“My Mechanic just told me I need a Stress Test ???"
In an earlier post we already determined that the specific gravity of our battery was within normal parameters. To recap, the specific gravity we tested indicated on a cell-by-cell basis that our battery was reasonably healthy. It was in an acceptable range for a wet cell battery roughly 1.255 - 1.275 limit depending on ambient temperature for a wet cell battery with a few years under its belt. So why have I noticed my engine turning over a bit sluggishly the last few times I went out and started her? If my specific gravity is within limits why do I need to look further at its overall health? I certainly don’t want to get left high and dry after flying out in search of the best $100.00 Saturday afternoon hamburger I’ve ever eaten this side east of the Mississippi.
In comes the need to “stress test” your battery when it starts giving indications of not being at its best. Your mechanic will want to perform a load test to see how resilient it is while being subjected to the stress of starting under hostile conditions like the cold temperatures it would be subjected too on a January morning. A good carbon-pile battery load tester will actually subject the battery to the same conditions your battery would be subjected too once you turn the ignition key and the starter energizes. By subjecting the battery to this “load” for about 15 seconds you then have the ability to analyze the residual voltage remaining from a calibrated chart immediately at the conclusion of the test.
This reading will give you a go-no-go indication of just how much residual power is left after being subjected to a very realistic simulation of starting conditions. A carbon pile load tester literally sucks roughly the same amount of current out of your battery while energized during the test as does the starting sequence. A good load test is probably the most decisive test your mechanic can run on your battery to determine its overall health and insure the likelihood of it not letting you down at the most inopportune time.
There are many reasons an aircraft battery can fail. Incorrect installation, loose battery hold-downs cause excessive vibration which can result in damage to the plates. Improper maintenance, low electrolytic fluid and corrosion on battery connections can greatly reduce battery life and affect battery performance. Overcharging, caused by a high voltage regulator setting or incorrect battery charging can cause excessive gassing, heat and water loss. Undercharging, also caused by faulty voltage regulation, or sitting in a low state of charge for too long. Undercharging can cause lead sulfate to gradually build up and crystalize on the plates and greatly reduce the battery’s capacity and ability to be recharged. By letting your mechanic add the battery “stress test” to the battery preventative maintenance functions he performs will greatly reduce the chance of being stranded at your favorite FBO on a Sunday afternoon when the closest maintenance relief will cost you double time to come in that day. Triple time if it happens to bite you on Super Bowl Sunday.
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