Roger Long wrote:

Should I leave the charger on for some period of time regardless of what the
LED's are doing?

Giving a simple answer is not easy, Roger. But my answer is Yes, leave
the charger in float as long as possible.

Are you hoping to get maximum longevity from your AGM batteries? Or
just acceptable performance?

Unfortunately, experts disagree on exactly how to get maximum longevity
from AGMs when used with the use pattern you describe. The experts I
consulted for my Concorde AGMs said best practice would include:

· when possible, recharge every day the battery bank is used and as
soon as possible after use;
· when not in use, maintain the bank at 100% State of Charge by
continuous float charging;
· avoid Depths of Discharge approaching or greater than 80% of
amp-hour capacity;
· avoid recharging after shallow discharges of less than 10% of
capacity; and
· never discharge the bank to or below 11.8 volts.

If not keeping the bank on float when the boat is idle, the experts
advised me to leave the bank float until the charge drops below 1 A (my
bank has a nominal amp-hour capacity of 500 A-hr). That's a longer
float than one would specify for conventional wet lead-acid batts.

In addition:
· equalise the battery when the Charge Efficiency Factor falls below
90 or every three months.

AGMs have a lower shelf discharge than conventional wet lead-acid
batts, so you should not be surprised that your charger brings you bank
up to float quickly after a few months of non use. The first question
for you, given the above, is whether you should charge the battery bank
(ie too shallow a depth of discharge) after a few months of non use.
And question two for you is whether you should add a battery monitor
that delivers you information about the depth of discharge and the
current going into the battery.

As to when your particular charger transitions from acceptance to
float: check the specs. Some chargers impose a time limit on acceptance
for AGM and conventional wet lead-acid batts of 1 hour and 3 hrs for
gel batts. Other chargers have a predetermined point on the acceptance
curve (ie during the acceptance phase, the charger holds the voltage
across the bank constant - usually at or close to the bulk charge limit
- and slowly drops the current flowing into the bank. When the current
has dropped to a preset value (either preset by the manufacturer or by
you when you matched your charger to the amp-hour capacity of your
bank), the charger transitiions to float. That transition point is
usually 5 A, 10 A, 15 A - whichever is appropriate for your battery
bank or for what the manufacturer guesses is the likely capacity of
your battery bank. So question 3 for you is whether you should care
about the float LED or check the float charge instead and only turn off
the charger when it has dropped to a low value (eg 0.2 A, which is what
I'd guess might be appropriate for your battery bank).

All of the above is only relevant to occasional use of AGMs (as opposed
to constant use - most batts when used constantly live a lot longer
than those in occasional use). And much is contentious (ie I expect
someone to contradict what I've said).

Cheers

Bil

wrote in news:1165722539.265878.179840@
73g2000cwn.googlegroups.com:

The experts I
consulted for my Concorde AGMs said best practice would include:

ú when possible, recharge every day the battery bank is used and as
soon as possible after use;

True of ANY float battery, like lead acids. By the way, the Lithium-Ion
batteries in your cellphone, laptop and other gadgets is a FLOAT battery,
too, and should be fully recharged asap, even if you discharged it just a
little.

ú when not in use, maintain the bank at 100% State of Charge by
continuous float charging;

I like float chargers that come on at 13.2 and go off at 14.4V and don't
come on again until the cell voltage drops to 13.2, once again...leaving
a 1.2V hysteresis gap so you don't gas them much. The little 1.5A
Schumaker or now called Vector or Black and Decker chargers are perfect!

ú avoid Depths of Discharge approaching or greater than 80% of
amp-hour capacity;

He sells batteries. It's understandable. Change the 80 to 50% and make
me happy, ok? I'm a BUYER...(c; If you need 400AH of use before
recharging, just double it and figure out how you're going to float and
store it....no matter how it's packaged.

ú avoid recharging after shallow discharges of less than 10% of
capacity; and

Nonsense and wrong. That car out in the garage does EXACTLY this EVERY
TIME it starts, normally. You crank the car for 1.5 seconds, then turn
this huge recharging alternator loose on it to INSTANTLY recharge it to
14.4VDC at some god-awful charging current, as much as it will stand,
even though you used 2% of its starting CCA rating for only 1.5 seconds.
How old is the car battery? 4 years, you say!

ú never discharge the bank to or below 11.8 volts.

Too deep. Too vague. Look at the chart on page 3 of:
http://www.homepower.com/files/battvoltandsoc.pdf
Those lines are DISCHARGE CURRENT lines. Capacity/100 amps (C/100) to
(C/3) Let's say it's a 225AH boat battery, deep cycle of course. C/100
= 2.25A If the load current is light, 2.25A, his 80% discharged point
comes (from the graph) at 12.1VDC because the current through the series
cell resistance is so small....

If we discharged it to 11.8V, from the graph at 2.25A, you're nearly
DEAD-dead to lower it that far...way too deep for comfort!

Now look at C/3..225/3=75A..same battery. 75A causes a LOT MORE voltage
drop pulled through the internal cell resistance. At HIS, not mine, 80%
discharge level at 75A load battery voltage is way down to 10.35V! So,
his flat statement is useless. This is a warm battery, by the way, 78F
on page 5 with the discharge chart on it. Temperature varies it as it
varies internal cell resistance.

So what does Joe Boater do with HIS voltmeter? He opens that battery box
with the Battery Switch to OFF and measures 13.5VDC with NO LOAD,
declares the batteries in great condition because they are AGM batteries
and closes it back up. "It doesn't need maintenance.", he declares to
noone in particular. "These are Cadillac Supreme AGM batteries I paid
$1299 each for!", proudly. Joe has no idea cell 3 is deader'n a doorknob
because he didn't LOAD TEST the cell. Dead cells have great voltage with
NO LOAD!


Larry
--
Why is it, in any city, all traffic lights act as if they have rotary
timers in them, like they did in 1955, and are all set to create
maximum inconvenience and block traffic movement, entirely?

Larry wrote in
:

So what does Joe Boater do with HIS voltmeter? He opens that battery
box with the Battery Switch to OFF and measures 13.5VDC with NO LOAD,
declares the batteries in great condition because they are AGM
batteries and closes it back up. "It doesn't need maintenance.", he
declares to noone in particular. "These are Cadillac Supreme AGM
batteries I paid $1299 each for!", proudly. Joe has no idea cell 3 is
deader'n a doorknob because he didn't LOAD TEST the cell. Dead cells
have great voltage with NO LOAD!



Speaking of the ability to measure their voltage, It's most unfortunate
that manufacturers have chosen, for economy, to discontinue batteries
with replaceable cells with EXTERNAL crossover leads. With each cell's
terminals coming out the top of the battery, one could measure the loaded
voltage for each cell very easily to compare them. That's unfortunately,
no longer possible. Even if we could just get them to put a test point
on each cell it would be wonderful. Now, the only way I can load a
battery and measure individual cell output voltage is with some stainless
steel, sharp-tipped probes I made. Only the probe tips are exposed, the
shaft of them is coated with nail polish to keep as much acid as possible
off them.

To use them, obviously only on wetcells, you take the caps off and poke
the probe points into the lead plate, directly, one in each cell. If you
measure around 2V, it's one cell. 4V, use the other plate as you have
two cells in circuit. You'll soon see how they're connected and use the
same polarity plate in each hole. Harbor Freight has a great 50A battery
tester from China really cheap. It has a nichrome load "heater" you
switch on with a momentary contact switch and an analog meter I find is
very accurate tested against my DVM.
Item No. 93784-2VGA
http://www.harborfreight.com/
HOLY SMOKE, LOOK! It's on the front page of their website ON SALE for
$9.99 again! I'll go down in the morning and buy a few more....boat
buddy Christmas presents...(c; Those without a store can order online...
$10! BUY IT!! While you're there, buy several of those 9-LED mini
flashlights for $5! Hell, that's less than Waste Marine wants for a
BULB!

Loaded, the "dead cell" shows up really fast with nowhere near 2V across
it. Weak cells show up as in imbalanced cell with less voltage than the
other ones.

Larry
--
Why is it, in any city, all traffic lights act as if they have rotary
timers in them, like they did in 1955, and are all set to create
maximum inconvenience and block traffic movement, entirely?