South Leicester Aeronutz website.
Lithium Polymer Cells
We are assuming that the manufactures reccomendations for use are conservative.
For example we use 50mA Ni Cd cells way beyond what the manufactures data sheet suggest.So, now we have these new lithium polymer cells we are "finding our way" by experience.
At present we are charging them at less than 1C, where C means the capacity of the cell. So with a 140mA hr cell we are charging at less than 140mA.
It is thought that the cells should not be run down below 3.0v and a load of 1 Amp should not be exceded for the 140mA hr size cell.
In general the less load you put on the cell the better.A good combination seems to be the motor supplied for the "B2" park flier (sold as spares) with a Union 80 mm prop fitted directly too it. This combination with one Lithium polymer 140mA hr cell weighs the same as the KPOO and U80 with two 50mA Ni Cd cells, as used in Mark's direct drive Corsair (see video clip on Indoor R/C web page) The KP00 produced about 7g of thrust while the B2 motor combination produces 10g of thrust and about 650mA for the first few seconds of its 15 minute run. In fact you cant use a KP00 direct drive with one polymer cell as it uses too much current, use a geared one instead.
Caution!
Lithium cells must be charged properly, using a proper lithium cells charger, otherwise it might explode. Flitehook sell a one by Potensky that can do two cells in series while Bob Selman in the US has one for charging one cell.
Don't not connect the two terminals of the cells together (short ciruit) otherwise the cell may explode. Make sure the battery is properly stored when not in use and fixed securely when inside the plane. Put tape over the terminals to avoid short ciruits and use black and red wires to show the positive and negative leads.
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Graham Stabler has 100 of the super 140mA hr lithium Polymer cells. He will share them with you at a rate of £7 each if you live in England, which seems very reasonable to me. They weigh about as much as one 50mA Nicd's but provide lots more voltage, about 3.5v with a one 0.8 Amp load. See his little web page for more details hereMatt has found the terminal tabs a difficut to fix to and sends us the following advice:
"Kokam Li Poly cells have aluminum tabs on the positive terminals.
I have some thoughts on this:
1. If you solder the tabs, us clamping tweezers to heat sink the tab,
between the solder spot and the cell, to prevent the heat from
destroying the plastic seal around the tab were it goes into the cell.
2. You should consider welding wires to both tabs, since welding
doesn't put much heat into the tabs.
3. Spot welders work well, 8-50 Watt seconds depending on wire gauge.
4. I have found that welding stranded wire onto the tabs works well,
use wire with very fine strands, and non-tinned wires if possible.
5. I was also able to weld on the wires using a resistance soldering
tool that is relatively cheap $450US. This is from Micro Mark hobby
supply. I used the 250W unit with the tweezer tip. I pulsed the
main power while the wire was clamped to the tab with the tweezer
tips. The ad from the catalog is attached. It is basically just a
250W step down, adjustable transformer, giving lots of amps. The
optional foot switch would be a good accessory.
6. The welds made with the resistance soldering gadget were equal
quality to the welds made with our Unitek spot welder.