Inside a 12V lithium replacement pack sits a decision most buyers only notice when it goes wrong: which board protects the cells. The Surlon Power 4S 100A BMS protection board is the answer for four-cell LiFePO4 strings, and it is the 12V LiFePO4 battery protection circuit that turns a stack of cells into something an equipment maker is willing to put its name on. It takes over the protection role in lead-acid conversions, where the old block had none of this electronics and the battery compartment was never designed around a circuit board.
The layout is easy to work with. A green PCB carries a large aluminum plate across the power stage, screw terminals for the heavy cables, and connector ports along one edge for the signal side. A printed terminal map runs B-, B1, B2, B3, B4 and B+ down the cell side, with P+/C+, P-/C-, Load and Charger on the output side, alongside RS485 A and B, a Bluetooth module and an ON/OFF switch.
What separates this board from a plain 4S protector is the smart layer. High and low temperature protection sits on top of the voltage and current supervision, so a pack is stopped from charging in cold conditions and from running hot under load. Bluetooth lets a technician read the pack without opening the enclosure, and the RS485 pair carries the same information to a vehicle controller or a system display. Several boards can also serve one installation, with parallel charging and communication keeping the strings coordinated.
Pack assemblers building 12V LiFePO4 replacements buy it, and so do equipment makers moving a product line off sealed lead-acid and service teams repairing existing lithium packs. Because this is a component rather than a finished battery, the useful conversation starts with your pack drawing: cell configuration, continuous and peak load, charger profile, and the space left around the terminals.
| Parameter | Detail |
|---|---|
| Model | BMS04S100A |
| Series configuration | 4S — four LiFePO4 cells in series |
| Pack voltage class | 12V class (12.8 V nominal for LiFePO4) |
| Current class | 100 A |
| Cell sensing inputs | B-, B1, B2, B3, B4, B+ |
| Output terminals | P+/C+ for load and charger positive; P-/C- for load and charger negative |
| Temperature protection | High and low temperature protection on charge and discharge |
| Communication | Bluetooth module; RS485 A/B pair |
| Control | On-board ON/OFF switch |
| Heat spreading | Aluminum plate over the power stage |
| Terminals | Screw terminals for power wiring; connector ports along the board edge |
| Board outline (as drawn) | 180 mm × 80 mm × 15 mm |
Bluetooth changes how a 12V LiFePO4 battery protection circuit is commissioned and serviced. Instead of opening a sealed battery box to probe cell voltages, a technician pairs with the board and reads cell voltages, pack current and temperature on a phone or tablet. On a production line that turns a multi-step bench check into a single pass; in the field it turns a return-to-depot diagnosis into something the service technician can finish on site.
The RS485 A and B pair takes the same data further. Wired into a vehicle controller, a dash display or a data logger, it lets the host system see the pack state and react to it, for example by derating a load or lighting a warning before the board has to disconnect anything. That is the difference between a pack that simply trips and a machine that tells the operator first.
Two things are worth settling early. Ask which parameters are readable and writable over each interface, because the answer depends on the firmware in the configuration you order rather than on the model name alone. Then decide who owns the data: your technicians reading it on a supplier app, or your own system collecting it over RS485. Both routes exist, but the second one needs the protocol documentation up front.
Access also deserves a thought. A board that can be read over Bluetooth can be read by anyone in range who has the right access, so if the pack sits in a shared workshop or a rental fleet, decide who should be allowed to pair and change settings before the machines leave the building.
Not every 12V system stays at one string. Equipment that needs more runtime, or a design that has to keep the battery box shallow, often ends up with two or more 4S strings side by side, each with its own board. This board is built for that arrangement: it supports parallel charging and carries the communication that keeps the strings working as one system rather than as separate batteries that happen to share a cabinet.
The practical benefits go beyond capacity. Serviceability is the obvious one, because if a string fails the technician identifies which board is reporting the fault and replaces that string instead of the whole bank. Manufacturing is the second: a modular layout lets the same board go into a 12V pack today and into a multi-string cabinet tomorrow without a redesign.
Three things make or break a parallel installation. Cable lengths and resistance between strings should be matched, otherwise one string does more of the work and ages faster. The communication wiring and addressing need to be planned before the box is closed, not after the first charge. And the host system should be told what to expect, one aggregated state of charge or one reading per string.
Bring the string layout to us at the quoting stage. As a smart BMS board factory we would rather configure the communication up front than have you rework the wiring after the packs are built.
The board rarely travels alone. Most projects arrive as a pack decision: which cells, which board, and sometimes which finished battery. Three neighbouring products answer questions this product cannot.
If your 4S pack pulls more than a 100 A class board should carry, the 4S150A BMS is the next step up in the same four-cell family, with the same 12V application and a higher current class. Ask for its protection data before comparing, because a current rating on its own does not tell you how a board behaves.
If the project is a 48V pack instead, the ESS 16S100A BMS and ESS 16S200A BMS cover sixteen cells in series at two current classes. They follow the same protection philosophy but they are not the same board, so read their own figures rather than carrying anything across.
And if you would rather buy a finished pack than assemble one, the 12.8V 100Ah LiFePO4 SLA replacement battery is the natural companion: the same four-cell architecture, already built, tested and packaged. Because we run as a smart BMS board factory, the board, the pack and the paperwork come from the same team, which shortens the loop whenever a configuration has to change.
Technical questions reach the people who build the packs. Our engineering group in Shenzhen reviews your device's voltage window, load profile, enclosure space and charger before proposing a configuration; our sample group then builds units so you can validate fit and runtime before production. Cell selection, BMS design and pack assembly stay in-house, with quality checks in process and at final inspection, and a documentation team handling certificates, test reports and shipping papers. When a unit behaves unexpectedly in the field, our engineers help trace the fault and advise on installation and commissioning.
The 4S 100A BMS protection board is built for four LiFePO4 cells in series, the 12V class used in most lead-acid replacements. Each cell is monitored on its own tap from B1 to B4, so the board sees cell-level voltage rather than only the pack total. If you are working on a 48V pack, the sixteen-cell boards in the same range are the right starting point instead.
They share the output port. P+/C+ is the positive terminal used by both the charger and the load, and P-/C- is the matching negative. That common-port arrangement is why the wiring stays short: one heavy pair leaves the board and splits at the equipment. Wire it with the load and charger disconnected, then bring them in after the cell taps have been checked.
The module gives a phone or tablet access to the pack without opening the enclosure, which is what makes commissioning and field diagnosis quick. Which parameters are visible, and which can be changed, depends on the firmware in the configuration you order, so ask for that list rather than assuming it matches another board. Bluetooth also raises an access question, so decide who should be able to pair before the machines go into service.
Yes. The board is designed for multi-module use with parallel charging, and the communication path lets the strings coordinate. Plan two details early: match cable lengths and resistance between strings so the load is shared evenly, and agree with your host system whether it wants one aggregated reading or one per string.
The RS485 A and B terminals carry pack data to a vehicle controller, display or logger over a wired pair, which lets the host react before the board has to disconnect anything. Wire A to A and B to B, terminate the pair as your host expects, and ask for the protocol documentation for the configuration you are buying.
Both charge and discharge are supervised against high and low temperature, which is the protection a voltage-only board cannot provide: it stops a cold pack from being charged and a hot pack from being worked. The exact cut-in and cut-out temperatures, delay times and release conditions belong to the configuration you order and come with the model data.
Treat that as something to verify, not to assume. A 12V LiFePO4 battery protection circuit looks after the cells, but the charger still has to deliver the right voltage profile and stop at the right point for a lithium pack. Send the charger model and its settings with your pack details and we will review the combination before you commit to a configuration.
