In short
- A passive balancer burns a little energy from the highest cells; it never moves charge to the lowest one.
- It only works near the top of charge, so a pack that never fills is never balanced.
- Small, slow drifts are its job; a large gap that grows needs a closer look at the cells or the connections.
There are two families of balancers. Active ones move charge from the fullest cell to the emptiest. Passive ones, found on many Daly smart BMS boards, simply bleed a small current from the cells that are highest, through a resistor, until the others catch up. Check your model’s documentation for its balancing current; on passive boards it is usually small.
When it works
Balancing starts above a set cell voltage and when the gap between cells is above a threshold. On a LiFePO4 pack that happens near full charge, when the cells leave their flat plateau. A pack that spends its life between 30 and 90 % gives the balancer almost no time to work.
What it can fix
A gap of a few tens of millivolts at the top of charge, slowly closing over a few full charges: that is exactly what a passive balancer is for. Cells from the same batch drift a little over months, and the balancer keeps them in step.
What it cannot fix
A cell with clearly less capacity will always reach the top first and the bottom first. The balancer trims it at the top every day, but it cannot give it capacity it does not have. Likewise, a cell that only looks low under load is usually a connection problem; no balancer helps there.
Reading the data
Daly Monitor reads each cell and the balancing state, and keeps the gap at the top of each charge. Look at the trend over two weeks: shrinking or stable means the balancer copes. Growing, always on the same cell, means a weaker cell or a loose busbar. Some owners then add an active balancer to the pack; that is a build decision best taken with the cell data in hand.
Common questions
Does Daly Monitor control the balancer?
No. It only reads the BMS. Balancing settings are changed with Daly’s own app or software.
Why does my balancer almost never switch on?
Usually because the pack rarely reaches the voltage where balancing starts. Check whether your inverter stops charging early.
Is a 50 mV gap at the top of charge bad?
Not on its own, especially on a new pack. What matters is whether it shrinks or grows over the following weeks.
