Oversize, Insulate, Buss, Crimp, Solder
& Safety.
For those of you who have ever had to
install or replace batteries, you probably never want
to have to do it again. Batteries are expensive, heavy
and dangerous. Unfortunately, there is no magic spell
to keep your batteries young and healthy forever, but
there are a number of steps we should take, besides
putting a good charge into them, to help keep your batteries
healthy and happy for years to come.
SAFETY FIRST
Safety has got to be a primary concern whenever you
are working with batteries. Even though they are low
voltage, an arc across the positive and negative terminals
of a battery can be extremely dangerous and can destroy
the battery. Looking at an alternating current (AC)
sine, we can see that voltage delivery comes in waves.
These rapid pulses of power range in voltage from zero
to whatever the peak voltage is in the given system.
When AC voltage reaches zero it allows your muscles
a brief but repeated life saving chance to relax and
release in the event of electric shock. Direct current
(DC) power doesn't want to let go of you like alternating
current (AC) power. DC voltage remains consistent in
its delivery, making it very dangerous stuff, especially
at higher voltages. Be aware and respectful of the electrical
dangers involved with batteries and electricity at all
times. This should be common sense, but always disconnect
the battery bank from all sources of charging and discharging
before working on them. When installing a new battery
bank, draw a diagram before you wire, this could greatly
reduce the possibility of making a simple mistake. Minimize
your chances of getting zapped by using taped or insulated
tools and remove all jewelry and metal watches. Also,
tape the loose ends of cable that you're working on,
thick battery cables seem to flop around just looking
for trouble. We like to use Class T 400A fuses connected
directly to the positive terminal of a battery string,
so no matter what else is going on in the system, we
know that our batteries are fused. I know… for
you do-it-yourselfers fuses and disconnects can be annoying
and expensive, but they are required by code and more
importantly they might save your life, so use them.
If you aren't sure what size fuses or which disconnects
to use in your system, call us or your local product
supplier and we'd be glad to help.
You also have to be aware of the chemical dangers involved
when working with batteries. Lead acid batteries contain
sulfuric acid, which can do a lot more than just eat
holes in your favorite pair of jeans. Batteries are
flammable and explosive so always work on and store
batteries in a ventilated area. Have plenty of baking
soda or other neutralizer readily available in case
of a spill. Wear protective clothing, rubber gloves
and eye protection and have fresh water available in
case the electrolyte splashes on your skin or in your
eyes. Wash your hands thoroughly and frequently. You
probably don't want to earn a new nickname like "Sparky"
or "French Fry" so please keep open flames
and sparks away from batteries. In order to avoid common
sparks and arcs, I like to make my final connections
at the buss bar or inverter not the battery bank. Also,
discharge any body static electricity before working
with battery terminals and generally refrain from smoking
around batteries.
Deep cycle batteries have thick lead plates inside
that make them very heavy. Get help lifting and moving
batteries, you really don't want to drop a battery on
your foot or throw out your back for no good reason.
We've dropped more than enough batteries to know that
it's never a good thing, while getting help always is.
OVERSIZE CABLES
Typically when we size a renewable energy system, because
of the higher cost of larger wire, we may be comfortable
allowing and accounting for a 2% line drop loss. Although,
we won't really follow this rule when it comes to battery
cables. Oversize your battery cable and shoot for a
0% loss. American Wire Gauge (AWG) #4/0 is the minimum
wire size we suggest for typical battery banks, but
500 MCM sounds good too. All right I'm kidding, 500
MCM is far too difficult to work with. We generally
like X-Flex #4/0 cable, similar to welding cable with
its fine strands and flexibility. Flexible cable is
a lot more cooperative and can make your short battery-to-battery
connections and longer runs much easier to deal with.
You'll find that most Trace inverters don't give us
much room to work with so flexible leads are pretty
important although Outback Power Systems has done a
super job of making this much less of an issue with
their well designed system components. The point is,
in low voltage systems we need all the current carrying
capacity we can get. We don't want our cable size to
choke our batteries and we don't want any high resistance
connections interfering with our flow. A big pipeline
will reduce resistance and give us a greater load surge
capacity when the inverter asks for it.
KEEP 'EM WARM
Insulating your batteries is an important step in battery
protection and maintenance and for maximum performance.
You may have heard the myth that tells us not to place
batteries directly on cement because it will somehow
suck the life out of them. This story has been framed
to me as if cement has some special osmosis like ability
to reach into a battery and magically neutralize the
acid or otherwise drain the life out of it. This of
course is not true. Actually cement holds moisture and
dissipates heat rapidly so that it tends to be naturally
kept cool. Like you, batteries don't want to be cold
and miserable. The percentage of rated battery capacity
has a direct relationship to temperature in that as
battery temperature decreases so does its capacity.
Different batteries can vary in their desired temperature
but generally try to keep them above 25o Celsius or
77o Fahrenheit. Trojan usually benchmarks at a test
condition temperature of 80oF or about 27oC. Also keep
the cell-to-cell temperature variance to a minimum,
I've read +/- 5oF. In other words, don't allow some
batteries to be left out in the cold while others remain
warm and toasty. Taking all things into account, an
ideal placement for batteries would be in a very well
insulated, vented battery box on a southern wall (assuming
you're in the northern hemisphere), inside a warm or heated power shed. If the desired operating temperature
of your batteries cannot be met naturally, you'll either
have to compensate for the loss during the system sizing
or you can apply space heat a number of efficient ways
or as a diversion load. Simply put, cold temperatures
slow down our electrons when we want them to be warm,
happy and excited so insulate your batteries and they'll
surely appreciate it.
SERIES/PARALLEL VS. BUSS
It's almost common knowledge that the more batteries
you have in parallel, the more difficult it is to evenly
charge them. This is why we prefer the buss bar method
of connecting batteries instead of the ol' series-parallel
method. Using buss bars distributes what I'd like to
coin, charge/discharge impact over more batteries so
that they all are treated as equally and fairly as possible.
Charge/discharge impact is the extra use and abuse of
the batteries that the leads connect to for inputting
and outputting power. The thing to understand here is
that the batteries connected to the leads do most of
the work, they cycle deeper and more frequently, while
the interior batteries just replace what was consumed
from the battery ahead of it. See the diagram below
for a demonstration of this idea.
I've heard one way to help balance a series/parallel
bank is to connect the leads to interior batteries but
I've also been told that it's best to connect the leads
to the outer, opposite cornered batteries. Yeah, two
completely conflicting arguments that I would rather
stay out of by simply using buss bars. In case you haven't
noticed by now, equality is the name of the battery
game, it's true that one bad apple can spoil the bunch.
So we tend to keep all battery cables and the positive
and negative leads equal in length. Obviously it will
take more cable to properly perform the buss method
but the cost of bars and a few extra feet of cable in
most cases is more than justified. The buss method looks
neater, makes troubleshooting easier, allows us to place
batteries in a wider variety of configurations for easier
access and/or for location specific restrictions and
as I've generically demonstrated, distributes charge/discharge
impact over more batteries. Batteries and buss bars
can be great friends.
WE CRIMP & SOLDER
Now, I've been told by reliable sources that soldering
lugs onto battery cables is actually unnecessary. It's
been said that crimping really is "good enough."
I wish I could agree because it would save us time and
a little bit of money on our systems, unfortunately
I can't. When we install a renewable energy system,
the goal is that the system will remain working for
at least the lifetime of the purchaser. Although we
know batteries must be replaced eventually, nothing
else in the system should, barring improper installation,
defects or abuse. This lifetime goal includes the battery
cables. When you only crimp lugs to battery cables you
leave room for corrosion to snuggle in, build up and
eventually create a point of resistance. This corrosive
buildup over time can loosen the crimp by eating away
at the cable or lug and may actually allow the cable
to be pulled out of the lug or worse. Surely we all
have made plenty of bad crimps, some we knew about and
some we didn't, soldering eliminates any question of
a bad crimp. When you solder the lug to the cable, you
make them "one" or as close to "one"
as reasonably possible. There should be no argument
that soldered connections are better than crimped connections.
AVOID CELL CONTAMINATION
Another thing that you should be aware of when we're
discussing battery care and maintenance is battery cell
contamination. I don't know if this is common knowledge,
but it definitely should be. Some time ago I watched
the video "An Introduction to Storage Batteries
for Renewable Energy Systems" with Richard Perez.
One of the many points he made clear was how hydrometers
hold a very real potential for cell contamination. Hydrometers
are rarely kept sterile, in fact they are rarely even
kept clean, so when you are testing the specific gravity
of a cell, there's a good chance you could be contaminating
it. If you contaminate a cell with foreign substances
cell damage is likely, and we know if one cell in a
battery goes, usually they all got to go. Open your
batteries up only when absolutely necessary, and definitely
avoid sticking dirty things in them.
- Ryan
