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Battery Repair |
R. W. Stuart Capacity testing indicated a bad battery in my Chan 02 Futaba FP6NFK xmtr which was detected by charging at 1/10 rate for 24 hours and then subsequently testing as shown below. This is the xmtr used for the 80-4 cycle powered Cub. The xmtr panel meter is used for the test. It measures battery voltage and is calibrated 0 to 100% and should read 100% or better for a freshly charged good battery. The meter is red-lined at 70%, but the xmtr has useable output at 70%. A good battery will hold up for several hours before reaching the 70% point, but I personally would never operate at 70%- why push your luck!! Also an accumulated two hours of flying is more than anybody can handle in a normal flight session. The test is surprisingly simple; just turn the xmtr on and record the meter reading at intervals. The antenna may be stubbed or extended, but a stubbed antenna will not radiate more than 50 yards or so and your constant "on" signal will bother less people. The energy used is the same in either case. If the meter reading starts low or if the rate of meter decline is observable, take readings more often. A good battery will hold the meter reading above 70% for several hours and might hold the meter reading at or above 100% for the first hour. The battery used in the FP6NFK is 9.6 VDC (nominal) 500 mahr, but when newly charged may read as high as 10.5 VDC. It is called a Ppack 8iB and is composed of eight cells stacked two high in four columns. Each cell is wrapped in a heat-shrink tube and two of these cells are connected + to - and end to end, and then slipped into a slightly larger heat-shrink tube, making an assembly two cells long. Four of these two cell assemblies are then organized into a bundle that can be connected in series- both ends of the four two cell assemblies are open so that proper connections can be made. The connections are made by spot welding thin nickle straps from cell to cell. Termination wires are soldered to the series set of eight cells and a "J" plug is crimped to the two wires- red for + and black for -. Finally the whole thing is put into a heat-shrink sleeve with the red and black wires and plug hanging out. This then eventually plugs into a jack that is part of the xmtr. Cell replacement requires locating the suspect cell or cells- any bad cell will read less voltage than the good cells even though the battery is not charged. Two good cells in a two cell pack will read twice the single good cell voltage. First open the battery being careful about shorting cells- even low charge cells have some wallop left. Generally on a discharged battery bad cells will read zero voltage while good cells will read about half volt. Remove the nickle straps between the two cell packs, test each two cell pack and if ok do not open it further. If half bad open it up and find the bad cell and replace it with a good one. The nickle straps can be removed by rolling the strap on the tip end of needle nose pliers- it will peel off of the cell as the spot weld fails. Carefully clean away the burr from the battery top and bottom and tin it with solder- rosin core. Rebuild the good cells into a battery using electrical tape to tie the assembly together, wire in light (20 gage) jumpers as needed and connect the red and black leads of the plug set-- plus red and negative black. Go easy on the tape or the "fat battery" will not go back into your transmitter. All cells are connected in series. The safest approach is to buy a new pack. |
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