On Mar 16, 4:00*pm, ContestID67 wrote:
Each year I like to test my batteries and replace those that do not
have enough capacity for a typical flight of 3-4-ish hours with all
the electronics running. I run two batteries so that removes a worry
about loosing power during a record flight. *But how do you perform a
good real world test?

My test is basically connecting a resistive load to the battery,
measure the battery voltage every 10 minutes or so. *Then wait for the
battery voltage to drop to 11.5Vdc (an arbitratry but safe value).
Simple.

I create an Excel spreadsheet that explains all this - the testing
that I perform, the test rig that I used and templates for gathering
the data and then graphing the results. * Seehttp://aviation.derosaweb.net/#batterytest.

I’d love to hear any comments that you might have. *Enjoy.

John DeRosa
Johnatderosaweb.com

John,
I have used that method and it works well, but.............
First, as I am sure you know, you want a load that is similar to the
real-life load. I use a 12 volt lamp (AKA light bulb) and because I
have a lot of stuff I use a 10 watt lamp to create a 830 mA load which
is about what I pull.

If you are testing every 10 minutes you are working kind of hard. My
battery, a 12120, takes hours to run down.

11.5 volts cut off is way too conservative. The published data curve
for the 12120 ................................wait, I am wrong. I
looked it up and I use 11.8 volts. but 11.5 is fine as well.

I use an Eagle Tree MicroPower V3 logger and get a computer generated
log of the discharge. Then I fly with the logger and get an idea of
my real-world consumption and compare the two. Works great. Others
use a pretty common logger with a built-in load, I prefer the Eagle
Tree because it will log a flight one day and a battery the next.

Do you do your test in cold air to simulate high altitude, or just
room temp?

ps. If you are replacing the 12120 battery look at the 12140 or the
12150. Same size, heavier, and more capacity.

Brian