|09-11-2007, 03:44 PM||#21|
Join Date: Sep 2006
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Alright, so here's the scoop;
Did some testing today on one of the assembled packs that was shipped to me to see where we stand.
First, I did a full discharge/charge cycle to help wake the cells up.
I then did 1 minute discharge tests on the pack using a propped brushless motor.
On my first test, I discharged the pack at an 8.5C rate (21A). Would've gone higher but I don't have a bigger prop right now!
When the pack was first connected, mean voltage was 12.39V. After a one minute discharge, pack voltage was down to 10.00 volts, with a max watt output of 212. Not that bad.
After this test, I noticed that the tabs connecting each cell were getting excessively warm. Upon closer look I can see that the tabs that are used for the cell connections are very thin, providing too much resistance for the current going through them. I took some small pieces of 14 gauge wire, soldered them across each cell, and then repeated the above test. Result were much better this time.
After a 1 minute discharge at 9C (amperage climbed a tad higher to 22.0 A because of the freer flowing current), cell voltage was only down to 10.26 V with a higher current draw than the first test, the end result was that the pack was able to deliver more power to the motor and also heat up less. Watt output was 225.
So, from these tests, we can see that for starters, the packs C rating is a true C rating and not hyped. If you push the packs up over 12C, you will likely see heavy voltage sag based on the values i've seen at 9C.
Secondly, performance is on par with most lithium batteries in the same range, including TP Pro-Lites and, surprisingly, Align batteries which actually have a 20C rating.
I am now talking with the MFG to see if thicker tabs can be had for welding across the cells. If they cannot supply the thicker tabs, I will likely only order loose cells from them instead of pre-assembled packs, and folks can then build their own. Or, I will only order the smaller capacity packs (e.g 1100 mAh) pre-assembled, and the larger cells will be sold individually.
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