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Annunciator light functionality - NiCads : Skip's Corner

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Skip's Corner

 

 

 

Annunciator light functionality - NiCads

 

 

The Question –

Working on King Air 300 FA-85 with RG380E/44 installed. Have minor issue with Batt charge annunciator and can not locate wiring changes made when ACFT went from NiCad to Lead acid. If you could assist or point me in direction who could please do. Thanks for your time.

 

The Answer –

The CONCORDE King Air STC has the option of taking one of the battery charging cable shunt sensing lead off if the charge light is a nuisance to the operator.

But, it is a great system and the light comes on as long as at least 7 to 10 amps are charging the battery. Normally, with a healthy battery the light goes out before takeoff. IF THE CHARGING SYSTEM IS SET PER THE BEECH MM AT 28 TO 28.5 DCV.

Most of the NiCad's are 20 cell and the charging system is set upwards of 29DCV which is too high for our 24V batteries and the charge light stays on for a long time .

The reason we like to leave the charge light system functional is that it is a CURRENT SENSING SYSTEM And if the light comes on during flight, the pilot merely disconnects the battery that is just showing signs of an internal short , but fully charged and if later the generating system fails, the charged battery can be put back on line to support the load requirements.

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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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Battery Storage and Installation Preparation – Just the Facts Please!

 

Why it is important to properly store an aircraft battery and how to accomplish this?

Proper storage of an aircraft battery is important because it directly impacts the battery's performance capability as well as its total service life. To understand this, let me describe what happens to the battery during storage. When a battery is in storage, it gradually loses charge even though there is no load on the battery. This process is known as self-discharge and is illustrated in the chart shown on the screen. The capacity retention ratio, or state of charge, decays with time and the rate of decay is strongly affected by the storage temperature. The higher the temperature, the faster the battery loses its charge. As a battery self-discharges, the plates become sulfated and the internal resistance of the battery increases. If the sulfate level in the plates gets too high, the battery will take a lot longer to charge and will not last as long.


To actually see sulfation, take a look at the high magnification photos of sulfated plates and un-sulfated plates shown on the screen. The photo on the left shows the sulfated plate with large sulfate crystals. This is what causes the high resistance in the battery. To prevent the sulfate levels from getting too high, the battery needs to be boost charged to get it back to 100% state of charge. The photo on the right shows the plate after charging, which erases the sulfate crystals. Fortunately, a simple check of the battery's open-circuit voltage with a digital multimeter can be used to determine the condition of the battery.


The table shown on the screen summarizes the instructions from the CMM. A fully charged battery will have an OCV of about 13 volts for a 12-volt battery and about 26 volts for a 24-volt battery. While in storage, the OCV should not be allowed to drop below 12.5 volts for a 12-volt battery or below 25.0 volts for a 24-volt battery. The OCV should be checked every two to four months depending on the storage temperature. If the OCV is getting close to these values, the batteries should be boost charged with a constant potential charger.


Note that if the OCV is allowed to drop below the minimum, a capacity test will be necessary before it can be installed in an aircraft. This is to make sure that the sulfated plates can be restored to a good condition, so obviously, it is best to not let the OCV drop below the minimum. The worst thing that you can do is to put the battery on a shelf indefinitely and ignore the battery's state of charge. Eventually, the battery can become so sulfated that it will not recover and will have to be scrapped.


Another thing that is covered in the CMM is the storage temperature. Ideally, the storage temperature should be below 68 degrees F or 20 degrees C. Referring back to the capacity retention chart, you can see why cooler temperatures are preferred. At 20 degrees C, it takes about 15 months to reach 50% state of charge. At 30 degrees C, it only takes nine months to reach 50% state of charge. And at 10 degrees C, it takes well over 18 months to reach 50% state of charge. So, the cooler it is during storage, the longer you can go before a boost charge is necessary. However, if you cannot avoid storing the battery at warmer temperatures, it just means you will have to boost charge the battery more often.

 

One of the popular myths I hear is not to store it on a concrete floor because this will cause the battery to discharge very quickly. Is this correct?

 

No, that is not correct. That myth is a carryover from early automotive batteries that sometimes had acid residue on the case, which could contact the concrete. This would cause a rapid self-discharge of the battery. Today's lead-acid batteries do not have this issue. The only factor that affects the rate at which a battery self-discharges is the ambient temperature. Cooler is always better.

 

I think the easiest way to cover this topic is by referring to the flow chart shown on the screen. First, we want to do a visual inspection to check the overall physical condition of the battery to make sure there are no obvious signs of damage. If you see any damage, don't install the battery because it may not be airworthy and it's not worth the risk. Next, measure the open-circuit voltage of the battery with a digital multimeter. As long as the voltage is equal to or greater than 25.5 volts, the battery can be installed. If the voltage is equal to or greater than 25.0 volts but less than 25.5 volts, then it will need a constant potential boost charge before installing it in the aircraft. If the voltage is less than 25.0 volts, then you will have to charge the battery at constant potential and follow that up with a capacity test.


As long as the battery passes the capacity test, it is acceptable for aircraft installation. Note, that for a 12-volt battery, all of the voltage requirements are cut in half.

The flowchart is included in Appendix B of the CMM. I also want to point out that the CMM is a governing document for servicing Concorde aircraft batteries, and this video does not take the place of the CMM. If you have any questions regarding the CMM, please contact Concorde's customer service department. Thank you, everyone. Be safe.

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