Technical centre
BMS Technical Centre
How a battery management system is specified, and which numbers actually determine whether it fits your pack. This section explains concepts; the catalogue lives under Shop.
What a BMS actually does
A definition first, before any parameter. The two questions below are the ones people type into a search box; each is answered directly, then the rest of the page explains how to check the numbers.
- What does a BMS actually do?
- A battery management system is the protection and monitoring board between a lithium pack and its charger and loads. It watches each cell voltage, limits charge and discharge when a cell goes outside its safe window, balances cells so they stay at the same state of charge, and reports or cuts off through a communication interface. It does not create capacity, and it does not decide the pack chemistry — those choices are made before a board is selected.
- Common BMS questions
- Work out the size you need
- Which numbers decide whether a BMS fits my pack?
- Four of them: the rated series range, the continuous current, the peak current together with its duration, and the port topology. Each has to come from the current manufacturer document for that exact model, not from the model name and not from another listing. A figure without its context is not a specification — a peak current with no duration and a series range read out of a part number are the two most common ways a wrong board gets chosen.
- Compare verified specifications
- Sizing calculator
Where to read next
Two pages: one compares parameters across models, one explains the concepts behind them. Both are written to be checked against a source document.
- Specification comparison
Side-by-side series range, current ratings and protocols. Populated only with verified values — a blank cell is a statement.
- BMS questions
Series count, common-port vs separate-port, protocol compatibility, balancing behaviour.
The four numbers that decide fit
These are the parameters that most often cause a wrong selection. Each must come from the manufacturer's current document for the specific model — not from a model name, and not from another listing.
| Parameter | What it constrains | Common mistake |
|---|---|---|
| Series range | Which pack voltages the board can monitor and protect. | Reading the series count out of the model name — naming conventions are not reliable. |
| Continuous current | Sustained load the board will pass without overheating. | Confusing it with the protection trip threshold or the shunt range. |
| Peak current and its duration | Short inrush from motors and inverter start-up. | Quoting a peak figure with no time attached — the number is meaningless alone. |
| Port topology | Whether charge and discharge share a path (common port) or not. | Assuming the topology carries across a whole family. |
What we will not do here
We do not publish ratings inferred from model numbers, from marketplace listings, or from a previous manual revision. Where a figure is not yet checked against the current manufacturer document, it is shown as pending rather than estimated.
This makes the site less complete — deliberately.
Active vs passive balancing
Balancing keeps every cell in a pack at the same voltage. The two methods do it differently, and the right choice depends on pack size and how the pack is used — not on which sounds more advanced.
| Method | How it works | When it pays off |
|---|---|---|
| Passive balancing | Bleeds the highest cells by burning off a little energy as heat. Simple, low cost, and enough for small, evenly matched packs. | Small packs (4S–8S), low current, cells bought together and kept at a similar state of charge. |
| Active balancing | Moves energy from higher cells to lower ones, so less is wasted. Keeps a large pack tighter across a long idle. | Larger packs (16S–24S), mixed or aged cells, or systems that sit partly charged for long periods. |
See the active balancers we listBalancing questions answered
Where to go next
Sizing, application and the catalogue each answer a different part of the same question.
- Sizing calculator
Turn chemistry, series count and load into the voltage window and continuous current your pack needs.
- BMS by application
What RV, off-grid, marine and mobility builds each demand from a board.
- Smart BMS catalogue
Boards with verified series range, continuous current and port arrangement.
- How to read a BMS model number
Why the model string is not a reliable spec source — and what to check instead.