On Sat, Dec 17, 2011 at 12:20:10PM -0800, Myles Twete wrote:
>
> I think it's a case of damned if you do and damned if you don't.
>
> Take the case of an Optima Yellow Top D34/78 AGM 12v/55ah battery.
[snip]
Myles, if nothing else, you've managed to make me feel better. :) I know
that I haven't done anything stupid to these batteries - I've been as
careful with them as a hen with a clutch of eggs, given that this is my
first experience with AGMs - but if *you* can cook off a string or two,
then even if I find out that I've done something that's killed mine, I
won't feel quite as bad. :)))
> If you never charge it above 13.5v, you might doom it to a sulfated limited
> life.
>
> If you regularly charge it above 14.7v AND HOLD IT THERE, you will probably dry
> it out quickly and won't be able to rehydrate it (unlike a Hawker G! enesis AGM
> battery).
The MeanWell charger that I've got actually has a nifty 8-stage charging
curve that I haven't used yet - it zaps the batteries with short
transients of ~15V, which theoretically eliminates the need for
equalization. MeanWell _says_ that it's OK for AGMs, but I've been
rather hesitant about using it.
Interestingly enough, LifeLine recommends equalizing their AGMs at 15.5V
for 8 hours:
http://www.bdbatteries.com/mcharging_procedures.php
> If you don't at least occasionally charge to near 14.7v, you'll probably
> sulfate the battery earlier than its normal life expectations would suggest.
That's exactly why I'm so concerned about what's happening now.
Undercharging has, in my experience, killed more batteries than
overcharging ever did.
> Here are the charging recommendations from OPTIMA for their D34/78 batteries:
>
> http://www.optimabatteries.com/_media/documents/specs/D34_78.pdf
Yep; quite similar to LifeLine's recommendations.
I just dug around on the Net some more and managed to find this, from Deka:
IMPORTANT CHARGING INSTRUCTIONS: WARRANTY VOID IF OPENED OR IMPROPERLY
CHARGED. Do not install in a sealed container. Constant under or
overcharging will damage any battery and shorten its life! Use a good
constant potential, voltage-regulated charger. For 12-volt batteries,
charge to at least 14.4 volts but no more than 14.6 volts at 68°F
(20°C). The open circuit voltage of a fully charged 12-volt AGM battery
is 12.8V. However, as the battery charges, the building internal
pressure (voltage) causes resistance to the charge. Therefore, the
on-charge voltage must be higher (at least 14.2V for 12-volt) to
overcome this internal pressure (voltage) during charging.
But I also spotted something else that's starting to make sense: this
decrease in capacity is quite recent, and looking at the temperature
chart for Deka AGM charging shows the following:
Temp F Charge(optimum) (maximum)
60-70 14.45 14.75
50-60 14.60 14.90
40-50 14.80 15.10
<=40 15.10 15.40
...and neither of my chargers is temperature-compensated. Given the
range of temps that I've been living in - or more precisely, that my
batteries have been living in, next to the hull - this just might
explain things.
I'll still need to find some way to raise the charge voltage, but now I
at least have some factor that makes sense (decreasing temps requiring
higher charging voltages.) It's the first thing that I've come across
that tracks along with what I've been experiencing.
> Bottom line: Follow the manufacturer's recommendations.
[grin] I'll do my best - now that I've found them and have made some
sense of them. Thanks, Myles!
--
Ben Okopnik
-=-=-=-=-=-
No comments:
Post a Comment