GEL CELL BATTERIES – RECOVERING LOST CAPACITY By Rod Ruddick I still believe that gliding can be a very safe sport, but I’ve learned the hard way that the mountains can be a dangerous, unforgiving place. For the glider pilot, this means adopting decision-making that is mountain-specific and takes these specialised risks into account. If the majority of your experience has been in a very different environment, such as the flatlands of the UK in my case, you need to be particularly careful. You may be a perfectly safe and competent pilot, but are you mountain-safe? In crisp contrast to the rigidly procedural conduct of scheduled commercial flights that make them the safest possible form of transportation, glider pilots are under a much greater burden to be continually evaluating changing conditions and making safe decisions. An accurate perception of risk is critical. I have a few recommendations to make, and I encourage you to discuss this subject further within your own club. Always get a briefing If you plan on flying into a new area, need a reminder, or will be entering the area in an unfamiliar weather pattern, it’s up to you to take five minutes to get a briefing from someone with greater experience. An excellent rule of thumb is that if the cost of not doing something greatly outweighs the cost of doing that thing, you should always do it. This is one of those cases. Clubs should specifically highlight unlandable areas on charts. It would be helpful for new, visiting or foreign pilots to see all unlandable areas visually represented on local charts. A red border or light cross-hatch would serve as a keen reminder, particularly in the mountains where it is easy to quickly become trapped, even at relatively high altitude. Seen altogether, it might initially be quite surprising how many of these areas exist that we regularly fly over. There is no substitute for training. I’ve read seemingly countless accident reports, but not once has one of these accident reports come to mind while flying. In an emergency situation there is no time to think, and in my case, all of my decisions came back down to basic training and actions I had practiced countless times in the air. I would encourage clubs to incorporate mountain-specific drills into their training programs. For example, setting up a glider in a 1,000 ft/min descent and asking the student to land the aircraft would emphasize how little time there is to react if caught in heavy sink. I can imagine various exercises that could be set up in a motor glider on a calm day in the mountains to illustrate marginal or unsafe situations on a soaring day. Compared to passively reading an accident report and nodding in complacent agreement, these types of drills drive home the message to the student and become an active part of their decision-making process. Update your glider’s safety kit. One unexpected factor in my landing is that no one knew whether I was alive. My radio wasn’t able to transmit and because of my injuries I was limited in my signalling options. Other glider pilots weren’t able to descend low enough to see me sitting on the wing of the glider without ending up in the valley themselves. A set of flares (red, green, white) would have been extremely useful. A signalling mirror would be another useful addition. Leave these items in your glider’s first aid kit next time you go flying. You can read a first person account of the accident on my blog at http://omarama.wordpress.com/2010/12/2/
Wellington pilot Rod Ruddick provides instruction for minimising a common problem with the standard batteries used in gliding. Most glider pilots are aware that, over time, our standard gel cell lead acid batteries lose some of their capacity even using proprietary gel cell chargers. Often the answer is to have a rule such as: replace batteries every two years regardless. This is an expensive option and when your batteries are in special packs in the wings say, it is also very inconvenient. The mechanism causing this slow degradation is sulphation – the formation of lead sulphate during discharge and any delay before recharging which allows the sulphate crystals to harden. Also consider that, after charging, the battery has a small self discharge amounting to a few milliamps which, if you don’t fly for say, three weeks amounts to a small amount of sulphate that becomes permanent. The process is cumulative. One solution to the problem is to have a permanent float charging system in your trailer or hangar. The alternative solution uses a pulse charging technique to break up the sulphate crystals and restore most if not all of the battery capacity. It is used after completing a normal battery charge process and may take several days to complete its work. It cannot recover batteries with a dead cell (10 volts after charging) or batteries which have been overcharged resulting in loss of electrolyte (gassing). The figure shows the pulse charger circuit which I use. The power FET’s are 12 to 30 A devices with a 50V rating and will require heatsinking. A common heatsink for the FETs will suffice as the two drains are connected anyway. Heatsinking is also needed for the RUR820 Diode. The charge pump capacitors are 63V film types as are the snubber caps. Keep battery lead length short to minimise inductance and maintain a short high current pulse. The LED flasher circuit was added to give a charge current indication. LED flash rate is a fraction of the charge pulse rate. Regulation uses a smoothed fraction of the output to control the pulse rate.
December 2010
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