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When is a car battery fully charged

when is a car battery fully charged


"People kill more deep cycle batteries with poor maintenance practices, than die of old age!"

Lead sulfation actually starts when you remove the charging voltage a lead-acid battery. The lead sulfate crystals are converted back to lead during the normal charging cycle. The real question is, if all of the lead sulfate crystals are not turned back into lead, how long does it take before they become so hard that they can not be converted? The answer is that varies--it could be weeks or months and depends on a number of factors such as the quality of the lead, temperature, plate chemistry, porosity, Depth-of-Discharge (DoD), electrolyte stratification, etc. Porosity is a measure of how porous the plates are.

During the normal discharge process, lead and sulfur combine into 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, continually undercharged, the electrolyte level is below the top of the plates, or the electrolyte is stratified, some of the soft lead sulfate re-crystallizes into hard lead sulfate and it cannot be reconverted during subsequent recharging. This creation of hard crystals is commonly called permanent or hard "sulfation". When it is present, the battery shows a higher voltage than its true voltage; thus, fooling the voltage regulator or smart charger into thinking that the battery is fully charged. This causes the charger to prematurely lower its output voltage or current, leaving the battery undercharged. If a wet lead-acid battery is not periodically recharged, undercharged or not properly maintained, sulfation will account for approximately 85% of premature 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 reduce a battery's cranking performance, capacity, and ability to hold a charge or be recharged. This occurs deep cycle and some starting batteries are typically used for short periods, seasonal powersports or applications, vacations, weekend trips, etc. and then are stored the rest of the year to slowly naturally self-discharge. Most starting batteries are normally used several times a month, so sulfation rarely becomes a problem unless they are undercharged or the plates are not covered with electrolyte.

As a consequence of parasitic (key-off) loads or natural self-discharge, permanent sulfation occurs as a wet lead-acid battery discharges while in long term storage. Parasitic load is the constant electrical load present on a battery while it is installed in a vehicle even when the power is turned off. The load is from the continuous operation of appliances, such as an emmissions control unit, clock, security system, maintenance of radio station presets, etc. While disconnecting the negative battery cable will eliminate a parasitic load, it has no effect on the natural self-discharge of a lead-acid battery. Self-discharge is accelerated by temperature. For batteries that are over 77° F (25° C), the self-discharge rate doubles with a 18° F (10° C) rise in temperature. Thus, sulfation is a huge problem for wet lead-acid batteries not being used, sitting on a dealer's shelf, or in a stored vehicle, especially in HOT temperatures.

"All lead-acid batteries are perishable!"

16.1. How Can I Tell If my Battery Has Permanent Sulfation?

Chances are that your battery has some permanent sulfation, if it exhibits one or more of the following conditions:

    If it will not "take" a charge or "hold" a recharge.

Especially if the temperature in the storage area was consistently over 77° F (25° C), if your wet (flooded) Standard (Sb/Sb) or wet Low Maintenance (Sb/Ca) battery has been not been recharged for over three months, "Maintenance Free" (Ca/Ca) battery for six months, and AGM (Ca/Ca) or Gel Cell (Ca/Ca) VRLA battery for one year.

While recharging in a well ventilated area within the expected time to charge the battery, the ammeter does not drop to below 2% below the Amp Hour (C/20) rating or the battery is warm or hot. For example, if you have a ten amp charger and a fully discharged 60 Amp Hour (C/20) or 100 minute Reserve Capacity rated battery, the battery should be fully charged within 12 hours.

If the Specific Gravity is low in all cells after the battery has been on a charger for the expected recharging time.

If the temperature compensated absorption charging voltage is correct and the battery is gassing or boiling excessively.

Poor cranking performance or low Amp Hour capacity.

When the SoC measured by a hydrometer, which is more accurate, does not materially agree with the SoC measured by a digital voltmeter

16.2. How do I prevent permanent 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 in three ways. Based on the battery type you are using, the best solution is to use an external charger in a well ventilated area that is capable of delivering a continuous, temperature compensated "float" charge at the battery manufacturer's recommended float or maintenance voltage for a fully charged battery. For 12-volt batteries, depending on the battery type, usually have fixed float voltages between 13.1 VDC and 13.9 VDC, measured at

80° F (26.7° C) with an accurate (0.5% or better) digital voltmeter. For a six-volt battery, measured voltages are one half of those for a 12-volt battery. This can best be accomplished by continuously charging using a three-stage for AGM (Ca/Ca) or Gel Cell (Ca/Ca) VRLA batteries or four stage for wet (flooded) batteries, "smart" microprocessor controlled charger. If you already have a two-stage charger, then use a voltage-regulated "float" charger or battery "maintainer", set at the correct temperature compensated float voltage to "float" or maintain a fully charged battery. If you need Web addresses or telephone numbers of charger manufacturers, please see the Chargers and Float Chargers and Battery Maintainers sections of Battery Information Links List . A cheap, unregulated "trickle" or a manual two-stage charger can overcharge a battery and destroy it by drying out the electrolyte.

A second method is to periodically recharge (or "top off") the battery when the State-of-Charge drops to 80% or below. Maintaining a high State-of-Charge tends to prevent irreversible permanent sulfation. The frequency of recharging depends on the parasitic load, temperature, battery's health, and battery type. Lower temperatures slow down electrochemical reactions and higher temperatures will significantly increase them. A battery stored at 95° F (35° C) will self-discharge twice as fast than one stored at 77° F (25° C). Standard (Sb/Sb) batteries have a very high self-discharge rate. AGM (Ca/Ca) and Gel Cell (Ca/Ca) VRLA batteries have very low rates. Please see Section 7.1 for more information on battery types.

There are trade-offs between the economics of continuous "float" charging, where self-discharge and resulting sulfation does not occur, and periodic charging with the increased potential for a shorter battery life due to permanent sulfation. If you decide to periodically recharge the batteries while in storage, increasing recharge frequency, disconnecting any parasitic load, or storing them in colder temperatures will impede the self-discharge and reduce the possibility for permanent sulfation, but will also reduce the total number of life cycles.

A third technique is to use a solar panel, wind or water generator designed to "float" charge batteries. This is a popular solution when AC power is unavailable for charging. The size of a solar panel, wind or water generator required will depend on the average amount of available natural resource, battery capacity and temperature. Normally a minimum of a five watt panel is required for an average car battery. A charge controller (voltage regulator) is required when the peak current output exceeds 1.5% of the Amp Hour capacity (C/20) rating of the battery.

A desulfator may be used in conjunction with any of the above methods.

16.3. How do I recover sulfated batteries?

Here are some methods to try to recover permanently sulfated batteries:

16.3.1. Light Sulfation

Check the electrolyte levels and try one of the following three methods for removing light sulfation: Equalize the battery. Please see Section 9.1.4. for more information on equalizing. Apply a constant current at 0.6% of the battery's Reserve Capacity or 1% of the Amp Hour capacity (C/20) rating for 48 to 120 hours, depending on the electrolyte temperature and capacity of the battery, at 14.4 VDC or more, depending on the battery type. For example, if the battery has a RC rating of 100 minutes or 60 Amp Hours (C/20) rating, use approximately .6 amps. Cycle (discharge to 50% and recharge) the battery a several times and retest its capacity. You might have to increase the voltage in order to break down the hard lead sulfate crystals. If the battery gets above 125° F (51.7° C) then stop charging and allow the battery to cool before continuing. Use a desulfator. pulse charger or desulfating mode on a battery charger. A list of some desulfator or pulse charger manufacturers is available on the Battery References Links List at .

16.3.2. Heavy Sulfation

Check the electrolyte levels and try one of the following two methods for removing heavy sulfation: Replace the old electrolyte with distilled, deionized or demineralized 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 (battery acid), and recharge. If the specific gravity exceeds 1.300, then remove the new electrolyte, wash the sediment out, and start over from the beginning 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 125° F (51.7° C) then stop charging and allow the battery to cool down before continuing. Cycle (discharge to 50% and recharge) the battery a several times and retest its 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. Use a desulfator. pulse charger or desulfating mode on a battery charger. A list of some desulfator or pulse charger manufacturers is available on the Battery References Links List at .

16.4. Where Can I Find Additional Information On Sulfation?

Please read Collyn Rivers' article, Battery Pulsing Devices . A circuit diagram of a desulfator can be found in this article by Alistair Couper Lead-Acid Battery Desulfator .

Category: Bank

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