描述
A battery pack is only as strong as its weakest cell, and the weakest cell gets weaker every cycle. Capacity decays at slightly different rates across a pack, and once the spread widens the BMS starts reading a single low cell as a whole-pack problem. It cuts in early on charge, cuts out early on discharge, and the usable capacity of a pack you already paid for shrinks month by month.
The Cell Keeper attacks that drift directly. It is an active equaliser rather than a passive bleed resistor, so charge is transferred from the higher cells into the lower ones through a capacitor bank instead of being burned off as heat. Balance current runs from 0 up to 5.5A, and it drops as the pack approaches balance, which is the behaviour you want: fast correction when the spread is wide, gentle correction when the cells are close. Accuracy is held within 5 millivolts.
Coverage runs from 3S to 17S in the standard editions, with a 10S to 24S smart edition rated at 4A for larger packs, and the working range of 1.8V to 4.5V per cell covers ternary lithium, lithium iron phosphate and lithium titanate. Editions marked LTO are for lithium titanate packs only, while unmarked editions suit ternary lithium and LiFePO4. Recommended pack capacity is 60 to 300Ah. A manual sleep switch and under-voltage sleep protection both cut standby draw below 0.1mA, so a stored pack does not flatten itself while it waits.
Balancing will not add capacity to a pack. It stops you losing the capacity you already bought.
How Active Balancing Works
- ✦ Active capacitor energy transfer instead of heat-burning passive bleed
- ✦ Balance current from 0 to 5.5A, reducing automatically as the pack approaches balance
- ✦ Balance voltage accuracy held within 5 millivolts
- ✦ Coverage from 3S to 17S, plus a 10S to 24S smart edition rated at 4A
- ✦ Working range of 1.8V to 4.5V per cell for ternary lithium, LiFePO4 and LTO
- ✦ Ultra-low internal resistance MOS on a 2OZ copper PCB
- ✦ Manual sleep switch and under-voltage sleep protection below 3.0V, standby under 0.1mA
- ✦ Recommended for packs of 60 to 300Ah, CE certified
Electrical And Build Details
- Type: Active battery balancer, capacitor energy transfer
- Balance current: 0 to 5.5A, self-reducing toward balance
- Balance accuracy: Within 5mV
- Coverage: 3S to 17S standard, 10S to 24S smart edition at 4A
- Working voltage: 1.8V to 4.5V per cell
- Battery chemistries: Ternary lithium, LiFePO4, LTO (LTO editions for lithium titanate only)
- Recommended pack capacity: 60 to 300Ah
- Quiescent current: About 12mA
- Sleep current: Under 0.1mA with manual sleep switch
- Under-voltage protection: Sleeps below 3.0V, standby under 0.1mA
- Board: 2OZ copper thickness, ultra-low internal resistance MOS
- Certification: CE
- Battery included: No
- Charger included: No
Where Pack Drift Costs Real Money
The Cell Keeper is fitted by people running packs that cost real money to replace. A solar or off-grid bank of lithium iron phosphate cells benefits most, because those packs are expected to last a decade and small drift compounds across that time. Electric bike, scooter and golf cart owners use it where a replacement pack is hundreds of dollars. Diy pack builders fit it from the start rather than discovering imbalance later. In each case the arithmetic is straightforward: the balancer costs a fraction of the cells it protects, and the pack keeps delivering the capacity it was specified for.
Matching A Balancer To A Pack
Q: What is the difference between active balancing and a conventional BMS?
A conventional BMS often balances passively, burning excess charge from high cells as heat. This unit moves that charge into the lower cells by capacitor transfer, so the energy stays in the pack and the correction is faster.
Q: Which edition do I need for my pack?
Match the series count first: 3-4S, 6-8S, 12-16S and 17-21S cover the standard list, and the Smart 10-24S edition at 4A covers larger packs. Then check the chemistry note, because editions marked LTO are for lithium titanate only.
Q: Which chemistries are supported?
Ternary lithium, lithium iron phosphate and lithium titanate, working across 1.8V to 4.5V per cell. Unmarked editions suit ternary lithium and LiFePO4.
Q: Will it drain my pack when the vehicle is parked?
No. The manual sleep switch and the under-voltage sleep protection both drop current below 0.1mA when the balancer is idle.
Q: How large a pack can it serve?
Packs of 60 to 300Ah are recommended. The balance current is sized for correction, not for charging, so the pack's own charger still does the charging.
Q: Does the balance current stay at 5A all the time?
It reduces as the cells converge. The closer the pack is to balance, the smaller the current, which keeps the process gentle on cells that are already close.
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