Download Amateur Radio Electrical Power Sources

Amateur Radio Electrical Power Sources
Waterville Area Wireless Association
Feb 2012 - Steve Roderick - KA1C
Types of Electrical Power & Their Sources
There are 6 common sources of electricity, which are...
- Magnetism produces electricity with a generator powered by wind, water, or a fossil fuel engine
- Chemicals produce electricity with cells & batteries, both dry & wet
- Light
produces electricity with a solar cell or solar panel
- Heat
produces electricity with a thermo-couple (2 dissimilar metals fastened together)
- Friction
produces static electricity (lightening, feet on a rug, clothing, or dryer static cling)
- Pressure
produces piezo-electricity from a crystal (a mic, phonograph needle, or a grill igniter)
When a difference of potential exists we say we have a voltage, such as the difference between the positive &
negative terminals of a size “D” dry cell. This voltage would be close to 1.55 volts for a fully charged zinccarbon dry cell. This force, called electromotive force, is why Ohm’s Law uses the letter “E” for voltage.
Generally, voltages are either alternating current or direct current, known as AC or DC.
Question: How can you tell if an electrician is being shocked by AC or DC?
Answer: If it's AC, his teeth chatter violently. If it's DC, they just clamp shut!
AC Voltage Sources
AC can be obtained from your local power company, an internal combustion engine generator, a wind
generator, or an inverter connected to a source of DC power, such as a battery.
Advantages of AC Power
AC is usually produced with reasonably steady currents & voltages, which tend to hold their values and not
drop off like a discharging battery would. They are fairly economical, reliable, and it is easy to change their
voltage and/or current with a transformer.
Disadvantages of AC Power
Production of AC power usually means you are physically tied to one location. If you use a generator, there are
fumes to deal with, refueling needs, and safe fuel storage. A generator is usually off-line while refueling takes
place, while a battery will remain on line while being charged. A wind generator is another possible source, but
also limits you to one location. Both wind & fossil fuel generators are known to create some environmental
noise.
DC Voltage Sources
The most practical sources of direct current are from batteries and cells, solar panels, and wind generators. DC
power is also available from an AC operated power supply, and many units from Astron, Tripplite, etc., produce
good, stable, well-regulated & filtered DC power. Most units will have over voltage & over current protection,
and will not be bothered by RF from your radio if the radio is properly grounded. Linear power supplies are
very heavy, inefficient, but produce very little RFI, while switching power supplies may create tremendous
amounts of RFI, but are very efficient and light weight.
Advantages of DC Power
Batteries and cells are very portable, and some solar panels are somewhat portable. Many types of rechargeable
batteries are available, such as NiCad, NiMih, Li-Ion, automotive starting, deep cycle, marine, AGM, & gelled,
and these can be reused many times. There are also many types of non-rechargeable batteries and cells, and
even though they cannot be recharged, they can be purchased locally. This makes replacement fairly easily.
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Disadvantages of DC Power
DC power is seldom steady when produced by chemical means. As the battery or cell discharges, the voltage
and current are slowly but constantly diminishing, and if not recharged in time, may damage the battery. At
some point in the discharge curve, your electronic device will cease to operate properly, possibly causing
distortion of the your signal, and will eventually stop working altogether.
Older NiCad batteries suffered from memory effect. This is where if you didn’t discharge the battery down to a
specific end point, they wouldn’t take a full charge the next time. During each charge cycle, the battery charges
less and less until it becomes useless. If properly cared for, you could expect about 300 cycles of charging &
use. Leaving these types of batteries in the charger to “cook” would also shorten their life. Many types of
batteries used in power tools are delivered in “life support” mode, meaning they are charged only to a point
where their shelf life is maximized, and where they have the best chance of the longest life. The warnings to
“fully charge before use” are very important, as attempting to use a non-fully charged battery on “life support”
may very well end its life.
Automotive batteries are considered starting batteries. They are not designed for running continuous loads, so
when you connect your radio, they usually don’t last very long in a slow drain. They are designed for
producing large amounts of current for short periods of time, and like to be immediately recharged. Recharging
them produces explosive hydrogen gas. Remember: when connecting jumper cables, connect good battery
positive to dead battery positive, then good battery negative to the “frame of the dead battery vehicle!” This
will charge the dead battery from the good one and the alternator of the running car. Connecting the last
negative cable will cause the dead battery to produce hydrogen gas, and it will also cause a connection “spark”,
but the spark will be far enough away from the hydrogen gas. I hear smoking while doing this can also be fun
to watch; from a distance!
Question: What's the difference between men and batteries?
Answer: Batteries always have a positive side.
Other thoughts on Dry Cells & Batteries
With chemical voltage sources, a cell is a unit of one, while a battery is more than one cell; so technically, a
“D” cell is not a battery. A nine-volt battery is a battery, because it is made from 6 individual 1.5-volt dry cells
wired together in series (6 x 1.5 = 9). All dry cells produce the same 1.5 volts, regardless of their size. The
bigger sizes such as C and D just produce more current. Common sizes include AAA, AA, C, and D. There
used to be sizes A and B, but no longer.
If you were to ask someone for a B-battery, would they think you were stuttering?
Some Available Currents and Capacities from Batteries and Cells
Cell
carbon/zinc
Alkaline
NiCad
AAA
20 ma
100 ma
600 ma
AA
25 ma
150 ma
1000 ma
C
80 ma
480 ma
3000 ma (3 amps)
D
150 ma
650 ma
10,000 ma (10amps)
N (12v)
20 ma
85 ma
300 ma
Ampere-hours (ah) of various sizes of carbon-zinc cells are:
AA - 0.4ah
C - 1.5ah
D - 3.4ah
F - 5.2ah (cells used in 6v lantern battery)
Alkaline cells usually have capacities roughly 1.5 - 2.5 times higher.
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Question: If you get batteries free of charge, does that mean they are dead?
In very cold weather, always warm up your car battery by turning on the headlights for about 10 seconds, then
shut them off and wait 10 seconds before starting the car. This will run a small current through the battery, thus
warming it up, before you call on it for a very heavy amp load. It is like stretching before exercising.
A common problem with dry batteries and cells is shelf life. This is how long they will remain charged while
just sitting there on the shelf. This is similar to a loaf of bread sitting on the shelf and drying out, and after
about a month, the bread probably isn’t much good! Battery & cell shelf life is caused by the electrolyte in the
battery or cell drying out, especially from excessive heat. Do not store your good batteries & cells in a warm
environment. A cold cellar, etc., is much better for them. A freezer is a great place for long-term battery & cell
storage, probably inside a plastic zip-lock bag.
If you short out a battery or cell with a small diameter wire, you just created a light bulb, or a toaster, or both!
If you short out a hi-capacity battery or cell with a large diameter conductor, the battery will probably explode.
Don’t place spare HT batteries in your pocket with your change, etc. (Fire or explosion in a delicate area!)
Always fuse both leads of a radio right where it connects to the battery.
Gelled batteries are probably best for ham radio power sources because they can be charged with the 13.8v
station power supply.
Absorbed glass mat (AGM) batteries would need a higher charge voltage such as 14.2v. Always place storage
batteries in a marine battery box with the cover on it.
Thoughts on charging of Wet (flooded) Batteries
12-volt (13.6v actually) car batteries are made from 6 individual wet cells with lead plates. The more plates
they have, the more capacity & heaviness. More plates do not create more voltage, just more amp-hours.
Wet cells make up the batteries we have in our car. The chemical reaction between the sulfuric acid and the
lead plates generates 2.2 volts of electricity. Most car batteries are not sealed, and will spill or leak acid if not
kept upright. To neutralize battery acid, use a chemical base like baking soda (and water).
Sealed lead-acid batteries will not leak, although they may discharge gasses if not charged properly. Sealed
lead-acid batteries come in two forms: Gel cells and AGM (absorbed glass mat).
Gel cells are somewhat more difficult to manufacture as getting the gel just right is a problem. Instead of a
liquid, the acid is in a gel form, which remains between the lead plates. Gel cells are said to work better than
AGM batteries in conditions where they have long use and frequent cycling. Golf carts and wheelchairs are
uses where gel cells work better than AGMs. The batteries are more deeply discharged and are used frequently,
then recharged.
AGM’s seem more efficient at uses where they are deeply discharged but only infrequently, being kept on a
floating charge. Uninterruptible power supplies is one such use. The battery in a UPS is kept fully charged
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while the power is on, but when the power goes off, the computers, monitors, printers, and such pull a lot of
current from the battery until they can be shut down properly.
The differences between gel cells and AGMs may make no difference to non-critical users who need a big
capacity, portable battery, for occasional use. This includes ham radio operators who need a big battery for a
day or two in the field, or for campers who want to take a battery on camping trips to run lights, etc.
Using a charged battery discharges it. Wet cells and dry cells "self discharge" over time (shelf life), while wet
cells can maintain a workable charge for about a year after the last full charge. When cold, wet cells loose
power and cannot deliver their rated charge. Instead of waiting a year for the battery to run down, either
recharge your wet battery every six months, or keep it fully charged all the time by putting a floating charge on
it.
When manufacturers give a rated capacity, it is based on a draw of 1/20th of the rated capacity. This is
sometimes expressed by the formula 1/20 x C, where C is the rated capacity. If the battery has a manual, it may
have a chart showing different capacities based on different draws. If the discharge rate is greater than 1/20 x
C, the battery will not last for its rated capacity. For example, a 10 amp-hour battery discharged at 1/4 x C will
not last for the expected time.
"Full" discharge for a 12V lead-acid car battery is considered to be 10V. When fully charged, a 12v battery will
measure over 13.2V at the terminals. When the battery shows 10V at the terminals with no load, the
manufacturer deems the battery fully discharged. Frequent full discharges will damage the battery, causing the
lead plates to sulfate. If you have a 7 amp-hour battery, and drain it at the recommended 1/20 x C until the
battery is at or less than 10V, you will damage the battery, and it will no longer take a full charge and deliver its
rated capacity.
Consider an electric scooter. If you use the cart for a couple of days without recharging it, even draining it at
the preferred rate, you will have drained it deeper than it should have been, and it will be dead before you finish
your second day. The battery will now be over discharged, and probably never provide the rated output again.
On the other hand, if you have a UPS and the power fails while you have a job to finish, your running the
computer, monitor, and printer for 30 minutes to print, save, and shut down the system will draw only 7 amps
for 0.5 hours. You have drawn only (7 amps x 0.5 hour =) 3.5 amps from a 7 amp-hour battery. It will recover.
When charging a battery, the rule of thumb is to divide the capacity by 10 (C/10) to recharge a battery. With
the 7 amp-hour battery, we want about 700 milliamps to recharge it. A hundred or so milliamps either way will
do no damage. Smaller amperages will take longer to charge and may not ever fully re-charge a big battery.
Larger charging amperages may damage the battery. The higher current will heat the solution (liquid or gel),
causing it to give off gasses. Sealed batteries have one-way valves to vent the gas, but remember, the gas is
hydrogen, which is explosive! Do not charge batteries in an enclosed box. With non-sealed lead-acid batteries,
the liquid will evaporate when overheated, exposing the lead plates and allowing them to sulfate.
A rule of thumb says that it can take over half a day to fully charge a battery, and 15 hours is not uncommon.
If your charger is too big for the battery (providing, for example, 2 amps for a 7 amp-hour battery) and the
charger provides a switch from charge to maintaining a float charge, the battery may never provide enough
resistance to the charger for it to sense that the battery is fully charged and to switch from charge to float. This
means you will still be charging the battery as long as the charger is connected, and you will overcharge the
battery.
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When trickle charging a flooded cell battery that is below 10v, use about 50ma to bring it up to 10 volts, just in
case there is a dead or shorted cell. Once a battery reaches 10 volts, it can be bulk or high current charged until
it reaches its peak voltage of 13.8v and the current has diminished to 1/10 of maximum charge. At this point, it
should be float-charged to maintain 13.5v indefinitely (in storage or standby?)
Some common gelled battery recommended charging currents
3 - 12ah
1amp
13 - 32ah
4amp
33 - 50ah
7amp
51ah & up 10amp
Remember: Batteries do not make electricity; they store it. They do this best under very specific conditions.
Typical efficiency in a lead-acid car battery is 85-95%. Alkaline and NiCad batteries reach about 65%. True
deep cycle AGM's can approach 98%.
One important fact is that all of the batteries commonly used in deep cycle applications are lead-acid. This
includes the standard flooded-cell (wet) batteries, gelled, and AGM. They all use the same chemistry, although
the actual construction of the plates, etc., varies.
Major Battery Types
Batteries are divided in two ways, by application or what they are used for, and construction or how they are
built.
The major applications are automotive, marine, and deep-cycle. Deep-cycle includes solar electric (PV),
backup power, and RV and boat "house" batteries.
The major construction types are flooded (wet), gelled, and AGM (Absorbed Glass Mat). AGM batteries are
also sometimes called "starved electrolyte" or "dry", because the fiberglass mat is only 95% saturated with
sulfuric acid and there is no excess liquid.
Flooded cells may be standard, with removable caps, or the so-called "maintenance free" which means they are
designed to die one week after the warranty runs out! All gelled batteries are sealed and are "valve regulated",
which means that a tiny valve keeps a slight positive pressure. Nearly all AGM batteries are sealed valve
regulated (commonly referred to as "VRLA" - Valve Regulated Lead-Acid). Most valve regulated are under
some pressure - 1 to 4 psi at sea level.
These are some typical (minimum/maximum) 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.
Expected life of batteries if used in deep cycle service
Car starting battery 3-12 months
Marine battery
1-6 years
Golf cart battery
2-7 years
AGM deep cycle
4-7 years
Gelled deep cycle
2-5 years
Telephone (float)
2-20 years
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Starting, Marine, and Deep-Cycle Batteries
Starting (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
cycles if deep cycled, while they may last for thousands of cycles in normal starting use (2-5% discharge).
Deep cycle batteries are designed to be discharged down as much as 80% of capacity, 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. Although these can be cycled down to 20% charge, the best lifespan vs. cost method is to keep the
average cycle at about 50% discharge.
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 cart battery is quite popular for small systems and RV’s. The
problem is that “golf cart” 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 cart battery can vary considerably – ranging from the
cheap off brand with thin plates, up to the true deep cycle brands.
Marine batteries are usually a “hybrid”, and fall between the starting and deep-cycle batteries. 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 or 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.
Gelled electrolyte
Gelled batteries, or “Gel Cells” contain acid that has been “gelled” by the addition of silica gel, turning the acid
into a solid mass that looks like gooey Jell-O. The advantage of these batteries is that it is impossible to spill
acid even if they are broken. However, there are several disadvantages. One is that they must be charged at a
slower rate (C/20) to prevent excess gas from damaging the cells. They cannot be fast charged on a
conventional automotive charger or they may be permanently damaged. This is not usually a problem with
solar electric systems, but if an auxiliary generator or inverter bulk charger is used, current must be limited to
the manufacturers specifications. Most good-quality inverters commonly used in solar electric systems can be
set to limit charging current to the batteries.
Some other disadvantages of gel cells are that they must be charged at a lower voltage (2/10th’s less) than
flooded or AGM batteries. If overcharged, voids can develop in the gel, which will never heal, causing a loss in
battery capacity. In hot climates, water loss can be enough over 2-4 years to cause premature battery death.
The newer AGM (absorbed glass mat) batteries have all the advantages of gelled, with none of the
disadvantages.
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AGM, or Absorbed Glass Mat Batteries
A newer type of sealed battery uses "Absorbed Glass Mats", or AGM between the plates. This is a very fine
fiber boron-silicate glass mat. These types of batteries have all the advantages of gelled, but can take much
more abuse. These are also called "starved electrolyte", as the mat is about 95% saturated rather than fully
soaked. That also means that they will not leak acid even if broken.
AGM batteries have several advantages over both gelled and flooded, at about the same cost as gelled.
Since most all of the electrolyte (acid) is contained in the glass mats, they cannot spill, even if broken. This also
means that since they are non-hazardous, the shipping costs are lower. In addition, since there is no liquid to
freeze and expand, they are practically immune from freezing damage.
Nearly all AGM batteries are "recombinant" - what that means is that the oxygen and hydrogen recombine
INSIDE the battery. These use gas phase transfer of oxygen to the negative plates to recombine them back into
water while charging and prevent the loss of water through electrolysis. The recombining is typically 99+%
efficient, so almost no water is lost.
The charging voltages are the same as for any standard battery - no need for any special adjustments or
problems with incompatible chargers or charge controls. And, since the internal resistance is extremely low,
there is almost no heating of the battery even under heavy charge and discharge currents. Most AGM batteries
have no charge or discharge current limits.
AGM's have a very low self-discharge - from 1% to 3% per month is usual. This means that they can sit in
storage for much longer periods without charging than standard batteries.
AGM's do not have any liquid to spill, and even under severe overcharge conditions, hydrogen emission is far
below the 4% max specified for aircraft and enclosed spaces. The plates in AGM's are tightly packed and
rigidly mounted, and will withstand shock and vibration better than any standard battery.
Even with all the advantages listed above, there is still a place for the standard flooded deep cycle battery.
AGM's will cost about 1.5 to 2 times as much as flooded batteries of the same capacity. In many installations,
where the batteries are set in an area where you don't have to worry about fumes or leakage, a standard or
industrial deep cycle is a better economic choice. AGM batteries main advantages are no maintenance,
completely sealed against fumes, hydrogen, or leakage, non-spilling even if they are broken, and can survive
most freezes. Not everyone needs these features, though.
Cycles vs. Life
A battery "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 has 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.
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Battery 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 to 10%. This happens
because at very shallow cycles, the lead dioxide tends to build up in clumps on the positive plates rather in an
even film.
Myth: The old myth about not storing batteries on concrete floors is just that - a myth. This story has been
around for 100 years, and originated back when battery cases were made up of wood and asphalt. The acid
would leak from them, and form a slow-discharging circuit through the now acid-soaked and conductive floor.
Amp-Hour Capacity
All deep cycle batteries are rated in amp-hours. An amp-hour is one amp for one hour, or 10 amps for 1/10 of
an hour and so forth. It is amps x hours. If you have something that pulls 20 amps, and you use it for 20
minutes, then the amp-hours used would be 20 (amps) x .333 (hours), or 6.67 AH. The generally accepted AH
rating time period for batteries used in solar electric and backup power systems (and for nearly all deep cycle
batteries) is the "20 hour rate". This means that it is discharged down to 10.5 volts over a 20-hour period while
the total actual amp-hours it supplies is measured. Sometimes ratings at the 6-hour rate and 100-hour rate are
also given for comparison and for different applications. The 6-hour rate is often used for industrial batteries, as
that is a typical daily duty cycle. Sometimes the 100-hour rate is given just to make the battery look better than
it really is, but it is also useful for figuring battery capacity for long-term backup amp-hour requirements.
Battery Charging
Battery charging takes place in 3 basic stages: Bulk, Absorption, and Float.
Bulk Charge - The first stage of 3-stage battery charging. Current is sent to batteries at the maximum safe rate
they will accept until voltage rises to near (80-90%) full charge level. Voltages at this stage typically range
from 10.5 volts to 15 volts. There is no "correct" voltage for bulk charging, but there may be limits on the
maximum current that the battery and/or wiring can take.
Absorption Charge: The 2nd stage of 3-stage battery charging. Voltage remains constant and current gradually
tapers off as internal resistance increases during charging. It is during this stage that the charger puts out
maximum voltage. Voltages at this stage are typically around 14.2 to 15.5 volts.
Float Charge: The 3rd stage of 3-stage battery charging. After batteries reach full charge, charging voltage is
reduced to a lower level (typically 12.8 to 13.2) to reduce gassing and prolong battery life. This is often
referred to as a maintenance or trickle charge, since it's main purpose is to keep an already charged battery from
discharging. PWM, or "pulse width modulation" accomplishes the same thing. In PWM, the controller or
charger senses tiny voltage drops in the battery and sends very short charging cycles (pulses) to the battery.
This may occur several hundred times per minute. It is called "pulse width" because the width of the pulses
may vary from a few microseconds to several seconds. Note that for long term float service, such as backup
power systems that are seldom discharged, the float voltage should be around 13.02 to 13.20 volts.
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Chargers: Most garage and consumer (automotive) type battery chargers are bulk charge only, and have little
(if any) voltage regulation. They are fine for a quick boost to low batteries, but not to leave on for long periods.
Among the regulated chargers, there are the voltage regulated ones which keep a constant regulated voltage on
the batteries. If these are set to the correct voltages for your batteries, they will keep the batteries charged
without damage. These are sometimes called "taper charge" - as if that is a selling point. What taper charge
really means is that as the battery gets charged up, the voltage goes up, so the amps out of the charger goes
down. They charge OK, but a charger rated at 20 amps may only be supplying 5 amps when the batteries are
80% charged. To get around this, many companies have come out with "smart", or multi-stage chargers. These
use a variable voltage to keep the charging amps much more constant for faster charging.
Charge controllers
A charge controller is a regulator that goes between the solar panels and the batteries. Regulators for solar
systems are designed to keep the batteries charged at peak without overcharging.
Battery Charging Voltages and Currents:
Most flooded batteries should be charged at no more than the "C/8" rate for any sustained period. "C/8" is the
battery capacity at the 20-hour rate divided by 8. For a 220 AH battery, this would equal 26 Amps.
Gelled cells should be charged at no more than the C/20 rate, or 5% of their amp-hour capacity.
Charging at 15.5 volts will give you a 100% charge on lead-acid batteries. Once the charging voltage reaches
2.583 volts per cell, charging should stop or be reduced to a trickle charge. Note that flooded batteries MUST
bubble (gas) somewhat to insure a full charge, and to mix the electrolyte. Float voltage for lead-acid batteries
should be about 2.15 to 2.23 volts per cell, or about 12.9-13.4 volts for a 12-volt battery. At higher
temperatures (over 85 degrees F) this should be reduced to about 2.10 volts per cell.
Never add acid to a battery except to replace spilled liquid. Distilled or de-ionized water should be used to top
off non-sealed batteries. Float and charging voltages for gelled batteries are usually about 2/10th volt less than
for flooded to reduce water loss. Note that many shunt-type charge controllers sold for solar systems will NOT
give you a full charge - check the specifications first. To get a full charge, you must continue to apply a current
after the battery voltage reaches the cutoff point of most of these types of controllers.
Flooded battery life can be extended if an equalizing charge is applied every 10 to 40 days. This is a charge
that is about 10% higher than normal full charge voltage, and is applied for about 2 to 16 hours. This makes
sure that all the cells are equally charged, and the gas bubbles mix the electrolyte. If the liquid in standard wet
cells is not mixed, the electrolyte becomes "stratified". You can a have very strong solution at the bottom, and
very weak at the top of the cell. With stratification, you can test a battery with a hydrometer and get readings
that are quite a ways off. If you cannot equalize for some reason, you should let the battery sit for at least 24
hours and then use the hydrometer. AGM and gelled should be equalized 2-4 times a year at most - check the
manufacturers recommendations, especially on gelled.
Battery Aging
As batteries age, their maintenance requirements change. This means longer charging time and/or higher finish
rate (higher amperage at the end of the charge). Usually older batteries need to be watered more often. And,
their capacity decreases.
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Mini Factoids
Nearly all batteries will not reach full capacity until cycled 10-30 times. A brand new battery will have a
capacity of about 5-10% less than the rated capacity.
Batteries should be watered after charging unless the plates are exposed, then add just enough water to cover the
plates. After a full charge, the water level should be even in all cells and usually 1/4" to 1/2" below the bottom
of the fill well in the cell (depends on battery size and type).
In situations where multiple batteries are connected in series, parallel, or series/parallel, replacement batteries
should be the same size, type and manufacturer (if possible). Age and usage level should be the same as the
companion batteries. Do not put a new battery in a pack that is more than 6 months old or has more than 75
cycles on it. Either replace with all new or use a good used battery.
The vent caps on flooded batteries should remain on the battery while charging. This prevents a lot of the water
loss and splashing that may occur when they are bubbling.
When you first buy a new set of flooded (wet) batteries, you should fully charge and equalize them, and then
take a hydrometer reading for future reference. Since not all batteries have exactly the same acid strength, this
will give you a baseline for future readings.
When using a small solar panel to keep a float (maintenance) charge on a battery (without using a charge
controller), choose a panel that will give a maximum output of about 1/300th to 1/1000th of the amp-hour
capacity. For a pair of golf cart batteries, that would be about a 1 to 5 watt panel - the smaller panel if you get 5
or more hours of sun per day, the larger one for those long cloudy winter days in the northeast.
Lead-acid batteries do NOT have a memory, and the rumor that they should be fully discharged to avoid this
"memory" is totally false and will lead to early battery failure.
Inactivity can be extremely harmful to a battery. It is a VERY poor idea to buy new batteries and "save" them
for later. Either buy them when you need them, or keep them on a continual trickle charge. The best thinking
is, if you buy them now use them now.
Only clean water should be used for cleaning the outside of batteries. Solvents or spray cleaners should not be
used.
Some Battery Terms and Explanations
Ampere or Amp - An ampere or an amp is a unit of measurement for an electrical current. One amp is the
amount of current produced by an electromotive force of one volt pushing through the resistance of one ohm. It
is named for the French physicist Andre Marie Ampere. The abbreviation for amp is A, but its mathematical
symbol is "I". Small currents are measured in milliamps or thousandths of an amp.
Amp Hour or Ampere-Hour - A unit of measurement of a battery's electrical storage capacity. Current
multiplied by time in hours equals ampere-hours. One amp hour is equal to a current of one ampere flowing for
one hour. Also, 1 amp hour is equal to 1,000 mAh
Ampere-Hour Capacity - The number of ampere-hours that can be delivered by a battery on a single
discharge.
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Actual Capacity or Available Capacity - The total battery capacity, usually expressed in ampere-hours or
milliampere-hours, available to perform work. The actual capacity of a particular battery is determined by a
number of factors, including the cut-off voltage, discharge rate, temperature, method of charge, and the age and
life history of the battery.
Battery - An electrochemical device used to store energy. The term is usually applied to a group of two or
more electric cells connected together electrically. In common usage, the term “battery” is also sometimes
applied to a single cell, such as an “AA battery”.
Battery Capacity - The electric output of a cell or battery on a service test delivered before the cell reaches a
specified final electrical condition, and may be expressed in ampere-hours, watt- hours, or similar units. The
capacity in watt-hours is equal to the capacity in ampere-hours multiplied by the battery voltage.
Battery Charger - A device capable of replacing electrical energy in a battery.
Battery-Charge Rate - The current expressed in amperes (A) or milliamps (ma) at which a battery is charged.
Cutoff Voltage - The prescribed lower-limit voltage at which battery discharge is considered complete. The
cutoff voltage is usually chosen so that the maximum useful capacity of the battery is realized.
C - Used to signify a rate of charge or discharge equal to the capacity of a battery divided by 1 hour. Thus C for
a 1600 mAh battery would be 1.6 A, C/5 for the same battery would be 320 ma and C/10 would be 160 ma.
Capacity - The capacity of a battery is a measure of the amount of energy that it can deliver in a single
discharge. Battery capacity is normally listed as amp-hours (or milliamp-hours) or as watt-hours.
Cell - An electrochemical device composed of positive and negative plates and electrolyte, which is capable of
storing electrical energy. Two or more cells are combined together to form batteries.
Charge Rate - The amount of current applied to battery during the charging process. This rate is commonly
expressed as a fraction of the capacity of the battery. For example, the C/2 or C/5.
Charging - The process of supplying electrical energy for conversion to stored chemical energy.
Constant-Current Charge - A charging process in which the current applied to the battery is maintained at a
constant value.
Constant-Voltage Charge - A charging process in which the voltage applied to a battery is held at a constant
value.
Cycle - One sequence of a charge and a discharge.
Deep Cycle - A cycle in which the discharge is continued until the battery reaches it’s cut-off voltage, usually
80% of discharge.
Shallow Cycling - Charge and discharge cycles, which do not allow the battery to approach its cutoff voltage.
Shallow cycling of NiCd cells leads to “memory effect”. Shallow cycling is not detrimental to NiMH cells and
it is the most beneficial for lead acid batteries.
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Cycle Life - For rechargeable batteries, the total number of charge/discharge cycles the cell can sustain before
its capacity is significantly reduced. The end of life is usually considered to be when the cell or battery delivers
only 80% of its rated ampere-hour capacity. NiMH batteries typically have a cycle life of 500 cycles. NiCd
batteries can have a cycle life of over 1,000 cycles. The cycle of a battery is greatly influenced by the type of
depth of the cycle (deep or shallow), and the method of recharging. Improper charge cycle cutoff can greatly
reduce the cycle life of a battery.
Direct Current (DC) - The type of electrical current that a battery can supply. One terminal is always positive
and another is always negative.
Discharge - The conversion of the chemical energy of the battery into electric energy, causing the battery to
become drained or discharged.
Depth of Discharge (DOD) - The amount of energy that has been removed from a battery (or battery pack).
Usually expressed as a percentage of the total capacity of the battery. For example, 50% depth of discharge
means that half of the energy in the battery has been used. 80% DOD means that eighty percent of the energy
has been discharged, so the battery now holds only 20% of its full charge.
End-of-Discharge Voltage - The voltage of the battery at termination of a discharge.
Energy - Output Capability - expressed as capacity times voltage, or watt-hours.
Float Charging - Method of recharging in which a secondary cell is continuously connected to a constantvoltage supply that maintains the cell in fully charged condition. Typically applied to lead acid batteries.
Internal Resistance - The resistance to the flow of an electric current within the cell or battery itself.
Memory Effect - A phenomenon in which a cell, operated in successive cycles to less than full depth of
discharge, temporarily loses the remainder of its capacity at normal voltage levels (usually applies only to NiCd cells). Note: memory effect can be induced in NiCd cells even if the level of discharge is not the same
during each cycle. Memory effect is reversible. (Not sure I agree. – Steve)
Ohm’s Law - The formula that describes the amount of current flowing through a circuit. Ohm's Law - In a
given electrical circuit, the amount of current in amperes (I) is equal to the pressure in volts (E) divided by the
resistance, in ohms (R). Ohm's law can be shown by three different formulas:
- To find Current I = E/R
- To find Voltage E = I x R
The problem with Mr. Ohm is he couldn’t resister!
- To find Resistance R = E/I
Open Circuit - Condition of a battery, which is neither on charge, nor on discharge (i.e., disconnected from a
circuit or load).
Open-Circuit Voltage - The difference in potential between the terminals of a cell when the circuit is open
(i.e., a no-load condition).
Oxidation - A chemical reaction that results in the release of electrons by an electrode’s active material.
(Rust or corrosion.)
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Parallel Connection - The arrangement of cells in a battery made by connecting all positive terminals together
and all negative terminals together. The voltage of the group remains the same as the voltage of the individual
cell. The capacity is increased in proportion to the number of cells.
Polarity - Refers to the charges residing at the terminals of a battery, either positive or negative.
Positive Terminal - The terminal of a battery toward which electrons flow to, through the external circuit when
the cell discharges.
Primary Battery - A battery made up of primary cells. See Primary Cell.
Primary Cell - A cell designed to produce electric current through an electrochemical reaction that is not
efficiently reversible. The cell, when discharged, cannot be efficiently recharged by an electric current.
Zinc-carbon, alkaline, lithium, and zinc-air are common types of primary cells.
Rated Capacity - The number of ampere-hours a cell can deliver under specific conditions (rate of discharge,
end voltage, temperature); usually the manufacturer’s rating.
Rechargeable - Capable of being recharged efficiently, to like new status; refers to secondary cells or batteries.
Recombination - State in which the gases normally formed within the battery cell during its operation, are
recombined to form water.
Secondary Battery - A battery made up of secondary cells. See Storage Battery; Storage Cell.
Self-Discharge - Discharge that takes place while the battery is in an open-circuit condition, by itself, without a
load connected to it. This is shelf life for a battery or cell.
Series Connection - The arrangement of cells in a battery configured by connecting the positive terminal of
each successive cell to the negative terminal of the next adjacent cell so that their voltages are cumulative.
See Parallel Connection.
Shelf Life - For a dry cell, the period of time (measured from date of manufacture), at a storage temperature of
21 degrees C (69 degrees F), after which the cell retains a specified percentage (usually 90%) of its original
energy content.
Short-Circuit - A condition that occurs when a shortened electrical path is unintentionally created without any
resistance or load. Batteries can supply hundreds of amps if short-circuited, potentially melting the terminals,
exploding the case or housing, creating sparks, and spewing acid electrolyte everywhere. Wear eye protection!
Short-Circuit Current - That current which is delivered when a cell is short-circuited (i.e., the positive and
negative terminals are directly connected with a low-resistance conductor).
Starting-Lighting-Ignition (SLI) Battery - A battery designed to start internal combustion engines and to
power the electrical systems in automobiles when the engine is not running. SLI batteries can be used in
emergency lighting situations.
Storage Battery - An assembly of identical cells in which the electrochemical action is reversible so that the
battery may be recharged by passing a current through the cells in the opposite direction to that of discharge.
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Taper Charge - A charge regime delivering moderately high-rate charging current when the battery is at a low
state of charge and tapering the current to lower rates as the battery becomes more fully charged.
Terminals - The parts of a battery to which the external electric circuit wires are connected.
Thermal Runaway - A condition whereby a cell on charge or discharge will destroy itself through internal heat
generation caused by high overcharge or high rate of discharge or other abusive conditions.
Trickle Charging - A method of recharging in which a secondary battery or cell is either continuously or
intermittently connected to a constant-current supply that maintains the cell in fully charged condition.
Vent - A normally sealed mechanism that allows for the controlled escape of gases from within a cell.
Volt - The unit of measurement of electromotive force, or difference of potential, which will cause a current of
one ampere to flow through a resistance of one ohm.
Voltage, cutoff - Voltage at the end of useful discharge. (See Voltage, end-point.)
Voltage, end-point - Cell voltage below that which the connected equipment will not operate, or below which
operation is not recommended.
Voltage, nominal - Voltage of a fully charged cell when delivering rated current.
Watt - A measurement of total power. It is amperes multiplied by volts. 120 volts @ 1 amp = 120 watts.
12 volts @ 10 amps also = 120 watts.
Wet Cell - A cell, the electrolyte of which is in liquid form and free to flow and move.
The source of the terms listed above came from the following web site.
http://www.xmarks.com/site/www.windsun.com/Batteries/Battery_FAQ.htm
Suggested reading:
ARRL Emergency Power for Radio Communications
By Mike Bryce – WB8VGE
$19.95
Most batteries don't just die. They are killed by a lack of knowledge!