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As batteries age?

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Posted by Mark on December 29, 2004, 11:33 pm
 
Hello all,
Three years into our off grid life with 14 PW95's, SW4024, C60, and 12
L16HC's. All is well other than its seeming that something is changing
with our batteries. As of late, our TriMetric meter is flashing "LoBat"
earlier than ever before. It would never start to hit low battery until
we were down in the 60% range (60% on the trimetric). Now it often
flashes low battery when we are just at, or just below, the 70% range.
This is to say anything below 80% and we may see low battery on the
meter when our fridge or any major load is on.

All I have been able to figure is that the batteries are aging? I have
always kept the batteries topped off well and we have never run them
down to 60%. Perhaps 64-65% is the lowest we have ever let them go
before firing up the generator and that has only been a handfull of
times in three years.

Do you need to reduce the battery capacity setting in the Trimetric as
the batteries age?

As a separate question, when this gets to a point where we cant deal
with it any more do we just abandon (scrap) our existing battery bank or
do we setup a second separate bank? I was hoping to get close to the 11
year life the HC's called out when we bought them however, it is seeming
we may be lucky to get 50 to 75 percent of that.

Thanks,
Mark & Shauna


Posted by Jack Hayes on December 30, 2004, 2:30 am
 


Have you done any S.G. checks? The Trimetric or any other battery meter will
not provide accurate battery charge level over a long period of time. These
meters measure AH in and AH out so any inaccuracy or charge efficiency error
will over time result in incorrect information.

Jack



Posted by Mark on December 31, 2004, 9:08 pm
 

Jack Hayes wrote:

    Thanks for the reply. I do check the SG periodically. This morning we
were getting low battery indication with the Trimetric showing us at 80%
capacity however on measuring the SG this afternoon I am getting
readings in the 1175 - 1200 range. Low for sure.
    I understand what you mean about the trimetric's metering being "dumb"
perse just measuring amps across the shunt. I guess I was using it as an
indicator. We have been noticing that it seems we are not getting what
we used to out of the batteries even after several good days. I wasnt
sure if it was an issue of them not getting as fully charged as I was
thinking or if they are depleating more rapidly. A few factors are
involved here, one is that its winter here and they are of course cold.
This hasnt really been an issue in the past two winters though. The
other is that we seem to be having something going on with our fridge in
that it is running much more than it ever has before. We are in the
process of trying to figure out what the cause is but still working on it.
    To sumarize, there clearly seems to be a shortfall of power here as of
late. We are not sure if its on the consumption side or the storage
side. I guess I should be better monitoring the Trimetric for
weekly/monthly consumption as that would rule out the consumption. I
havent kept logs of this to this point but will start.
    I guess I am just trying to get a starting point of what to do from here.
    Thanks for any input, that is  if you can make any sense of my
blubbering ;)

Thanks again, Mark


Posted by Ron Rosenfeld on December 31, 2004, 11:30 pm
 

1.175 is a state of charge of about 38% at 77F.  It will be less at lower
temperatures.

From what you've posted, it seems as if your batteries are in need of a
prolonged equalization.

First of all, be sure you are using an accurate device to measure the
specific gravity.  It should probably be readable to at least three
decimals -- e.g. 1.178.  Also, you need some method to measure the battery
temperature, so you can compensate for that, and also monitor it during the
charging process.  You can do this with a glass thermometer, although I use
one of those gadgets that shines a lasar beam at the battery, and reads the
surface temperature directly.

Once you are sure you are getting accurate readings, and that there isn't a
bad cell somewhere in your string, one way is to charge at the bulk voltage
until the charge tapers off; then increase to the equalization voltage.

While doing this, monitor temperature and water levels.  Add distilled
water as needed, and, if the temperature gets over 110F (or whatever your
manufacturer recommends), slow down the charging (lower the voltage) until
the temperature falls.

Continue to charge at the equalize voltage until the specific gravity stops
rising at, for example, two hour intervals (or longer).  At this point, the
specific gravity should be at least 1.265, and there should not be more
than (depending on the manufacturer's data) about 0.010 difference between
any two cells.

Depending on how badly sulfated your batteries are, this process may take
24-72 or more hours.

The key things to watch are the battery temperature, and the water level.
If the former gets to high, or the latter too low, you may damage your
batteries, or cause more severe problems.

Good Luck.

This process is detailed somewhere on the web, but I don't have the URL
handy just now.  I'll try to look for it later, but a party is calling :-).




--ron

Posted by Mark on January 1, 2005, 10:41 pm
 Ron Rosenfeld wrote:

Ron, Firstly thanks for your reply. At this point I am in complete
agreement from what I have read, and been told here, that we are in need
of a long equalization. One question would be does this have to be done
continuously? Can I do it over a few days? As you can imagine, the time
constraints of 24-72 hours of continuous charging may be more than I can
tackle right now.


On the temperature side, I am charging/equalizing via an SW4024 which is
equiped with the battery temp. sensor so it is compensating for the
battery temperature. I just ran out and checked the "meters" menu on the
SW and didnt see where it would tell me what the battery temp. is but I
could see that it clearly is compensating by a couple tenths of a degree.

I dont however have a meter for reading SG which reads that accurately.
The one I have been using is like a radiator hydrometer which reads in
.025 increments via a floating indicator (1.150 - 1.175 - 1.200 etc.). I
will look into a more accurate one.


This is what I started yesterday. I bulk charged until it was holding my
bulk voltage setting and the amperage had dropped by about 1/2 what it
had started at. In this case the SW was charging at about 85 amps to
start with and I continued bulk charging until the amps had droped to
about 45. This was at a bulk voltage setting of 28.8 which temp.
compensated a bit higher. At this point I switched to equalize on the SW
with an equ. voltage of 30.8. Now, in about 10 hours of charging the
batteries have yet to hit the 30.8 voltage. The highest I have seen has
been 30.5 so far. However, the ten hours has been split over two
sessions as I had to sleep last night. One issue I am having is for some
reason the SW is kicking out of charging about every 8-10 minutes but
then resumes in about 15-20 seconds. I have yet to figure out why this
is happening. I dont recall it happening before. It will kick out of
charging, the AC2 in good light remains lit, then it will resume
charging a few seconds later. I have tried backing down on the generator
amps thinking it is overloading the generator but that doesnt make any
difference even when backing down by as much as 10 amps. I am easily
able to charge for hours on end under the "bulk" setting without any
problem, charger never kicks out, however when I go to equalize its
starts kicking out. I thought perhaps it was kicking out on battery temp
but they are all very cool to the touch. At present the SW is holding at
30.5 volts, 74.5 amps. The only drawback to the charger kicking out is
it seems to lose a couple tenths of a volt, which it has to regain when
charging resumes.

I have been checking the water levels and topped them all this A.M.


At last check my SG had risen to about 1.200 but I am headed out for
another check in a bit.
** just ran out and checked before I send this, they are now approaching
1.250. They were reading between 1.225 on the low end and 1.250 on the
high end but most were closer to 1.250.


Well, like I say, I am about 10 hours in at this point, broken into two
sessions, and it would seem I have a ways to go as the equ. voltage has
not even been reached yet. I had better go out and get a few more cans
of gasoline. :)


I will watch the water and will have to figure a way to check the temp
other than relying on the SW/BTS. Thanks again, I will keep you posted...

Mark



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