On Mon, 26 Jan 2004 22:12:53 -0500, "Charles T. Low"
wrote:

Doug,

Thanks, very helpful.

So, does this seem valid to you? - An accurate voltage reading is a good
indicator of a battery's condition, but specific gravity is better, and a
slow load test (to 50%) is the best? Or are they testing different things,
all of which are important? Could it do well on a load test without good
voltage or sg's?

No. The voltage of 6 cells depleted to 50% of charge, as low as you
should go, is nearly the same as one at 85% charge....when there is no
load. If you're not pulling a constant current through the internal
resistance of the battery, it doesn't drop until the battery is WAY
TOO DISCHARGED.

Specific gravity is the ONLY real way to monitor cell condition and %
of charge because the A-H rating of a battery CHANGES as load changes.
(Notice how the rating printed on the side of the battery is at an X
amp rate.) The more the load current, the lower the amp-hour rating
of the battery really is. But, it's specific gravity ALWAYS tells the
real story. It's just a pain in the ass to measure.....until I found
this Australian instrument I find really neat.

And, what use is a commercial load tester, then? Why do they make them? Is
it better than an sg but not as good as a slow load test?

The load tester INCLUDES that PREDICTABLE current load that pulls down
the voltage from the internal series cell resistance caused by
discharge coating the plates with insulating lead sulphate as it
discharges and a weakening acid concentration as it is used up. It is
useable as a predictor of % of charge, but not as accurate as specific
gravity.'

It is also used in troubleshooting to find that dead cell. When you
load 6 cells in series and one of them is dead, the 50A load really
draws it down hard by the 2V lost in the dead cell. It was never
intended as a charge meter, but a troubleshooting tool.


Larry W4CSC

Is it just me or did the US and UK just capture 1/3
of the world's sweetest oil supply? What idiot wants to
GIVE IT BACK?!!