Nanotech LiPo break in, do they improve with a few cycles?

[zombiess]

I just ran my 30S2P 25-50C NanoTech pack (made from 6AH cells) yesterday for it's first break in at 60A max for my Hubzilla hill climb test. I did notice I still had some decent sag, but I'm not quite sure exactly how much it because I was not paying close attention. Looked like about 2-3V of sag at 60A vs the 4-6A sag I got on my 30S3P 20C Turnigy pack (made from 5AH cells) with the same settings, but I have to double check those numbers when I'm paying closer attention. This was my very first charge on them. I was talking to Farfle tonight and he said that the Nano Tech packs tend to both increase in capacity a little and drop in resistance after a few cycles. Has anyone here noticed this to be the case with their cells? I realize running 30S that I'm going to get more voltage sag than an average user just because I have so many cells in series; I also might have a wiring harness issue causing higher resistance than I should have.

I'm planning a new wiring harness build anyways so I'll eliminate that as a possible issue.

[Kin]

My experience with LiPo has been that they improve after some cycles. You will surely be able to confirm that soon, hopefully.

I've heard on the forums that there's a chemical stabilizer for shelf life that breaks down after a few cycles. Not sure how true that is, but it feels like a good explanation.

Also, you seem to indicate that you have two situations

12ah of 25-50C Nano
2-3V sag

15ah of 20 Turnigy.
4-6v sag.

Assuming the nano is avg twice as good as the 20C turnigy [I never considered nano so I don't actually know what to make of their two number rating system],
To get half as much sag for nano makes sense, assuming that the deliverying capabilities (C rating) are very related to internal resistance [though I think internal resistance might differ from output capabilities, since the latter is limited my movement of atoms while the former on more abundant charge carriers. But please bear in mind if I sound like I'm trying to sound like what I know what I'm talking about, i dont really].

Also to ask for the current that would be 1C of the Turnigy
is to ask for 1.25C of the Nano [since there is only 12 ah of Nano and 15 of turnigy)

[neptronix]

That's the low end of nanotech and we're talking about 10AH versus 15AH of 20C Turnigy ...
I have no experience with nanotech, but IMHO i've never seen a lithium battery 'break in'.

Do you have a balancing charger or other device that is capable of measuring internal resistance? that will tell you the truth.

BTW, 2-3v of sag on a 120v pack is not bad at all. The sag per cell is super low when you divide that by 30 cells.

[zombiess]

I need to test it at 85A draw where my 30S3P pack was sagging about 7-8V and see if it's any better.

[mvly]

well my experience is they (nano tech) balance charge quicker after like 5 cycles or so from new. As for capacity, i can't tell. i never run them low.

[liveforphysics]

You picked the dog's of the nano-tech cells, but yes, after about 10 cycles or so, more areas that did not become intercalation points from initial activation charge will open up, and both performance and capacity will increase slightly.

[dogman]

I agree, they do perk up after a few cycles. I've only seen it take one or two cycles for 30c lipo. 5-6 for 2c lifepo4.

What I could detect was a tendency to be more balanced, which improves capacity, rather than less sag later.

[zombiess]

You picked the dog's of the nano-tech cells, but yes, after about 10 cycles or so, more areas that did not become intercalation points from initial activation charge will open up, and both performance and capacity will increase slightly.

What's bad about these versions? I didn't know there were good and bad versions, just that this was all they had in stock. Should I return them for a better version? I hope I didn't waste my $800 on these, no point in having them if they are no better than my regular 20C packs. If they suck I'm going to get rid of them and get something else, but before I do that, please define what you mean when you say they are dogs of the nano-tech cells, why are they bad when compared to the 5AH nanos or the 8AH nanos or xxx nanos? What makes these cells worse?

Wish it was easier to find info on this site, so much is buried in threads on other topics completely unrelated to what I'm looking for because people don't start new threads and continue to post completely unrelated info in the same thread totally changing it's substance. I searched about these packs before I bought them but didn't find anything. Would be nice if people started threads about each individual thing they are doing vs 80 page threads that start off like "check out these awesome batteries I'm testing" and then half way through they talk about how to cut Styrofoam dolphin sculptures for their mothers front yard and a few pages later it turns into what style of bike lock is best.

I've been chastised for starting new threads for each topic instead of keeping everything in one giant long thread full of unrelated info, but I thought that's what threading was supposed to be used for?

[amberwolf]

Another thing that can be done is that if someone is posting factual info about specific things, a wiki article could be added to or created:
http://endless-sphere.com/w


I've been trying to at least add links to posts or threads that can be used to create articles from, but have not enough time to write up articles themselves yet.

[rjoe]

Wish it was easier to find info on this site, so much is buried in threads on other topics completely unrelated to what I'm looking for because people don't start new threads and continue to post completely unrelated info in the same thread totally changing it's substance. I searched about these packs before I bought them but didn't find anything. Would be nice if people started threads about each individual thing they are doing vs 80 page threads that start off like "check out these awesome batteries I'm testing" and then half way through they talk about how to cut Styrofoam dolphin sculptures for their mothers front yard and a few pages later it turns into what style of bike lock is best.

to prove your point, I will be responding to this point also.

I get much better results searching on google than using the forum search function because results are sorted according to relevance rather than date. Often, I'm not even trying to search this site specifically, but ES comes up in google's results with about 4 threads of exactly what I need.

[liveforphysics]

You picked the dog's of the nano-tech cells, but yes, after about 10 cycles or so, more areas that did not become intercalation points from initial activation charge will open up, and both performance and capacity will increase slightly.

What's bad about these versions? I didn't know there were good and bad versions, just that this was all they had in stock. Should I return them for a better version? I hope I didn't waste my $800 on these, no point in having them if they are no better than my regular 20C packs.

They are a great RC LiPo cell, and should make a great pack for a long time (unless overcharged or overdischarged etc).

However, if your goal is to minimize voltage sag, they have about 2.5x the internal resistance of the 45-90C cells.

So, if you're seeing 3v of drop on your 30s2p pack at 60amps right now, lets work out the internal resistance. Lets first see the voltage drop per cell group. 3v/30s = 0.1v/cell group. It's 2p, so 30amps per cell drops it 0.1v. This means you're averaging 3.3mOhm/cell.

If your old pack was 5v of sag at 60amps on 30s3p, then it's 0.16v drop per cell group. 60amps/3p means 20amps drops a cell 0.167v. This means each cell averages ~8.3mOhm.

So, your Nano's are performing a bit more than twice as well as your 20C cells.

However, the 45-90c cells generally are ~1.2-1.5mOhm, so your sag would be halved. However, you're currently only losing a shade under 3% of power to sag, which means going to an imaginary perfect no-sag battery would only have the ability to yield a 3% gain in performance at best, and realistically, going to the 45-90C packs would only give you about 1.5% more power.

If you're really pushing for every last bit of power for a given amount of battery weight, go for the 45-90C packs, or the new 65-130C packs.

It all depends on how much money per watt of performance is worth to you (and that's nobodies decision but your own), but these packs would give you an extra ~1.5-1.8% power over your current pack. It would be a lot of money to spend for less than 2%.

http://www.hobbyking.com/hobbyking/stor ... _Pack.html

[Kin]

Option2: Put a few more packs in parallel. I understand this might not be an option for other design constraints.

[zombiess]

Option2: Put a few more packs in parallel. I understand this might not be an option for other design constraints.

I believe my bag has room for 5 more of the 6AH cells

[dogman]

Whatever battery you are using, it seems to me that the process should be to decide what voltage under load you desire. Then use enough starting voltage to have your target voltage under load. So if you expect 3v of sag, add one cell to the string.

Wouldn't adding one cell to the series bring the volts up 3v or so? Sounds cheaper to me than buying 90c. I'm not knocking the nano's, expecially if the highest possible performance is desired, such as at the track. But if the result is the same, why not swap a 5s pack for a 6s or whatever of the 50c, and end up with the voltage the same under load.

[nicobie]

I noticed my nano packs tended to balance a bit better after a few cycles. I was running the 35-50c cells and really liked the low voltage drop.

[zombiess]

I noticed my nano packs tended to balance a bit better after a few cycles. I was running the 35-50c cells and really liked the low voltage drop.

Oddly enough even with all the LiPo I have I don't have any problems with packs going out of balance. I have 21 packs of the 20C 6S packs and only 1 has a weak cell that was caused by me over discharging it and puffing it, then depuffing it. If I drop it down to 3.6V it will be out of balance by about 30-40mV but will come back to normal when I charge it.

[zombiess]

Figured I'd do an update, did a second cycle on the batteries. Upped the current draw to around 92A battery current draw, 125A phase. Starting voltage was 124.5V. Rode around for about 2 miles watching voltage sag from around 124V down to 115V so about 9V of sag. I then tried to bring the voltage down to a stable level. Finally got it stabilized to around 117V resting, then did some pulls at just over 90A. Voltage sagged to 111V so only about 6V of sag when pulling over 90A. That seems pretty darn good. Bad news is some of my wiring got warm especially around the fuse holder which has an amp rated for 80A in it.

Once I got the motor to full speed which was 58-60mph the amperage dropped from 90A down to about 68A on level ground. When climbing a slight 1.5% grade at WOT top speed was 57mph and it was drawing 74A.

Looks like I can improve my voltage drop even more by changing up my wiring some. Should be even better once I add 5 more packs so I can run 30S3P