how I can do it.I have a rough sketch of it here:

author: brucehoult
author_rank: Super Contributor
timestamp: August 12, 2025, 09:21:06 am
content: If you can connect the charger to the battery terminals, or you can connect the load (with regulator) to the battery terminals, then you can simply connect both at the same time and all is fine.BMS is a problem for the battery itself. It really doesn't matter whether the battery is a lead/acid (and the charger is a smart lead/acid charger), or the battery is LFP and had a BMS between the battery and the battery terminals.

author: Cpuch22
author_rank: Contributor
timestamp: August 12, 2025, 11:45:30 pm
content: Search for hot swap voltage controllers.Here are some by TI with integrated FETs they also have some with external FEThttps://www.ti.com/power-management/power-switches/efuse-hotswap-controllers/products.html#339=Internal&849=40%3B110&sort=-1;asc&

author: Cpuch22
author_rank: Contributor
timestamp: August 13, 2025, 12:36:05 am
content: For an example of the hot swap controllers in use, check out my schematic in this thread (scroll down to the last post which has the most recent schematic revision). I'm doing pretty much exactly what you want to do; with priority power path to the power supply and secondary power path to the battery. My version is lower voltage and power output than what you want to do, but there are similar IC's that will handle your requirements.https://www.eevblog.com/forum/projects/precision-calibratior-project-(voltage-and-current)-work-in-progress/25/

author: themadhippy
author_rank: Super Contributor
timestamp: August 13, 2025, 12:44:28 am
content: type of battery? could be as easy as a resistor and a diode or 2

author: ledtester
author_rank: Super Contributor
timestamp: August 13, 2025, 02:07:09 am
content: There are numerous designs for a "Wifi router UPS" on youtube which seems to be the kind of device you are interested in. For example there's this one:https://www.eevblog.com/forum/chat/pls-review-my-diagram/msg5562483/#msg5562483

author: chinneii
author_rank: Newbie
timestamp: August 13, 2025, 09:33:09 am
content: Hi all, thanks for all the recommendations, since my application requires me to avoid PCB designing completely, I have come up with a workaround, but I am unsure if it is feasible for this application.The design basically incorporates a DPDT relay that has one terminal connected to the wall outlet, and one terminal connected to the relay, with both ends connected to the load. The NC side is connected to the battery. The battery is also connected to a charger attached to the wall plug connection. I plan to include diodes to prevent backflow. Is there any risk in doing it this way? It is quite a simplistic solution that I came up with, which rouses some concerns on the safety department.Thanks again to everyone

author: Cpuch22
author_rank: Contributor
timestamp: August 13, 2025, 10:03:23 am
content: You will need some beefy diodes. You will have a constant 3W of power dissipation in your diodes with 100w of power draw. Also you will need some large capacitance to prevent the system from turning off when the relay switches since relays switch much slower than a mosfet for example.

author: chinneii
author_rank: Newbie
timestamp: August 13, 2025, 10:10:09 am
content: If my system does not focus on being uninterrupted, but mainly just availability of switching from one power system to another, would this suffice? I have drawn up a schematic on this.1. What am i missing? Any safety precautions except fuses that were not incorporated?2. Is there any off the shelf improvements that can be done with items in a plug and play type manner, including some basic soldering is fine.3. any critical design flaw?some notes:1. I do not need it to maintain power when switching power sources, but I need to ensure when switching sources no damage is done to the load2. It is a simple, low cost system to be built as a prototype

author: ledtester
author_rank: Super Contributor
timestamp: August 13, 2025, 10:15:26 am
content: Quote from: chinneii on August 13, 2025, 10:10:09 amWhat is your load?

author: chinneii
author_rank: Newbie
timestamp: August 13, 2025, 10:19:28 am
content: My load is a Zebra Fx9600 (78W), LED and a few DC power fans

author: Cpuch22
author_rank: Contributor
timestamp: August 13, 2025, 02:03:13 pm
content: It's probably good to install a fuse at minimum on the L and N and maybe some MOVs, potentially a diode across the relay coil to protect against inductive spikes.