Re: [PSUBS-MAILIST] What do Hydro-caps do?

["D. Blake" <dblake@bright.net>]

Check out this file I found at http://www.independent-power.com/  It seems
to explain what you are asking.
Big Dave

Independent Power & Light
Deep Cycle Lead Acid Storage Batteries

The Equalization Charge and More
An equalize charge is often defined as a controlled overcharge. I prefer to
think of it as a true 100% full charge of your battery bank. Since finishing
the
last ten percent of a full charge takes a disproportionally long amount of
time
and is less efficient in energy use (especially so when charging with a
generator). We do not recommend attempting to complete a full charge every
time
you charge. If your renewable energy charging resource (pv, micro-hydro, or
wind) accomplishes this regularly then that is great (as long as you have a
good
charge controller in your system that will prevent excessive overcharging).
The equalize charge should be accomplished at least once per month to ensure
that the individual cells within the batteries are fully charged, equal to
one
another, and that the electrolyte is stirred up by the gassing of the cells.
You
may have to do an equalize charge with your generator (when there is not
enough
natural power to accomplish battery equalization with your renewable source
alone). Depending on how unequal your battery cells are the equalization
charge
may take an additional two hours after a good amp hour meter considers your
batteries fully charged. If the weather has been very cloudy (with pv
systems),
or you have been using more power than usual, and you have neglected to
perform
the equalization charge once per month then the length of time to equalize
your
cells could take from several hours to a few days.
After the equalization charge is finished check the cells to see if you need
to
add distilled water. Never add distilled water unless the batteries are
fully
charged because the electrolyte level increases as the voltage increases.
Since
during battery gassing the cells lose water and not sulfuric acid never add
battery acid to your cells. The electrolyte will become too acidic and eat
your
battery plates.
If your battery, bank consists of separate 2 volt cells (such as the
Surrette
Solar series) you are in luck. This type of a battery bank generally lasts
much
longer than battery banks of 6, or 12 volt batteries because the plates are
much
thicker and the cells hold more electrolyte. Tests and real life experiences
have shown these 2 volt cells to be capable of 2,750 deep cycles compared to
700
for the typical 6, or 12 volt deep cycle battery. You also enjoy the
benefits of
maintaining far less cells for your bank; typically a total of 6 cells for a
twelve volt bank and 12 cells for a 24 volts for up to 1,400 amp hours of
storage. Compare this with maintaining 36 cells in a battery bank of twelve
6
volt golf batteries series-paralleled for 1,320 amp hours at 12 volts. And
you
get the additional benefit of having to add distilled water less often
because
the 2 volt cells have a larger reservoir for electrolyte above the plates.
You
also can check each cells voltage with a hand held digital voltmeter and
compare
readings of all the cells of the bank so that you can tell how equal all the
cells are. Cells voltages should all be within .05 volts, for batteries at
rest
(no charging or discharging happening) for example the highest reading may
be
2.15 volts and the lowest reading may be 2.10 volts. If your cells vary by
more
than this than you should charge your batteries until all cells fall within
.05
volts.
If your bank consists of 6 volt or 12 volt batteries that do not allow you
to
take voltage readings of each individual 2 volt cell then checking each cell
with a battery hydrometer is the only way to be absolutely sure that your
batteries are equalized. Each cell is fully charged at, about, 1.270 points
sg
(specific gravity) on a temperature compensated battery hydrometer. This
reading
may actually vary slightly due to manufacturers different specs for various
battery types. Some batteries may be fully charged at 1.260 sg. Equalized
cells
will all be fully charged, and all within .010 points sg of each other.
Unequal cells, as measured by specific gravity with a battery hydrometer are
a
normal fact of life with deep cycle batteries. Over several charge/discharge
cycles the individual 2 volt cells (3 per each 6 volt battery) drift apart
in
voltage and the only way to bring them all back to an equal state of charge
is
to overcharge the entire battery bank until the cells lowest in charge catch
up
with the other cells. Cells that are in a low state of charge will begin to
sulfate, that is the lead sulfate on the plates stays there because it is
not
driven off during a complete recharging of that cell. The longer the sulfate
stays on the battery plate the more crystalized and hard it becomes making
it
more difficult to get it off the plates and back in the electrolyte
solution.
Sulfation on the plates means less plate area for the electrochemical
process to
take place which results in reduced storage capacity. This can happen within
a
few weeks and become a problem. I have seen good battery banks become
reduced to
the point where they stored half of their normal power after just 6 weeks
without a good equalization charge. This low capacity problem was corrected
with
a seriously long equalization charge.
Tests have shown that use of a battery DeSulfator, a sweeping pulse device
that
uses a very small amount of your battery bank's power to send a variable
frequency, variable voltage boost, will dissolve lead sulfate crystals back
into
the battery's electrolyte solution. These devices are a great insurance
policy
against plate sulfation but they do not let you totally avoid the
equalization
charge. The DeSulfator will shorten the time necessary to equalize but you
still
need to make sure that the electrolyte gets sufficiently stirred up so it
does
not become stratified and eat away the lower portions of the battery plates
thus
destroying your valuable batteries.
The severity of your batteries sulfation condition and the charge rate of
your
PV array and, or, your engine generator powered battery charger (may be
combined
in your inverter) will determine the actual length of time the equalization
charge takes. A reasonable charge rate for efficient equalization charging
is
between C/10 to C/20. The charge rate is simply your battery bank capacity
in
amp hours divided by your charging current. For example: With a battery bank
capacity of 1,000 amp hrs and a PV array charging current of 30 amps your
rate
is stated as C/33. Add in your generator driven battery charger along with
the
PV charging and your charge rate could drop to C/11 (if the battery charger
was
actually putting out 60 amps).
During a good long charge the batteries will eventually gas rapidly. This is
necessary as it stirs up and redistributes the heavier sulfuric acid
(battery
electrolyte is 65% water and 35% sulfuric acid) so that it will not settle
on
the bottom of the cells. Safely vent these gases outdoors (see my battery
box
and auto vent fan descriptions in the Mid-Size System design).
Actual battery storage capacily usually stated in amp hours, depends on
temperature. The colder the batteries the less storage capacity available.
At 50
degrees F storage capacity is reduced by about 15%. At 32 degrees F storage
capacity is reduced by about 30%. Also the voltage necessary to charge
batteries
increases as they become colder. With the Trace Engineering line of PV
charge
controllers and inverter/Chargers we have available an optional temperature
sensing unit which automatically compensates for this condition by allowing
progressively higher charging voltages as the batteries become colder.
However
it can not make the batteries recover their full storage capacity, only a
temperature of 78 degrees F can do that. A couple of more points about
temperature and lead acid batteries. A battery at a 20% state of charge will
freeze (and most likely become ruined) at about 18 degrees F. Cold batteries
are
also less efficient in their transfer of energy. But don't get too carried
away
keeping your batteries warm because too warm is not good either. Above 80
degrees F shortens the life of the batteries and also increases their self
discharge rate. 78 degrees is perfect, I manage to keep my batteries between
60
to 65 degrees F and I'm happy with that. We have many battery banks
operating
fine at 40 to 50 degrees F also. You just have to compensate for the reduced
amp
hour storage capacity by buying more amp hours of battery than you would for
a
65 degree battery temperature.
These batteries are rated for cyclic use of up to 80% of capacity. That is
you
can drain the batteries down to 20% state of charge without harming them as
long
as they are completely recharged soon thereafter. Lead acid batteries will
last
longer if they are cycled less deeply. By using only 10% to 60% of capacity
before recharging your battery bank will give you good service for many
years. I
have seen, twice now, in my fourteen years of working with these batteries a
cell that would not take a charge no matter what I did. In both cases the
problem showed up soon after installation of the system with a check of
specific
gravity (two good cells in battery read 1.270 bad cell 1.050). Manufacturing
defects do happen and they show up very early on. So check with the
hydrometer
for bad cells. If they cannot be equalized as I have described (and the cell
goes dead), and you are doing everything else you should be doing as to the
proper charging of the batteries then I will replace the battery that the
bad
cell is in. This offer is good for one year after purchase with Trojan
batteries. Surrette batteries carry a longer warranty.
Rotate your batteries? Yes! If you really want to get the most out of your
battery investment then by all means rotate. Years of experience have shown
that
the cells at the ends of the battery bank (the main positive cable comes out
of
one end and the negative out of the opposite end) usually fail before the
other
batteries in the bank. We (manufacturers, engineers, practitioners) do not
exactly agree on the cause of why this happens but that is not too
important. To
rotate the individual cells, or batteries, simply disconnect them and move
them
to the middle of the bank once per year. This is also a good time to check
tightness of all your connections in the battery bank and through to the
disconnect, inverter, and ac load center. If you are also seeing a
performance
drop on your charging sources, or poor performance on your loads check
tightness
of all applicable connections. It is paramount that all connections be of
low
resistance and of high mechanical integrity, especially in a low voltage
system.

If you can not, or do not want to perform annual system maintenance yourself
then hire an experienced professional (such as myself - Independent Power &
Light) to help you get the best performance and longest life out of your
system.
If you are simply using an accurate voltmeter, along with occasional checks
with
your hydrometer, this chart should be helpful in determining your batteries
state of charge.
Charge LevelSpecific GravityVoltage 2V nVoltage 6V nVoltage 12V
            nVoltage 24V n
            100.00%1.2702.136.3812.7525.50
            75.00%1.2242.086.2412.4824.96
            50.00%1.1702.026.0612.1224.24
            20.00%1.0971.945.8211.6423.28
            0.00%1.0451.895.6711.3422.68

n stands for nominal voltage
They are also only accurate for batteries at rest. Meaning that the voltage
is
not lowered by a load, or elevated by a charging source. You have the most
accuracy after a half hour of rest time.
I recommend The Tri-Metric meter for users who want more information from a
meter. This meter uses a remote current measuring shunt and an on board
microprocessor to calculate ampere flow in and out of your batteries. It
also
measures and tracks battery voltage. It displays voltage, net current
(amps),
and battery % full.
It also tracks and can display amp hours discharged, days ago since last
"full"
(not equalized) charge, lifetime amp hours discharged, minimum battery
volts,
and maximum battery volts. In addition it can also be set up to remind you
when
it is time to equalize charge. I use this meter myself and like it a lot!
I sell this meter for $160, plus $30 for the necessary shunt.

End

-----Original Message-----
From: Marsee Skidmore <heyred@email.msn.com>
To: personal_submersibles@psubs.org <personal_submersibles@psubs.org>
Date: Saturday, March 04, 2000 1:41 PM
Subject: Re: [PSUBS-MAILIST] What do Hydro-caps do?


>Tell us more about periodic controlled overcharge. How much and how
often? -
>Joe
>
>----- Original Message -----
>From: David Buchner <buchner@wcta.net>
>To: <personal_submersibles@psubs.org>
>Sent: Friday, March 03, 2000 8:29 AM
>Subject: Re: [PSUBS-MAILIST] What do Hydro-caps do?
>
>> However if you don't give the batteries a regular controlled overcharge,
>they won't last as long either -- and they cost way more!
>>
>> --
>> David
>> Osage MN USA
>> buchner@wcta.net - http://customer.wcta.net/buchner
>>