Ni-Cad Aircraft Battery
Ni-Cad Aircraft Battery
(OP)
I know that this is not the Aircraft related forum, but my question is specific to batteries, so I seek battery professionals.
I am in a remote field location in support of a company operation and am experiencing a recurring problem on our aircraft APU starter batteries.
The batteries are Marathon Power 20 cell Nickel-Cadmium Aircraft Batteries. They are charged by a dedicated Charger/Monitor. This charger is on during flight.
The power units will start on the ground. After flying 8+ hours at 33,000 ft, the battery is not able to start the unit. After three hours, or so, the batteries are again capable of starting. No failure indication occurs except for no start.
This is occuring on multiple aircraft and has not been a problem in the past.
Have I got a bad batch of batteries or is there something else wrong? These batteries are rated for flight and I can not see how they could freeze, especially with the charger on. I am not able to properly check these batteries where I am and I have a long lead time before receiving replacements.
Any help would be appreciated!
I am in a remote field location in support of a company operation and am experiencing a recurring problem on our aircraft APU starter batteries.
The batteries are Marathon Power 20 cell Nickel-Cadmium Aircraft Batteries. They are charged by a dedicated Charger/Monitor. This charger is on during flight.
The power units will start on the ground. After flying 8+ hours at 33,000 ft, the battery is not able to start the unit. After three hours, or so, the batteries are again capable of starting. No failure indication occurs except for no start.
This is occuring on multiple aircraft and has not been a problem in the past.
Have I got a bad batch of batteries or is there something else wrong? These batteries are rated for flight and I can not see how they could freeze, especially with the charger on. I am not able to properly check these batteries where I am and I have a long lead time before receiving replacements.
Any help would be appreciated!





RE: Ni-Cad Aircraft Battery
Can't you arrange to monitor the temperature at the battery case? A relatively simple heat transfer calculation based on the case temperature and the amount of trickle charge should reveal what the temperature wihin the battery is.
TTFN
RE: Ni-Cad Aircraft Battery
I also read somewhere that the internal resistance of Ni-Cad batteries help prevent freezing.
If the battery is freezing, would this be considered normal or is the battery bad. I can not reconfigure an aircraft with test equipment without going through some extreme pain.
Thanks for your answer. I am getting a crash course in Ni-Cad batteries (something I have taken for granted)!
RE: Ni-Cad Aircraft Battery
It's also possible that something has changed in the manufacturing of the batteries to make them more susceptible to whatever happens in the aircraft. Since most materials also contract when they cold, there may be some dimensional changes that increase contact resistance in the discharge path. Likewise, there may have been process changes that affect the chemistry of the batteries themselves.
TTFN
RE: Ni-Cad Aircraft Battery
Sorry, but somebody had to ask.
A.
RE: Ni-Cad Aircraft Battery
After a few hours, the batteries are fine. They are charged and work as advertised. If an external battery (one that has not flown) is dropped into the system, the APU will start. That leads me to believe that the system itself is good.
Could the electrolite level be serviced wrong to cause the battery to freeze in flight but work on the ground? And if so, wouldn't this level eventually reduce itself to a more normal operating level through the constant charging process?
When I get this figured out, I will report my findings, in case anyone else ever stubbles on something like this.
RE: Ni-Cad Aircraft Battery
A.
RE: Ni-Cad Aircraft Battery
Thanks
RE: Ni-Cad Aircraft Battery
I was going to suggest having a look at the aircraft's battery connector (having seen some odd problems with wayword dustcaps on the terminals in the past), but notice your problem is with multiple aircraft, so it doesn't sound like that.
Not much help I'm afraid. Good luck.
A.
RE: Ni-Cad Aircraft Battery
If this circuit faulted, and the battery continued to charge below -25C, would this be the cause of the battery freezing?
I have flown one aircraft with the battery charger disabled, and when it came back, the battery worked fine. I would take this to mean that charging in flight does not keep the battery from freezing.
During charging process, gassing of the water component of the electrolyte occurs. Maybe charging below -25C is causing freezing of this gas or the electrolyte?
RE: Ni-Cad Aircraft Battery
However, the thermistor issue re-raises the question about the mechanical integrity of the connections. Since the thermistor, being only a resistor, should have no failure mechanisms associated with a rather balmy -25ÂșC, the open circuit behavior that goes away with time suggests again that the cold temperature is causing one or more connections to open.
Immediately upon landing, can you measure the voltage of tha battery as well as the starting current when you try to start the APU?
TTFN