Q-talk 6 - QUICKIE ELECTRICAL SYSTEM REVISITED
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- Category: Q-Talk Articles
- Published: Saturday, 31 October 1987 06:11
- Written by Neal Current
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Earlier readers of QUICKTALK may recall in Issues 2 & 3 that my partner (Richard Chandos) and I reviewed the standard Quickie electrical system. In particular, we focused on what we believe to be a considerable shortcoming in the system as supplied with the kit.
Because the Quickie ignition is dependent upon a battery instead of a standard aircraft magneto system, it is very important that the battery be kept in excellent working order. Our review shows that if the battery voltage should ever drop below about 10.2 volts, ignition cannot be sustained and the engine stops dead. As will be discussed, this type of incident is quite possible for an aircraft in the air.
The ONAN/PHELON alternator and rectifier-voltage regulator (VR) were designed for use with automotive batteries, which are substantially larger than the Quickie battery. These large batteries are safely able to accept much larger charging currents than the Quickie 12N5-3B battery. Exceeding the safe charging limit shortens the battery life and slowly degrades the battery through oxidation of the positive plates until it gradually becomes less dependable and safe. The Quickie alternator will supply almost 10 TIMES the safe charging current to a discharged battery at high RPM operation. This is because the regulator dumps the entire charging current (about 7.5 amps) into the battery until the battery voltage rises to approximately 14.0 volts.
A new battery not in use will self discharge at a rate of 1.0 to 1.5% per day. Therefore, if the aircraft has not been flown for quite a while (resulting in considerable discharge) the battery will be overcharged during high RPM flying for long periods of time until the battery rises to 14.0 volts and the VR automatically cuts back 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. A pilot, throttled back for a long final approach, may not notice the slowly decreasing voltage reading until it is too late and the engine quits.
Our original article made the following recommendations for all Quickie pilots:
1. Using an almost discharged battery and an idling engine on the ground, mark your voltmeter with a red line to indicate the reading at which your engine will fail, should the voltage drop below that line. Then watch your battery like a hawk when throttled back in the air. If the voltage ever approaches the red line, get the RPM up quickly.
2. Externally charge your battery at a rate of 0.5 amps until the terminal voltage reaches 14.0 volts the night before a flight if it has been long enough since the last flight to significantly discharge the battery (say, 30% down or with an open terminal voltage of 12.4 volts or less).
3. Minimize the time at low RPM after initial engine warm-up to lessen battery discharge.
Since more Quickies are flying now, and pilots who aren't careful about keeping their batteries topped off may be having problems with their batteries (not to mention the questionably designed VR's), perhaps we owe it to fellow QBAers to report on our electrical system revisions. Our latest system has a re-wound alternator stator, a capacitor discharge ignition (CDI), a magneto-equivalent capacitor battery eliminator, dual batteries and other back-up features. It has been tested on the ground only (never flown) and works fine. It is much too complex for the average builder to construct, but there is a simpler alternator/VR ignition system that anyone could build. It has complete dual redundancy (for reliability) from the alternator and regulator through the battery. If the builder cannot afford the extra battery weight, a single battery can be used and he can still retain the alternator stator winding and VR redundancy. The stator wires are modified at the end, but it is not rewound. Even without the alternator and VR redundancy 2 batteries improve safety greatly.
To provide others with a clearer understanding of the standard Onan electrical configuration as well as a discussion of the modifications we have researched, copies of our 64-page report are being made available for a small postage and photocopying donation through the QBA. The report summarizes the limitations of the standard electrical system before introducing the different mods we tried. We start with the simplest modifications possible and sketch them, showing progressively more complex alternatives. In each subsequent approach, we trade off reliability versus complexity. Hopefully, readers wishing to investigate the integrity of their electrical system will find the summary of our work valuable, or at least interesting.
Interested builders may contact the QBA for the report, meanwhile, I will be glad to discuss any electrical configuration ideas with individuals who would like to call me at (805) 967-0767.
Neal Current (#399)
6270 Westmoreland Pl.
Goleta, CA 93117
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