Glacier Girl

My Feedback: (4)

Hmm, I had that all laid out in nice columns, system I guess decided it didn't like them.

Anyhow, I'll start recharge with Blinky on and get back with readings on both packs.

Then, I think I'll move everything outside to run a 10 amp discharge run, as the dropping cell volts and imbalance already seen have me a little concerned one or both of these packs may go south on me during the testing.

Will report back later. Gotta go work on the HDL too.

Swift427

I was expecting your two lipos to be closer to 11.4v-11.7v assuming you hadn't done anything with them. My guess is that you fully charged them at one time and then decided to store them instead of putting them in a plane and flying. Assuming they have been resting for 1-2 months after a full charge (12.5v) there would be some discharge. One could assume Pack 2's cells are more equal in quality than Pack 1's cells which have .16v more discharge.

What may have occured is that Pack 1 having more diverse cell quality and being fully charged at 1C=2.2amps to 12.6v then quickly retreated to 12.20 as soon as the 12.6v charge was done. Even with the Blinky when charging at 1C it can't keep up with the equalizing when there is a mismatch of cells. Proof of this is when the Blinky continues to blink for several minutes after a full charge at 1C (when the cells are not equally matched). The greater the mismatch the longer a couple of the Blinky LEDs will continue to blink after charging at 1C. After some testing I now change the charge from .8C to .5C during the 12.0v to 12.45v charge (with the Blinky still connected) and then the voltage only retreats from 12.49 to 12.45(approx. example) after 30 minutes and the Blinky won't blink at all after chargeing, indicating the cells are equalized.

Your tests should at least indicate which cells can't keep up the pace so you can discard them and use the best cells to make up a good 3S or 4S pack.

I'm doing some similar testing (G-Z) of these three: Electrifly .910mAh 15C, CommonSenseRC 2000mAh 8C, and ParkZone 2200mAh 12C for a comparison to your tests. Will post some of my findings tomorrow. I'm also seeing that any 10amp continuous discharge static testing below 11.0 volts isn't necessary in order to get an idea of the cell's actual C (max cont. discharge) rating based on the rise in temperature especially if the temp has already risen between 120-140 degrees at 11.0v. I'll check back again tomorrow.

Glacier Girl

My Feedback: (4)

Well I did a little real world testing today( mostly as I haven't been out flying for so long), but also what I saw in attempting a 10 amp discharge test. I recharged both packs last night, at 1 amp, with Blinky connected, still showing the one questionable cell in each pack.

Rested packs for one hour after Blinky stopped. Both packs showed approx 12.42 volts.

Applied 10 amp discharge and both packs started loosing voltage within 1 min 30-45 seconds, badly. Within 4 min I was down to 10 volts. Shut off the system as it was obvious both packs were not going to hold up with out something going bad.

Let packs rest overnight and checked voltages this morning, same cell in each pack, as before was just barely at 3 volts, others were in the 3.5- 3.7 range.

Balanced the packs out again, rested them, then recharged at 1 amp.

Pretty much same scenerio as before, as to low cell never blinking.

Finished charging. rested packs while I was working on HDL.

Went out to the soccer field this afternoon, Repropped my foamy Nasty P40 to get an approx 10.2 amp draw. Take off was just fine, kept the throttle wide open.

Just like in the dischage testing, after approx 90 seconds, I could tell the plane was loosing it's zip. Flew for another 4 minutes until it was obvious the bird wasn't going to stay up much longer. Landed, and I swear I hit cut off just as I touched down. Started checking temps. Motor and esc were cold, pack was very warm. Removed pack A, and installed pack B. Nearly identical performance, droppping off between 1 3/4 and 2 min. And then a slow loss until again, she wasn't going to stay up. Same temps as with first pack.

Got loaded up, and returned home. Both packs had the same slightly puffy feel to them after 1/2 hour. Let them sit another half hour and tested voltages.

Pack A was at 9.7 volts, Pack B was at 9.9 volts.

Pack A had one cell at 2.9 volts, one at 3.3 and one at 3.5
Pack B had 3.1, 3.3, and 3.5.

Pack A has an obvious bad cell, and B has one that's highly questionable, on an approx 10 amp draw. Also I seriously doubt the mAH ratings on the packs, and/or C ratings.

Looks like I be making a pair of 2 cell packs for very light duty usage out of these.

Swift427

Here's my numbers on the three LiPos tested12.44v(avg) to 9.6v LVC. I took bounce back voltage readings after: 1min, 5min, 15min, 30min and 1hr. The most cell variance with the 3 batteries tested was 0.14v (10.11v = 3.35v / 3.45v / 3.31v). The static bench test lasted 6:02 minutes with the TX throttle left in the same position (100w to 80w = 12.44v to 9.6v). Depleted capacity was 878mAh. How does one figure a more realistic 'C' discharge rating on this LiPo if the average amperage draw was 8 amps?

In the following test the throttle was advanced to an initial motor load of only 75w and left there. The following bounce back voltages were taken 1 hour after LVC.

10.30v = 3.42v / 3.49v / 3.39v = Electrifly 910mAh 15C
10.62v = 3.53v / 3.57v / 3.52v = CommonSense 2000mAh 8C
11.44v = 3.81v / 3.82v / 3.81v = ParkZone 2200mAh 12C
(the only one to feel as warm as my hand at LVC was the 910 15C)

Conclusion: The PZ LiPo has the best matched cells of my 3 tested LiPos.

As far as their rated capacity (910, 2000, 2200) when discharged from 12.44v to 9.6v at a conservative-to-moderate rate they ranged from 89%-96% of vendors capacity label.

What do you think about manufacturers 'C' discharge ratings? IMO, it seems they should be reduced by about 75% if you want to get more cycles, performance, flying time. For example what is your opinion as to the following 75% rating if we knew for a fact it lowered the LVC temp from 140 F(vendors high temp limit) to 125 F.

910 15C downsized to .910 x 11C = 10 amps max cont discharge w/15a burst
2000 8C downsized to 2.00 x 6C = 12 amps max cont discharge w/18a burst
2200 12C downsized to 2.20 x 9C = 20 amps max cont discharge w/30a burst

-or even-

2200 12C downsized to 2.00 x 9C = 18 amps mcd w/27a burst - In other words do the majority of vendors over rate the discharge of their LiPos so much that if discharged at there rating they may only be good for 25 cycles ???

Swift427

Packs with cells of unlike capacity will mostly balance out any difference in individual cell voltages within .02v when stored/resting over time, but it doesn't mean the cells are of equal quality.
QA1 = 4.04v / 4.02v / 4.03v = 12.09v = before Blinky (previously stored)
QA1 = 4.01v / 4.02v / 4.02v = 12.05v = after Blinky balancing
QA2 = 4.07v / 4.08v / 4.09v = 12.25v = before Blinky (previously stored)
QA2 = 4.07v / 4.08v / 4.08v = 12.24v = after Blinky balancing

What kinda surprised me is how long it can take a Blinky to equalize cell voltages in a 3S pack when the 3 cells aren't all that out of balance (0.02v).
QA1 = 20:30 minutes = depleting 0.04v
QA2 = 07:13 minutes = depleting 0.01v
This does point out that the Blinky does not deplete the voltage as much as some may believe even after 20 minutes (only 0.04v).

What is the MOST TELLTALE is imbalance in cell voltages during bounce back.
QA1 = 3.51v / 2.98v / 3.16v = 9.65v = immediately after LVC
QA1 = 3.54v / 3.20v / 3.58v = 10.32v = 1 hour after LVC
QA2 = 3.09v / 3.25v / 3.26v = 9.60v = immediately after LVC
QA2 = 3.21v / 3.67v / 3.68v = 10.56v = 1 hour after LVC
This suggests cell 1 of QA1 has the least mAh capacity of the six cells. Next are cells 2 & 3 of QA2 (3.25v & 3.26v) having almost identical capacity. It's apparent that pack QA1 is the most unequal in each cell's mAh capacity. Being that these two LiPos are new, stored and conservatively conditioned one would have to CONCLUDE that manufacturer quality control was lacking.

If you were going to make up one good 3S pack with the most mAh capacity would you use cell 1 of QA1 with cells 2 & 3 of QA2?

If any puffing occurred my guess would be cell 2 of QA1. Which one puffed?

It might be of some advantage to do individual cell tests once the packs are disassembled to check each cell's mAh capacity and bounce back voltage to decide which to pair together and whether it will be one 4S pack, one 3S pack or two 2S packs. When unequally paired together as with these two packs the cells interact/affect each other. For example cell 3 of QA1 and cells 2 & 3 of QA2 all rebounded the same amount after 1 hour (0.42v) appearing as if all three are of equal quality (maybe, maybe not). Whereas, cell 1 of QA1 only rebounded/settled in 0.03v more after 1 hour indicating it's rebound voltage was being siphoned off by cells 2 & 3 as the pack also began equalizing cell voltages as well as rebounding. It would only be a matter of days or weeks until each cell is within 0.02v of each other when sitting idle/stored.

Will you check individual cell mAh capacity and bounce back voltages before finally deciding which to pair together and whether its going to be: One 4S, One 3S or Two 2S packs?

Keep us posted on the journey/progress of QA1 and QA2 into Q4, Q3, or Q2A & Q2B

Glacier Girl

My Feedback: (4)

Swift, I would say other then the big guys like Thunder Power, who can spec out the quality of cells they want and QC them, the lesser brands are hit or miss.

Lesser brands supply could be, at best, over runs of a quality spec'd cell, or cells that didn't pass QC, or even the low bid mfg products. And if no QC is done by the buyer, they are at the mfg's mercy as to what they get. And what we buy.

And it seems, at least with the ZIPPY brand, country of origin has a lot to do with the quality of the cells. China cells are so-so, Korean are better.

As for C and mAH ratings, again, unless you are dealing with somebody like TP, you are on your own to test them to see if they are as advertised, or not.

Also, at least for me, I try and follow the 80% rule, never exceed 80% of a pack's output, in a set up, to increase pack life.

So in wrap up, if it's not a name brand cell, or a well know supplier who stands behind their product, we would be best to check to see if our prospective dealer has done any QC/testing of a cell for us, or take our chances.

Sometimes we could luck out, but more then likely, if the price is too good to be true, the quality will be just the opposite.

otrcman

GG & Swift

This has been a most interesting conversation to monitor. I've learned a lot about lipo technology from your testing and analysis and really appreciate what you are doing.

While I haven't done as much careful record keeping as you two have, my observations pretty much match yours. My balancer is an ETEC, which works pretty much like the Blinky. What I have observed it that the time required to achieve balance after a flight is a telling measure of the condition of the pack. If the pack is vastly out of balance at the conclusion of a flight, then that seems to be an indication that the pack is not up to the job. Either I am either using it too hard or the quality is poor. If I determine that I'm using it well within the manufacturer's specs, then I'd say the quality is poor.

On an older pack, excessive time to balance after a flight seems to be an indication that one cell is going over the hill, particularly if the pack has given good service in the past.

General Observation #1: Using a pack near the maximum rate that the manufacturer specifies is probably going to shorten the life of most any brand lipo. Perhaps the best brands can operate nearer their maximum rated capacity and the poorer brands need greater margins.

General Observation #2: Depleting a pack all the way down to Low Voltage Cutoff can shorten the life of a pack. I guess both #1 and #2 are saying the same thing. i.e. drawing any one cell of a pack below 3.0V is going to permanently harm the pack whether you do it by pulling too many amps or running too many minutes.

Sure would be nice if we had some industry standard by which all the manufacturers had to rate their packs so we consumers had more information to help us choose which brands to buy.

Dick

Swift427

This is a learning experience for me so please let me know if I'm asking too many questions for the time you wish to spend on this subject/thread. Let's take the example of the Electrifly 910 15C. From 12.44v to 9.6v = 878mAh or 96% of the 910mAh of rated capacity. Eighty percent of 910mAh is 728mAh. Does that mean this LiPo is actually under rated which occasionally happens or should the LVC been around 10.6 volts so only 728 mAh were depleted? If 12.45v to 9.6v is suppose to consume 80% then would that mean that the Electrifly's actually capacity is closer to 1100mAh. ???

With the throttle fixed and the drawdown going from 12.44v (consuming 100w) to 9.6v (consuming 80w) the expended time only lasted 6:02 minutes. How exactly do you figure what the flying time should be of any LiPo. Does it have anything to do at all with its 'C' max cont discharge rating. So as an example with the Align 2200mAh 22C what would be the highest continuous discharge that theoretically should still allow for at least 10 minutes of flight if it were truly a 2200mAh 22C LiPo. ??? Also, do you think 22C means you can draw that much without the LiPo exceeding 140 F? . ??? (I realize that 'C' ratings are often suspect, if not nebulous (e.g. Align 2200 22C), so how does one determine a LiPos true 'C' rating other than how high a discharge without the battery temp going above 140 F. ???

Another question is assuming the cells in your Align packs were all from the same manufacturing run is it mostly a matter of differences in internal resistance (impedance) that determines both the mAh capacity as well as the max cont discharge rating. ???

As a newbie I don't know the answers to these questions as it's still kind of confusing, so my questions aren't meant to confuse, but hopefully clarify Li-Poly Power. I thought this thread may be as good as any for further exploration. I'm not even close to being any kind of an expert, but I get the sense that you have more experience and may be willing to take the time to answer some of my questions. If these questions and others are insignificant to the vast majority of parkflyers who may abuse their LiPos and don't know why their LiPos only last 25 cycles then say so now and I won't post anymore on this thread. And you don't need to answer any of the above ???

Glacier Girl

My Feedback: (4)

Ok, by my usage spec of 80%, I'm going by the rated amp capability of the pack. If it says it's good for 30 amps constant, I try and set up my system to only draw 80% of that from the pack. So 30 x 80%=24.

Lipos don't like to be mistreated in any sense, so not over extending them by excessive amp amounts or time frames, they just tend to last longer. At least what I've found.

Now as for a pack being under rated, at least the name brands, I would say yep. Just a built in safety factor for them, and us. Even though they may know the pack willl handle a 25 amp draw, safely, they may tell you never to exceed 20.

Less chance of something going wrong by over amping them, and also they may last longer which makes you a happy camper and more likely to buy from them again.

Ditto charging them, the lower the rate the less it seems to affect the life of the pack.
Lastly, and I in no way recommend this to anyone, but one of the posters on another site I frequent, is charging lipos up to a 3C rate with success.



Little off the subject but in my Stryker days, I ran nothing but Mega motors, they were rated between 23 and 28 amps by Mega. I ran 50 plus amps through them all the time, and NEVER had an electrical related motor failure.

My honest opinion, Mega knew these motors could handle a lot more then they listed them at, but in listing that way, I bet they didn't see many electrical warranty repairs.

Same thing with the battery suppliers. Under rated packs, mean less warranty replacements, and longer lives from their product.
Which in turn usually means satisfied customers returning to buy more product from them.

Swift427

Thanks for explanation. Now it makes more sense to me.

In summary would you agree that bounce back cell voltage comparisons (10min & 1hr) are the best indicator of the condition of a LiPo with respect to how equally matched the cells are (mAh storage capacity)?

Glacier Girl

My Feedback: (4)

[quote]ORIGINAL: Swift427


If in fact you know the cells were balanced before discharging them, yes I would agree.
I guess you could also note the cell voltages when you first get a pack too, if they are off already it's not a good sign.

Swift427

The following is a recent email reply I got from CommonSenseRC
"As for your question on how much imbalance is tolerable, you don't want to have any imbalance at all on your pack at all. What we define as imbalance is a difference of 50 millivolts between cells, or 0.05v. Anything greater than that needs to be balanced right away."

I've noticed that if there is an imbalance when being charged to 12.45v the pack will fall back to say 12.25v instead of holding 3S voltage at 12.44v or 12.43v.

What's your take on the underlined part of the following LiPo Vendor advice?

"For years we have sat quietly aside watching the proponents of "pack balancing" spew forth misinformation. The truth is that a properly matched pack will not require balancing. Yes, we're sure this is a shock to many of you who have fallen for the balancing gimmick. Yes, Apogee was the first to put commercial grade plugs on all packs due to customer demand. We've had and seen enough.

Pack balancing is a gimmick perpetuated by companies who make balancers, and by other companies who do not match battery cells within the pack. A properly matched pack will not require balancing, and in fact will mask a failing cell. Balancing is a band aid for companies who lack the proper equipment to do cell matching. All Apogee packs have been cell matched since the day we started.

Due to misinformation, more packs have been damaged during balancing than have been helped. If you insist on balancing a pack (If it makes you feel warm and fuzzy inside, and you sleep better at night, have at it), please, please, only balance fully charged packs.

Why only balance fully charged packs? All properly matched cells are mated together so that the high and low voltages will coincide. There may be mid-point voltage variances. Balancing a partially charged pack can cause the high and low voltages to become unbalanced. Again, please, if you insist on the balancing gimmick, please only balance fully charged packs."

Glacier Girl

My Feedback: (4)

honestly, I don't know. But I would say, that yes if you have in a perfect world, perfectly matched cells in a pack, you shouldn't have to balance them.

But then mfgs. allow tolerences/ variances in their packs, as we don't live in a perfect world.

So at least by what Common Sense writes, if I buy their pack and fully charge it, or fully deplete to cut off, and any of the cells are not EXACTLY equal to the others I have a defective pack, and Common Sense would owe me a replacement.

Nah, I'll stick to balancing, just to be sure, at least in my mind.

Swift427

I got my BP Hobbies battery monitor today and it is calibrated AOK (same cell readings as my digital multimeter). So, no more taking readings like 3.80v / 7.61v / 11.40v and then having to use my pocket calculator to figure each cell like 3.80v / 3.81v / 3.79v. The battery monitor gives individual cell readout every few seconds and depending on where the decimal point is located you know whether the readout is for cell 1, 2, or 3 NEAT!

I've been doing some more research and now understand the importance of each cell's internal resistance (ir) as the primary factor in equally matching/mating cell's in a quality pack. Top-tier expensive LiPos have hand picked/tested cells each having the same internal resistance.

So, my logic tells me that the three cells having the greatest bounce back of 0.42v, also have the least internal resistance; while the cell with the highest voltage reading and the least amount of bounce back (3.51v-3.54v cell) appears to have the most ir of the 6 cells. Was the 3.51v cell by any chance the one with the highest temperature when discharged under load? You said one of the cells puffed. Do you see can correlation with its BB voltage or LVC voltage?

So, my logic at this point is thinking that perhaps the three cells with the most & same amount of bounce back (0.42v) would be the three cells I would choose when making up a new 3S pack of equally matched cells. What are your thoughts at this point as to which cells you plan on pairing together and why?

Glacier Girl

My Feedback: (4)

Honestly, I haven't given it a lot of thought. Dang HDL's.[:@]

As to your thinking, yes, the lowest resistance would be the better of the cells.
Also the cell dropping voltage faster then the others would be a good indication of a bad one, or one that is not correctly labled for C and capacity rating, compaired to the others.


And lastly, when I do get around to cutting the pack apart and building a new on, it will ONLY be used in something cheap and with a low amp draw, just to be safe.

Oh and kinda on the subject. If you ever try and peel apart cells in a pack, it can be a real bugger. Very easy to bend or damage a cell. Little trick I came up with. Dose the seams between the cells with CA debonder. It loosens up the adhesive between the cells, and makes em easy to pull apart. If they still act a little stubborn, use a popcicle stick to slice down between the cells.

Swift427

You mentioned some indication of possible puffing. Is there any correlation to the puffing with either the 3.51v-3.54v cell or the 2.98v-3.20v cell. I'm still scratching my head trying to make some sense of it. Can we conclude that the 3.51v-3.54v cell is the best cell of the lot? Have you been able to draw any conclusions about the superiority(e.g. 3.51v-3.54v) or inferiority(e.g. 2.98v-3.20v) of any of the other 4 cells based on their LCV and bounce back voltage with respect to their mates LVC and bounce back voltage.

QA1 = 3.51v / 2.98v / 3.16v = 9.65v = immediately after LVC
QA1 = 3.54v / 3.20v / 3.58v = 10.32v = 1 hour after LVC
QA2 = 3.09v / 3.25v / 3.26v = 9.60v = immediately after LVC
QA2 = 3.21v / 3.67v / 3.68v = 10.56v = 1 hour after LVC

Which of the above three cells in Pack 1 is the bad cell; which ? one in Pack 2

Swift427

NO WAY!
A bounce back of only 0.03v in one hour raises a RED flag. Looking at the bounce back voltages should give us a pretty good idea of the "obvious bad cell" in Pack A and the "highly questionable one" in Pack B.

Am I getting warm? [8D]

Glacier Girl

My Feedback: (4)

Yeah I think you got it. The mismatch of voltages after they were balanced, charged, then discharged is a pretty clear sign something isn't right in the pack. Bounce back variances show that also.

Bad cell obviously, but was it bad as in poor quality or bad as in mislabeled as to it's abilities? Or I guess it could even be both.

As for puffy, both packs showed it on ALL of the cells, not just the questionable ones, after the discharge cycle.

cell 2 in QA1, and cell 1 in QA2 would be the questionable ones. Both dropped below .2 volts variance from other cells in the pack, and this was only on a 10 amp draw.
Again, after being balanced, cycled, rebalanced, charged, balanced again, then discharged.

I could only guess at what would have happened had I tried even 80% draw of the supposed rating of these packs. 3 Mile Island all over again.

Glacier Girl

My Feedback: (4)

Well, both packs are what I would consider history.

Test flew them both today, both in systems pulling way under 20 amps.
Neither pack flown over 5 min, more like 3 min and both showed dropping power.

Landed both birds and found identical versions of swollen sausages for packs.

Had to pry them out as they had swollen so badly. Did not even attempt to check voltages, they immediatly went into the battery bunker.

Maybe tomorrow I'll venture to check them, but for now I ain't touching them.[:@]