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Practical information about the Multi4 Charger
General information
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Because FMA’s cell balancing technology monitors individual cells, you don’t need to cool
a pack before charging it. Go from flying to charging to flying again without waiting. FMA
cell-balancing chargers are the only ones that can charge a pack immediately after discharge
without damaging the pack.
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Cells in a pack have different voltages when they are discharged. The Multi4 Charger bal
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ances (equalizes) cell voltages while it is charging the pack.
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During charging, cells that charge the fastest are the weakest cells in the pack. At the end of
charging, cells with the highest voltage are weakest. This happens because weaker cells have
lower capacity, and they charge faster than stronger cells.
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If the Multi4 Charger displays LOW VOLT RESTORE, the pack was overdischarged during
its last use. The charger will attempt to repair LiPo cells measuring between 0.5V and 2.7V,
or A123 cells measuring 0V to 2.0V. To avoid additional damage to restored cells, do not
overdischarge a repaired pack.
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By definition, end of life for a LiPo cell is when the cell can only be charged to 80% of its
original capacity rating. The number of charge/discharge cycles a cell undergoes before
reaching end of life depends on several factors, including cell quality, discharge rate, inter
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nal heat generated during use, and other parameters. Cells in an older pack may be more
out of balance, but the Multi4 Charger will still balance them to within 5mV by the end of
charge. For this reason, it may take longer to balance older packs. The charger may show
FUEL=99% for several hours while it is balancing a high capacity (3Ah and up) “veteran”
pack that is severely out of balance, but User Presets might be set to stop balancing after a
preset time. Often, the last few millivolts of balancing take a very long time and do not sig
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nificantly improve overall pack charge or performance.
Charging packs
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You can top off packs, or remove them when they are partially charged. There is no way to
damage a pack when using the Cellpro Multi4 Charger.
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If a pack is at 80% or less of its capacity when connected to an auto-detect speed controller,
the controller may lower its cut-off voltage. This could overdischarge the pack during the
flight. Auto-detect speed controllers should properly set cut-off voltage if packs are charged
to at least 90%.
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To save time, stop charging when the pack reaches about 95% of capacity. That last 5% takes
the longest. By default, User Presets notify you with two beeps when a pack reaches 90% of
capacity (that threshold can be easily adjusted using the Charge Control Software).
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Some cells may sag 0.10V within an hour after charging. This is normal as packs age.
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When charging an A123 pack that has been discharged very low, the charger initially may
not be able to accurately count cells in the pack. To eliminate the possibility of an inaccurate
count, the charger applies current to “wake up” the cells, then recounts.
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Overdischarging an A123 pack below 2.0V/cell will damage the cells (contrary to some
reports). The Cellpro Multi4 Charger requires a minimum pack voltage of 1.5V to activate
charging. If an A123 pack is below this voltage, do not try to repair the pack by boosting
voltage. Even if you manage to repair the pack, it will not have many cycles left and the char
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ger will reject it for multiple reasons (as indicated by displayed safety codes).
