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Thermal Runaway in AGM Batteries : Skip's Corner

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Can AGM Batteries Suffer Thermal Runaway like Lithium Ion Batteries?

 

 

The Question –

Can AGM Batteries suffer thermal runaway like Lithium Ion Batteries: Are they safe?

 

The Answer –

Does everyone know that when our RG series batteries are subject to the destructive overcharge test that they do NOT thermally runaway?

They get HOT about 260F, the electrolyte boils, the water turns to steam and the excessive internal pressure opens the vent valves releasing the steam (H20) NO ACID is expelled.  This continues for about 10 minutes and as soon as the battery runs out of water the charge current stops and the battery starts to cool down to ambient.

 

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Arcing Conditions : Skips Corner

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Arcing Conditions

 

 

The Question –

We have an RG380E/44 battery, S/N: 40450578 that has slight arcing on the negative battery terminal from a loose connection at the connector. We have replaced the aircraft connector but I cannot find any information in the CMM, (5-0171, Rev P), regarding how to repair this condition. Can you advise on how to repair so that I have manufacturers data/recommendations for repair and return to service please?

 

The Answer –

The battery terminal pins are .375 or 3/8” in diameter. Make sure you remove any copper deposits from the plug socket terminals so the pins will have maximum contact with the airframe plug sockets.

Make a go-no-go gage from a 3/8 drill rod or bolt that you can use to check ALL YOUR AIRFRAME PLUG SOCKETS. There needs to be enough tension on each socket, so that the 3/8” diameter gage will not slip out when the airframe plug is inverted.

The battery terminal pins are silver plated, protect them from corrosion using ACF-50 in the plug sockets.

 

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Battery Safety – How Does This Affect You

 

 

All safety precautions are covered in our component maintenance manuals, more commonly known as the CMMs. There's a CMM for RG series main aircraft batteries and a separate CMM for RG series emergency aircraft batteries. The safety aspects are the same in both CMMs. A list of the safety hazards is shown on the screen. These include, A, low capacity hazard, B, electrical burn hazard, C, danger of exploding batteries, D, chemical burn hazard, and E, damage to equipment.

 

Regarding the low capacity hazard, the FAA generally requires aircraft batteries to provide backup power in the event of a generator system failure. Never use a battery that has less than 80% of its rated capacity and never jumpstart an aircraft that has a dead or a discharged battery. Think aircraft safety, not just battery safety.

 

Regarding the electrical burn hazard, batteries can generate very high levels of current if the terminals are shorted together. The object that causes the short circuit will get very hot due to the high current and will cause a burn hazard. To prevent electrical burns, take off any metallic jewelry such as bracelets and necklaces that could potentially cause a short circuit across the battery terminals. Also, do not allow your belt buckle to contact the battery connector. Getting burned by a shorted belt buckle is more common than you might think. Obviously, it's not a good idea to place tools or other metal objects across battery terminals. For example, you may be tempted to use a steel ruler or a caliper to measure the distance between battery terminals, as some of us have found out the hard way, severe damage to you and the tool can happen pretty rapidly. As an extra precaution, it's a good idea to install battery terminal protectors when the battery is not connected to test equipment.

 

Regarding the danger of exploding batteries, lead acid batteries can cause explosions because they produce hydrogen and oxygen while on charge. However, there should not be any danger of explosion if you take the following precautions. First, make sure the work area is well ventilated so any hydrogen given off by the battery gets adequately diluted. Second, don't smoke, use an open flame or cause sparking near a battery. Remember that there could be local areas of hydrogen build up in the vicinity of the battery even if the work area is well ventilated. Third, wear proper eye protection when servicing batteries such as safety goggles or a face shield. And finally, do not charge a battery at constant current when it is installed in the aircraft. Constant current charging should only be done in a well ventilated area because a significant amount of hydrogen gas may be released from the battery. Battery compartments on most aircraft do not have adequate ventilation to handle the extra volume of hydrogen that is released so this would cause a potential explosion hazard on the aircraft.

 

Regarding the chemical burn hazard, lead acid batteries contain sulfuric acid in the electrolyte which can cause severe chemical burns. To avoid chemical burns, the following precautions should be taken. Never remove or damage the vent valves, avoid contact with the battery's electrolyte if the battery gets cracked or broken open. Don't touch your eyes after touching the battery, wash your hands first. If electrolyte does get into your eyes or on your skin, flush thoroughly with clean, cool water for several minutes and get medical attention as soon as possible. And finally, the last point is regarding equipment damage. To prevent equipment damage, ensure that the aircraft battery switch, external power source or the charger analyzer is in the off position before connecting or disconnecting the battery. If the circuit is not off when making or breaking connections, the battery terminals may arc and cause damage to the battery, equipment cables or both.

 

If these instructions are followed, then all potential safety hazards will be fully mitigated. Also, as a reminder, the CMMs provide full coverage of the safety hazards and precautions.

 

To complete your training, please take time to read the safety summary in the CMM. Also, take time to read the SDS, safety data sheet, for additional information. The CMM and SDS are posted on the Concorde Battery website for easy access. Finally, if you have any questions on this subject, contact Concorde's customer service department. Thank you everyone. Be safe.

 

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Bulging Batteries : Skip's Corner

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Bulging Batteries

  

The Question –

Is a sealed battery airworthy if it is bulging?

 

The Answer –

Yes, this is normal when the internal gas pressure is higher than the outside atmospheric pressure, it’s a GOOD sign as each cell pressure relief valve is not leaking.

The cell pressure relief valves remain closed normally but do burp occasionally to relieve excess internal pressure while in service. The recombinant gas battery requires a positive internal pressure to operate normally.

The case will go concave if the aircraft makes a rapid descent from a high altitude.

ALL rechargeable batteries of any type are called “secondary” and ALL have pressure relief valves to prevent the battery case from rupturing or bursting due to high gas pressure that may be caused by overcharging with higher than recommended voltage from either internal or external power. Sometimes this happens to batteries that are shipped in a charged state that are of normal shape at the time of shipment and are subject to either higher or lower atmospheric pressure during transit.

See Page 9 of Document Number 5-0324 “ CONCORDE RG SERIES AIRCRAFT BATTERY OWNER/OPERATOR MANUAL “ packed with each battery.

 

 

 

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