How to read the Graphs properly

[wrathofkhan]

Hello, I have figured out how to run the eLogger, and captured some data/graphs.

I would like to find out how to read the 'numbers' properly. I am attaching below a graph, which is from my Swift helicopter with 5s lipo setup. I would like to find out if the batteries are good, or not ... I am guessing they are not that good, since the voltage drops close to 3.2 volts per cell under load. My setup is not for extreme 3d.

Is my analysis correct?

[StarmanDXE]

Yes. 3.2 volts is a large sag. My "better" used packs sag to about 3.7 or so and then down to around 3.3 after 8 minutes of ~10A nominal draw.

Looks to me like, with your nominal draw of around 22A, your pack voltage is closer to 3.5v. But, with the current peaks, it looks like your voltage is sagging a lot. I am not entirely sure, but that is probably a bad sign... What is the capacity and "C" rating of the packs you have?


Also, I think the "Watts" data is pretty superfluous on a chart like this and is just getting in the way :o

[wrathofkhan]

thanks for your input STARMAN. the pack i used the graph for is 25c/Hyperion (which is the same as FP).

the numbers are all over, listed below is a chart from trex tuning wherein they are testing some brand new packs out. it is only 3s, but if you check the volts/cell ... it is comparable. actually, my used one has better numbers. would you care to PM me one of your graphs ... thanks

http://www.trextuning.com/kokam-revo-airthunder.php

[StarmanDXE]

the pack i used the graph for is 25c/Hyperion (which is the same as FP).Ok, but what's the capacity?


would you care to PM me one of your graphs ... thanksYou can see some of my graphs in this thread: http://www.rcgroups.com/forums/showthread.php?t=759049

The first graph is one of my better batteries. The 2nd graph is of one of the bad batteries.

[wrathofkhan]

opps, sorry ... i overlooked. the capacity is 3700, 20c

[StarmanDXE]

So, you should be good up to 74 amps and your peaks are only at 55. Looks like a bad lipo (like mine :()

[wrathofkhan]

Actually, this is how I am reading the 3 graphs ... the reason I had initially posted was to find out if I am reading the graphs correctly:

Your pack#1 - 4 cell
Minimum Volts - 11.15 (2.79/cell)
Maximum Volts - 16.47 (4.12/cell)
Average Volts - 14.09 (3.52/cell)

Your pack#2 - 4 cell
Minimum Volts - 13.16 (3.29/cell)
Maximum Volts - 16.41 (4.10/cell)
Average Volts - 14.27 (3.57/cell)

My pack (5 cell)
Minimum Volts - 16.43 (3.29/cell)
Maximum Volts - 20.55 (4.11/cell)
Average Volts - 18.86 (3.77/cell)

your #2 and my pack has similar properties. i am just not sure if 3.3volts/cell is ok or not. 3.77 for average is OK as far as i know ... below 2.7v i heard is not good at all.

i wish others would chime in with some actual numbers, but as far as i know 3.7v is fine, and low should be around 3.4

[StarmanDXE]

You're reading these graphs to 2 decimal places? That seems a bit precise :rolleyes:


I just noticed: my 2nd graph is actually 2 different batteries. Looks to me like the numbers are closer to:

2100 #1 - 4 cell
Minimum Volts - 13.5 (3.4/cell)
Maximum Volts - 16.5 (4.1/cell)

2000 #2 - 4 cell
Minimum Volts - 12.5 (3.1/cell)
Maximum Volts - 16.4 (4.1/cell)

2000 #3 - 4 cell
Minimum Volts - 12.8 (3.2/cell)
Maximum Volts - 16.4 (4.1/cell)


Your pack - 5 cell
Minimum Volts - 17 (3.4/cell) (I can't tell what the voltage is at around the 2.5 minute mark)
Maximum Volts - 20.5 (4.1/cell)


From what I understand, 4.2v is considered fully charged and your cells shouldn't go below 3v (3.3v if you want to play it safe).

[back2la]

from my understanding, full charged amount is not important (unless cells are charged over 4.3v, then it is no good).

the other two numbers, average and low are much more important ... specially the low point!

Bob