Rick's Free Auto Repair Advice

Sulfation in lead acid batteries

What is battery sulfation?

How battery sulfation occurs. Batteries produce power through a chemical reaction between the lead plates and the electrolyte (battery acid). Car battery acid is a diluted solution of sulfuric acid H2SO4. In simple terms, the battery acid provides the sulfate, hydrogen, and oxygen needed to interact with the pates and produce power.

When a car battery is discharged through use or from self-discharge from non-use, the sulfate that was in the acid becomes attached to the surface of the plates. The sulfate crystals reduce the plate’s surface area, which, in turn, reduces the battery’s ability to produce power. Worse yet, the sulfate crystals act as an electrical insulator, increasing the battery’s internal resistance. When fully sulfated, the battery acid has given up most of its supply of sulfate and hydrogen. All that’s left is water H2O. That’s why discharged car batteries freeze in cold weather.

The alternator pushes the sulfate and hydrogen off the plates and forces it back into solution, which turns the H2O back into H2SO4.

There are two types of battery sulfation

Sulfation can be the reversible (soft crystal) type or permanent (hard crystal) type. If reversible sulfation is caught early, it can be reversed by recharging at the proper rate. However, if the sulfation is ignored and left in place for weeks or months, large portions of the lead plate surface become permanently unavailable. That dramatically reduces the battery’s ability to produce starting power. It may fail to produce enough power to operate the starter in warm weather and may even fail to provide enough power to light the lights in cold weather.

The longer a battery sits in a discharged state, the more likely the battery is permanently damaged. As a battery sits in the discharged state, the sulfate crystals grow in size and harden. After a certain period of time, they’re impossible to remove, even with recharging. At that point, the battery must be replaced.

What causes car battery sulfation?

• Deep discharge—like leaving your lights on overnight

• Self-discharge—all lead-acid batteries self-discharge about 1-2% per day, depending on the storage temperature (faster in higher heat).

• Long periods of discharge— The longer you leave a battery in a discharged state, the more the sulfation process becomes a problem.

• Faulty charging system—If the alternator isn’t working in your car, you’ll draw more power

Can you desulfate a battery?

If the sulfation is the reversible soft crystal type you can reverse it by recharging. But the recharging process is somewhat tricky. For example, a battery charger that’s equipped with a six-phase battery reconditioning routine may start by recharging process at a low voltage, around 4-volts and 7-amps. That’s called the energizing phase. Why low voltage? Because a sulfated battery has developed high internal resistance. If you hit it with high voltage right off the bat, that high resistance will create HIGH HEAT, and that heat will warp the plates and short out the battery.

Next, the charger boosts the charging current to around 13.5 amps while slowly ramping up the voltage to a peak of around 14.5 in phase 3. In the third or absorption phase, it maintains constant voltage while ramping down the amps. The 4th phase drops the voltage slightly and the amperage a bit further. In the 5th or resting phase, it drops current flow to 0 while maintaining around 12.5 volts. The 6th phase exercises the battery by pulling a load on the battery until it reaches the final restoration phase where it raises amperage and voltage one last time. The key to reconditioning a battery after sulfation is to prevent overcharging and overheating.

If the sulfation crystals have hardened, there’s no way to reverse the process and the battery must be replaced and recycled

©, 2020 Rick Muscoplat

Posted on by Rick Muscoplat


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