Battery Monitors and Maintenance
The Questions
How do I know the true condition of my airborne NiCd battery packs? Is my pack good enough
for one more flight? How close am I getting to the 'danger' point of a low receiver pack?
Common Misconceptions
1) I had my batteries on charge overnight - they have to be OK. (wrong!)
2) I check my flight pack with an expanded scale volt meter. That tells me that the
pack is safe to fly. (wrong!)
3) I always fly 'X' number of flights, that's how I know it's safe to fly that many
today. (wrong!)
Get To Know Your Batteries!
There is no single method of knowing the condition of your NiCds. You must get to know
your batteries and act accordingly. There are several things you can to to almost
guarantee you won't have battery related problems when at the field. These suggestions
come from over 30 years of experience in R/C - watching countless unnecessary crashes due
to battery neglect and/or misunderstanding.
Install an On-board Battery Monitor
| This is very important! I'm not speaking of a monitor that just displays the voltage
when the system is idling (no servos being moved). The monitor must display the LOWEST
voltage the battery saw during the last flight - under full load of the servos in actual
flight conditions. The BC6 'glitch
counter/battery monitor' is such a device. I am not affiliated with them in any way, I
just used the monitor and am very impressed with it's functions. |
Upon landing, the BC6 will show you the lowest voltage of your pack during the flight.
It has a row of LEDs (lights) that indicate this voltage. As the pack drops in voltage
during your flights, the LEDs indicate this drop. So, when you you stop flying (or
recharge your pack)? It takes some testing because we are all flying different battery and
servo configurations. For example, using the same servos in a plane with a 600 mAh pack
will not yield the same results as using an 1800 mAh pack in that same plane. The BC6 will
indicate, for example, that the pack is at 1/2 capacity, but 1/2 capacity of a 600 MAh
pack may only be good for one more flight, whereas 1/2 capacity of an 1800 MAh pack in the
same plane may be good for 4 more flights.
Run the Tests
So, to determine when to stop flying, it is important for you to perform the following
test. Fly your plane/helicopter , keeping track of your total flight time, until the BC6
indicates a half charged battery, then stop flying and put your pack on a battery cycler
(an AccuCycle works fine for this - more on that later). The cycler will display the
current left in your pack and, with a simple calculation, you can determine the remaining
flights you could have had. The calculation is:
First, subtract the remaining capacity from the total capacity of your pack to get
capacity used.
Then, multiply the total capacity of your pack by the total flight time in hours and
divide that number by the capacity used from above.
The result is the total flight time you could have safely used your flight pack.
Example:
600 - 200 = 400
600 * 1.2 / 400 = 1.8
You can see that you could have safely flown 1.8 hours instead of the 1.2 that you
flew. Next time out, you know you can fly until you get a lower LED. Once you know which
LED to call your 'stop flying' indicator - you're done. Just fly until that LED is lit and
go home or recharge!
Battery Cycling
The best way to know your battery packs are healthy is to cycle them.
There are quite a few battery cyclers on the market today. I use the Hobbico AccuCycle
just because it is relatively inexpensive and does everything I need it to do. It's about
$100. You should cycle your batteries once every couple of months. Here's how. First, give
your pack a full charge. Then, let it set for a couple of days and cycle it. If you are
getting less than 80% of it's rated capacity, it's time for a new pack. How else do you
know? I've seen packs that last anywhere from a month, all the way up to 5 years. And
don't worry about the cycling process taking life from your packs, as NiCds are good for
about 1,000 cycles!
Redundancy
As we go to more and more expensive plane and/or helicopters, some thought should be given
to redundancy. In my more expensive birds, I run dual batteries and switch harnesses.
Check out this link if you're interested in how it's done. |