Things that Work!
Home Power tests the Hydrocaps
One of the perpetual chores in home power systems is watering the 
batteries.  These large lead-acid cells always seem thirsty for distilled 
water.  As these batteries recharge, some of their water escapes.  
Periodic watering of these large cells is essential for battery survival.  
Failure to do so results in the early demise of these expensive batteries.  
Hydrocaps are devices which greatly reduce the battery's water consumption 
and also offer vital safety and operating features.
The Lead-Acid Recharging Process
The electrolyte in lead acid batteries is a dilute (Å25%) solution 
of sulphuric acid in water.  As the lead-acid cell reaches a full 
state of charge, some the water in the electrolyte is broken down 
into hydrogen and oxygen gasses by the recharging current.  These 
gasses escape from the vent on the top of each cell.  This process, 
called "gassing", accounts for the water lost from the cells.  The 
actual amount of water the cell loses during recharging depends on 
several factors.  High temperatures (>90¡F), high rates of recharge 
(>C/20), and elevated voltage limits (>2.44 VDC per cell) all increase 
the amount of gassing that occurs during the recharging process.
If all the cells in a lead-acid battery are to be totally refilled 
and equalized, then a certain amount of gassing will have to take 
place.  It's up to us to deal with this situation.  First, we must 
add distilled water to the cells to make up for the water hydrolyzed 
into hydrogen and oxygen.  Second, we must deal with the potentially 
explosive mixture of hydrogen and oxygen being vented from the cells.  
Hydrocaps offer solutions to both these problems.
Hydrocaps
A Hydrocap is a catalytic gas recombiner than converts hydrogen and 
oxygen gasses into pure water.  A catalyst is a substance which encourages 
other substances into chemical change without actually participating 
in that change, sort of a chemical ambassador.  The process occurring 
in the Hydrocap is similar to that occurring in an automotive catalytic 
converter.
The Hydrocap replaces the regular cell cap.  When the cell is gassing, 
the hydrogen and oxygen gasses are vented into the Hydrocap.  Inside 
the Hydrocap, a catalyst of platinum and other platinum group metals 
recombine the gasses into pure water.  This water is then dripped 
back into the cell.  The Hydrocap recycles the water that the cell 
gives off as hydrogen and oxygen gasses.  This eliminates the danger 
posed by the hydrogen gas and vastly reduces watering the cells.
When the cell is gassing, some of the recharging energy is not being 
stored in the cell, but is breaking down water into its constituent 
elements- hydrogen and oxygen.  Some of the energy used in the conversion 
of water into hydrogen and oxygen is retrieved by the Hydrocap.  
When the Hydrocap is operating it gets warm.  This heat energy is 
a by product of the catalytic recombination of the hydrogen and oxygen 
back into water.  While this may seem just an interesting aside, 
we found the Hydrocap's warmth very useful as an indicator of the 
cell's state of charge.
Testing the Hydrocap
We installed 6 Hydrocaps on two Trojan L-16W batteries (350 Ampere-hours 
at 12 VDC) in the Plywood Palace on 9 March 1989.  These batteries 
are recharged by a motley assortment of five PV panels (Å200 peak 
Watts) and our home made Mark VI engine/generator system (12 to 16 
VDC from 5 to 100 Amps).  See HP2, page 25, for a description of 
this engine/generator system.  I usually add about a pint of distilled 
water to each cell per month.  Each cell (and this battery has six) 
has an electrolyte capacity of three quarts.  We've been cycling 
this battery about three times a week; this means lots of recharging 
and its associated water consumption.  Basically, this battery is 
consuming about $8 worth of distilled water a year.
I removed the cell caps, filled the cells with water, and replaced 
the stock caps with Hydrocaps.  I then fired up the Mark VI engine/generator 
to recharge the battery and check out the Hydrocaps' operation.  
The battery was already just about full from the PVs' daily input.  
It only took a few minutes before the battery voltage rose to 14.5 
VDC at 17 Amperes input (about a C/20 rate for this battery).  The 
battery was now gassing slightly.  I raised the voltage limit on 
the Mark VI to 14.8 VDC and now I could hear the cells gassing violently.  
Each of the Hydrocaps was starting to get warm.  I continued to recharge 
the battery for a while and found that for this particular battery 
the Hydrocaps stayed warm (but not hot) with a voltage limit of 14.6 
VDC.  I found this fascinating.  For the very first time I had some 
feedback on how much each cell was actually gassing.  The more a 
cell gassed, the hotter its Hydrocap became.  This battery is over 
9 years old and has one cell which is slightly weaker than the rest.  
I've determined this by long term voltage measurement of the individual 
cells during all sorts of charge/discharge rates.  Sure enuff, the 
Hydrocap on that particular cell was the slowest to warm up.
The heat output of each Hydrocap provides three valuable bits of 
battery information.  One, it allows the user to accurately determine 
the voltage at which his battery gasses (a good voltage setpoint 
for regulators).  Two, it allows early detection (and correction 
via equalizing) of a weak cell by its relatively cooler Hydrocap.  
Three, when all the Hydrocaps reach the same temperature, then all 
the cells are equalized (at the same state of charge).  And accessing 
this information is low tech, just feel the temperature of the Hydrocaps!
It's now been over two months since the Hydrocaps were installed 
on our L-16Ws.  I checked the water before writing this and all of 
the cells are still full.  I have not added a drop of water to the 
battery during this test period.  Operation without the Hydrocaps 
would have consumed about 1.5 gallons of distilled water during this 
interval.  I assume that I will have to eventually add some water 
to the battery, even with the Hydrocaps.  From the virtually zero 
decrease in electrolyte level to date, I think that yearly watering 
of the cells is possible in well proportioned systems.  Every time 
we open a battery's cell to add water we risk contamination of that 
cell.  Batteries are chemical machines and depend on the purity of 
their reactants for longevity.  Hydrocaps reduce the frequency of 
required water addition and thereby lessen the possibility of cell 
contamination.
The top surfaces of our batteries are staying cleaner.  During recharging 
without Hydrocaps, a fine mist of acid electrolyte is expelled from 
the cells along with the hydrogen and oxygen gasses.  With the Hydrocaps, 
there is actually a negative pressure within the cap.  The gas recombination 
creates a slight vacuum within the Hydrocap, and the acid mist is 
washed back down into the cell by the recombined water.  Slick.  
The process keeps the acid electrolyte from reaching the top of the 
battery's case and corroding everything.  Cleaning the tops of our 
batteries is one of my least favorite chores.  My nose always itches 
when I've got acid on my fingersÉ
Based on a catalytic reaction, the Hydrocaps last a long time.  The 
manufacturer says, and I quote, "The life expectancy of a Hydrocap 
is more than 5 years with overcharge rates below 3 Amperes for two 
hours each day." What this means to those of us using PVs as energy 
sources in properly proportioned systems, is very long lifetimes.  
If our power sources aren't grossly overcharging our batteries, then 
a set of Hydrocaps should last between ten and twenty years.  Sizing 
Hydrocaps
Since different batteries have different cap sizes and styles, the 
Hydrocaps must be fitted for a particular battery.  The manufacturer 
aided us, as he does all his customers, in selecting the right size, 
shape and overcharge rate for our battery system.  Fortunately, Hydrocap 
makes a specific model that will fit most any battery and situation.  
Hydrocap Cost
The manufacturer sells Hydrocaps directly to the end user for $5.50 
each, delivered, in quantities of six or more.  I figure that over 
the lifetime of a set of Hydrocaps I'll spend at least two times 
their purchase price on distilled water alone.  And this doesn't 
include my time to refill and cleanup the batteries, or the added 
safety factor of greatly reduced explosive hydrogen surrounding the 
batteries during recharging, or the interesting and useful information 
offered the the cap's heat.  The Hydrocaps are worth at least what 
they cost.
Hydrocap Access
Contact Mr. George Peroni at Hydrocap Corp., 975 N.W. 95 Street, 
Miami, FL 33150 ¥ telephone: 305-696-2504.  George not only sized 
our Hydrocaps, but was very helpful in providing technical information 
about his product.  Conclusion
Hydrocaps are a must for lead-acid battery users.  They increase 
the safety of the battery area by reducing explosive hydrogen gas.  
They are cost-effective by their savings in distilled water alone.  
They reduce battery maintenance while increasing battery longevity 
and reliability.  They also offer direct tactile feedback regarding 
the state of charge of the battery's individual cells.  We're now 
running Hydrocaps on all our cells and are specifying them on all 
the batteries that Electron Connection Ltd. installs.  Hydrocaps 
should be considered necessary, basic equipment for any system using 
lead-acid batteries. RP