Posts: 2595
Joined: 3/8/2005 From: , CA, USA Status: offline
Some of the literature I have read said that "newly manufactured and shipped" LiPos should be "broken in". Basically that for the the first few runs, the LiPo should not be drained above 6C and that it would not perform to it's full ability. I had never really heard this before so I wanted to check if it was some kind of "urban myth" or if it was really based on fact.
The battery in question is a venom 4000mAH, 11.1V LiPo. Personally I have found these LiPos to perform decently. Much better than venom NIMH's which IMO are among the worst NIMHs out there. It is freshly shipped from Tower. I know there might be better options out there, but I figured I could use an extra battery and wanted to take advantage of the $20. off on orders over $150. from tower when I needed new parts for my broken truck anyways.
To quote the literature that came with the battery:
"1. New LiPO battery packs may require 12 or more charge/discharge cycles before the battery's optimum performance is reached. During this time, it is recommended that the battery pack is not discharged over 7C. 7C = 7 * 1C, where..."
Setup
To do a quick "sanity check" I used the V and A readouts on a HP E3610A power supply.
So the measured value of the "0.5 ohm" load is ~0.6 ohm. The measured value of the "0.25 ohm" load is ~0.34 ohm.
Why the mismatched values? The wiring between the power supply and the resistor is ~22 gauge and around a meter long, plus the connections on the power supply side aren't too great, go figure. Either way it's good enough for a quick "sanity check". Looking at the numbers I would guess the wiring and connectors add roughly 0.1 ohm.
Experiment #1
1) Battery fully charged and balanced (12.6V). 2) Battery discharged w/ 0.5 ohm load, 40 sec (photo #1) 3) Battery discharged w/ 0.25 ohm load, 40 sec (photo #2) 4) Battery discharged @7.5A, using an Intellipeak ICE charger, total discharge of 3AH capacity as measured by the charger. End voltage ~10.9V as measured by the charger. 5) Wait roughly 300 seconds. 6) Battery discharged w/ 0.5 ohm load, 29 seconds (photo #3). After 29 seconds, battery voltage was nearing 9V, so I halted the test.
I would have done a 0.25 ohm test, but I did not want to risk it as discharging the battery more might damage it.
Analysis #1
The 0.5-ohm load amounts to ~23A or ~6C. The 0.25-ohm load amounts to ~44A or ~11C.
2) 40 seconds of dicharge with the 0.5-ohm load (~23A) is about 256mAH capacity. 3) 40 seconds of discharge with the .025-ohm load (~44A) is about 488mAH capacity. 6) 29 seconds of discharge with the 0.5-ohm load (~19A) is about 158mAH capacity.
256mAH + 488mAH + 3000mAH + 158mAH = 3902mAH approximentally. Which is fine considering the battery's rating is 4000mAH. Capacity checks out.
For (2), photo #1, the voltage was acceptable. For 40 seconds, the voltage was above 11V. For (3), photo #2, the voltage was not acceptable. It began above 11V but within 5 seconds dropped below 11V. By the end of the 40 seconds, it had dropped to almost 10.7V. For (6), photo #3, the battery was reaching the end of its charge. Dropped pretty quickly toward the end.
I'll do more testing in the middle of the discharge next time.
I'll post it here. We'll see if the discharge voltages improve with subsequent cycles.
Posts: 2595
Joined: 3/8/2005 From: , CA, USA Status: offline
Note: The first charge was done by charging each cell individually to 4.2V. Hereafter, unless it proves to be a problem, charging will be done using the balancer. I've tested this balancer and it works to my satisfaction. The balancer is basically a 4.2V clamp. If the voltage of an individual cell rises above 4.2V, it starts to draw current, up to 0.1A.
Photo #1 is the charging station. Photo #2 is the discharge setup.
Posts: 2595
Joined: 3/8/2005 From: , CA, USA Status: offline
I don't have time to post a full analysis yet, but look at the difference between the 1st 0.25 ohm discharge in experiment #1 and experiment #2. experiment #2 is a small but noticeable improvement. Maybe once I've done enough tests, I'll post an overlay (transparency) of all the graphs from the different experiments merged together.
Posts: 2595
Joined: 3/8/2005 From: , CA, USA Status: offline
lol now that LiPos are allowed in racing you can expect to see more testing like this, it is a minor thing to the rest-of-world (ie. mythbusters or TV shows in general) but to racers every little bit is huge -- remember all the stuff like matching, zapping, pulse charging, memory effect, voltage depression, etc. for NIMH cells? Which of these things turned out to be myths or folklore and which turned out to have some basis in reality -- now that ROAR is going to allow LiPo their use will be virtually universal. LiPo is a whole new technology and Racers will start to face these questions -- Can LiPo be 'zapped', how much overcharge / overvoltage is 'safe', what about 'breaking in' new batteries, etc. Here the question is simple:
'Does a new LiPo need to be broken in? If so, quantify the gain from doing so. Is it significant? If so, how signficant'. Etc. Personally I really do not care if the answer is yes or no. I just want to know which. To me a 'good' or 'sucessful' result is just being able to answer the questions above based on tests, measurements, and some degree of sound science. The only flaw here being the small sample size, but who knows, I might find myself buying more batteries once the MMMax comes out and I'll be able to refine / repeat the testing here.
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LiPo "break-in" (experiment) - 
