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Tech Talk - Winterize Your Batteries

From Greg Doster extracted with Permission from Red Scholefield's
"The Battery Clinic" in Nov. 2005 "Model Aviation"

           Whether going into storage or coming out of a hot summer with little activity, your packs need some attention. For us that are lucky to have a nice cool building season it's time to put your transmitter and receiver packs into hibernation. Remove them from the model and the transmitter and place them in a cool place. Like the refrigerator. If your packs are left in the aircraft or transmitter and they develop a short, it can leak and ruin the transmitter as electrolyte creeps along the wire to the pc board. Receiver wiring can also get the "black wire disease"(see below) turning the switch and leads into high resistance paths which can ruin your whole day.

           The state of the charge doesn't matter when you put them away; you are going to take care of that next spring. However, this is a good time to cycle the packs and note the capacity so you can compare next spring to assure that all is well.

           Black wire syndrome,

           Black wire syndrome is an occurrence in battery packs (Ni-Cds or NiMH) where the negative wire becomes corroded (turns from shiny copper to blue black). This is a result of either a shorted cell in the pack, the normal wear-out failure mode of Ni-Cd/NiMH, or cell reversal when a pack is left under load for an extended period.

           The sealing mechanism of a cell depends to some degree on maintaining a potential across the seal interface. Once this potential goes to zero, the cell undergoes what is known as creep leakage.

           "With other cells in the pack, at some potential above zero the leakage (electrolyte) is 'driven' along the negative lead. It can travel for some distance, making the wire impossible to solder and at the same time greatly reducing it's ability to carry current and, even worse, making the wire somewhat brittle.

           "A switch left on in an airplane or transmitter for several months can cause this creepage to go all the way to the switch itself, destroying the battery lead as well as the switch harness. There is no cure. The effected lead, connector, and switch harness must be replaced.

           "This leakage creep takes time, so periodic inspection of the packs, making sure that there are no shorted cells, ensures against the problem. The cells should also be inspected for any evidence of white powder (electrolyte mixed with carbon dioxide in the air to form potassium carbonate). In humid conditions this can revert back to mobile electrolyte, free to creep along the negative lead.

           "Some 'salting,' as this white powder is referred to, does not necessarily mean that the cell has leaked. There may have been some slight amount of residual electrolyte left on the cell during the manufacturing process. This can be removed with simple household vinegar and then washed with water, after which it is dried by applying a little warmth from your heat gun."

           It is also important to note that the electrolyte in Lithium batteries do not seem to be corrosive to copper.

You can read the whole article starting on pg. 151 of the November 2005 issue of AMA's "Model Aviation" or at Red's Site The R/C Battery Clinic

           Greg Doster

           Macon Aero Modelers, Inc.

           Macon Aero Modelers, Inc. would like to extend our thanks to "Red Scholefield" for allowing us to reprint excerpts from his article.    For more information you can reach 'Red' by email at: "red@rcbatteryclinic.com"

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