"Roger Long" wrote in
news
Returning to the dock after a long period of running the engine, it
goes through the cycle in about the same time it did today so I've
always figured it was a good indictor of a full charge.



About the only thing you can test on AGMs is with a load tester. Even
then, it's hard to know what condition the rolled up plates are really in
and how much of their fixed acid load hass been eaten away into lead
sulphate crystals stuck in the gauze.

Measuring a freshly-charged battery voltage with most of the acid eaten
away shows a fully charged battery, so that's useless. They charge
really quickly, compared to brand new ones, as the available dissolved
lead sulphate quickly replates the lead that's left and converts back to
whatever specific gravity it can produce you can't measure.

One thing you CAN watch if you can charge them individually, or if they
are in parallel and you can monitor each AGM's charging current, watch
for one battery that charges QUICKER than the others. Good batteries
take more time, significantly more time, to recharge at X amps than
batteries with bad cells in them.

The only way I know of really testing gelcells and AGMs is to load test
them with a known load close to their rated load current and time how
long it takes the voltage to drop to a preset level under load. Keeping
a log of these tests can graph its condition over time. The older they
get, the more they sulphate, the less their actual AH capacity....same as
any other lead-acid battery.

Nothing compares to dipping a temperature-compensated proper hydrometer
into the electrolyte of a fully charged wetcell, in each cell
individually, to compare that reading with your history log readings.
Fully charged, cell 3 in battery 4 doesn't come up as far as the rest of
them. It barely makes 1.210 any more. That cell is sulphated, its acid
converted to lead sulphate laying in the bottom of the cell. Battery 4
needs replacing. As battery 4 is toast, anyways, we can SLOWLY add more
acid and balance the cells in battery 4 to regain capacity, at the
expense and risk of eating holes in the plates. We'll replace Battery 4
back home port. Until then, we'll balance the cell gravity and remeasure
it more often. Perks the battery 4 capacity right up out in the
boonies...or at sea.

Keeping the lights on is what it's all about....(c;

http://www.homeenergysystemsinc.com/LeadLifetime.htm
Read the last line at the bottom of this informative webpage from the
home energy pros living off the wind.

THAT will light this thread up.....full charge!

On page 3 of this document:
http://www.homepower.com/files/battvoltandsoc.pdf
is a useful chart of discharging cell voltage vs real battery capacity.

Look at the C/10 rate, capacity divided by 10, which is reasonable.
Let's say the house batteries are 225AH/10 = 22.5A load. With a 22.5A
load, it follows the C/10 curve. 50% discharge is at an easy-to-remember
crossroad of exactly 12.0VDC. So, if you fix the load on a fully-charged
battery at 22.5A, it should discharge the battery to 12.0V, which is 50%
of capacity in 5 hours. (Ten hours at 22.5A = 225AH, 100%
discharged...in theory). This is at a CERTAIN TEMPERATURE! Temperature
of the cells tears AH ratings up...very temperature sensitive. Always
track them at, relatively, the same temperature.

Read the part about internal resistance, which is what causes these
curves. UNloaded, the cell voltage at any charge above dead is nearly
the same...bad cell or good! That's why we LOAD test the battery...The
LOAD current working against the series resistance of the cells, which
increases as the acid is used up, causes the voltage drop. A DEAD cell,
one where there is no acid left, leaves distilled water, which is an
INSULATOR! All its acid has been converted to lead sulphate crystals
which is unrecoverable in the space provided for it under the plates. No
amount of forcing is going to bring that cell back...we only deal with
IONIC lead sulphate in SOLUTION...pulling it apart into lead and
sulphuric acid, again, by electric force in a plating process...charging.



Larry
--
Hand me my hydrometer and please be careful you don't bang it against
anything, thanks.....