- We receive numerous phone calls from owners or pilots who work their own aircraft. To better understand what kind of aircraft alternator is needed, we ask a series of questions:
- What is the part number?
- What voltage is the aircraft?
- Is your alternator belt or gear driven?
- What is the amperage?
If we still cannot get a direct answer or identify the part number, we often jokingly ask “What color is the aircraft?” However, if they land eyes on their alternator, the physical description, and help from an application guide, we can often send them the correct aircraft part.
A typical rant from our aircraft alternator specialist is that automotive parts stores have up-to-date application guides for thousands of vehicles, but the aviation industry is so proprietary and uncommon applications are practically impossible to research. Sometimes the customer is locked into dealing with the manufacturer (if they are still in business) and buying an obscenely expensive part. PMA’s are a godsend! To be fair, safety is the number one concern when substitution is the only alternative (it would seem an industry wide current application guide is in order). As problem solving goes, this phone call is easy to resolve.
- Another frequent phone call is, “I replaced X, Y, or Z part but my charging system still does not work.” Our first question is, what was the original problem?
So many times, it is easier for the aircraft mechanic to guess at what needs to be replaced than to troubleshoot the actual problem. Many experienced mechanics can get the guess right and correct the problem the first time around. Especially if they have seen this exact problem many times before.
However, installing aircraft parts until the problem goes away is expensive. Sometimes during installation of a replacement part another problem is created. The part that was replaced was good but now there seems to be a different problem and the replacement part is suspected! A common myth is that rebuilt aircraft parts are “junk”, which is truly not the case. We see a lot of perfectly good parts returned as defective out of the box.
Our technical assistance team is more confident in helping you troubleshoot when you:
- Have the correct service manual in front of you.
- Have done extensive testing and verifying before calling.
- Have a background in basic electrical theory.
- Have reliable test equipment you can trust.
- All aircraft charging systems need a good battery.
Most Technical Assistance calls concerning charging systems only briefly address the battery. We ask, “How is the condition of the battery?” There is almost always a brief silence on the other end. We say, “Did it test good?” Many Different responses follow, from “it starts the airplane” to a voltage reading someone took. We always must ask if it is a traditional lead acid battery or a nicad type. The test and verification procedure is different for a “lead acid” or AGM battery than the nicad (nickel cadmium). A lead acid battery can be de-sulfated to an extent and charged as a means of restoration. Our own personal view on lead acid batteries is if it is more than four years old or has been fully discharged numerous times, they are suspicious. Nicad batteries can be cycled, and with some special procedures be reconditioned. Nicad batteries also have their own personal drawbacks such as heat and high internal resistance. Two conditions must be established: the battery’s ability to accept a charge and the battery’s ability to operate at its rated capacity. The aircraft charging system diagnostic procedure begins with a fully charged battery and usually that part is overlooked.
Many charging system anomalies are caused by an aircraft battery in poor condition. Sometimes substituting a known “good” battery will change the charging system abnormalities to normal. This will not fix a “no charge” or “discharge” condition, but those situations are somewhat easier to resolve. With the invention of on-board computerized electrical system monitors and retrofitted digital instrument panels, early charging system components can cause what appear to be erratic “readings” that previously suited the battery just fine. However, sometimes there is no problem whatsoever. The aircraft battery is being charged correctly and will supply all necessary electrical power to land in the case of a charging system failure. A known good battery is a cheap insurance policy for many reasons.
This article is meant to help aircraft owners and pilots who work on their own aircraft understand how important it is to research more while diagnosing their aircraft electrical system problems. We encourage them to continue doing so, however it is best to consult with an experienced aircraft mechanic when faced with issues beyond their knowledge. It can help save them money in the long run. Thanks for reading!
Aircraft Accessories of Oklahoma
FAA Approved Repair Station (#RV3R829L)
2740 N. Sheridan Rd.
Tulsa, Oklahoma 74115