Handling,
dismantling, charging or discharging a battery, are hazardous
operations (risk of fire, explosion, etc...) when carried out by
unauthorised personnel. Use described here is out of the scope of
normal use of this battery and you may apply it to your own needs
only if you solely take the responsibility. The author is not
responsible in case of accident.
Note : The tests presented hereafter were carried out in 1996 and 1997. Since then, Lithium-Ion batteries have made a lot of progress and some of them are now (in 2003) able to deliver current up to 5 to 6C continuously (Lithium-Ion Polymer batteries). However, safety rules regarding charging and balancing are still valid and more than ever indispensable. I am still using the Nokia charger to charge and balance my Kokam Li-Po 2S1P 640 mAh packs.
At first
glance, using a Lithium-Ion battery on an Indoor plane could seem a
little bit luxurious. However, a cost analysis in actual situation
leads to the opposite as shown hereafter (prices in US$ are
approximate):
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7 x 50 mAh cells: |
Price: 28 $ |
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Nokia BLJ-2 battery: |
Price: 98 $ | ||||
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Mass: |
28 g |
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Mass: |
32 g | ||||
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Delta-peak Ultra duo plus II charger: |
Price: 300 $ |
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Nokia DTK-9 desktop kit charger: |
Price:118 $ | ||||
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TOTAL PRICE: |
328 $ |
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TOTAL PRICE: |
216 $ | ||||
Moreover, you
need at least three 7 x 50 mAh packs (total price: 84 $) to achieve 3
flights of 3 minutes each during a one-hour session in your favourite
club. As a matter of fact, it is hazardous charging 50 mAh cells,
standard charge type, at more than twice their nominal capacity, i.e.
100 mA (and delta-peak chargers operating at such current are not
very common). While only one 400 mAh Lithium-Ion allows for 4 flights
of 6 minutes each without difficulty!
Nota:
1/ Exceeding 6 minute flights could overloaded the motor...
2/ Without more information, you should not try to draw more than a
0,5 A mean current (0,4 à 0,9 A) from this battery. Only use
it on the XXS Hi-tech fitted with the WES DC 5-2.4 motor.
The nominal
voltage of a Lithium-Ion cell is 3,6 V. Therefore, we only need two
cells to get a 7,2 V battery. During charging, voltage on each cell
must not exceed 4,2 V. While discharging, you must not go below 2,75
V. Hence, the charging equipment must monitor each cell individually
and continuously balance charging between the two cells.
In a Nokia BLJ-2
battery, you have in fact two 400 mAh cells connected in series (with
middle point output) and an electronic control circuit for charging
and decharging each cell.
For Indoor use,
the two cells are separated from the electronic circuit and wired
with a 3-pins connector. The BEC speed-controller will limit the
discharge to 5,5 V (ideally, discharge of each cell should be
monitored). For charging, the electronic circuit is put on the
desktop charger and connected to the cells by a 3-wire cable
(positive terminal, negative terminal and middle point).
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On the right: the 2 cells under a shrinking sleeve. On the left, the electronic circuit of the battery. |
Nota:
Lithium-Ion
technology is quite new and there is large disparity between
samples. Theoretically, life time is about 1500 operating cycles
(500 for Ni-Cd), self discharging rate 5% per year (1% per day for
Ni-Cd). In a word, a very promising technology, when settled...
Various
capacities are available: 400 mAh, 900 mAh, 1300 mAh, 2300 mAh. An
higher capacity should allow for an higher output current but that
needs to be confirmed as these batteries are currently designed for
mobile phones the current of which is about 0,4 A.
These data are
only based on my own experience. If you have further information,
please share them within the Indoor community.
Lithium-Ion
are still expensive, fragile and not very reliable and NiMH batteries
are a good alternative choice. They can be found in standard sizes at
low price but only some of them are suitable for Indoor use. Only
the first model presented below is able to supply our motors with the
right current. Its capacity to mass ratio is good : 34 g for 7
150mAh cells (and 12 $ !!) to be compared to 28 g for 7 NiCd 50 mAh
cells or to 44 g for 7 NiCd 120 mAh cells.
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Name: 15F8H Type: NiMH Size: 6F22 Metal external case Voltage: 9 V Capacity: 150mAh Cells: 7 Mass: 42 g |
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Name: AccuPlus Ultra Type: NiMH Size: 6F22 Plastic external case Voltage: 9 V Capacity: 120 mAh Cells: 7 Mass: 43 g |
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Name: Rechargeable Type: NiMH Size: 6F22 Plastic external box Voltage: 9 V Capacity: 160 mAh Cells: 2 (equivalent to 4+3) Mass: 42 g |
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If you want
to get more information on batteries and learn more about some
strange effects (the "memory effect" is not at all what people
think!), you should visit the two following sites:
For safety
precaution rules when using NiMH batteries, also visit
this page.
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