16. HOW CAN I REVIVE A SULFATED BATTERY?
Last Updated on July 11, 2004
INDEX:
16.1. How Can I Tell If my Battery Has Permanent
Sulfation?
16.2. How Do I Prevent Permanent Sulfation?
16.3. How Do I Recover Sulfated Batteries?
16.4. Where Can I Find Additional Information On Sulfation?
People kill more deep cycle batteries
with poor charging practices, than die of old age!
During the normal 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, continually undercharged,
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 permanent "sulfation". It
accounts for approximately 85% 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. This is because deep cycle
batteries are typically used for short periods, vacations,
weekend trips, etc, and then are stored the rest of
the year to slowly self discharge. Car batteries are
normally used several times a month, so sulfation rarely
becomes a problem.
As a consequence of parasitic load
and natural self-discharge, permanent sulfation occurs
as the 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 a clock, security system, maintenance of radio station
presets, etc.) While disconnecting the negative
battery cable will eliminate the parasitic load, it
has no effect on the natural self-discharge of a car
battery. Self discharge is accelerated by temperature.
Thus, sulfation can be a huge problem for lead-acid
batteries not being used, sitting on a dealer's shelf,
or in a parked vehicle, especially in HOT temperatures.
Car and deep cycle 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 your wet Standard (Sb/Sb) or wet Low
Maintenance (Sb/Ca) battery has been not been recharged
for over three months, especially if the storage
area was warm or hot. (Six months for wet Maintenance
Free (Ca/Ca) or one year for VRLA AGM or Gel Cell.)
- While recharging, the ammeter does not
drop to within 2% (C/50) of the AH capacity of the
battery within twice the capacity divided by the
charging rate in hours and the battery is warm or
hot. For example, if you have a 50 AH battery and
a ten amp charger, the battery should be fully charged
within 10 hours (2 x 50 AH/10 amps = 10 hours).
- If the temperature compensated absorption
charging voltage is correct and the battery is gassing
excessively.
- Poor performance.
- If the battery will not take or "hold" a
charge.
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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 does not form. 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 13.8 VDC, measured at 80° F (26.7° C)
with an accurate (.5% or better) digital voltmeter.
Based on the battery type you are using, charging
can best be accomplished with a microprocessor
controlled, three stage (for AGM or Gel Cell batteries)
or four stage (for wet batteries) "smart" charger
or by voltage-regulated float charger to "float" or
maintain fully a charged battery. A cheap, unregulated "trickle" charger
or manual two stage charger can overcharge 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. Maintaining a high State-of-Charge
(SoC) 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 or water generator designed
to float charge the battery. This is a popular solution
when AC power is unavailable for charging.
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16.3. How do I recover
sulfated batteries?
Here are three methods to try
to recover permanently sulfated batteries:
16.3.1. Light Sulfation
Check the electrolyte levels and
apply a constant current at 2% of the battery's RC
or 1% of the AH capacity rating for 48 to 120 hours
at 14.4 VDC or more, 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 125° F (51.7° C)
then stop charging and allow the battery to cool down
before continuing.
16.3.2. 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 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.
16.3.3. Desulfators
Use a desulfator also known as
a pulse charger. A list of some of the desulfator or
pulse charger manufacturers is available on the Battery References
Links List. Despite manufacturer's claims,
some battery experts feel that desulfators and pulse
chargers do not work any better at removing permanent
sulfation than do constant voltage chargers.
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16.4. Where Can I Find
Additional Information On Sulfation?
The jury is still out, but here
are some articles on Sulfation, Desulfation and Desulfators
by Alistair Couper,
Lead Acid Battery Desulfation Pulse Generator; http://www.shaka.com/~kalepa/desulf.htm.
Some Technical Details on Lead Acid Batteries: The Chemistry of Sulfation,
and Why Pulsing Helps, http://www.flex.com/~kalepa/technotes.htm
and
Desulfator Frequently Asked Questions.
http://www.shaka.com/~kalepa/faq.htm
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