In a previous reply, I mentioned my DIY battery project, and a friend was interested. So, I'm starting a new thread to share the assembly process and materials used, essentially making it an open-source project.
I think that when going out for outdoor activities, you need to bring a lot of things. The battery is something that needs to be considered in terms of size and weight, but also safety. Also, considering the voltage of the battery, I don't think large single batteries, lead-acid batteries, or lithium-ion batteries are suitable. Furthermore, since launching and listening are done intermittently, it's unlikely that you will continuously launch, so the capacity doesn't need to be too large.
The final solution selected cylindrical lithium iron phosphate battery cells, and considering the current situation, I believe there are two types of battery cells that are particularly suitable:
1, 15Ah Guoxuan 33140 battery cell
2、 23Ah Ningde 34200 battery cell
The prices of these two batteries are not very high, but there are many negative reviews online. I haven't found any major issues while using them, so the decision depends on your specific needs. There is no such thing as something that is both cheap and good; it always comes down to value for money.
The current output of my radio is around 21A, and for both of the batteries mentioned, full power transmission would require a discharge rate of approximately 1.0-1.5C. Therefore, using just four batteries in series is sufficient. The battery pack can easily handle this load.
Now, let's talk about the various accessories and materials. They are relatively simple and easy to obtain. The main focus of this battery is on safety, affordability, and convenience. To avoid any suspicion of advertising, I won't provide links; instead, I'll only share photos of the products. You can easily find them using the "image search" function on Taobao.
1、Casing
The 80x250x85 size is suitable for the Ningde 34200 battery cell, and the 80x180x85 size is suitable for the Guoxuan 33140 battery cell.
2、 Protective board
Considering the discharge current is 21A, I chose a BMS with short-circuit current protection in the range of 50A-60A. Additionally, since it's an iron lithium battery, the BMS should also have active balancing functionality, which is why I used this particular one.
The board uses an aluminum base, which allows for natural heat dissipation without the need for additional heatsinks. The board's current protection capability is customizable, with a maximum of 100A. For specific functionality details, please refer to the user manual.
3、 Battery cell
The battery cells are arranged in a 2x2 grid, supported by a frame. Ideally, the vendor selling the battery cells should be able to assist with assembly using laser welding, preferably with copper tape connections. Furthermore, it is essential to ensure that the purchased battery cells are properly segmented.
4、Sockets
The brand and model are Amass XT60E-F.
5、 Internal wiring
Protective board B- and battery pack B- are connected using 4 square iron-fluorine coated silver wire. This type of wire is semi-flexible and has a certain degree of plasticity, making it easy to fix. Note that the resistance of this wire will affect the short-circuit protection current of the protective board. The remaining cables use 12 AWG silicone wire, which is soft and easy to route.
6、Battery meter
Because the phosphate iron lithium battery's actual capacity cannot be determined by its voltage, it is best to use a coulomb meter in series between the radio and the battery to easily measure and monitor the capacity, discharge current, and battery voltage. You can find many of these online at seafood markets; they are also open-source products. This one I have has a maximum continuous current of 30A.
7、Radio power cord
The main cable uses 12 AWG silicone wire, with a 30A fuse. This creates a dual-fuse system for battery protection. On one side of the radio connector, 14 AWG wire is connected in parallel and then welded to the main 12 AWG line. Finally, a nylon protective sleeve is applied to the outside of the cable for protection and bundling.
8、Assembly
The overall assembly is now quite straightforward. To protect the battery pack, it's best to use稞纸 or thin EVA foam for cushioning. Once the battery cells are placed in the housing, you need to trim any excess connection keys on the battery holder. The top cover may not fit perfectly; simply use a diagonal cutter to trim the excess parts of the battery holder.
For the installation of the XT60 connector, drilling holes can be done using either an angle grinder or a drill; the material is easy to work with. When welding the connector, it's important to pay attention because the space is quite small. First, weld the cable to the XT60 connector, then insert the cable and battery pack into the housing, then cut the cable according to the situation, and finally weld it to the battery pack.
9、 Charging
I used a 10A charging current, and after fully charging the battery, it was only slightly warm. The charger is based on a model used for RC (radio-controlled) aircraft.
10、 Usage time
In the photo, there is a 15Ah Guoxian battery pack. The operating time outdoors depends on the intervals between transmitting and listening, and is approximately 1.5-2 hours.
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