VRLA Batteries Explained

“Overdressed, oversexed, overpaid bus drivers” was how airline owner Harry Steele referred to them, and I myself recently referred to them as “data entry clerks” (in a good-natured, tongue-in-cheek ribbing, of course). Those poor airline pilots take a lot of abuse from the rest of us in the airline business, but of course, the point that I was making was that their livelihood is being threatened due to advances in avionics technology. But before we maintenance types get too smug, let us consider the effect of technology on our own profession.

When I entered the avionics field in the late 1970s, many of the “old guys” I worked with were transitioning from the airline’s fleet of DC-3s, C-46s, C-47s etc. to the newer Boeing 737-200. The experience and skills exhibited by these gentlemen (no women fixing airplanes in those days) were more akin to the expertise of an electrician, rather than that of an electronics technician. My generation of avionics technicians came largely from the community colleges, and were more familiar with transistors and circuit boards than vacuum tubes and wiring. The nature of the job was transitioning in order to accommodate the shifting technologies.

Perhaps the most valued skill a technician of this era could possess was the ability to troubleshoot systems. Continuity checks, a solid understanding of how a system was designed to operate, and vast accumulated experience enabled the skilled avionics tech to quickly and properly troubleshoot and repair snags. The greatest maintenance costs to an airline were the result of poor troubleshooting, rather than the cost of the actual repairs that solved the problems.

The ability to remove a component, test, repair, and re-install it has been the job of the aircraft technician for quite some time. In fact, an examination of Transport Canada’s AWM 566 Appendix “C” will reveal the phrase “Test, Troubleshoot, Repair, Adjust, Remove and Replace” repeated throughout. However, with changes in technology, we now have extensive and effective built-in test equipment (BITE) checks which can be performed using plug-in or on-board computer systems. Computer memories now store ongoing and intermittent faults which can aid the technician in locating problems that would previously have been signed off as “Unable to duplicate on ground at YYZ. Ground checked serviceable”. (Don’t pilots just love to read those words in the log book?)

Many of the components which were repairable in the past, are now disposable “consumables” which are simply replaced rather than repaired. Many snags that once required a physical adjustment by a technician now require manipulation of software commands, which in some cases can even be made from a remote location. Fly-by-wire technology has seen the need for the rigging and tensioning of cables, pulleys, and bell cranks all but eliminated. Even the simple but time-consuming task of checking and servicing the aircraft’s batteries is being eliminated, which (finally) brings me to the subject of this month’s article, ”Valve Regulated Lead Acid Batteries Explained”.

To receive accreditation from a Transport Canada-approved college, all students must service both lead-acid and nickel-cadmium batteries. Due to the safety hazards associated with these tasks, quite a bit of classroom time is spent preparing the students for the performance of these projects. For example, the student must demonstrate an understanding of the procedures and materials used in the event of an electrolyte spill (i.e., boric acid will neutralize nicad electrolyte; baking soda will neutralize a sulphuric acid spill).

Having recently replaced the battery in my car with a new maintenance-free unit, I decided to investigate the latest in maintenance-free aircraft battery technology.* Unlike the gel-cell battery I installed in my car, the maintenance-free valve regulated, recombinant gas aircraft battery uses a liquid sulphuric acid electrolyte solution. However, contained within the cells of this type of battery are layers of glass mat, which absorb and retain the electrolyte, not unlike a sponge. This means that there is essentially no free liquid electrolyte that could spill.

The chemical reaction that takes place within a lead-acid battery during discharge results in hydrogen ions combining with oxygen ions, which, of course, creates water (H2O). This water dilutes the sulphuric acid electrolyte solution, causing a decrease in specific gravity and a reduction in the battery’s ability to deliver current. (This explains why checking the S.G. of a lead acid battery enables us to determine the state of charge: the more discharged the battery is, the more water there is, and thus, the lower the S.G.) When the battery is recharged, hydrogen gas and oxygen gas are generated. In a traditional battery flooded with liquid electrolyte, these gasses are vented to the atmosphere, reducing the amount of water (H20) in the battery, and necessitating a “top up” of distilled water from time to time. In a recombinant gas battery, the hydrogen and oxygen gasses are recombined within the cell, eliminating the need to add water, resulting in a maintenance-free battery. The fact that there is no liquid electrolyte to spill, no need to add water, and that the battery case is a non-vented sealed unit makes it not only maintenance-free, but also means it can be operated at any attitude, including those encountered during aerobatic manoeuvres.

The advances in battery technology have resulted in some operators electing to switch from nicads to these VRLA/RG batteries. Could we one day perhaps see viable electric airplanes as a result of the continued advances in the technology? Moves are underway toward that end, at least in the private, recreational flying arena. The trend toward eliminating the repair and servicing of not just batteries, but many major aircraft components, is a reality that we are already facing.

How will this affect the aircraft maintenance profession? Will we see a shift away from the traditional role of the AME/A&P? Will we see the role of the troubleshooter replaced by computer/software analysts? Will we see mechanics replaced by technician/parts changers? Will we see the occupation of the aircraft maintainer go the way of the wireless operator, navigator, flight engineer and pilot? I welcome your thoughts.

*Thanks to Patty Montbriand at Concorde Battery for providing me with technical information, and training aids.

Q: How do recombinant gas, relief valve lead acid batteries prevent the spillage of electrolyte?

Answer to previous question:

Q: What is the most effective way of reducing HIRF interference?

A:  Properly installed shielded wiring is the most effective way of reducing HIRF interference.