QuickTalk 3 - QUICKIE ELECTRICAL SYSTEM
- Category: Q-Talk Articles
- Published: Friday, 30 April 1982 07:11
- Written by Jim Masal
- Hits: 1241
(The following is the conclusion of an article by Neal Current and Richard Chandos begun in Issue #2. Neal and Richard are electronics engineers with Santa Barbara Research Center. They have been extensively investigating the present system.)
As was mentioned in the last article, YUASA repudiated its earlier claim of maximum charge currents of 1/10th the amp-hour rating. Since our last article, we have received a lot of detailed data in the form of curves on battery operation from the Director of Engineering at YUASA-GENERAL BATTERY CORP. In brief summary, the most important graphs show that:
a. Battery overcharging significantly reduces battery life, although the way YUASA conducted the tests differs from the way the Quickie system overcharges (and discharges) the battery.
b. Overcharging quickly lowers the water and acid level.
c. If a 12N5-4B battery at 40-45 degrees C. is discharged by 50% at 2.5A for 1 hour and then recharged at 0.63A for 5 hours (cyclically) and every 25 cycles the time is measured to discharge the battery at a 2.5A rate to a voltage of 10.2V, the time decreases from 1.6 hours initially to 0.8 hours in 230 cycles. The 10.2V is just about the minimum at which the Quickie ignition will operate. These test conditions are again different from the way the Quickie system operates, but they are much less damaging to the battery than repeated overcharges of the type that might result in some Quickie operations. Although intelligent Quickie operation might never result in discharge levels as low as 50%, the overcharge that could result (without extreme care) would probably lower the number of operational cycles significantly below the 230 achieved by YUASA.
d. If the battery is 50% discharged at the time it is recharged, significant overcharge will flow for significant time. This will reduce battery life. By how much is impossible to tell since the YUASA data was probably taken with a conventional DC power supply. With the Quickie half-wave rectified AC system, the higher instantaneous current densities for the same average charge current would obviously be harder on the battery than a smoothed DC power supply would.
If the starting, idling and low rpm times are kept very low, the overcharging time when the rpm increases will be minimal before the battery voltage reaches approximately 14.0 volts and lowers the charge current. Although it still overstresses the battery above manufacturer's recommendations, it would not degrade the battery soon. This could explain the realization of 500 flight hours satisfactory service in specific cases. But at a controlled field on a cold day the start time plus low rpm idle and taxi, plus idling during waits for takeoff clearance could remove so much charge from the battery that the longer duration overcharge during increased rpm for takeoff would damage the battery progressively.
As the battery's condition deteriorates due to excessive charging, its susceptibility to degradation increases and a regeneration phenomenon develops, resulting prematurely in the demise of the battery. Therefore, in the Quickie system, the rate at which the battery degrades is dependent on how deeply and how often it is discharged before running up the rpm to dump the full alternator current into the battery. When the battery is not in use it will self discharge at a rate of 1.0 to 1.5% per day. If the plane has not been flown for quite a while or previous discharge has been great, the battery will be over-charged for long periods of time until the battery voltage rises to approximately 14.0V and the voltage regulator automatically cuts back the charge current. The standard Quickie instrumentation does not include an ammeter to monitor the charge current and if it did, it would generally be unacceptable to control the rpm to limit the charge current.
As the battery degrades, it will tolerate less and less total idling time (or time below charging rpm) before it cannot sustain the ignition and the engine quilts. Suppose this happens in the air and an inattentive pilot, used to normal voltmeter readings, does not happen to notice the falling voltmeter reading at low rpm in time to increase the engine speed until the battery charges. His ignition will fail. The windmilling prop might lull him into a false sense of security until he gets so low that when he finally gives it the throttle and realizes he has no engine. It might be too late to pick a safe forced landing spot.
In summary of the overcharging seriousness, we believe that the disparity between the Quickie system and the tests used by YUASA to gather life data precludes estimating battery life for the many possible operating modes to which Quickie pilots will subject their batteries. Suffice it to say that the knowledge that Quickie battery life could be much less than would be expected from an automobile battery if it is not operated intelligently could be valuable to the safety of the pilot. Suggestions for minimizing battery problems are:
1. Find a low battery (not your flying battery) and with a charger applied and removed judiciously, measure the lowest voltage at which the engine will idle. Put a bright red line on the voltmeter at that voltage if on scale. If not on scale, get a voltmeter with which it is on scale so you can mark a red line on it. Then watch the battery voltage during throttled back times like a hawk and if the voltage ever approaches the red line, get the rpm up fast. Then replace the battery if even after full charge it gets close to the red line too soon.
2. Always externally charge the battery at a 0.5A rate until the terminal voltage reaches 14.0V the night before a flight if it has been long enough since the last flight to significantly discharge (say 30%) the battery (open terminal voltage of 12.4V or lower).
3. Minimize the time at low rpm after initial engine warm-up to minimize battery discharge.
By following the above suggestions, the normal pilot should be able to increase the useful life of his airplane's battery while being aware of system limitations. It is hoped that this information will be useful to all Quickie owners to help fully understand their aircraft.
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