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Battery Information:

Battery Info.

Content links:

Battery System Sizing SIZING YOUR BATTERY SYSTEM

Deep Cycle Battery DEEP CYCLE BATTERY

Electrolyte ELECTROLYTE

VRLA (valve regulated lead acid) Battery VRLA BATTERY

Gel Cell Battery GEL CELL BATTERY

AGM (absorbed glass mat) Battery AGM Battery

Flooded Type Deep Cycle Battery FLOODED TYPE BATTERY

Self-Discharge Rate SELF-DISCHARGE RATE

Charge Rate CHARGE RATE

Electrolyte Level ELECTROLYTE LEVEL

Equalization Charging EQUALIZATION CHARGING

State of Charge STATE OF CHARGE

Battery Life BATTERY LIFE

Battery Location BATTERY LOCATION

Used Batteries USED BATTERIES

Battery Safety Battery Safety

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Sizing Your Battery Bank - having the proper size battery or battery

bank can mean the difference between success or disappointment in

an alternative energy or stand-by power system.

First off, I do not think it is possible to oversize a battery system. The larger

the battery bank, the less work it has to do and the longer it will last.

Many people undersize their battery bank thinking that just because the

batteries are deep-cycle you can work them to the bone and they will

continue to take it.

In an undersize battery system the batteries are continually depleted into a

deep state of discharge and then forced to play catch up.

These wide swings of battery state of charge shorten the battery life in

addition to doing something that most people don't consider.

If the battery system is not matched to the loads and it is drawn down too

low - time to fire up the generator. The money you spent on your photovolatic,

wind or hydro system will be sitting idle while you get to enjoy the sounds

and smells of a generator.

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DEEP CYCLE BATTERY - these batteries are made to be discharged

(run down) to a very low percentage rate of full charge. Their plates are thicker

than automotive SLA (starter,lighting,accessories) types. They will not work

well to start an engine as they are not designed to produce a lot of power

(amperage) over a short period of time. This is where a regular automotive

battery shines. By the same token, an automotive starter battery is designed

to put out a lot of amps for a short period of time but not to have a large

percentage of its capacity used. When an automotive battery is heavily

discharged or left in a low state of charge (less that 60% of capacity) it is

time to call a tow truck. In a stand-by or alternative energy environment this will

not work. Deep cycle batteries are designed to be cycled to a relatively low

state of charge (in many cases, 20% of capacity.) Their storage capacity is

measured in amp hours with a given discharge time (usually a 20 hour rate

{sometimes a 100 hr. rate}.) In theory a 100 amp hour battery will produce five

amps (five amp hours) for twenty hours before it is exhausted. Automotive

batteries are rated in cold cranking amps which are meaningless for back-up

or alternative energy purposes.

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ELECTROLYTE - the liquid in a storage battery which is composed of acid

and water. NOTE - a battery (of any kind) does not store electricity, very few

things will. A storage battery converts elecitricity coming in and stores it in the

form of chemical energy. When power is pulled from the battery it converts the

chemical energy back into electrical energy. There are always some losses in

these conversions.

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VRLA (VALVE REGULATED LEAD ACID) BATTERY - the GEL Cell and

AGM batteries are considered sealed batteries.

Water can not be added to them.

If any electrolyte is lost, it is lost for good.

The plugs on the top or sides of these batteries are pressure relief valves.

If, by overcharging one of these batteries, the pressure will vent (and possibly

some electrolyte), it will be released through these valves.

This is done to keep the battery case from bursting when improperly used.

As these batteries operate at higher internal pressure than the surrounding

air, oxygen and hydrogen gasses produced during charging (greater than 99%

as a rule) are recombined internally back into water for the electrolyte.

VRLA type batteries do not accept high amperage/voltage rates of recharging

as well as a conventional flooded battery.

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GEL CELL BATTERY - the electrolyte is mixed with a silica material which

converts it into a gelatin.

This keeps the water and acid mixed and allows the battery to be used in

any position as there is no liquid to run out.

These are the safest for use indoors.

They are the least affected by temperature extremes (especially freezing.)

Their tolerance for being stored at a low state of charge levels is excellent.

They do not tolerate overcharging well but as a rule can handle a higher

charging voltage than an AGM battery.

Cost is approx. $ 2.00 per amp hour.

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AGM (ABSORBED GLASS MAT) BATTERY- the liquid electrolyte has been

absorbed into a fiberglass cloth mat between the plates.

These have good deep cycle characteristics and can be used in all positions.

They are less affected by temperature extremes than a flooded type battery

but are more sensitive than a gel cell battery.

AGM batteries do not tolerate storage at a low state of charge as well as a

gel cell.

This type of battery does not handle overcharging - especially at a high

charging voltage.

Can be used indoors. Cost is approx. $ 1.50 per amp hour.

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FLOODED TYPE DEEP CYCLE BATTERY - similar to the kind used in

automobiles in that the electrolyte is in a liquid form. Excellent deep cycle

characteristics. Must be vented outdoors to dissipate the hydrogen gas which

is produced during charging. Can not tolerate temperature extremes as well

as Gel cell or AGM batteries. Should not be left in a low charge state as

permanent damage could result. These are the best deal for large storage

needs. Cost is approx. $ 0.50 per amp hour.

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SELF-DISCHARGE RATE - a fully charged battery will lose from one to four

percent of its charge per day when stored without being connected to a

charging system (maintenance type) @ 75 deg.F. The higher the temperature,

the higher the rate of self-discharge. Gel cell and AGM batteries have a very

low rate of self-discharge.

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CHARGE RATE - a good charge rate is approximately 10% of the total

capacity (of the battery or battery bank) per hour (i.e.- 200 amp hour battery

charged at 20 amps.) This is called C-10 and will reduce electrolyte loss and

damage to the plates. NEVER attempt to charge a battery that is frozen, it

can get ugly.

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ELECTROLYTE LEVEL - flooded type batteries should have their levels

checked monthly (more often if under heavy usage.) Do not overfill, as the

liquid will expand (due to gas bubbles and a rise in temperature) when it is

being charged. Electrolyte levels should never be allowed to fall below the

top of the plates. When resting in a low discharge state for a long period of

time the electrolyte can crystalize in the plates and permanently damage them.

We use a jug type of battery filler. It will only dispense

water when the nozzle is pressed into the cell opening and will shut off

automatically when the level reaches the nozzle. These are available from

auto parts houses such as J.C. Whitney and others for less than ten dollars.

As long as you always make sure that the gasket is in the groove after refilling,

these last for years.

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EQUALIZATION CHARGING - flooded type batteries should have an

equalization charge (controlled over-charging) done periodically. This

keeps the acid mixed throughout, loosens and removes some of the

sulfates that form on the surface of the battery plates (reducing capacity)

and can help if the battery has a weak cell. When equalizing a battery it

is a good idea to cover the caps with a paper towel, wet spots (spitting)

can indicate a weak or bad cell. Before doing an equalization charge,

make sure that the battery is at or near a full charge. This will reduce

heating which may occur when rapidly bringing a battery up from a low

charge state to an equalized state. NEVER top off the liquid level before

an equalization charge (make sure it covers the plates) as it can run out

of the cells when it expands and outgasses. It is a good idea to loosen

the battery caps prior to an equalization charge due to the high pressures

which can be created in the cells.

NEVER EQUALIZE CHARGE A SEALED BATTERY.

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STATE OF CHARGE (S.O.C.) - this is a measurement of how much

useable power is left in a battery or battery bank. This can be determined

by one of three ways.

The first two methods are accurate only if done when the battery has been

at rest for several hours. As a battery is being charged or discharged the

chemistry and physical characteristics of the elecrolyte change. Gas bubbles

are produced and the temperature as well as the acid to water ratio changes.

These changes can greatly affect the readings using the first two methods.

1st. - voltage measurement, on a battery at rest this method can show state

of charge by comparing the voltage to a chart showing the percentage of

charge relative to voltage. A freshly charged battery can show a higher,

inaccurate voltage, than one at rest. A recently discharged battery can show

a lower voltage than one at rest.

2nd. - electrolyte density measurement, a sample of the electrolyte is drawn

into a hydrometer which shows the density of the liquid. The heavier the

electrolyte (higher gravity), the more acid in solution, the higher the state of

charge. A freshly charged battery will have gas bubbles in the electrolyte

which can show a lower gravity and indicate a lower S.O.C. than actually

exists. A recently used battery can show an inaccurate S.O.C. due to acid

absorption in the battery plates which will disperse into the electrolyte upon

resting.

Both methods are effective when checking for a weak cell in a flooded

battery with filler caps which allow access to the electrolyte.

3rd. - amp hour metering, this method uses an amp hour meter which is set

using the specifications of a new battery or battery bank at full charge. It

measures and records power (amps) going into and coming out of the

battery and keeps an electronic balance sheet. You can see why this would

not work well on a used battery system as there would be no accurate

starting point. These meter systems run from a few hundred to several

hundred dollars.

Please see: Measuring Battery State of Charge.

IN SUMMARY: the most important thing is to properly maintain your battery

or battery bank and learn its characteristics.

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BATTERY LIFE - depends more on the user than any other factor. Do not

allow the battery to become overheated as this will dramatically shorten its

lifespan. A battery has a lower freezing temperature when it is fully charged.

Keep the electrolyte levels where they belong and make sure that all posts,

cables and connections are clean and tight. It is a good idea to coat

exposed metal posts and connections with a battery preservative.

Manufacturers rate battery life by the number of charge/dis-charge cycles.

The more times a battery is discharged to a very deep state, the shorter the

life span will be. As a rule, a larger battery bank will last longer than a smaller

one when both have the same input and output. The larger bank will

discharge to a higher percentage of capacity than the smaller one.

A little maintenance goes a long way to protecting your investment.

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BATTERY LOCATION - as we have said, don't let your batteries get too

hot or too cold, and please vent them to the outdoors. Vapors coming

off of flooded batteries can be very corrosive, especially when the battery is

undergoing an equalization charge. When being charged, a flooded battery

produces hydrogen gas which is explosive.

Just as important is accessibility.

If you can't get to your batteries, can't easily see the electrolyte levels or

can't easily top off the electrolyte, YOU WON'T. The first battery bank we

had consisted of eight, 6 volt - 220 amp hour golf cart batteries, two to a

shelf. The shelves were so close together that I had to use my finger

(real smart) or a mirror to check the electrolyte levels along with a bulb

type water dispenser to top them off (as well as to run them over.) After

the first set of batteries died prematurely, I figured out what was wrong.

Now we can check and water our battery bank in minutes and without any

difficulties. Human nature, being what it is; if it is a pain in the neck to do,

you will not do it.

If you locate your batteries outdoors it is recommended that you try to

keep the battery enclosure out of direct sunlight as battery life is greatly

shortened by high temperatures. Keep an airspace between

each battery to keep them from over heating. In cold climates, insulate

the enclosure as when the batteries are subjected to low temperatures

the chemical reactions which take place in them slows down.

Lead acid batteries work best and last longest when kept at 75 degrees

fahrenheit.

Keep your battery tops clean and we coat all exposed metal parts of the

battery terminals and lugs with a coating of sealer made for batteries.

This greasy product works great - but do not get any of it on your clothes

as it will stain them permantly. On system rehabilitation jobs I gave up on

wearing anything but old clothes because of this.

DO NOT MIX BATTERY SIZES, TYPES OR AGES IN A BATTERY BANK

OR SYSTEM.

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USED BATTERIES - I am a big fan on reusing everything we can. I do,

however have serious reservations about used batteries. Unless you know

the history and how the batteries have been maintained, you could buying a

pig in a poke. With batteries of unknown history, you could set your self up for

some serious disappointments and wind up with a lot of lead that you have to

dispose of properly. In some of the systems I have either upgraded or

reworked the client will offer me the batteries to resell. I tell them that I will

take them and dispose of them properly (to be recycled.) I have done this

with batteries that were only a few months old. It is bad enough to let yourself

done, it would be even worse if I let you down.

A note on Nickel-Cadmium storage batteries: some

years ago it seemed like everyone was selling and

praising used Ni-Cad batteries. There were companies

that refurbished them. After a couple of years the

interest died out. The batteries (even used ones)

were very expensive and had poor reliability. They also

had different charging requirements than lead acid

batteries. If you run across any and consider buying

them, please give it a lot of thought.

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BATTERY SAFETY

NEVER WORK ON OR NEAR A BATTERY WITHOUT PROPER

EYE PROTECTION. THE ELECTROLYTE CONTAINS ACID

(ALL TYPES OF LEAD BASED STORAGE BATTERIES)

AND CAN DAMAGE EYES AND SKIN, AS WELL AS

ANYTHING IT COMES INTO CONTACTWITH.

IF YOU ARE USING NICKLE-CADMIUM BATTERIES THEY

ALSO CONTAIN A CORROSIVE ELECTROLYTE.

NEVER EXPOSE BATTERIES TO A SPARK OR OPEN FLAME,

ESPECIALLY WHEN THEY ARE BEING CHARGED.

THE HYDROGEN GAS PRODUCED IS EXPLOSIVE.

BE CAREFUL around battery terminals and posts. An improper

connection or misplaced wrench can produce a devastating arcing

short circuit. Storage batteries contain enough energy to cause metals

to become liquid and spray in all directions. We use a small palm

ratchet wrench (it is too short to reach from post to post) when

tightening battery terminals. Also, watch when handling cables as they

can short out a battery if carelessly handled. I didn't read this

somewhere, I have done it. Aside from the safety concerns, nothing

makes you look more like one of the Three Stooges than shorting out

a battery bank when connecting the cables.

ALWAYS OBSERVE PROPER POLARITY!

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A note on battery terminals. If your battery(s) have wing nuts to hold the

lugs in place, we recommend that you replace them with regular nuts. You

will get a more secure connection. On installations where the lugs have to

be disconnected on a regular basis, and without tools, then the wing nuts

make sense.

HOW TO WIRE BATTERIES TO PRODUCE 12 VOLTS D.C. :

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HOW TO WIRE BATTERIES TO PRODUCE 24 VOLTS D.C. :

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HOW TO WIRE BATTERIES TO PRODUCE 48 VOLTS D.C. :

It is plus to minus and so on. This adds up the voltage of each battery.

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Measuring Battery State of Charge.

Battery voltage will vary for the same state-of-charge depending on

whether the battery is being charged or discharged, and what the current

flow is in relation to the size of the battery. The chart below gives you an

idea of state-of-charge for various battery conditions in flooded cell lead

acid batteries. Voltage varies with temperature. While charging, a lower

temperature will increase battery voltage. Voltage is 0.9 volts higher on a

12 volt battery at 32 deg. F than at 70 deg.F. While discharging, a higher

temperature will increase battery voltage. There is little temperature effect

while the battery is standing at rest.

This information is courtesy of Ralph Heisy, Bogart Engineering and from

Applied Power.

Battery Voltage Battery Condition @ 77 deg. F. 12 Volt 24 Volt
battery during equalization charge	over 15	over 30
battery near full charge while charging	14.4 to 15.0	28.8 to 30.0
battery near full discharge while charging	12.3 to 13.2	24.6 to 26.4
battery fully charged with light load	12.4 to 12.7	24.8 to 25.4
battery fully charged with heavy load	11.5 to 12.5	23.0 to 25.0
no charge or discharge for 6 hours - 100% charged	12.7	25.4
no charge or discharge for 6 hours - 80% charged	12.5	25.0
no charge or discharge for 6 hours - 60% charged	12.2	24.4
no charge or discharge for 6 hours - 40% charged	11.9	23.8
no charge or discharge for 6 hours - 20% charged	11.6	23.2
no charge or discharge for 6 hours - fully discharged	11.4	22.8
battery near full discharge while discharging	10.2 to 11.2	20.4 to 22.4

A hydrometer (which measures specific gravity [the density of a solid or

liquid in relationship to pure water which has a specific gravity of 1.0])

is very accurate at measuring battery state-of-charge if you measure the

electrolyte near the plates. Unfortunately, you can only measure the

electrolyte at the top of the battery. When a battery is being charged or

discharged, a chemical reaction takes place at the border between the

lead plates and the electrolyte. During charging, the electrolyte changes

from water to sulfuric acid. The acid becomes stronger and the specific

gravity rises as the battery charges. It takes several hours for the electrolyte

to mix and the gas bubbles to break out of the liquid so that you can get

an accurate reading at the top of the battery.

Always try to take readings after a long period of no charge or discharge.

The chart below gives state-of-charge vs. specific gravity of the electrolyte.

These readings are correct at 75 deg. F.

state of charge specific gravity

100% charged 1.265

75% charged 1.239

50% charged 1.2

25% charged 1.17

fully discharged 1.11

Please remember to use the thermometer inside of the hydrometer to

correct for temperature. 75 deg. F is the base-line (standard) and any

reading above or below this temperature must be corrected for an

accurate reading.

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