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Rolls Technical Bulletins

 

 

Surrette Technical Bulletins:


#501 A Sulfated Battery

How many times have you heard the expression, "The Battery Won't Take A Charge" or "The Battery Won't Hold A Charge" ? More often than not, the culprit is hardened sulfate on the battery plates. Below we will attempt to explain what that means, what the causes are, and some measures to prevent the sulfate from permanently damaging your battery.

Let's look inside a battery cell. Basically, there are the positive plates, the negative plates, separators (to keep the plates apart), and electrolyte (sulfuric acid and water).

In normal use, battery plates are getting sulfated all the time. When a battery is being discharged the lead active material on the plates will react with the sulfate from the electrolyte forming a lead sulfate on the plates. When there is no lead active material and or sulfate from the electrolyte remaining the battery then is completely discharged. After a battery reaches this state, it must be recharged. During recharge, the lead sulfate is re-converted into lead active material and the sulfate returned to the electrolyte.

When the sulfate is removed from the electrolyte the specific gravity is reduced and the reverse takes place when the sulfate is returned to the electrolyte. This is why the state of charge can be determined with the use of an hydrometer.

If a battery is left standing in a discharged condition the lead sulfate will become hard and have a high electrical resistance. This is what is normally called a sulfated battery. The lead sulfate may become so hard that normal recharging will not break it down. Most charging sources, engine alternators and battery chargers, are voltage regulated. Their charging current is controlled by the battery's state of charge. During charging, battery voltage rises until it meets the charger's regulated voltage, lowering the current output along the way.

When hard sulfate is present, the battery shows a false voltage, higher than it's true voltage, fooling the voltage regulator into thinking that the battery is fully charged. This causes the charger to prematurely lower it's current output, leaving the battery discharged. Charging at a higher than normal voltage and low current may be necessary to break down the hardened sulfate.

Hardened sulfate also forms in a battery that is constantly being cycled in the middle of its capacity range (somewhere between 80% charged and 80% discharged), and is never recharged to 100%. Over time, a portion of the plate's active materials turns into hard sulfate.

If the battery is continually cycled in this manner, it will lose more and more of its capacity until it no longer has enough capacity to perform the task for which it was intended. An equalizing charge, applied routinely every three to four weeks, should prevent the sulfate from hardening.

In both cases, the fact that the battery "won't take a charge" is a result of improper charging procedures which allowed the sulfate to harden. In most instances, it is possible to salvage a battery with hardened sulfate. The battery should be charged from an outside source at 2.6 to 2.7 - volts per cell and a low current rate (approximately 5 Amps for small batteries and 10-Amps for larger ones) until the specific gravity of the electrolyte starts to rise. (This indicates that the sulfate is breaking down.) Be careful not to let the internal temperature of the battery rise above 125o F. If it does, turn the charger off and let the battery cool. Then, continue charging until each cell in the battery is brought up to full charge (nominal 1.265 specific gravity or higher). This time needed to complete this recharge depends on how long the battery has been discharged and how hard the sulfate has become.

The next time your batteries don't seem to be taking or holding a charge, check the specific gravity with a hydrometer. If all cells are low even after a long time on charge, chances are you've got some hardened sulfate that has accumulated on the plates. By following the instructions outlined above, the problem may be corrected.

With a sealed battery the same problem can exist. Unfortunately hydrometer readings cannot be taken to determine the problem. If you subject a sealed battery to overcharging you may lose the electrolyte and ruin the battery.
SEE INFORMATION BULLETIN 503.

 #502 Marine Battery Sizing

In sizing batteries for a boat, the rule of thumb is to double what you think you need. In a car, we say you need one cranking amp for every cubic inch displacement of the engine. For marine application you should use two cranking amps not that a marine engine starts harder, but you should have than extra margin of safety.

For lighting batteries the same rule applies. Double what you think you need. An approximate way of determining battery sizing is to measure the average current draw per hour with all equipment running and lights on. If you don't have an ammeter for doing this then make a list of all the equipment and lights, recording the current draw from the name plate. If the information is supplied in watts then divide the watts by the voltage. A 60 watt light bulb on a 12 volt system draws approximately 5 amps.

 Once the current draw is known, certain assumptions will have to be made. An electric refrigerator which draws approximately 5 amps will run approximately one half the time. Therefore, it would draw approximately 60 amp hours in 24 hours.

Once an estimate of the total ampere hours is known over a 24 hour period then determine the number of days the batteries are to last before recharging. Double this figure. A conservative approach to determining battery sizing is to match this figure with the 20 hour rating of the battery.

Remember when batteries are connected in parallel (positive to positive and negative to negative) the ampere hour capacity doubles and the voltage remains the same.

The reverse is true with batteries connected in series. The voltage doubles and ampere hour capacity remains the same.

The lighting and accessory batteries should be deep cycle such as Rolls Series 4000. The starting batteries should be reliable and of high quality such as Rolls Series 3000. Deep cycle batteries may be used for starting with excellent results.

Sample Current Draw

Estimated Current Draw of Various Lighting/Elec. Items

Group

Device

Amps

Communications

CB Receiver

1.00

Communications

SSB Receiver

1.50

Communications

SSB Transmit

25.00

Communications

VHF Receive

1.50

Communications

VHF Transmit

5.00

Entertainment

Tape receiver

1.00

Refrigeration

Refrigeration typical)

5.00

General Lighting

Cabin Light (40W)

3.50

General Lighting

Fluorescent Light (26W)

1.80

General Lighting

Fluorescent Light (8W)

.70

General Lighting

Hand Held Spotlight

10.00

General Lighting

Spreader Light

8.00

Heat

Forced Air (11,000 BTU)

3.00

Heat

Forced Air (28,000 BTU)

10.00

Instrument

Knot meter

0.10

Instrument

Wind Speed Indicator

0.10

Misc..

Anchor Windlass

80.00

Misc..

Auto Pilot

4.00

Misc..

Bilge Pump

2.50

Misc..

Cabin Fan

1.00

Misc..

Fuel Pump

3.00

Misc..

Horn

3.00

Misc..

Inverter (Sm. Microwave)

100.00

Misc.....

Inverter (NiCad Charger)

1.50

Misc....

Propane Valve

1.00

Navigation

Depth Sounder

0.10

Navigation

Loran

1.00

Navigation

Radar

4.00

Navigation

Recording Depth Sounder

0.50

Navigation

Satnav (average)

0.20

Navigation

Weather Fax

2.40

Navigation Light

Anchor Light

1.00

Navigation Light

Masthead/Steaming Light

1.00

Navigation Light

Running Lights

3.00

Navigation Light

Strobe Light

0.70

Navigation Light

Tri-Color Light

2.00

Pump

Bilge Pump

5.00

Pump

Fresh Water Pump

5.00

Pump

Head Pump

18.00

Pump

Wash Down Pump

10.00

 #502C BASIC GUIDE LINES FOR SIZING MARINE BATTERIES

Series 400 & 500 (4000 & 5000 Rolls) for Deep Cycling

Example of "Light Cycling" would be a house battery for a sailboat 30 feet and under with lights only and limited night sailing.

Example of "Deep Cycling" would be the same as above, but with the addition of an electric refrigerator, auto helm, etc.

A simple guideline to determine sizing of house batteries

 
The best method is to determine the requirements of the boat. Below only serves as a
rough guide and would be considered as the minimum requirements of the vessel.

Length Of Boat

Capacity Of House Batteries

28 Feet

136 Amp Hour

29 Feet

160 Amp Hour

30 Feet

180 Amp Hour

31 Feet

202 Amp Hour

32 Feet

224 Amp Hour

33 Feet

248 Amp Hour

34 Feet

272 Amp Hour

35 Feet

298 Amp Hour

36 Feet

324 Amp Hour

37 Feet

352 Amp Hour

38 Feet

380 Amp Hour

39 Feet

410 Amp Hour

40 Feet

440 Amp Hour

41 Feet

472 Amp Hour

42 Feet

504 Amp Hour

43 Feet

538 Amp Hour

44 Feet

572 Amp Hour

45 Feet

608 Amp Hour

46 Feet

644 Amp Hour

47 Feet

682 Amp Hour

48 Feet

720 Amp Hour

49 Feet

760 Amp Hour

50 Feet

800 Amp Hour

 
The rules may change with the addition of an Inverter or other electrical equipment. On a 12 volt system divide 5 into the wattage of the Inverter to determine the size batteries required. On a 24 volt system divide by 10.

If the Inverter is to be run for more than a maximum of 15 minutes at close to full capacity, a larger battery bank will be required!

The exception may be if power is being supplied to the batteries from an alternator or other source.

Depending on the size of the boat it may be desirable to break the house batteries up into 2 or more systems for safety reasons. The essentials should be on one bank and the non-essentials on the other bank. Essentials are considered anything to do with safety, such as electronic equipment. Non-essentials are such things as an electrical refrigerator.

On a 12 volt system when 2 batteries are used to obtain the capacity for the house bank the question usually arises as to whether to use two 6 volts in series or two 12 volt in parallel. With two 12 volts in parallel if one battery should fail, the battery can be disconnected and still have a "live" system. With two 6 volts this is not so.

When installing two batteries in parallel the batteries must be:

  1. New
  2. The Same Age
  3. The Same Size
  4. The Same Make

Connections must be:

  1. Perfectly Clean
  2. Tight and Secure

The starting battery or batteries should be isolated from the house batteries, and used only for starting the engine. This battery or batteries can be a Series 300 (3000 Rolls), or a good quality automotive type. The Series 400 and 500 will normally work fine for starting, but in many cases the user is paying more money than is necessary. However, the Series 400 & 500 will pay for itself due to it's heavy construction and long life!

#503 Marine Battery DesignMaintenance Free or Gelled Electrolyte

So-called new no maintenance batteries with a marine label are not that much different than automotive no-maintenance batteries except the price. The reference to Gelled (Prevailer) has caused confusion. The gel only serves to hold the battery electrolyte captive and in deep cycle service it results in lower capacity than their rating. Batteries made with this construction are usually acid starved without sufficient electrolyte to activate the plates. The result is low capacity size for size.

By sealing the battery, there is no practical way of determining the battery's condition if the battery can't be checked with a hydrometer, the boat owner could be starting a cruise with low batteries; in an emergency it could result in battery failure just when the battery power is needed most.

The buyer of a Gelled type battery should be cautioned that the voltage setting of the regulator may have to be changed. The Prevailer has a 14.1 maximum volt limitation. Most alternators are preset at 14.2 to 14.5 volts and must be reduced in order to protect Gelled electrolyte batteries. Some distributors of Gelled type batteries have suppressed the fact that the ship's charging system may require an expensive modification to accommodate this type battery.

Most so-called sealed batteries are assembled in gray propylene cases - same as most automotive batteries. Rolls uses only black rubber containers on all series 4000, including the smaller size marine Batteries. White propylene cases are used only on our 3rd line series.

Promoters of these types of batteries are highly sales motivated. They fail to put the boat owner on notice that, in the event of improper voltage regulator setting, the battery could dry out and, if so, there would be no way to replace the water so that the battery could continue to function.

They refer to cranking power. They have no more than the average maintenance free automotive battery, which depends on a multiple of thin plates - the thinner the plates, the shorter the battery life, and the less able to stand abuse and overcharging.

The maintenance-free automotive batteries normally have plates as thin as .0500 thick, with low density porous active material (oxide) which does not lend itself to deep cycling or overcharging. It does have one advantage: it uses less lead and is a cheaper way to make a battery.

With low capacity characteristics inherent in Gelled electrolyte batteries, their claims of faster recharge ability exist partly because there is less capacity to return to the battery. These claims are immeasurable because the only state of charge measurement is surface voltage which is not an accurate indicator for calcium lead alloy batteries. Because Gelled batteries are acid starved they have less capacity and also less problems with sulfation.

The positive plates in a lead acid battery are the limiting factor in life expectancy in deep cycling marine service. The so-called new sealed battery has very fragile thin plates no different than common automotive batteries.

Gelled batteries, such as the Prevailer battery, costs approximately 40% more than Rolls Marine Series 4000 and 100% more than American made automotive batteries. They use a cheap polypropylene case compared to rubber and they are clearly designed for float operation and a periodic deep cycling. Periodic deep cycle normally is not suitable or will not qualify as a deep cycle battery. Most automotive batteries qualify for periodic deep cycle service.

The above is only a brief comparison to reflect the fact that there is little if any difference, except the higher price, with the average North American car battery.

 #504 - Marine Battery Design

There is considerable confusion in the marketplace concerning marine batteries. The confusion centers around what is a marine battery? What is the difference between a marine, deep cycle, automotive and R./V. (Recreational Vehicle)? How to maintain, etc..

Many battery manufacturers sell their product to the marine trade by supplying their regular automotive and truck batteries with marine labels. This is difficult for the average layman to detect.

Rolls definition of a marine battery is one that is designed for maximum reliability. Remember, there are no service stations at sea. Maximum reliability is achieved by utilizing heavy positive and negative plating, dense active material, reinforced grid design, premium insulation which usually includes a thick woven glass mat, cell protector, rubber container, heavy intercell connections and on larger batteries multi-cell construction.

The majority of failures in lead acid batteries are contributed to the positive plates. The grid which is part of the plate is referred to as the current carrying conductor. The plate consists of the grid plus the active material. The active material chemically produces electricity which is conducted by the grid via inter cell connectors to the terminals.

Every time the average battery is discharged a small portion of the active material becomes inactive or lost because of expansion. On recharging the current chemically converts the active material from a lead sulfate to lead dioxide. This same current also converts a small portion of the lead in the grid to lead dioxide. This is sometimes referred to as a grid corrosion.

By now, you have probably guessed why the heavy positive plates and the reinforced grid design. The heavy positive plates provides more active material. By using a denser active material, more material can be held within a given space.

The reinforced grid design is accomplished by providing more metal in the grid. More metal can be lost from grid corrosion without harmfully affecting the battery. Overcharging will accelerate positive grid corrosion. Starting batteries are subjected to overcharge conditions when the engine is running. The electrical system is designed to replace a little more current than is lost via self discharge.

We often use the expression "The chain is only as strong as the weakest link". This is true in battery engineering. That is why a high quality marine battery will utilize high quality insulation to compliment the heavy plate construction. In most cases a thick woven glass mat will be placed against the positive plate. This is used to maintain the active material on the grid which extends the useful life of the battery. The glass mat is also referred to as a retaining mat. The best insulation is PVC, rubber or polyethylene. Glass matting should be a minimum of 0.020 thick to be effective.

The cell protector, made of perforated vinyl, fits on top of the cell immediately under the vent opening. The protector mat prevents damage to the insulation when a hydrometer is inserted into the vent opening.

Rubber containers are desirable in marine deep discharge type batteries. Rubber is more rigid and does not have the tendency to bulge. This is most important in deep discharge batteries.

Heavy intercell connectors are important to provide that extra margin of safety during high discharge. Thin intercell connectors used in solid top construction may melt under severe loads.

A good quality marine battery is initially expensive although inexpensive when considering the life expectancy. Multi-cell construction can be repaired in the event of damage. Solid top construction cannot.

Maintenance-free is the worst choice. If the electrical system malfunctions, the electrolyte may boil out. If maintenance-free, there is no way of replacing it. There is no way of checking the battery's electrolyte to determine whether the battery is in a charged or discharged condition. Yes, you will have the first signs of trouble when it starts failing. Okay, if you are alongside the dock, but tragic if you are still at sea or beginning a planned weekend. Even after repairs to a malfunctioned electrical system, the maintenance-free battery, if discharged will quite often have to be replaced. In many instances they will not accept recharging. Most maintenance-free batteries have calcium in the lead grids which forms calcium oxide on the surface of the grid when the battery is discharged. The calcium oxide forms a barrier between the grid and active material which makes recharging very difficult.

 #505 - Marine Battery Ratings

Most buyers of marine batteries compare products on the market by the number of plates, 20 hour capacity, reserve capacity, and the cranking performance. Before continuing, I would like to explain the meaning of the last three items.

The 20 hour rating is the capacity of the battery determined over 20 hours at 80of (26.7oC). A battery rated at 100 A.H. for 20 hours means that if you divide 20 into 100 the battery can be discharged at 5 amperes continuously for 20 hours. Likewise, if the rating was at 8 hours then divide 8 into 100. This would mean that the battery could discharge 12.5 amperes for 8 hours.

Marine batteries are usually rated at the 20 hour or 8 hour rating. The 8 hour rating is usually approximately 82% of the 20 hour rating.

The reserve capacity is defined as the number of minutes a battery can be discharged at 25 amperes. The temperature again is 80oF or 26.7oC.

The cranking performance is a measure of the maximum load a battery can withstand for 30 seconds at 0oF or 17.8oC. The cut off voltage is 7.2 volts for a 12 volt battery.

The cranking performance of a battery is determined by the square inches of surface area of the positive plates.

The 20 hour, 8 hour and reserve capacity of a battery is determined by the amount of cubic inches of active material. To obtain the maximum in these ratings the battery would be designed with fewer, but much heavier plates.

In order to demonstrate the confusion that rating presents to the layman, I have made a comparison between Rolls and a leading R.V type battery.

.

Rolls type T-12-131

R.V....... Type Group 27

20 Hour Rating

92 Amp Hour

95 Amp Hour

Reserve Capacity

264

155

Cranking Ability

361 CCA

450 CCA

Weight

77 lbs..

50 lbs..

Density of Active Mat

73

66

Number of Plates

54

78

Size of Plates

63/8x63/4x103/4

5x55/8x7

Insulation

Polyethylene/Glass Mat

Impregnated Paper

Dimensions

113/4x63/4x103/4

12.4x6.7x8.8

  Both batteries are approximately the same dimension except the Rolls is higher. The R.V....... is a little longer because of the rope handles. Both batteries will deliver approximately 90 A.H. when new. But this is where the similarities stop.

The Rolls is conservatively rated because of the thickness of the plate and density of the active material. Because of the thickness and density the electrolyte cannot penetrate the inner service of the plate. However, as the Rolls ages this unused material comes into use and the battery actually increases in capacity. When both batteries are subjected to hard service the R.V....... type drops off in capacity very quickly. The Rolls increases in capacity and maintains this capacity over along life span.

The Rolls does not have as good a cranking performance because of the lower exposed plate area and also due to the thick woven glass mat. The thick woven glass mat retards the flow of electrolyte and thus reduces the cranking performance by approximately 10%. However, the glass mat adds to the life expectancy and reliability of the battery. The R.V....... battery has a thin glass mat which is ineffective.

If the initial performance was the guide then the R.V....... would be the better buy. However, when you think of the long term investment the Rolls is by far the better buy. Also, do not forget about the safety of a reliable product when at sea. Remember "quality hurts only once".

 When comparing batteries ask about the ratings as this will determine the physical size of a battery you will need. But do not stop, ask additional questions. It is most important that you know the type of insulation. Cellulose (impregnated paper) is the least desirable. Ask about the thickness of the glass mat. It should be nothing less than 0.020. Ask about plate thickness and height. The weight of the battery is a good guide as to the thickness and height of the plates. A thin plate battery will weigh less. If your dealer is knowledgeable and is not trying to confuse you, he will have the facts.

#506 - Winter Storage

Prior to placing batteries into winter storage make certain the electrolyte level is approximately 1.2" (30.4mm) above the top of the separators. The electrolyte level in very cold batteries will be lower than normal, so let batteries warm to a normal temperature before judging electrolyte levels.

Once the electrolyte level is correct ensure that the batteries are fully charged. Ensure that the battery tops are clean and dry. See Information Bulletin 501 & 507.

Now the choice is whether to leave the batteries aboard your boat or remove and store in a cool dry area. If the batteries are stored aboard the boat, disconnect the terminal cables. This will prevent premature discharge of the batteries due to a ground in the electrical circuits or failure to turn a piece of electrical equipment off.

If the batteries become discharged, the electrolyte can freeze when stored below +20 o F (70oC). Below shows temperatures at which electrolyte, in various states of charge, starts to freeze.  

Specific Gravity (cor....... to 80oF/26C)

Freezing Temp

1.280 Spec. Grav.......(cor...... to 80oF/26C)

-92F (-69C)

1.265 Spec. Grav......(cor...... to 80oF/26C)

-72.3F (-57.4C)

1.250 Spec Grav......(cor..... to 80oF/26C)

-62F (-52.2C)

1.200 Spec Grav......(cor..... to 80oF/26C)

-16F (-26.7C)

1.150 Spec. Grav......(cor..... to 80oF/26C)

+5F (-15C)

1.100 Spec. Grav......(cor..... to 80oF/26C)

+19F (-7.2C)

 A 3/4 charged battery is in no danger of freezing. Therefore, batteries should be kept at least 3/4 charged, especially during winter weather.

The frequency of checking batteries depends greatly on temperature. The effect of temperature on self discharge for the average fully charged, new, conventional battery in good condition is approximately as follows:

  1. At 100oF (37.8oC) .0025 Sp.Gr....... per day
  2. At 80oF (26.7oC) .001 Sp.Gr...... per day
  3. At 50oF (10oC) .0003 Sp. Gr. per day

A fully charged battery stored at 80oF (26.7oC) will take 30 days before it self discharges 25 percent. At 50oF (10oC) the time period increases to 100 days. This will give you an idea of how often a battery should be checked.

Some makes of batteries will have a higher and some a lower rate of self discharge. This depends on the method of manufacture and purity of materials used

 #507 - Battery Charging and Systems

The battery is a major factor in regulation of the charging current by its change in counter voltage. Anything which affects the battery or regulator such as temperature, sulfation, etc... affects the charging current.

Low water consumption is an indication of proper regulator setting. When a battery uses more than 30-60 ml of water per cell per 40 hours of operation the regulator is set too high. The ideal voltage setting for a regulator may be defined as that setting which will keep the battery at or near full charge with a minimum use of water.

The correct voltage setting at 26.7C when using Rolls Marine Batteries is between 2.33 VPC and 2.36 VPC or 14 to 14.2 volts on a 12 volt system. Batteries that are not being exercised regularly the voltage setting should be reduced to approximately 2.17 VPC or 13.02 volts on a 12 volt system. This is common in a standby system or batteries left on charge over the winter months with the charger supplying the vessels requirements.

Some boat operators will charge at a higher voltage for a short period of time. This is referred to as an equalize charge. This is an acceptable procedure for batteries that are being cycled daily but certainly not necessary will reduce the life of the battery.

In most instances the best trade off for maximum battery life and the absence of problems in  marine applications is a multi-bank, dedicated correct fixed voltage system. This means heavy duty alternators designed for marine application and voltage regulation that does not drop below the desired level when the batteries approach full charge.

If charging voltage of 14-14.2 cannot be maintained the recharge time will increase. Voltage regulators with pronounced temperature voltage compensation curves as used in many automotive type systems are not usually suitable for recharging batteries in deep cycle applications. The alternator output voltage may fall below the necessary minimum long before the battery reaches full charge.

Multi-battery isolators are commonly used in charging systems. Beware of attempts to install isolators in systems using unmodified, internally mounted and internally sensed voltage regulators. The charging voltage will be too low which will lead to battery sulfation and possible battery failure.

Avoid paralleling or placing batteries in series that are of a different brand, size and age. Premature battery failures will result.

A serviceable battery's ability to resist charging increases as it approaches full charge and decreases as it becomes discharged. This is due to the battery's higher counter voltage or resistance as it approaches full charge. As a battery becomes more nearly charged a higher voltage would be required to maintain the same charging current. On a properly regulated charging system the charging current approaches zero as the battery approaches a fully charged condition. A battery with a defective cell would have lower counter voltage and thus the charging current would be at a higher than normal level. Of course the good cells would soon fail due to overcharging and also consume more water than normal.

Do not completely discharge a deep cycle battery if it can be avoided. The deeper the discharge the less life you will obtain from the battery. the ideal method of operation in to charge and discharge the batteries through the middle range of their capacity (50% - 85%). The reason for this is that the charge acceptance rate is fairly high in the middle range of the capacity. From 85% to 100% requires a small charging current over a longer period of time. This is usually undesirable in a sail boat as it would require running the engine for a long period of time. No problem if you are connected to shore power using a high quality marine charger.

At least once a month the battery system must be fully charged when operating in the middle range of the battery capacity. During each discharge a little more lead sulfate accumulates. If this lead sulfate is allowed to remain for too long a period it will become very difficult to remove. The reason is that the lead sulfate will become hard and have a high electrical resistance. This is what is normally called a sulfated battery. The lead sulfate may become so hard that normal recharging will not break it down. This is the reason many sail boat owners complain at the end of the season that their batteries will not accept a charge.

See Information Bulletin 501.

The amount of recharge a battery needs can be determined by measuring the specific gravity with a hydrometer. The chart below shows the approximate "percent of charge" at various specific gravity values at 26.7 C.

Charged

Specific Gravity

100%

1.265-1.275

75%

1.225-1.235

50%

1.190-1.200

25%

1.155-1.165

0%

1.120-1.130

 On a manual charging system the charging current at less than 75% charged can be 25% of the 20 hour rate. The rate can even be higher below 50% charged. Once the battery approaches 75% charged reduce to 10% of the 20 hour rate. At 85% reduce the rate to 3% of the 20 hour rate. At 100% the charge is discontinued. A well regulated fixed rate system will do this automatically.

#508 - Low Maintenance and Maintenance Free Batteries

So called low-maintenance batteries are not all the same! There is a vast difference from one manufacturer to another.

While they are designed to go further without adding water, water can be added and the battery cell condition can be checked. This is not possible with most maintenance free batteries.

With maintenance free, if the electrical system malfunctions, the electrolyte may go dry, and there is no way of replacing it! There is no way of checking the electrolyte level, nor is there a reliable way of determining the state of charge of the battery. Only an experienced technician can determine the state of charge with a high quality voltmeter. Yes, you will have the first of trouble when the battery starts to fail. Okay if you are alongside the dock, but tragic if you are still at sea or beginning a planned weekend.

Many maintenance free batteries will not accept a charge if totally discharged as they contain calcium oxide between the grid and the active material. The calcium oxide has a high electrical resistance and confuses the alternator or charger into thinking the battery is charged!

Good marine practice dictates periodically checking the battery (or batteries) before putting out to sea.

Remember:

When your batteries fail, the engine won't start, electronic equipment won't operate, lights won't light, and electrical accessories won't operate!

Regular or low maintenance batteries are a must for marine equipment. The condition of the battery can easily be checked by taking hydrometer readings of each cell. The hydrometer readings will reveal the state of charge as well as possible trouble. Impending failure can be avoided by regularly checking the battery condition with a hydrometer.

Every boat owner should familiarize himself / herself with the use of a good hydrometer and have one on board at all times. The other alternative is to wait until the battery fails,
Then you will know the results of using equipment you can't check!! 

# 509 - Preventative Maintenance of Rolls Deep Cycle Batteries

Before installing the battery system check for physical damage, electrolyte level, state of charge, etc..

Insure that the battery compartment is well vented and will prevent the entrance of water, dirt, etc.. Believe it or not one of the most severe abuses that a deep cycle battery will receive is cleanliness, or lack of it. Dirt, corrosion, water and acid will rob a battery of a full life. A clean well kept battery will extend the useful life of the battery. Remove dirt and dust accumulations from the top of the battery. Wash the top of the battery with clean water and soda solution to neutralize any acid accumulation. Approximately 100 grams to a liter of water is sufficient. Baking soda used in the home is satisfactory. Rinse with clean water and dry. Ensure vent caps are in place and no soda solutions enters the battery.

 Before installing the batteries, clean the contact surfaces of the lead terminal post and battery terminals with a wire brush. Apply a thin coat of Vaseline to all contact points and connector bolts. After all connections have been securely tightened, they should be gone over and tightened a second time.

Check the height of the electrolyte twice a month. If necessary replace with approved water only. Many times domestic water is satisfactory. Water with a high mineral content is not satisfactory. Do not use water that is difficult to create a lather when washing your hands with soap and water.

Never fill the cells above the bottom of the vent well (must be at least 1 inch below the top of the vent opening). Over filling will cause loss of electrolyte and reduce the battery capacity. Never add acid to the battery.

Avoid over discharging of the battery as the useful life will be reduced. The rule of thumb is not to exceed 80 percent of the capacity of the battery. On a 12 volt system this would be approximately 11 volts. Remember over discharging or low voltage will also reduce the life of most electrical equipment.

Battery capacity is based on each cell having an electrolyte temperature of 77 degrees F (25 degrees C). Temperatures below 77 degrees F reduce the battery's effective capacity and lengthen the time to restore to full capacity. Temperatures above 77 degrees F will slightly increase capacity, but will also increase self discharge and shorten battery life.

If a battery becomes discharged the electrolyte can freeze. See list below.

Specific Gravity (cor..... to 80oF/26C)

Freezing Temp

1.280 Spec. Grav......(cor..... to 80oF/26C)

-92F (-69C)

1.265 Spec. Grav......(cor..... to 80oF/26C)

-71.3F (-57.4C)

1.250 Spec Grav......(cor..... to 80oF/26C)

-62F (-52.2C)

1.200 Spec Grav......(cor..... to 80oF/26C)

-16F (-26.7C)

1.150 Spec. Grav......(cor..... to 80oF/26C)

+5F (-15C)

1.100 Spec. Grav......(cor..... to 80oF/26C)

+19F (-7.2C)

 The state of charge of a battery can be measured with a hydrometer. The chart below shows the approximate "percent of charge" corrected for temperature at various specific gravity values.

Charged

Specific Gravity

Open Circuit Voltage

100%

1.265-1.275

12.6

75%

1.225-1.235

12.4

50%

1.190-1.200

12.2

25%

1.155-1.165

12.0

0%

1.120-1.130

11.7

  Determining state of charge by voltage is more difficult as there must be no load or surface voltage present.

When taking specific gravity measurements, it is important to correct for temperature to get a true reading. As a rule of thumb, specific gravity will change by 0.0003 for each ten degrees Fahrenheit change in temperature above or below 77 F (25 degrees C). Below 77F subtract from readings and above 77F add to the readings. As an example a reading of 1.265 at 67F corrected for temperature would be 1.262 and a reading of 1.265 at 87F corrected for temperature would be 1.268.

It is recommended that fully charged gravity and voltage readings be taken of each cell every month and compared with readings from the preceding period. The readings will indicate any marked difference in battery condition as well as differences between cells. A good rule of thumb is if there is 0.025 points or less between the high and low cell the battery is not defective. Low readings would indicate the battery being discharged.

Sometimes the battery may be operated between the middle range or it's capacity due to load demands and or lack of charging time. At least once every three to four weeks the battery system must be fully charged. During discharge sulfate is formed. If the sulfate is allowed to remain for too long a period it will become very difficult to remove and the battery system will not accept a charge.

For more information see bulletin #501.

The charging system can have a profound effect on the life of the battery. A high voltage setting can cause excessive gassing and water loss. Eventual damage to the battery system will take place. A low setting will leave the batteries in an under charged condition resulting in a loss of capacity and eventually the battery system may not take a charge. A proper setting will result in a minimum of water consumption and still able to maintain the batteries at full charge.

For more information see bulletin #507.

Remember batteries may expel explosive gases. Keep sparks, flames, burning cigarettes or any other ignition sources away from the battery system at all times. Always wear a face shield when working near batteries.

#600 - Activating Instructions for Diesel & Marine Batteries

  1. Inspect the cell for damage, Read Warning Label On Cell Before Proceeding
  2. Remove vent caps, fill each cell above the top of the splash guard (protection mat covering separators) with approved 1.240 specific gravity (warm climate) battery grade electrolyte. Keep sparks and flames away from battery at all times.
  3. Allow electrolyte to saturate plates and separators for 30 minutes. Temperature of electrolyte will rise and specific gravity will drop. Add electrolyte if not visible.
  4. Check for correct polarity with a voltmeter.
  5. Place on charge at the finishing rate (5% of the 8 or 20 hour rate). The rate may be increased if the battery does not begin to gas. Do not let the cell temperature exceed 115 degrees F (46 degrees C) If the temperature becomes excessive or the cells begin to gas vigorously, reduce the rate of charge. Continue charging until the cell (or cells) reach within .005 points of the specific gravity of the filling electrolyte corrected for 77 degrees F (25 degrees C)
  6. Top up or remove electrolyte as necessary for proper level. Never add electrolyte (only approved water) after activation.
  7. Replace vent caps and remove any spillage of electrolyte. If necessary clean with bicarbonate of soda and water ( 100 grams of soda to one liter of water) Rinse with water and wipe dry. Insure that soda solution does not get into cells.
  8. Shelf life of a dry charge battery is five years plus. Store in a cool dry area. The positive plate has an unlimited shelf life. The negative plate will revert to lead oxide when in the presence of water and oxygen. If this should happen, the battery is not ruined, but activation will take considerably longer! The electrolyte temperature will rise dramatically during activation. Do not place on charge until the temperature drops below 115 degrees F. Activation may take several days!
  9. Before installing the batteries, clean the contact surfaces of the lead terminal post and battery terminals with a wire brush. Apply a thin coat of Vaseline to all contact points and connector bolts. After all connections have been securely tightened, they should be gone over and tightened a second time. Preventative Maintenance (for more information see bulletin #509
  10. Check the height of the electrolyte twice a month. If necessary replace with approved water only. Many times domestic water is satisfactory. Water with a high mineral content is not satisfactory. Do not use water that is difficult to create a lather when washing your hands with soap and water.

 Never fill the cells above the bottom of the vent well. Over filling will cause loss of electrolyte and reduce the battery capacity. Never add acid to the battery (Only during activation)

  1. Avoid over discharging of the battery as the useful life will be reduced. The rule of thumb is not to exceed 80 percent of the capacity of the battery. On a 12 volt system this would be approximately 11 volts. Remember over discharging or low voltage will also reduce the life of most electrical equipment.
  2. Battery capacity is based on each cell having an electrolyte temperature of 77 degrees F (25 degrees C). Temperatures below 77 degrees F reduce the battery's effective capacity and lengthen the time to restore to full capacity. Temperatures above 77 degrees F will slightly increase capacity, but will also increase self discharge and shorten battery life.
  3. The state of charge of a battery can be measured with a hydrometer. The chart below shows the approximate "percent of charge" corrected for temperature at various specific gravity values.

Charged

Specific Gravity

Open Circuit Voltage

100%

1.265-1.275

2.10 VPC

75%

1.225-1.235

2.07 VPC

50%

1.190-1.200

2.03 VPC

25%

1.155-1.165

2.00 VPC

0%

1.120-1.130

1.95 VPC

Determining state of charge by voltage is more difficult as there must be no load or surface voltage present.

 Charged

Specific Gravity

Open Circuit Voltage

100%

1.265-1.275

2.10 VPC

75%

1.225-1.235

2.07 VPC

50%

1.190-1.200

2.03 VPC

25%

1.155-1.165

2.00 VPC

0%

1.120-1.130

1.95 VPC

  1. When taking specific gravity measurements, it is important to correct for temperature to get a true reading. As a rule of thumb, specific gravity will change by 0.003 for each ten degrees Fahrenheit change in temperature above or below 77 F (25 degrees C). Below 77F subtract from readings and above 77F add to the readings. As an example a reading of 1.250 at 67F corrected for temperature would be 1.247 and a reading of 1.250 at 87F corrected for temperature would be 1.253.

 It is recommended that fully charged gravity and voltage readings be taken of each cell every month and compared with readings from the preceding period. The readings will indicate any marked difference in battery condition as well as differences between cells. A good rule of thumb is if there is 0.025 points or less between the high and low cell the battery is not defective. Low readings would indicate the battery being discharged.

The charging system can have a profound effect on the life of the battery. A high voltage setting can cause excessive gassing and water loss. Eventual damage to the battery system will take place. A low setting will leave the batteries in an under charged condition resulting in a loss of capacity and eventually the battery system may not take a charge. A proper setting will result in a minimum of water consumption and still able to maintain the batteries at full charge.

  

 

Rolls Technical Bulletins
  Jan Watercraft Products, Since 2001
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