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(Richard Chandos and Neal Current (#399) are electronic engineers at Santa Barbara Research Center and have been actively investigating the characteristics which could contribute to shortened battery life and possible in-flight ignition problems.)


"The Quickie electrical system consists of a 15 amp alternator, a 15 amp (ONAN 10640-00-A, Phelon 191-1206) recitifier-regulator which has voltage regulation but no current limitation and a 12 volt 5 ampere-hour (12N5-38) battery with a voltmeter but no ammeter. The alternator will not charge the battery when the engine is idling.

The ONAN/PHELON alternator and recitifier-voltage regulator were designed for use with automotive batteries, which are substantially larger than the Quickie battery. They are rated at a reserve capacity between 105-135 minutes at 25 amps and 80 degrees. These ratings are equivalent to about 44-56 amp-hours for 1-3/4 to 2-1/4 hours. The point of this is that the battery for which the ONAN charging system was originally designed is rated at discharge currents approximately 10 times greater than the current at which the Quickie battery is rated. The large batteries are able to safely accept much larger charging currents (proportional to discharge current ratings) than the Quickie battery. The maximum charge current is not usually emphasized because exceeding it by reasonable amounts usually does not result in immediately catastrophic failure of the battery. But exceeding the limit does shorten the battery life and insidiously degrades the battery through an oxidation of the positive plates until it gradually becomes less dependable or safe long before it should. This could be disastrous for a Quickie with no magneto and a battery dependent ignition.

A technicality that should be mentioned about the ONAN system is that it is a half-wave rectifying system. This means that only the positive half cycle of the AC alternator charges the battery and the negative half cycle is wasted (not used). If the alternator current output rating is specified to apply to the current into the battery as indicated by a DC ammeter, the true rating of the Quickie system is actually 7.5 amps, rather than the 15 amps rated by the specifications. This is still greatly in excess of the maximum specified battery current to be discussed later.


Most pilots are conditioned to thinking in terms of a magneto with which the battery condition is relatively unimportant. Pilots finding a low or dead battery in a Cessa 150 will just prop it and let the alternator bring the weak battery's voltage up enough to run the radio and instruments which are normally light loads. Then they go flying with the weak battery. This is no problem with a magneto for ignition, but could be dangerous in a Quickie at low rpm with a weak battery overcharging. We realized there was a caution in a Quickie Newsletter to keep the battery in good condition, but when a battery is too weak to fly is a difficult question to answer.

The QAC-recommended 12N5-3B five amp-hour battery is a liquid electolyte, lead (sulphuric) acid motorcycle battery which is commonly abused in some applications because it is mistakenly thought to be capable of accepting heavy charge currents. However, YUASA GENERAL Battery Corp. of Reading, PA stated in a phone call (and later repudiated) that the maximum charge current of their 12N5-3B batteries must be limited to 1/10th the amp-hour rating (0.5 amps) if the battery is significantly discharged. The maximum charge current increases to three times that value if the battery is discharged by only 30% when the throttle is advanced. In other words, if the battery still has 70% of its charge left it can be safely charged at a rate of only 1.5 amps maximum without danger of shorting some cells or degrading the lifetime of the battery. Note that if the battery is discharged by more than 30%, the maximum charge current should be only 0.5 amps.

The ONAN/PHELON alternator will supply much more current than the maximum specified 0.5 or 1.5 amps because with the battery partially discharged, until the battery voltage rises to approximately 14.0 volts, the current is limited only by the alternator current (approx. 7.5 amps). During starting, idling, or throttling back for a long glide the battery could be discharged to where 70% or less of its capacity remains. The pilot should limit this type of flying or pay special attention to the voltmeter.




You can order a PDF or printed copy of QuickTalk #2 by using the Q-talk Back Issue Order Page.