Page 51 - Volume 15 Number 9

Aircraft batteries are designed to have less weight than a car battery and are therefore a little more...delicate
43.3g) follow all the procedures for your battery.
The typical flooded lead-acid 12- or 24-volt aircraft battery is not a “no-maintenance” item. Can you get an idea of the health of an airplane battery with one of those turkey- baster things (hydrometer) like you can a car battery? Yep, you just need to know the specific gravity readings to look for; the Duke’s at 100 percent charge (26.4v) is 1.320 specific gravity. A 75 percent charge at 25.4v is 1.270. The color markings on a hydrometer show above 1.260 in the green band and 1.275-1.300 is considered fully charged. Don’t forget there is an alternator or generator, as well as some type of voltage regulator in the battery system, too. The regulator must be set to the correct voltage within tenths of a volt. A bad voltage regulator once caused most of the battery acid to blow out the overflow drain line in my C-150; I could smell it in flight and it was my first emergency landing. Your battery is supposed have an annual capacity check as well. The tester is expensive (even for shops), so a lot of aircraft batteries are never tested.
Desulfator
I read a feature a few years ago in Aviation Consumer about a contraption called a desulfator. Allegedly it could not only charge the battery, but potentially “re-condition” a lead acid battery (both sealed and wet cell) by removing sulfates and thereby increasing the specific gravity of the electrolyte. The article gave an address for a guy who would explain how to build one. And no, he wasn’t a pawnshop operator named Jeebs.
A year or so later (June 2007) they published another story reviewing several off-the-shelf desulfators. One company was offering a big discount if you shipped them an old charger for exchange, so I did. I bought one 12-volt desulfator for
of events was starting to raise the little hairs on the back of my neck. Right motor wouldn’t start, rushed to make the trip happen anyway, now the battery is dead? This is too many bad things in a row. So we remove the battery and take it home to have it professionally charged while I try to figure out what I did wrong; and figure it out I do.
Although this is a battery story and not a magneto story, suffice it to say that on a Duke the magneto retard points and starter vibrator function through the p-lead circuit to retard the timing during the engine start. I would find out several months later that the p-lead was loose at the mag. Remember, the p-lead was only loose, not disconnected; the worst type of problem to diagnose: intermittent. The problem lasted well into my next battery’s life until we figured it out. I ended up running the battery down that morning trying to start the right motor. Trip cancelled, lesson learned.
Lead-acid batteries aren’t as bulletproof as we’re led to believe in our automotive upbringing. Aircraft batteries are designed to have less
weight than a car battery and are therefore a little more...delicate. So care and feeding is important. For example: When you buy a brand new lead acid airplane battery it comes with special charging procedures. They matter (constant current with increasing voltage then constant voltage/potential with decreasing current). You’re not supposed to fly with a weak battery and assume the airplane system will charge it in-flight; it may not. Your aircraft’s charging system is constant-voltage and will re-charge a discharged battery at an excessive rate; possibly overheating or destroying the battery. When your plane sits for a while, the battery will need charging. That’s important, too.
Checking the water (electrolyte) level only once a year during the annual is not good enough. When you add distilled water, you should charge the battery. When you charge the battery you should charge it out of the plane/vehicle (the charging process produces O2 and H). Your battery likes 80 degrees Fahrenheit, if it’s warmer or colder there are considerations. The list goes on, and on. If you’re doing this yourself, (FAR
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