BMS
BMS questions
These answers explain how to judge a BMS. They deliberately avoid quoting specifications for particular models — those belong on the product page, where they can carry a source.
Reading a model number
The three questions that get asked from the label on the board, and why none of them can be answered from the label.
- What does the "S" in a BMS model name actually mean?
- It refers to the number of cells in series, not the pack voltage. A 16S board monitors sixteen cells; the nominal pack voltage follows from cell chemistry — roughly 51.2 V for 16 LiFePO4 cells and 59.2 V for 16 NMC cells. The two are not interchangeable, and the board must be rated for the chemistry you are using.
- Can I read the current rating off the model number?
- No. Model naming conventions are not a specification. Boards with similar names can differ in continuous rating, peak rating and shunt range, and the naming scheme has changed across product generations. The only reliable source is the current manual for that specific model.
- What is the difference between continuous current and peak current?
- Continuous current is what the board can pass indefinitely without exceeding its thermal limit. Peak current is a short-duration allowance, typically for motor or inverter inrush. A peak figure without a stated duration is not a specification — 300 A for 100 ms and 300 A for 10 s describe very different hardware.
Topology is per model, not per family
Port arrangement decides how your charger and load connect. It is not something a product family has — it is something one board has.
- Common port or separate port — which do I need?
- In a common-port configuration, charging and discharging share the same terminals. In a separate-port configuration they have distinct paths, which matters when your charger and load are wired independently or when you need to limit charge current separately. This is a property of the specific board, not of a product family, so it must be checked per model.
What "pending" means, and what needs certification
The two questions about this site itself: why a value can be absent, and what must be verified before a claim about certification is published.
- Why does the site show "pending" instead of a number?
- Because that number has not yet been checked against the manufacturer's current document for that model. We would rather show that a value is unknown than publish an estimate that you might size a battery pack around. Every published value carries a named verifier, a source document and a verification date.
- Does a BMS with Bluetooth need separate certification?
- Yes, in both major markets. In the United States a Bluetooth device is an intentional radiator and needs FCC certification with an FCC ID. In the European Union it falls under the Radio Equipment Directive, which since 1 August 2025 also requires cybersecurity assessment under Article 3.3(d)(e)(f). We publish certification status only after verifying the certificate holder, the covered models and the validity period.
Wiring and safety questions
The one question in this list is answered directly. Everything involving a live connection goes to a person, because the cost of a wrong answer is hardware or fire.
- Can I use a BMS above its rated series count "just for testing"?
- No. Over-voltage on the monitoring inputs is not a graceful failure — it can destroy the board and, worse, leave a pack without protection. If your configuration is outside the documented range, ask us before connecting anything.
Not answered on this page
Wiring order, pre-charge behaviour, fuse selection and anything involving mains-connected equipment are escalated to a technician rather than answered in a FAQ. A wrong answer here damages hardware or creates a fire risk.Ask a person.
Document requests — CE or UN38.3 papers, who issues them and when they can be supplied — are answered on the compatibility guide.