PA28 Battery replacement

: Cory,

: Use a good DVM, like a Fluke 75. Use clip leads to connect it between
: the stud on the starter and the starter frame. Crank (mixture at
: cutoff), and read the voltmeter.

: If your voltage drops below 8V, find out why.

: Repeat the test with the voltmeter leads connected directly to the
: positive and negative poles of the battery. If the battery voltage
: drops below about 10V, then replace the battery. If the battery voltage
: holds above 10V, then use the voltmeter to do a binary search to find
: where the big voltage drop is. Fix that.

: Dont overlook that the voltage drop could be across the ground path
: between the battery neagive pole and the starter frame.

: Personally, I prefer the flooded cell batteries...

Did that this afternoon. It was actually snowing pretty hard here in VA (I'm
outside), so I wasn't too interested in mucking around under the cowling. Put the
DMM's probes *ON* the battery lugs (to eliminate all connections). It read between
9.0-9.35V depending on whether or not it was cranking at a compression stroke or not.
The battery read 12.4V IIRC before I cranked at all, so that'd be about a 75% SOC...
definately good enough to roll over OK.

I have not topped off the battery, but did a 2.5 hour cross country a week ago
and it's been acting up for awhile now. Unless the charging system is broken it's
gotta be the battery. The plane only has a loadmeter, not a voltmeter. Last time I
checked the charging voltage, however, it was fine and the loadmeter's indications
haven't changed since then.

From what I measured, I see about a 1V drop across all the cabling and
solenoids.... probably acceptable for such a long run. I suspect that PA-28's are
extra susceptible to battery strength with such long runs.

-Cory

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* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
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