JK-B4A24S 2S-24S 4A Battery Equalizer
4 A constant active balancer for 2S–24S packs, cascade support, manual power switch, Bluetooth app, RS485/CAN optional.
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- Every figure on this page carries a source document and a verification date
Every figure, with its source
Verified against the manufacturer's current documents. Items marked pending have not been confirmed and must not be relied on — they are shown as pending rather than estimated.
| Series range | 2S–24S · Li-ion / LiFePO4 / LTO / Lead-acid |
|---|---|
| Balance current | 4 A |
| Voltage accuracy | ±3 mV |
| External supply | DC 9~100V |
| Cascade | Yes |
| Protocols | BLE, RS485 (optional), CAN (optional) |
| Chemistry | Li-ion, LiFePO4, LTO, Lead-acid |
| Weight (as shipped) | 712 g |
Not sure this is the right model?
Three parameters decide this category, in the order they eliminate options. Check yours against them before ordering — a mismatched board fails under load, not on arrival.
1 · Pack capacity
Balance current has to be meaningful relative to cell capacity. On large cells and large packs a small balancer still works, but correcting a real delta takes days; the high-current class does the same job in hours.
2 · How far the pack has drifted
A pack that is healthy and drifts slowly does not need more current — it needs to be balanced regularly. A pack that sat unbalanced for months, or was assembled from cells at different ages, is the case where current decides whether recovery is practical at all.
3 · Where the unit will live
Higher current means more heat and a larger enclosure. A unit that has to sit inside a sealed battery box is a different choice from one used on a bench to bring a pack back.
Same board, different ratings
These share the enclosure, the terminals and the wiring. What changes is the series range and the current class — so if one of them does not fit your pack, the difference will be visible in the two numbers below.
- JK-B5A24S
5 A constant active balancer for 2S–24S packs, cascade support, manual power switch, Bluetooth app, RS485/CAN optional.
- JK-B15A24S
15 A constant active balancer for 2S–24S packs, cascade support, manual power switch, Bluetooth app, RS485/CAN optional.
Common questions
- How much balancing current does the JK-B4A24S deliver?
- The JK-B4A24S moves up to 4 A between cells while balancing, on packs from 2S to 24S Li-ion. How long it takes to level a pack depends on how far apart the cells are, not on pack capacity alone: a large imbalance on a large pack is what higher balance current is for.
- Which battery packs can the JK-B4A24S work with?
- JK-B4A24S is documented for 2S–24S Li-ion, 2S–24S LiFePO4, 2S–24S LTO, 2S–24S Lead-acid. Both ends of that range are hard boundaries: below the minimum the board cannot read a valid pack, and above the maximum the cell-sense inputs are over their rating. At the top of the range a 24S Li-ion pack sits near 101 V when fully charged, so check the charger output as well as the cell count.
- What can I connect to the JK-B4A24S?
- Communication on the JK-B4A24S: BLE, RS485 (optional), CAN (optional). Anything marked optional is not fitted as standard — if your inverter or monitoring system needs that bus, order it with the board instead of assuming it is there. Cell voltages and settings are readable over Bluetooth from the phone app.
- How do I read a JK BMS model number?
- A model string such as "B2A24S20P" encodes four things. "B2A" means a 2A active balancer (B1A = 1A). "24S" is the maximum series count the board is built for. "20P" is the current class, where 20 corresponds to 200A continuous discharge (10 = 100A, 15 = 150A, 30 = 300A). An "RP" suffix indicates the relay version with a separate port. This is a naming convention only — always confirm the actual rating on the specification table of the specific model, because a board can support a range of series counts below its maximum.
- How much balance current do I actually need?
- It depends on pack size and how mismatched the cells are. A larger pack has more cells to keep aligned and benefits from more balance current; a small pack rarely needs more than 1A. Higher balance current also means more heat and a larger board. If your cells are well matched and new, a 1A balancer is usually enough; if you are reviving an older pack with drift, 2A or more is worth it.
- What is the difference between a BMS and an active balancer?
- A BMS protects the pack: it cuts charge and discharge on over-voltage, under-voltage, over-current and over-temperature, and it reports cell data over Bluetooth or a wired bus. An active balancer only moves energy between cells to keep them at the same voltage. A BMS is required for safety; a balancer is an optimisation. Some JK boards combine both in one unit, which is why the model string contains a balance current (B1A, B2A) as well as a current class.
- Can one BMS work with LiFePO4, Li-ion and LTO batteries?
- Only if the chemistry is explicitly listed for that model. The three chemistries have different voltage windows per cell, so the protection thresholds differ. A board that supports all three selects the profile in the app; a board that supports only LiFePO4 will either refuse to start or apply the wrong cut-offs on a Li-ion pack. Never assume compatibility — check the chemistry field on the specification table.
- What does common-port and separate-port mean on a BMS?
- On a common-port (same-port) BMS, charging and discharging share one terminal pair. On a separate-port BMS, charge and discharge have their own paths, so the charge current can be limited independently — common on relay-based boards. Common-port is simpler to wire and is what most home storage builds use; separate-port matters when charge current must be much lower than discharge current.
How these numbers were chosen
The reasoning behind the figures on this page, written out so you can check the arithmetic rather than take the table on trust.
- Active vs passive balancing: where the energy goesPassive balancing turns excess into heat. Active balancing moves it to another cell. The difference matters more at low state of charge than at high.
- Chemistry decides the settings, not the boardThe same BMS on LiFePO4 and on NMC needs completely different voltage thresholds. Using one profile on the other chemistry damages cells quietly.
Wiring this board
Series count, charge path and pre-charge must match your pack
Wiring a BMS incorrectly can damage cells or create a fire risk. If your configuration is outside the documented range, ask before connecting — a photograph of the pack and the measured cell voltages are usually enough for us to tell you whether it is safe.