battery life

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In article , Tim Ward
writes
It looks like there's an opportunity for a data logger update here.

The logger is already in the aircraft. It's generally connected to the
battery.
An 8 bit A/D would give an accuracy of 20 mV across the 10-15V range.
Sampling once per minute or so should be adequate. Post-flight analysis
should give you a pretty accurate idea of the health of the battery..
Battery health information doesn't really need to be real time, since you're
probably not going to be able to replace it in the middle of a task, anyway.

Tim Ward


Tim Ward

Sampling the voltage will only give the percentage discharge. As a
battery ages, it's capacity drops. Thus for a new 7AH battery 50 percent
charge is 3.5AH, but for an old battery with a remaining capacity of
(say) 3AH will only have 1.5AH left at the 50 percent point.

Tim Newport-Peace

"Indecision is the Key to Flexibility."

Since battery discharge is at a linear rate, you can usually begin the
discharge with a resistor and closely monitor the voltage for say one half
hour. You can make a graph from the first half hour, monitored every 10
minutes or so, and extend the line created on a graph. It is a lot quicker
than waiting for the entire discharge.

Since capacity is the ability to resist change of voltage, you can also
determine the capacity by monitoring how quickly the voltage changes on
charge. Older batteries without the ability to hold a charge will also
charge much quicker (compared to other batteries that are full capacity).
This would be a useful test for a constant current charger rather than a
constant voltage type.

Colin Lamb N12HS



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"Tim Newport-Peace" ] wrote in message
...
X-no-archive: yes
In article , Tim Ward
writes
It looks like there's an opportunity for a data logger update here.

The logger is already in the aircraft. It's generally connected to the
battery.
An 8 bit A/D would give an accuracy of 20 mV across the 10-15V range.
Sampling once per minute or so should be adequate. Post-flight analysis
should give you a pretty accurate idea of the health of the battery..
Battery health information doesn't really need to be real time, since
you're
probably not going to be able to replace it in the middle of a task,
anyway.

Tim Ward


Tim Ward

Sampling the voltage will only give the percentage discharge. As a
battery ages, it's capacity drops. Thus for a new 7AH battery 50 percent
charge is 3.5AH, but for an old battery with a remaining capacity of
(say) 3AH will only have 1.5AH left at the 50 percent point.

Tim Newport-Peace

"Indecision is the Key to Flexibility."

Yep. By post-processing the collected data, you could compare the
discharge curves of the same battery with the same load, from flight to
flight and see how it was holding up. If it's not holding up well, buy a
new battery before you go flying again.

Tim Ward