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SAFETY INFORMATION and HANDLING PRECAUTIONS for lipo battery
Introduction: Modern Lithium Polymer batteries (LiPo, Li-Poly) are a preferred source of power for fl ying models because of their ability to store and
deliver large amounts of energy from light-weight packs. Performance wise, these new batteries have much more in common with model aircraft fuel
than with any previous battery technology and they deserve similar respect: For safe handling it is useful to Think of Lithium Polymer Batteries as
Fuel.
Treated with respect in knowledgeable hands, Lithium Polymer batteries have been proven world-wide to be a controllable, practical and enjoyable
power source for model aviation.
What can go wrong:
Fire can be caused by: 'Overcharging' (wrong charger or charger setting, unbalanced battery load, charger fouled by poor power supply), charging
a damaged cell or pack and short circuit (including crash damage).
Cells or packs can be damaged by: Over discharging (running 'too fl at' and/or too hot, discharging an unbalanced battery load), short circuit and
crash damage.
The defi nitions of 'overcharging' and 'too fl at' are detailed in the do's and don'ts section overleaf.
With the exception of a very small number of fi res that have resulted directly from crash damage at the fl ying fi eld, fi res have almost always occurred
during charging. These fi res have been almost exclusively permitted by avoidable human error. Therefore the main purpose of this information is:
A.
To provide information that can help you actively avoid a dangerous charging situation.
B.
To provide some standard precautions to limit loss or injury in case a fi re results anyway
Some Lithium Polymer Jargon Explained.
•
3s1p - means a battery pack containing 3 cells in series, 1 cell in parallel. 5s2p means a battery
pack containing 5 cells in series, 2 cells in parallel and so on.
•
Cells in series "s" add to the Voltage (V). For every "s" add 3.7 Volts (nominal). Parallel cells "p"
add to the capacity of the battery in mAh. A "2p" pack made from 2500mAh cells will become a
5000mAh pack, "3p" 7500mAh and so on. The choice of single or multiple "p" packs is a feature
of LiPo (for NiCd and NiMH packs the term "p" is redundant as these packs are invariably "1p")
•
For LiPo packs made with the identical kind of cells, a 3s2p pack can deliver twice the current for
roughly the same duration as a 3s1p pack, or the same current for roughly twice the length time.
•
In our 3s1p / 3s2p example, note that the 3s2p will be about twice the weight and size. For maximum power-to-weight performance in a model,
we would generally choose the 3s2p only when the required current approaches or exceeds the discharge "C" rating of the 3s1p.
•
"C" is a 1000:1 ratio of the capacity of a cell or pack in mAh to a given current in Amps. It is normally used to defi ne maximum current-handling
capabilities for charging (e.g.1C or 2C) and discharging. A large "C rating" for discharge permits high currents from smaller packs, for instance
a 20C continuous rated 5000mAh pack is able to deliver 100 Amps continuously. In this instance, 20C constant should be seen as the maxi-
mum "full throttle" that can be applied ongoing before damage to the pack will be inevitable. Like running a sports car at full throttle all the time,
habitually running a Lipo pack at its maximum C rating is not good practice.
•
3.7V is the nominal voltage for LiPo chemistry. The actual voltage per series cell will increase when fully charged to about 4.2V and decrease to
3.0Vat full permitted discharge.
•
4.25V is a maximum, charging at higher voltage is dangerous. 3.0V is a minimum, continuing to draw operating current (Amps) when the cell
has reached 3.0V will cause rapid overheating and damage.
•
For charging set-up we are principally concerned with the number of cells in SERIES. A 3s2p pack MUST be charged as a "3-cell" lithium poly-
mer (LiPo) pack, sometimes shown as a 11.1V pack (= 3 x 3.7V). We should normally limit the current during charging to a maximum of 1C, for
instance 5 Amps for a 5000mAh pack.
•
The new 20C chemistry can be charged at 2C and above for the fi rst 90% of its capacity, given proper supervision and / or an approprite LiPo
fast charger. For most LiPo chargers on the market, setting the charger to a 1C charge rate should be regarded as good practice.
22 •
An appropriate LiPo charger will normally prevent overcharging if this data is entered correctly.
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