What is a deep
The essential difference
is in the lead plates. In normal car batteries, these are
sponge type structure or consists of many thin plates,
giving a greater surface area to generate big amps for short
periods; whereas in deep cycle batteries, the lead plates
are thicker and solid.
A deep cycle battery
usually has multiple times the RC (reserve capacity) of a
car battery, but a substantially lesser CCA (Cold Cranking
Amps) rating - the focus is on consistent lower level supply
rather than intermittent short bursts of high supply.
Why not car
Car batteries are meant to
give large amounts of juice for a very short period. Once
they've done their work turning over the engine, they are
immediately recharged by the car's alternator.
In a solar power setup,
while the draw mightn't be as brutal in short bursts, it can
continue for a very long time - for example, overnight. Car
batteries just aren't made for this type of application and
will wear out quickly. I found this out the hard way.
Different types of
deep cycle batteries
These are very much like
car batteries only with thicker lead plates and have many of
the issues that car batteries have when used in a stand
alone power system - serviceable life, electrolyte
dissipation, stratification, transporting problems and the
dangers of explosive gas.
Gel deep cycle batteries
contain acid with the addition of silica, which turns the
acid into a jelly. Even when broken, the acid won't spill.
These batteries are ideal for daily use and deep discharge
and will work well in high temperatures. They can be
partially recharged without causing serious battery damage
and readily accept charging due to low internal resistance;
however they shouldn't be recharged using high voltages such
as what a car alternator cranks out.
AGM stands for Absorbed
Glass Mat. A Boron-Silicate glass mat is placed between the
lead plates, which immobilizes the electrolyte making it
unspillable. This type offers the same sorts of
benefits as gel batteries and AGMs are also tolerant to high
Another important safety
feature of both AGM and Gel is that either do not off-gas
under normal usage. They are hermetically sealed and
recombine the oxygen and hydrogen produced within the
The lifespan of a deep
cycle battery will vary considerably with how it is used,
how it is maintained and charged, temperature, and other
factors. In extreme cases, it can vary to extremes - we have
seen L-16's killed in less than a year by severe
overcharging, and we have a large set of surplus telephone
batteries that sees only occasional (5-10 times per year)
heavy service that are now over 25 years old. We have seen
gelled cells destroyed in one day when overcharged with a
large automotive charger. We have seen golf cart batteries
destroyed without ever being used in less than a year
because they were left sitting in a hot garage without being
charged. Even the so-called "dry charged" (where
you add acid when you need them) have a shelf life of 18
months at most. They are not totally dry - they are actually
filled with acid, the plates formed and charged, then the
acid is dumped out.
These are some typical
(minimum - maximum) typical expectations for batteries
if used in deep cycle service. There are so many
variables, such as depth of discharge, maintenance,
temperature, how often and how deep cycled, etc. that it is
almost impossible to give a fixed number.
- Starting: 3-12 months
- Marine: 1-6 years
- Golf cart: 2-7 years
- AGM deep cycle: 4-7
- Gelled deep cycle: 2-5
- Deep cycle (L-16 type
etc): 4-8 years
- Rolls-Surrette premium
deep cycle: 7-15 years
- Industrial deep cycle
(Crown and Rolls 4KS series): 10-20+ years
- Telephone (float): 2-20
years. These are usually special purpose "float
service", but often appear on the surplus market as
"deep cycle". They can vary considerably,
depending on age, usage, care, and type.
- NiFe (alkaline): 5-35
- NiCad: 1-20 years
(sometimes called SLI, for starting, lighting, ignition)
batteries are commonly used to start and run engines.
Engine starters need a very large starting current for a
very short time. Starting batteries have a large number
of thin plates for maximum surface area. The plates are
composed of a Lead "sponge", similar in
appearance to a very fine foam sponge. This gives a very
large surface area, but if deep cycled, this sponge will
quickly be consumed and fall to the bottom of the cells.
Automotive batteries will generally fail after 30-150
deep cycles if deep cycled, while they may last for
thousands of cycles in normal starting use (2-5%
- Deep cycle
batteries are designed to be discharged down as much as
80% time after time, and have much thicker plates. The
major difference between a true deep cycle battery and
others is that the plates are SOLID Lead plates - not
sponge. This gives less surface area, thus less
"instant" power like starting batteries need.
- Unfortunately, it is
often impossible to tell what you are really buying in
some of the discount stores or places that specialize in
automotive batteries. The golf car battery is quite
popular for small systems and RV's. The problem is that
"golf car" refers to a size of battery
(commonly called GC-2, or T-105), not the type or
construction - so the quality and construction of a golf
car battery can vary considerably - ranging from the
cheap off brand with thin plates up the true deep cycle
brands, such as Crown, Deka, Trojan, etc. In general,
you get what you pay for.
- Marine batteries
are usually a "hybrid", and fall between the
starting and deep-cycle batteries, though a few (Rolls-Surrette
and Concorde, for example) are true deep cycle. In the
hybrid, the plates may be composed of Lead sponge, but
it is coarser and heavier than that used in starting
batteries. It is often hard to tell what you are getting
in a "marine" battery, but most are a hybrid.
Starting batteries are usually rated at "CCA",
or cold cranking amps, or "MCA", Marine
cranking amps - the same as "CA". Any battery
with the capacity shown in CA or MCA may not be a true
deep-cycle battery. It is sometimes hard to tell, as the
term deep cycle is often
overused. CA and MCA ratings are at 32 degrees F, while
CCA is at zero degree F. Unfortunately, the only
positive way to tell with some batteries is to buy one
and cut it open - not much of an option.
Inadequate battery reserve power has long been the Achilles' heel of
RVers who like to get away from the usual trappings of civilization,
including hookups. While an AC generator can be used to supply
auxiliary power, it can't be operated continuously, and RVers who lack
both a generator and campground electrical hookups are very battery-
Beyond conventional 12-volt appliances, owners who have discovered the
benefits of power inverters (see "Inverters" - April 1994) to operate
120-volt AC appliances often find their previously adequate auxiliary
batteries lacking. To power all these newly added luxuries, batteries
must provide adequate output and must be kept in excellent condition.
The lead-acid battery types that are most common in successful RV
auxiliary-power applications are all of deep-cycle design. This is
important because a deep-cycle design stands up to repeated heavy
discharge-recharge usage much better than an ordinary automotive
battery. An automotive battery is designed to deliver very large
bursts of current for short periods (when starting an engine) and then
is immediately recharged (by the vehicles' alternator).
Most RV 12-volt DC and inverter power applications require the battery
to provide current for extended lengths of time before receiving any
recharge. An automotive battery will lose a significant percentage of
its full storage capacity after being heavily discharged just one time.
It will typically lose half of its capacity after 50 discharge-recharge
cycles. (A heavy discharge is one that removes all but 20 percent of the
battery's original full charge.)
By contrast, even the lightest-duty deep-cycle battery will typically
tolerate 200 to 300 such discharge-recharge cycles before reaching a
similar state; some of the heavier deep-cycle designs can exceed
10,000 such cycles. In short, no matter how "heavy duty" a battery is
claimed to be, if it isn't a deep-cycle design it won't last very long
in most inverter applications. The only battery in an RV that needn't
be of deep-cycle design is the one that starts the vehicle's engine.
When a battery becomes too old and weak to sustain a usable charge,
sulphation is most frequently the culprit. Every time a battery is
discharged, its sulfuric-acid solution is gradually broken down, leaving
deposits on the battery's lead plates. If the battery is promptly
recharged, most of this sulphation is driven back into solution, leaving
the plates in an essentially unchanged state. Leaving the battery in a
discharged state for extended periods, however, allows the sulphation to
harden into a form that permanently embeds itself within the plates.
Suplhation deposits permanently reduce the battery's storage capacity.
Chronic undercharging or excessive discharge also lead to plate
shedding, in which some of the active solid-plate material flakes off
and accumulates in the bottom of the battery. This accumulation
eventually sorts out the plates, resulting in a dead cell. Consequently,
if full storage capacity over a long service life is to be realized, it
is important to fully recharge a battery promptly and to avoid over-
Depth of discharge
- extending battery life
Deep cycle batteries are
designed to be discharged much lower than standard car
batteries and be recharged many more times. The life of a
deep cycle battery under normal conditions is anywhere from
3 - 10 years.
Like any other piece of
equipment, the more you hammer it, the less it will last you
and one of the key strategies for getting the longest life
out of your deep cycle battery relates to depth of
discharge; i.e, how much juice you suck out of it. If a
battery is discharged to 50% (around 12.06v under load or
12.24v with no load - this can be measured with a cheap
multimeter), it will last about twice as long as if it is
taken down to 80% discharge.
"cycle" is one complete discharge and recharge
cycle. It is usually considered to be discharging from 100%
to 20%, and then back to 100%. However, there are often
ratings for other depth of discharge cycles, the most common
ones are 10%, 20%, and 50%. You have to be careful when
looking at ratings that list how many cycles a battery is
rated for unless it also states how far down it is being
discharged. For example, one of the widely advertised
telephone type (float service) batteries have been
advertised as having a 20-year life. If you look at the fine
print, it has that rating only at 5% DOD - it is much less
when used in an application where they are cycled deeper on
a regular basis. Those same batteries are rated at less than
5 years if cycled to 50%. For example, most golf cart
batteries are rated for about 550 cycles to 50% discharge -
which equates to about 2 years.
life is directly related to how deep the
battery is cycled each time. If a battery is discharged to
50% every day, it will last about twice as long as if it is
cycled to 80% DOD. If cycled only 10% DOD, it will last
about 5 times as long as one cycled to 50%. Obviously, there
are some practical limitations on this - you don't usually
want to have a 5 ton pile of batteries sitting there just to
reduce the DOD. The most practical number to use is 50% DOD
on a regular basis. This does NOT mean you cannot go to 80%
once in a while. It's just that when designing a system when
you have some idea of the loads, you should figure on an average
DOD of around 50% for the best storage vs cost factor. Also,
there is an upper limit - a battery that is continually
cycled 5% or less will usually not last as long as one
cycled down 10%. This happens because at very shallow
cycles, the Lead Dioxide tends to build up in clumps on the
the positive plates rather in an even film. The graph above
shows how lifespan is affected by depth of discharge. The
chart is for a Concorde Lifeline battery, but all lead-acid
batteries will be similar in the shape of the curve,
although the number of cycles will vary.
How many/big a
battery to buy?
Really, the bigger/more
the better. For example, I have a 100 AH (amp hour) battery
and under normal weather conditions, even under partial
cloud, that does me fine. One day of total overcast isn't a
problem either, but a couple of gray days back to back and I
start getting around the 50% discharge mark at which point I
grudgingly have to fire up the generator.
As mentioned, given that
my 130 watt panel recharges the battery by midday under
sunny/mostly sunny conditions; that means I have spare
output that is being wasted - so I would have been wiser to
buy the 150 AH battery recommended to me which would help
better carry me through overcast days.
What's with the
AH, or amp hours, is how
deep cycle batteries are rated. If you have an appliance
that draws two amps; then it could run for 25 hours on a 100
AH battery before you'd hit the 50% DOD (depth of
Most appliances are rated
in watts rather than amps, so how do you make the
Use this simple formula:
Amps = Watts / Volts
Tip: Sometimes amps are
noted on appliances, check the manufacturer label on the
back of the item.
deep cycle battery needs
After determining the amp
rating of your appliances, then multiple each by the number
of hours of use per day. Then add up all those figures
and you'll get some idea of the sized battery you'll
need - but bear in mind the 50% depth of discharge
recommendation; i.e. a 100 AH battery really only gives you
50 AH if you wish for the battery to last well.
For example, if you
had a notebook computer running at 3 amps and a light
drawing 1 amp, a fully charged 100 amp hour battery could
run both for 12.5 hours without any input from your solar
panel before you'd hit the 50% discharge mark.
If determining the
amperage of all your appliances doesn't appeal to you; try
system builder that will give you a full system
recommendation based on your needs.
Figure 1 - Battery State of Charge
Charge Voltage Voltage Specific
Level (12v) (6v) Gravity
------ ------- ------- --------
100% 12.7 6.3 1.265
75% 12.4 6.2 1.225
50% 12.2 6.1 1.190
25% 12.0 6.0 1.155
0% 11.9 6.0 1.120
The maximum storage capacity of a deep-cycle lead-acid battery is
usually rated either in amp-hours, or in minutes of reserve capacity.
The amp-hour value refers to the number of amps a battery will deliver
over a specified period of time (generally implied to be 20 hours if not
specifically stated), before the battery has discharged to a useless
level (10.5 volts for a 12-volt battery).
The reserve capacity value specifies the number of continuous minutes
the battery can last while delivering 25 amps before dropping to this
same 10.5 volts. As a rule of thumb, for the smaller batteries you can
multiply the number of reserve minutes directly by 0.6 to arrive at an
approximate equivalent amp-hour rating for the battery.
Therefore, a 50 amp-hour battery (or a battery with approximately 83
minutes of reserve capacity) can be expected to deliver at least 2.5
amps for 20 continuous hours, or at least 1 amp for 50 continuous hours.
Note that at current drains much higher than those specified at the 20-
hour rate, however, the capacity of the battery starts to decline due
to internal losses and chemical inefficiencies at high currents.
Consequently, this same battery might only be able to deliver 5 amps for
nine hours (45 effective amp-hours), instead of the 10 hours (50 theo-
retical amp-hours) implied by the battery's amp-hour rating. In general,
bigger batteries can deliver higher currents without incurring this
The life expectancy of a deep-cycle battery, like all lead-acid
batteries, is directly dependent upon how heavily the battery is
routinely discharged before being recharged. Batteries that are
regularly discharged until only 10 percent of their rated capacity
remains have a much short life expectancy than identical batteries that
are rarely discharged below 50 percent. Therefore, you should not buy
a 100 amp-hour battery if you plan on routinely using all 100 amp-hours
A good rule of thumb is that a deep-cycle battery should not be depleted
beyond 80 percent of capacity, with 50 percent being even better. A 50
percent discharge represents a good compromise between battery life and
reasonable battery-bank size. Therefore, you would do well to buy at
least 200 amp-hours worth of batteries to meet an anticipated 100 amp-
hour discharge "budget".
Ambient temperature also has a strong effect on battery performance.
Performance of most batteries is rated at around 80 degrees F. At
higher temperatures, they have greater capacity, but their life span is
shortened, due to the acceleration of detrimental chemical reactions.
At lower temperatures, they last longer than normal (provided the
electrolyte is not allowed to freeze), but their capacity drops.
At 32 degrees F, typical capacity is reduced by 35 percent; at zero
degrees F, it is reduced by 60 percent; and at minus 20 degrees F, it
is reduced by better than 80 percent. A battery's ability to accept a
charge also drops along with the thermometer. In general, the best
trade-off between efficiency and long life occurs when the battery is
maintained at around room temperatures. For RV owners, this means that
batteries in a compartment that is insulated from extreme cold and heat
will last longer and deliver more consistent power.
As a battery is discharged, the sulfuric-acid solution inside each cell
is gradually converted to water. Consequently, the specific gravity of
this solution also drops as the battery discharges. This change can be
easily measured with a hydrometer in order to determine the battery's
state of charge. A good battery hydrometer includes a temperature-
correction scale (specific gravity versus battery charge varies somewhat
with temperature) and will often yield readings that are more precise
than those obtained with a voltmeter. Using a voltmeter is usually more
convenient, however, and is the only accurate method of checking sealed
batteries. Consult Figure 1 when determining the state of charge of a
battery, using either a voltmeter or a hydrometer.
Specific gravity readings should be taken by inserting the hydrometer
suction pipe into the battery cell, squirting the electrolyte into and
out of the hydrometer several times (electrolyte agitation improves
accuracy), and then reading the hydrometer while the suction tube is
still inserted into the cell. Keeping the suction tube in the cell
while taking readings minimizes the chance of spilling the electrolyte,
which could cause burns or destroy clothing. Read the hydrometer scale
at the center of the fluid inside the tube, not at the edges. Note that
any heavy battery charge or discharge currents drawn just prior to
taking specific gravity or voltage measurements will have an adverse
effect on the accuracy of the readings. The greatest accuracy is
obtained after the battery sits idle for at least 24 hours prior to
taking hydrometer or voltmeter readings.
Specific gravity readings are also helpful in determining the overall
health of a battery. For example, differences in specific gravity of
more than 0.050 between any two individual cells in a battery generally
indicate that the battery is headed for problems. By taking specific
gravity readings every month or so, owners can catch battery problems
before they cripple the entire system.
WHAT TO BUY
Regardless of what type of battery is selected, all the house batteries
in an RV should ideally be the same age, size, and brand. This is
because unsimilar batteries tend to charge and discharge at differing
rates, leading to some of the batteries in the group being consistently
undercharged during recharge and overstressed during discharge. Matching
batteries will ensure maximum life for the entire battery bank. If the
bank is diligently maintained, all batteries will wear out at about the
same time, allowing the entire bank to be changed out after a long
In buying batteries, look for similar date codes stamped on each one.
If the batteries have sat on the dealer's shelf for more than a month,
use a hydrometer or voltmeter to ensure that the state of charge has
been maintained. Don't buy old or partially discharged batteries. If
in doubt, ask the dealer about the date of manufacture and shelf
Among the deep-cycle variants, the most common type is the RV/marine,
typically sold by hardware and department stores and by RV-parts
counters in automotive package (or group) sizes 24 and 27. Typical
ratings for this class of battery are approximately 80 amp-hours (110
minutes) for size 24 and 105 amp-hours (170 minutes) for size 27. These
batteries represent a reasonable value in smaller systems that are
equipped with inverters, or in installations where space is at a
premium. As deep-cycle designs go, however, they are lightweights, with
relatively short life expectancy in heavy service (typically two to
three years). This deficiency is primarily due to the use of thin lead
plates in their construction and the low antimony content of the plates
The next most common deep-cycle version is probably the golf
cart/electric vehicle, typically sold through battery-supply houses,
some wholesale clubs, and occasionally department stores (frequently
by catalog only). These batteries are all of 6-volt design (connection
of two in series produces 12-volt output) and typically cost a tad more
per pair than a single size 27 RV/Marine battery. They provide superior
service in most RV applications (due to thicker plates and higher
antimony content) and probably represent the best value for installations
that can accommodate their large size (10-1/4 inch width, 7-inch depth,
and 11-inch height). Typical ratings are 220 amp-hours, or 400 minutes
of reserve capacity. Expected life is typically three to five years.
Note that connecting two 6-volt batteries in series does not double the
amp-hour or reserve capacity ratings, but connecting two of the resulting
12-volt battery banks in parallel (a total of four golf-cart batteries)
Gelled-electrolyte ("gel-cell") batteries are becoming cheaper and more
popular among Rvers. Available in group 24, 27, 4D, 8D, and 6-volt
golf-cart sizes, they offer very good performance with virtually zero
maintenance. Where ordinary "wet-cell" batteries require monthly checks
of electrolyte levels, the gel-cells are sealed, using an electrolyte
that is jellied with nothing to replenish. They also offer higher
charging efficiency than ordinary batteries and provide slightly higher
output voltage down to complete discharge. Expected life is two to
three years, although some models may better this estimate by a great
Examples of this class of battery are the Interstate, Dryfit Prevailer,
Sonnenschein, Deka, Johnson Dynasty, and Exide Nautilus Megacycle brands.
Don't confuse these batteries with the "maintenance-free" wet-electrolyte
RV/marine batteries being sold in some department stores under brand
names such as Delco Voyager and GNB Stowaway. Unlike the true gel-cells,
these batteries are basically sealed RV/marine batteries with slightly
altered plate chemistries that reduce battery gassing (and, consequently,
To determine how much battery capacity your application requires, add up
the total anticipated amp-hours of all the 12-volt DC appliances you
will be operating between recharges, including the demands of an inverter
if you have one. Select batteries that meet or exceed this amp-hour
value, plus a considerable safety margin. As an example, assume you will
be recharging the batteries every day adnd your appliance use habits
are as shown in Figure 2.
Figure 2 - TYPICAL POWER CONSUMPTIONS
AC Current Daily Total Daily
Appliance Consumption** Use Consumption
------------ -------------- ---------- --------------
TV set 5 Amp-hr 6.0 hours 30.0 Amp-hr
Microwave 85 Amp-hr 0.1 hours 8.5 Amp-hr
Hair Dryer 125 Amp-hr 0.1 hours 12.5 Amp-hr
VCR 3 Amp-hr 3.0 hours 9.0 Amp-hr
120-v Light 1 Amp-hr 3.0 hours 3.0 Amp-hr
120-v Light 1 Amp-hr 4.0 hours 4.0 Amp-hr
Blender 3 Amp-hr 0.1 hours 0.3 Amp-hr
Toaster 90 Amp-hr 0.1 hours 9.0 Amp-hr
Total AC appliance usage: 76.3 Amp-hr
** Measured at the 12-volt input to the inverter.
DC Current Daily Total Daily
Appliance Consumption** Use Consumption
------------ ------------ ---------- -------------
Refrigerator 0.25 Amp-hr 18.0 hours 4.5 Amp-hr
Propane Alarm 0.35 Amp-hr 24.0 hours 8.4 Amp-hr
Water Pump 4.00 Amp-hr 0.2 hours 0.8 Amp-hr
Cassette Player 2.00 Amp-hr 4.0 hours 8.0 Amp-hr
Porch Light 1.80 Amp-hr 3.0 hours 5.4 Amp-hr
Interior Light 1.80 Amp-hr 4.0 hours 7.2 Amp-hr
Total DC appliance usage: 34.3 Amp-hr
Total Battery Usage: 76.3 + 34.3 = 110.6 Amp-hr
In this case, figuring a 50 percent safety margin, you would need at
least 221.2 amp-hours worth of batteries. Consequently, installing a
pair of golf-cart batteries would meet your needs, with no power to
spare. likewise, three group-27 batteries would suffice, with some
HOW TO KEEP THEM HAPPY
Although routinely overlooked in battery manufacturers' literature and
in many reference, most deep-cycle batteries (with the exception of the
gel-cell and other sealed varieties) are benefited by a periodic
controlled overcharge, which is often referred to as an equalization
charge mode. To equalize a battery, the charging is allowed to continue
well after the point at which the battery is normally considered to be
"full", taking care to avoid excessive battery heating or electrolyte
In a typical equalization cycle, the battery voltage is allowed to rise
to approximately 16 volts, where it is maintained for up to eight hours
by adjustment of the charging current. This process helps to mix up the
electrolyte, which otherwise tends to "stratify" (i.e., separate into
overlapping layers of acid and water), and is also useful in removing
some sulfate deposits. When performed properly, equalization doesn't
make the battery boil over, but does produce fairly vigorous bubbling.
At the end of this cycle, you can expect to add some water.
Most battery manufacturers consider one equalization charge per month
to be appropriate for batteries that are in a continuous state of charge
and discharge; less often is adequate for batteries that see a lot of
standby service. Due to the generation of considerable gas that
accompanies this process, equalization shoud NEVER be performed on a
sealed or gel-cell battery.
Also, most 12-volt DC appliances will not tolerate the 16-plus volts,
so remember to disconnect everything or detach the battery cables before
you equalize. Refer to Figure 3 for the suggest maintenance charge and
equalization voltages for various batteries. Obviously, a charger with
equalization capability is needed; there is no way to alter voltage
output on most RV converters.
Figure 3 - BATTERY VOLTAGES
Charge Cutoff Maintenance Equalization
Voltage Voltage Voltage
Wet-Cell Battery 14.4 13.5 16.3
@ 80 degrees F
Wet-Cell Battery 13.9 13.3 15.8
@ 100 degrees F
Gel-Cell Battery 14.4 13.8 NA
@ 80 degrees F
Gel-Cell Battery 14.1 13.8 NA
@ 100 degrees F
The "charge cutoff voltage" is the battery voltage at which heavy
recharging should cease; the "maintenance voltage" is the voltage at
which the battery can be safely maintained for long periods of time
without excessive water loss.
As a final thought, remember that lead-acid batteries generate highly
explosive gases. The larger the battery bank, the more gas is produced.
Do not mount any battery in an unvented location, and avoid any sparks
or open flame around the battery (particularly during and shortly after
recharging). Making or breaking electrical connections at the battery
terminals is particularly dangerous. Battery explosions often shower
large areas with acid. Wear eye, face, and skin protection, and give
the bank plenty of time to "air out" before attempting any maintenance
three types of wiring configurations that are relatively
easy to learn. Once mastered, the job of wiring batteries or
solar modules becomes easy as pie. The three configurations
combination of the two known simply as series/parallel
In any DC
generating device such as a battery or solar module, you
will always have a negative (-) terminal and a positive (+).
Electrons or (current) flows from the negative terminal
through a load to the positive terminal.
For ease of
explanation we shall refer to a solar module or battery as a
To wire any
device in series you must connect the positive terminal of
one device to the negative terminal of the next device
When you wire devices in series the individual voltages of
each device is additive. In other words if each device in
the above example had the potential of producing 12 volts,
then 12 + 12 + 12 + 12 = 48 volts. If these devices were
batteries then the total voltage of the battery pack would
be 48 volts. If they were solar modules that produced 17
Volts each then the total voltage of the solar array would
be 68 volts.
The second important rule
to remember about series circuits is that the current or
amperage in a series circuit stays the same. So if these
devices were batteries and each battery had a rating of 12
Volts @ 220 Amp hours then the total value of this series
circuit would be 48 Volts @ 220 Amp hours. If they were
solar modules and each solar module had a rating of 17 volts
and were rated at 5 amps each then the total circuit value
would be 68 volts @ 5 amps.
In the example below two 6
Volt 350 Amp hour batteries were wired in series which
yields 6 Volts + 6 Volts = 12 Volts @ 350 Amp hours.
If the above devices were
solar modules which were rated at 17 volts each @ 4.4 amps
then this series circuit would yield 34 volts at 4.4 amps.
Remember the Voltage in
a series circuit is additive and the Current stays the same.
To wire any
device in parallel you must connect the positive terminal of
the first device to the positive terminal of the next device
and negative terminal of the first device to the negative
terminal of the next device.
When you wire devices in parallel the resulting Voltage and
Current is just the opposite of a series circuit. Instead
the Voltage in a parallel circuit stays the same and the
Current is additive. If each device in the above example had
the potential of producing 350 Amp hours then 350 + 350
= 700 Amp hours, the Voltage would stay the same.
devices were batteries then this parallel circuit would
yield total voltage of 12 volts @ 700 Amp hours. If these
devices were solar modules that produced 17 Volts @ 4.4 amps
each then the this parallel circuit would yield 17 Volts @
example below four 17 Volt @ 4.4 Amp solar panels were wired
in parallel which yields 4.4 Amps + 4.4 Amps + 4.4 Amps +
4.4 Amps = 17.6 amps total @ 17 volts
if the above
devices were batteries which were rated at 12 volts each @
220 Amps hours then this parallel circuit would yield 12
volts @ 880 Amp hours.
the Voltage in a parallel circuit stays the same and the
Current is additive.
Hold on to
your hats because here's where it gets a little wild.
Actually you've already learned all you need to know to
under stand series/parallel circuits.
Series/parallel circuit is simply two or more series
circuits that are wired together in parallel.
In the above
example two separate pairs of 6 Volt batteries have been
wired in series and each of these series pairs have been
wired together in parallel.
You might be
asking why in the world would someone want to put them self
through this ? Well lets say that you want to increase the
Amp hour rating of a battery pack so that you could run your
appliances longer but you needed to wire the pack in such a
way as to keep the battery pack at 12 volts, or you want to
increase the charging capacity of your solar array but you
needed to wire the solar modules in such a way as to keep
the solar array at 34 volts, well, series/parallel is the
only way to do that.
parallel circuits the current is additive so thus you
increase your run time or Amp hour capacity or in the case
of solar modules, you increase your charging current by
wiring the batteries or solar modules in parallel. Since we
need 12 volts and have 6 volt batteries or in the case of
solar modules we need 34 Volts and have 17 Volt modules on
hand on hand, wiring the batteries or solar modules in
series allows us to get the 12 Volts or 34 Volts that we
An easy way
to visualize it would be to start by wiring the batteries in
individual sets that will give you the voltage that you
need. Lets say that you need 24 volts but have six volt
batteries on hand. First wire four of the batteries in
series to get 24 volts. (Remember wire in series to increase
the voltage) and continue to wire additional sets of four
batteries until the batteries are used up.
each series set of four batteries in parallel to each other
(Positive to positive to positive and so on and then
negative to negative to negative and so on) until each
series set is wired together in parallel. If each series set
of batteries equals 24 Volts at 350 Amp hours then five
series sets wired to each other in parallel would give you a
24 Volt @ 1750 Amp hour battery pack.
a series circuit the current stays the same but the voltage
is additive. In a parallel circuit the voltage stays the
same but the current is additive
Here is a sample
for a 12v inverter and eight
below is a description of what he did to wire them.
(inverter is a 12V inverter, I had to wire the batteries
together to make up a
bank. To start with, each battery is 6V. Just like
with solar panels, connecting batteries in series (positive
to negative) causes the voltage to add while the current (AHr)
stays the same. So I connected the positive of one 6V,
225AHr battery to the negative of another 6V, 225AHr battery
to end up with a 12V, 225AHr series string of batteries.
That gave me my 12V. So I repeated this with the remaining 6
batteries giving me 4 separate 12V, 225AHr series strings.
Since connecting them further in series would give me too
high a voltage, all that was left was to connect these
strings in parallel. Connecting in parallel leaves the
voltage the same but the current (AHr) adds. So now I had 4
parallel connected strings for a total battery bank size of
12V, 900AHr (4 x 225). Unfortunately I was too busy
installing the system to remember to take a photo but the
following diagram illustrates what I did.)
- Battery wiring diagram. -
How to Size Wiring for Your
Properly sized wire can make
the difference between inadequate and full charging of a
battery system, between dim and bright lights, and
between feeble and full performance of tools and
appliances. Designers of low voltage power circuits are
often unaware of the implications of voltage drop and
In conventional home electrical
systems (120/240 volts ac), wire is sized primarily for
safe amperage carrying capacity (ampacity). The
overriding concern is fire safety. In low voltage
systems (12, 24, 48VDC) the overriding concern is power
loss. Wire must not be sized merely for the ampacity,
because there is less tolerance for voltage drop (except
for very short runs). For example, at a constant wattage
load, a 1V drop from 12V causes 10 times the power loss
of a 1V drop from 120V.
Universal Wire Sizing Chart
A 2-Step Process
This chart works for any voltage
or voltage drop, American (AWG) or metric (mm2)
sizing. It applies to typical DC circuits and to
some simple AC circuits (single-phase AC with
resistive loads, not motor loads, power factor =
1.0, line reactance negligible).
STEP 1: Calculate the
|VDI = (AMPS x FEET)/(%VOLT DROP x
|VDI = Voltage Drop Index (a
reference number based on resistance of
FEET = ONE-WAY wiring distance (1 meter
= 3.28 feet)
%VOLT DROP = Your choice of acceptable
voltage drop (example: use 3 for 3%)
STEP 2: Determine
Appropriate Wire Size from Chart
Compare your calculated VDI with
the VDI in the chart to determine the closest
wire size. Amps must not exceed the AMPACITY
indicated for the wire size.
by cross-sectional area
(VDI x 1.1 = mm2)
(VDI x 1.7 = mm2)
1 1.5 2.5 4 6 10 16 25 35 50 70 95 120
20 Amp load at 24V over a distance of
100 feet with 3% max. voltage drop
|VDI = (20x100)/(3x24) =
||For copper wire, the nearest VDI=31.
This indicates #2 AWG wire or 35mm2
NOTES: AWG=Amercan Wire Gauge. Ampacity is
based on the National Electrical Code (USA) for
30 degrees C (85 degrees F) ambient air
temperature, for no more than three insulated
conductors in raceway in freee air of cable
types AC, NM, NMC and SE; and conductor
insulation types TA, TBS, SA, AVB, SIS, RHH,
THHN and XHHW. For other conditions, refer to
National Electric Code or an engineering
Use the following chart as your
primary tool in solving wire sizing problems. It
replaces many pages of older sizing charts. You can
apply it to any working voltage, at any percent voltage
voltage drop for various electrical loads
A general rule is to size the
wire for approximately 2 or 3% drop at typical load.
When that turns out to be very expensive, consider some
of the following advice. Different electrical circuits
have different tolerances for voltage drop.
LIGHTING CIRCUITS, INCANDESCENT
AND QUARTZ HALOGEN (QH): Don't cheat on these! A 5%
voltage drop causes an approximate 10% loss in light
output. This is because the bulb not only receives less
power, but the cooler filament drops from white-hot
towards red-hot, emitting much less visible light.
LIGHTING CIRCUITS, FLUORESCENT:
Voltage drop causes a nearly proportional drop in light
output. Flourescents use 1/2 to 1/3 the current of
incandescent or QH bulbs for the same light output, so
they can use smaller wire. We advocate use of quality
fluorescent lights. Buzz, flicker and poor color
rendition are eliminated in most of today's compact
fluorescents, electronic ballasts and warm or full
DC MOTORS may be used in
renewable energy systems, especially for water pumps.
They operate at 10-50% higher efficiencies than AC
motors, and eliminate the costs and losses associated
with inverters. DC motors do NOT have excessive power
surge demands when starting, unlike AC induction motors.
Voltage drop during the starting surge simply results in
a "soft start".
AC INDUCTION MOTORS are
commonly found in large power tools, appliances and well
pumps. They exhibit very high surge demands when
starting. Significant voltage drop in these circuits may
cause failure to start and possible motor damage. Follow
the National Electrical Code. In the case of a well
pump, follow the manufacturer's instructions.
PV-DIRECT SOLAR WATER PUMP
circuits should be sized not for the nominal voltage (ie.
24V) but for the actual working voltage (in that case
approximately 34V). Without a battery to hold the
voltage down, the working voltage will be around the
peak power point voltage of the PV array.
PV BATTERY CHARGING CIRCUITS
are critical because voltage drop can cause a
disproportionate loss of charge current. To charge a
battery, a generating device must apply a higher voltage
than already exists within the battery. That's why most
PV modules are made for 16-18V peak power point. A
voltage drop greater than 5% will reduce this necessary
voltage difference, and can reduce charge current to the
battery by a much greater percentage. Our general
recommendation here is to size for a 2-3% voltage drop.
If you think that the PV array may be expanded in the
future, size the wire for future expansion. Your
customer will appreciate that when it comes time to add
to the array.
WIND GENERATOR CIRCUITS: At
most locations, a wind generator produces its full rated
current only during occasional windstorms or gusts. If
wire sized for low loss is large and very expensive, you
may consider sizing for a voltage drop as high as 10% at
the rated current. That loss will only occur
occasionally, when energy is most abundant. Consult the
wind system's instruction manual.
More techniques for cost
ALUMINUM WIRE may be more
economical than copper for some main lines. Power
companies use it because it is cheaper than copper and
lighter in weight, even though a larger size must be
used. It is safe when installed to code with AL-rated
terminals. You may wish to consider it for long,
expensive runs of #2 or larger. The cost difference
fluctuates with the metals market. It is stiff and hard
to bend, and not rated for submersible pumps.
HIGH VOLTAGE PV MODULES:
Consider using higher voltage modules and a MPPT solar
charge controller to down convert to the system voltage
(e.g. 12, 24 and 48V) to compensate for excessive
voltage drop. In some cases of long distance, the
increased module cost may be lower than the cost of
SOLAR TRACKING: Use a solar
tracker (e.g. Zomeworks or Unirac) so that a smaller
array can be used, particularly in high summer-use
situations (tracking gains the most energy in summer
when the sun takes the longest arc through the sky). The
smaller PV array will require smaller wire.
WATER WELL PUMPS: Consider a
slow-pumping, low power system with a storage tank to
accumulate water. This reduces both wire and pipe sizes
where long lifts or runs are involved. A PV array-direct
pumping system may eliminate a long wire run by using a
separate PV array located close to the pump. Many of our
solar water pumps are highly efficient DC pumps that are
available up to 48V. We also make AC versions and
converters to allow use of AC transmitted over great
distances. These pumps draw less running current, and
far less starting current than conventional AC pumps,
thus greatly reducing wire size requirements.
AWG Copper Wire Table
||Feet per Pound
Observe Proper Wire Size
The most important wiring practice
is to observe proper wire size. Failure to use adequate size
can result in fire. Even if fire doesn't result, wires that
are too small will cause marginal performance of electrical
Distance - Feet
Using the Table
The table shows the wire size
required for a 3% voltage drop in 12 Volt circuits.
To use the table, first calculate the total length of the
wire from the source to the device and back again. Next,
determine the amount of current in the wire. The wire gauge
is found at the intersection of Amps and Feet. In most load
circuits, a 3% drop is quite acceptable. In charging
circuits it often pays to have less of a drop. Always use
one size bigger if practical.
The National Electrical Code [NEC]
requires their own cable sizing for premises wiring. Refer
to the NEC rules to determine building wiring, as this page
relates to electronic equipment wiring. For reference, the
ampacity of copper wire at 300C for common wire
14 AWG may carry a maximum of 20 Amps in free air, or 15
Amps as part of a 3 conductor cable.
12 AWG may carry a maximum of 25 Amps in free air, or 20
Amps as part of a 3 conductor cable.
10 AWG may carry a maximum of 40 Amps in free air, or 30
Amps as part of a 3 conductor cable.
8 AWG may carry a maximum of 70 Amps in free air, or 50 Amps
as part of a 3 conductor cable.
How Much Voltage
Should Your Solar Panel Be?
A good question when
building solar panels is how much voltage do you
want it to put out? It's basically a question of
balancing size and power. First though, let's
talk about the minimum voltage that you'd need
for the 3 main renewable energy system voltages:
12V, 24V and 48V.
A fully charged 12 volt
battery doesn't exactly hold 12 volts. Usually
the fully charged voltage is anywhere from 12.6
volts and 14.8 volts (depending on the type of
battery you have). That means at a minimum your
solar panel will need to put out at least 15
volts. Since each solar cell puts out 0.55 volts
you'll need at least 27 cells to charge your
battery. Since each solar panel should have
cells that are multiples (2x2, 3x3 etc) your
panel should have at least 28 cells for
aesthetic reasons. It would look a little weird
to see a panel with only 27 cells.
The same applies to 24
and 48 volt panels. Fully charged 24 volt
batteries (usually two 12 volts wired in series)
hold between 25 and 30 volts. Your panel should
generate at least 30 volts (55 cells minimum). A
48 volt panel fully charged will be between 50
and 60 volts so you'll need to generate that
Basic about Solar Energy,
Solar Power and Solar Electricity.
In basic about solar energy, solar power and solar
eletricity we will talk about the basic things behind this
power. Formulas that will be used to find out which Solar
Panel you should use and which battery you should select.
And how much Solar Panels do you need to power up lights and
other applications. Here are the main things you need to
know and that will be used to calculate your needs. AC-DC
system, Volt, Current(Ampere), Power(Watt), Resistance,
Series and Parallel connecting.
Ac stands for Alternative Current. Alternative current is
almost that we found in wall outlet or electric outlet.
Clever say'd that we found in wall. It is 230 Volt. DC
stands for Direct Current. In solar panels it is used 12
volt dc system. DC is that current we can found in cells,
batteries, and using adapters or regulators. See the picture
of a dell charger. Dell charger also converts AC Current to
DC 5.4 Volt and 2410mA. Solar Panels also uses DC voltage
Voltage is the electromotive force (pressure) applied to an
electrical circuit measured in volts (E).
Example. P=200W, I=4.0A. If we have a value of watt and
ampere and we want to find out how much volt does it use
then we should use this from Power Circle. E=P/I.
200/4.0=50V. So we found voltage is 50V.
Current is the flow of electrons in an electrical circuit
measured in amperes (I).
Example. P=100W, E=12V. We want to find out how much ampere
does it use. We take a look at circle. I=P/E. 100/12=8.33A.
Current usage is 8.33A.
Power is the product of the voltage times the current in an
electrical circuit measured in watts (P).
Example. E=220V, I=0,4A. This example is taken from picture
of Dell Charger. We have 400mA=0,4A. Take a look at circle
P=E*I. 220V * 0,4A=88W. Answer is dell charger use 88Watt.
Resistance is the opposition to the flow of electrons in an
electrical circuit measured in ohms (R). Increased
resistance gives higher voltage and higher power(watt).
Example. E=12V, I=3.0A. We want to find out resistance. We
use formula R=E/I. 12V/3.0A = 4 Ohm.
Parallel Connecting - 12V
Parallel Connecting solar panels gives higher current. And
voltage will remain the same. Parallel Connecting is best
for us. Because we do not need high voltage. Normal battery
is 12v. And by selecting high voltage require higher voltage
charge controller. To connect solar panels in parallel we
have to connect plus + to plus and minus - to minus. See the
picture for details.
Series Connecting - 24V
By connecting Solar Panels in series connection. It will
increase Voltage and current Amps. will remain the same. To
connect solar panels in series we have to connect plus + to
- minus on next panel. See the picture for details. In this
example we have connected 2 solar panels in series which
will give 24v output.
Series and Parallel
Connecting - 24v System
If we are creating a 24v system. So then we have to connect
two solar panels in series and connect two series connected
panels in parallel as showed in figure under. Which
increases voltage to 24v and when we have connected two
other 24v connected solar panels in parallel so voltage
remains same and increases current Amps. If we want to
increase output current on 24v so we connect more solar
panels in parallel same way under as shown in figure under.