Tuesday, March 11, 2008

Car Battery Myths (Part 4 of 4)

Batteries naturally self discharge while in storage, and sulfation will begin occurring when the State-of-Charge is less than 100%. Please see Section 16 for more information on sulfation. Cold will slow the process down and heat will speed it up. Here are six simple steps to store your batteries that will protect them from sulfation and premature failure.

13.1. Physically inspect for damaged cases, remove any corrosion, and clean the tops of the batteries. If the battery is in a vehicle, remove the negative connection from the battery to eliminate the additional parasitic discharge.

13.2. Check the electrolyte levels and add distilled water as required, but avoid overfilling.

13.3. Fully charge and equalize, if required, using the procedures in Section 9.

13.4. Store in a cool dry place, but not so that it will freeze. The freezing point of a battery is determined by the State-of-Charge and the higher it is, the lower the freezing temperature. (Please see the State-of-Charge table in Section 4.) Based on the battery type you are using, connect a voltage regulated float charger (such as a ChargeTek, etc.) or a “smart,” microprocessor based three stage or four stage charger (such as a Battery Tender, BatteryMinder, etc.) to continuously “float” charge your battery. Do not use a cheap, unregulated “trickle” charger or a charger which was not designed for float charging or you will overcharge the battery.

13.5. A less desirable alternative to float recharging would be to periodically test the State-of-Charge using the procedure in Section 4.? When it is 80% or below, recharge using the procedures in Section 9. The frequency of testing and recharging will depend on the ambient storage temperature.

13.6. When you remove the batteries from storage, equalize wet (flooded) or AGM batteries, if required, using the procedure in Section 9.

14.1. Storing a battery on a concrete floor will discharge them.

A hundred years ago when battery cases were made of porous materials such as tar-lined wood boxes, so storing batteries on concrete floor would accelerate their discharge. Modern battery cases are made of polypropylene or hard rubber. These cases seal better, so external leakage-causing discharge is no longer a problem, provided the top of the battery is clean. Temperature stratification within very large batteries could accelerate their internal “leakage” or self-discharge if the battery is sitting on an extremely cold floor in a warm room or is installed in a submarine.

14.2. Driving a car will fully recharge a battery.

There are a number of factors affecting an alternator's ability to charge a battery, such as how much current from the alternator is diverted to the battery to charge it, how long the current is available, and the temperature. Generally, idling the engine or short stop-and-go trips during bad weather or at night might not fully recharge the battery. Please see Section 5.

14.3. A battery will not explode.

There two types of battery explosions are external and internal. Recharging a wet lead-acid battery produces hydrogen and oxygen gas. While spark retarding vent caps help prevent external battery explosions, sparks occur when jumping, connecting or disconnecting charger, or battery cables and ignite the gas. Internal explosions usually occur while starting the engine and normally blow the caps or cover off and splatter electrolyte all over the engine compartment. The most probable cause is from a combination of low electrolyte levels in the battery and a low resistance bridge formed between or across the top of the plates called "treeing" between a positive and negative plate. When heavy current flows in the battery, a spark occurs and ignites the residual gas in one or more of the cells. A second possible cause is a defect in the weld of one of the plate connecting straps.

Periodic preventive maintenance (Please see Section 3.), working on batteries in well-ventilated areas, or using sealed AGM or gel cell type batteries can significantly reduce the possibility of battery explosions. To neutralize the residual battery acid, be sure to thoroughly wash the engine compartment and the back of the hood with a solution of one-pound baking soda to one gallon of warm water. The largest number of battery explosions, while starting an engine, occurs in hot climates. While not fatal, battery explosions cause thousands of eye and burn injuries each year. Should a battery explosion occur and battery electrolyte (or battery acid) get in someones' eyes, flush them out with any drinkable liquid immediately because seconds count.

14.4. A battery will not lose its charge sitting in storage.

Depending on the type of battery and temperature, batteries have a natural self-discharge or internal electrochemical “leakage” at a 1% to 25% rate per month. Over time the battery will become sulfated and fully discharged. Higher temperatures accelerate this process. A battery stored at 95° F (35° C) will self-discharge twice as fast than one stored at 75° F (23.9° C). (Please see Section 15. and Section 16.)

14.5. “Maintenance free” batteries never require maintenance.

In hot climates, the water in the electrolyte is lost due to the high under hood temperatures. Water can also be lost due to excessive charging voltage or charging currents. Non-sealed batteries are recommended in hot climates so distilled water can be added when this occurs. (Please see Section 3. for other preventive maintenance that should be performed on “maintenance free” batteries.)

14.6. Test the alternator by disconnecting the battery with the engine running.

A battery as like a voltage stabilizer or filter to the pulsating DC produced by the alternator. Disconnecting a battery while the engine is running can destroy the sensitive electronic components connected to the electrical system such as the emission computer, audio system, cell phone, alarm system, etc., or the charging system because the peak voltage can rise to 40 volts or more. In the 1970s, removing a battery terminal was an accepted practice to test charging systems of that era. That is not the case today.

14.7. Pulse chargers, aspirins or additives will revive sulfated batteries.

Using pulse chargers or additives is a very controversial subject. Most battery experts agree that there is no conclusive proof that pulse chargers work any better than constant voltage chargers to remove sulfation. They also agree that there is no evidence that additives or aspirins provide any long-term benefits. Short term gains are achieved by increasing the acidity of the battery.

14.8. On really cold days turn your headlights on to “warm up” the battery up before starting your engine.

While there is no doubt that turning on your headlights will increase the current flow in a car battery, it also consumes valuable capacity that could be used to start the cold engine. Therefore, this is not recommended. For cold temperatures, externally powered battery warmers or blankets and engine block heaters are highly recommended if the vehicle can not be parked in a heated garage. AGM and Ni-Cad batteries will perform better than other types of wet Lead-acid batteries in extremely cold temperatures.

14.9. Car batteries last longer in hot climates than in cold ones.

Car batteries last an average of two thirds as long in hot climates as cold ones.? Heat kills car batteries, especially sealed maintenance free batteries. (Please see Section 11.1.)

14.10. Charging Cables or an Auto Jump Starter will start your car.

The cigarette lighter charging cable's advertising states “ charges weak batteries in minutes.” There is little doubt that charging cable products will certainly recharge your car battery if you have enough time and your battery is in good condition. Cigarette lighters are normally fused at 10 amps, so to be safe they probably limit current flow to 7.5 amps. Given the size of the cord, the amount might be even less.

They work by applying higher voltage from the good battery to “recharge” the bad one. Now let's assume it is a hot day and that you need just of 3% of the battery's capacity to start the engine from a 40 ampere-hour battery. This means you will need at least 7.5 amps for 10 minutes to flow from the good battery to the bad one. Now let's also assume that it is below freezing and you have left your lights on. You will need at least 50% capacity or 20 amp hours to start the vehicle. This will take over two hours to partially charge the dead battery.

An auto jump starter uses special high current batteries to provide up to 900 peak amps to start your engine. It can provide 200-300 amps for up to 8-10 seconds. After this, the unit has to be recharged for 24 to 48 hours. Standard AA alkaline batteries are used to trickle charge the special batteries. This type of emergency starter should start all but diesel engines up to six or eight times, depending on the condition of the engine and the temperature.

14.11. A larger capacity battery will damage my car.

A starter motor will only draw a fixed amount of current from the battery, based on the resistance of its load. A larger current capacity battery supplies only what is required. It will not damage your vehicle. Using batteries with higher or lower voltage or too tall can damage your vehicle.

14.12. Lead-acid batteries have memories.

Lead-acid batteries do not have the “memory effect” found with first generation Ni-Cad batteries; however, continuous undercharging will lower the capacity of the battery. Deep discharges can also damage starting batteries or can shorten their lives.

14.13. Bad batteries will not harm the charging system or starter.

A bad or weak battery causes more stress on a charging system or starter and can cause premature failures due having to compensate the voltage or current. If you replace a battery, alternator, voltage regulator or starter, you should test the other three components for latent or permanent damage.

The amount of time, usually referred to as "airport or garage time", that you can leave your vehicle parked and still start your engine is based on such things as the battery's State-of-Charge, the Reserve Capacity, the amount of natural self-discharge and parasitic load, and temperature. Car manufacturers normally design for at least 14 days or more airport time; they assume a fully charged battery in good condition, moderate weather, and no additions to the original car's parasitic load (for example, an after market alarm system). When a battery drops below 100% State-of-Charge, sulfation starts occurring, and this can also reduce the capacity of the battery.

If you leave your vehicle parked for more than two weeks, then you have several options:

15.1. The best option is to connect an voltage regulated float charger or solar float charger to your car battery. You will need 13.2 VDC and at least .5 amps (500 milliamps) to overcome the natural self-discharge and parasitic load.

15.2. Install a battery with a larger reserve capacity.

15.3. Jump the battery and hope that there is no latent damage.

15.4. Connect a battery in parallel.

15.5. Disconnect the negative terminal, but be sure that you have saved any security codes or radio stations presets that will have to be reprogrammed.

15.6. Replace the battery, especially if it is over three years old or sealed, and you live in a hot climate.

15.7. Have someone drive your car during the day on the highway every two weeks 10 to 15 minutes to recharge the battery.

Starting and other lead-acid batteries are perishable. During the discharge process, soft lead sulfate crystals are formed in the pores and on the surfaces of the positive and negative plates inside a lead-acid battery. When a battery is left in a discharged condition, is continually under charged, or the electrolyte level is below the top of the plates, some of the soft lead sulfate re-crystallizes into hard lead sulfate. It cannot be reconverted during subsequent recharging. This creation of hard crystals is commonly called "lead sulfation". It accounts for over 80% of the deep cycle lead-acid battery failures. The longer sulfation occurs, the larger and harder the lead sulfate crystals become. The positive plates will be light brown and the negative plates will be dull, off white. These crystals lessen a battery's capacity and ability to be recharged.

Sulfation is a result of lead-acid battery discharge while in storage, which is a consequence of parasitic load and natural self-discharge. Parasitic load is the constant electrical load present on a battery while it is installed in a vehicle even when the ignition switch is turned off. The load is from the continuous operation of electrical appliances, such as, an emissions computer, a clock, security system, maintenance of radio station presets, etc. While disconnecting the negative battery cable will eliminate the parasitic load, it has no affect on the other problem, the natural self-discharge of battery. Thus, sulfation can be a huge problem for lead-acid batteries while sitting on a dealer's shelf, in a basement, or in a parked vehicle, especially in hot temperatures.

16.1. How do I prevent sulfation?

The best way to prevent sulfation is to keep a lead-acid battery fully charged because lead sulfate is not formed. This can be accomplished three ways. The best solution is to use a charger that is capable of delivering a continuous "float" charge at the battery manufacturer's recommended float or maintenance voltage for a fully charged battery. 12-volt batteries, depending on the battery type, usually have fixed float voltages between 13.2 VDC and 13.6 VDC, measured at 70° F (21.1° C) with an accurate (.5% or better) digital voltmeter. Charging can best be accomplished with a microprocessor controlled three stage or four stage charger, such as a Battery Tender (Deltran), Truecharge (Statpower), BatteryMinder, Schumacher, etc., or by voltage regulated float charger set at the correct voltage, such as a ChargeTek, etc. By contrast, a cheap, unregulated "trickle" charger or manual two stage charger can over charge a battery and destroy it.

A second and less desirable method is to periodically recharge the battery when the State-of-Charge drops to 80% or below. At 70° F (21.1° C), a battery with 100% State-of-Charge measures approximately 1.261 Specific Gravity or 12.63 VDC and at 80% State-of-Charge, it measures 1.229 Specific Gravity or 12.47 VDC. Maintaining a high State-of-Charge tends to prevent irreversible sulfation. The recharge frequency is dependent on the parasitic load, temperature, the battery's condition, and plate formulation (battery type). Temperature matters! Lower temperatures slow down electro chemical reactions and higher temperatures speed them up. A battery stored at 95° F (35° C) will self-discharge twice as fast than one stored at 75° F (23.9° C).

A third technique is to use a regulated solar panel or wind generator designed to float charge the battery. This is a popular solution when AC power is unavailable for charging.

16.2. How do I recover sulfated batteries?

Here are three methods to try to recover sulfated batteries:

16.2.1. Light Sulfation

Apply a constant current from one to two amps for 48 to 120 hours at 14.4 VDC, depending on the electrolyte temperature and capacity of the battery. Cycle (discharge to 50% and recharge) the battery a couple of times and test its capacity. You might have to increase the voltage in order to break down the hard lead sulfate crystals. If the battery gets above 110° F (43.3° C) then stop charging and allow the battery to cool down before continuing.

16.2.2. Heavy Sulfation

Replace the electrolyte with DISTILLED water, let stand for one hour, apply a constant current at four amps at 13.8 VDC until there is no additional rise in specific gravity, remove the electrolyte, wash the sediment out, replace with fresh electrolyte, and recharge. If the specific gravity exceeds 1.300, then remove the old electrolyte, wash the sediment out, and start over with distilled water. You might have to increase the voltage in order to break down the hard lead sulfate crystals. If the battery gets above 110° F (43.3° C) then stop charging and allow the battery to cool down before continuing. Cycle (discharge to 50% and recharge) the battery a couple of times and test capacity. The sulfate crystals are more soluble in water than in electrolyte. As these crystals are dissolved, the sulfate is converted back into sulfuric acid and the specific gravity rises. This procedure will only work with some batteries.

16.2.3. Desulfators

Canadus Power Systems [Can-PULSE] (US), formally Solartech, http://www.canadus.com/

PulseTech (US), http://www.pulsetech.net/

No comments: