What's happening inside my batteries?

June 26, 2017

One of the most common areas of concern for Eclipse operators is battery life.  While common sense tells us that all batteries will eventually need to be replaced, the service life of Eclipse 500/550 batteries have failed to meet operators expectations.

 

What makes this situation curious is that the batteries installed in the aircraft are made by Enersys, a company who's battery technology is industry leading and with a reputation for long battery life.


So what causes your battery to fail prematurely?  In the studies we conducted, the primary cause of battery failure was high battery internal resistance.  Increased internal resistance restricts the amount of current that can flow out of the battery, effectively limiting the battery's capacity. This increase in internal resistance can typically be traced to two sources, sulfation of the negative plates within the battery and internal grid corrosion. 

 

What causes sulfation in my battery?

 

When a battery is being discharged, the sulfuric acid in the electrolyte is being depleted so that the electrolyte more closely resembles water (reducing battery charge). 

 

At the same time, sulfate from the acid is coating the plates and reducing the surface area over which the chemical reaction can take place (increasing resistance). Charging reverses the process, driving the sulfate back into the acid. 

 

When a current drain (load) is applied to the battery the sulfate ions move to the negative plates and give up their negative charge. The remaining sulfate combines with the active material on the plates to form lead sulfate. This reduces the strength of the electrolyte (charge), and the sulfate on the plates acts as an electrical insulator (increased internal resistance).

 

During use, small sulfate crystals form, but these are normal and are not harmful. During prolonged charge deprivation, however, the amorphous lead sulfate converts to a stable crystalline and deposits on the negative plates. This leads to the development of large crystals that reduce the battery’s active material, which is responsible for the performance.

 

This is known as sulfation. There are two types of sulfation: reversible (or soft sulfation), and permanent (or hard sulfation). 

 

Permanent sulfation sets in when the battery has been in a low state-of-charge for weeks or months. At this stage, no form of restoration has proven possible. 

 

What happens in my Eclipse Jet?

 

The Eclipse 500/550 has long been known to have a small constant amount of battery current drain acting on the System Battery at all times. This current drain is referred to as parasitic drain.

 

While the measured parasitic drain is only in milliamps, it can have a big effect.  For example, the parasitic drain will reduce your battery's capacity by 10% in just 16 days.  If the batteries are stored at high temperatures they will drain even faster.  So if you haven't flown your aircraft in a month, your battery will be in the same state of discharge as it would be during a battery capacity check.

 

Many operators choose to swap batteries side to side each 6 months. This process exposes both batteries to the damaging effects of the parasitic drain.

 

In order to extend the life of your batteries, the parasitic drain must be addressed. Fortunately, RAS has a solution.

 

 

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