lipo battery sag

[wasp]

i run a 9c and a lyen 18fet and 15c flightmax 5s lipo
after 2 years and 15000 kms i am seeing sag of 10v is this normal?
these batteries have been great(for the lowest end of lipo's)
i am running at 15s1p and seeing amp peaks of 82 and 4500w
these batteries have been abused (of the 8 i bought 3 are puffed and
1 came with a dead cell that i charged back up and ran anyways)
my question is this most of the 400 charges i put on these and ran 20s2p
but after "a friend" puffed them i have been running at 10s2p but have
started to run 15s1p and notice this sag...is it normal?
i'm still seeing 80% life and drops to 46.26v under load and 57 resting
just curious if this is normal?
looking at replacing with 8 of those 8ah packs from hk

 

[neptronix]

Yep, that's normal.
I bet those suckers are getting HOT too.

with an ~8C load ( 43amps ) on my 5ah zippy 20C batteries, they get pretty damn warm and drop about 4-5 volts when i hit the throttle on 15S.

15C on a 5ah pack = rated at 75 amps, however zippys are overrated, big time. So you are working them over their artificially inflated rating.. lol

you need 10ah of those, minimum..

 

[wasp]

Yep, that's normal.
I bet those suckers are getting HOT too.

with an ~8C load ( 43amps ) on my 5ah zippy 20C batteries, they get pretty damn warm and drop about 4-5 volts when i hit the throttle on 15S.

15C on a 5ah pack = rated at 75 amps, however zippys are overrated, big time. So you are working them over their artificially inflated rating.. lol

you need 10ah of those, minimum..

Thx for the quick response
I will patch some cells together and run 15s2p

 

[geetarboy]

Hey Wasp, I notice the same thing when I run 24s1p instead of 24s2p - they sag deep @ WOT. I try not to run it as hard with 4 packs of 6s5000mah as I do with 8 packs. I just got 4 nano-tech 6s 6000mah last week. I run those 24s1p and they don't sag as bad as a 24s2p of regular 20c lipo's. I have 4 zippy 15c 6s 5000mah's and they are all puffed, 1 is almost unusable now. They have about 150 cycles on them - I usually don't use more than 80% capacity, or 4 ah's. I won't buy anymore 15c lipo's. The nano-techs seem to be much better, but I only have 3 cycles on them so far...BTW that motor & controller of yours will handle 24s - No Problem

 

[neptronix]

Geetarboy, it's not that you need nano-tech. even though they are nice and all that..
For maximum battery life, on any chemistry, you need to run it a good bit below it's max C rating.

I know that my 20C zippy packs stay warm for almost an hour after i get done abusing them on hill climbs.
I also have calculated that i am losing 10% of the capacity to heat !!

When i run 2p, resulting in a 4p load, i get the rated mAH of the battery, and nothing gets above room temp. Voltage sag is about 1.25v average.

They are rated at 300 cycles for a reason.. because RC guys beat the crap out of those batteries. I have heard of 600 cycles on these and more, when babied a bit more

 

[geetarboy]

Geetarboy, it's not that you need nano-tech. even though they are nice and all that..
For maximum battery life, on any chemistry, you need to run it a good bit below it's max C rating.

I know that my 20C zippy packs stay warm for almost an hour after i get done abusing them on hill climbs.
I also have calculated that i am losing 10% of the capacity to heat !!

When i run 2p, resulting in a 4p load, i get the rated mAH of the battery, and nothing gets above room temp. Voltage sag is about 1.25v average.

They are rated at 300 cycles for a reason.. because RC guys beat the crap out of those batteries. I have heard of 600 cycles on these and more, when babied a bit more

I agree, the easier you are on them the longer they're gonna last. I peak out @ 5000 watts - which roughly comes out to about a 10c rate on a 24s1p 5000mah, if my math is correct, and that's enough to "puff" a 15c zippy. All my 20c & 25c packs get the same treatment and none of them are puffed...that's all I Know

 

[neptronix]

Well let me give you a little insight..

On my 20C zippys, they get warm at 8C and sag 3 volts on 10s.
On my 20C turnigys, they don't seem to get warm at all at 8C and sag ~1.5v on 10S.

I believe that C rate on the zippy are peak rates, and the C rates on the turnigy are continuous..

 

[dogman dan]

That's interesting. I wonder if the brand is the big difference, or just that there is a lot of difference between different factory runs of batteries.

My experience is this, 25 packs of lipo, some 20c zippy, some 30 c turnigy. Zero bad ones, and all seem to performs pretty simiar. Maybe the 20c doesn't work as good, but it's not real noticeable with a 10 ah pack. My 6s ones are all good too.

But 3 for 3 of 30c turnigy 4s packs have either arrived puffed, or puffed within about 20 cycles. Obviously a big difference with that particular batch of cells coming through the factory.

But even with this great lipo from HK, my same old advice remains, run em at half the c rate they claim if you want to be happiest.

 

[neptronix]

Interesting..

Yeah one of my turnigy 5s 5AH 20C packs went puffy just sitting there all winter, and i had put no cycles on it + the voltages were all balanced on the damn thing..

Then another turnigy had an odd duck cell which would enthusiastically charge quicker than all the others, then discharge way quicker. Must have been a 25C cell in a 20C pack or something....

But out of 4 zippys i did get one with a weak cell that went to 0v when all the other cells were at 3.5v

 

[aaronski]

I agree with Nephtronix, it would seem the turnigy's are under rated compared to zippy's. I think, c-rate for c-rate, I hit my cells the hardest here on the forum:

after 50 cycles, my turnigy 20c 2.6 ah pack, 66.6v can run 70 amps for ~20 seconds and 30 amps continuous... that's on 2.6 ah. it doesn't run long like that, but it will drain 2.2 ah before things start getting unbalanced.

if I go easy on it, 30A peak, 15A average, I get full rated AH going from 4.2 to 3.5v

I can't recall the vsag, but I think it was about 2-4 volts on 18s.


Only problem is I have puffed them when I ran them at 60A at the end of their discharge. they just fall off a cliff in terms of power, really does feel like you blew a fuse.

both times, one cell was puffed, but after letting them cool off, the puff vanished. I watch them as they charge now, but no ill effects yet.

 

[auraslip]

I came here to say how overrated the cheap lipo is with regards to it's C-rate, but damn! The abuse you put it through, and you still got 15000km?! That's pretty great if you think about! Your sag will increase over time though. Ri increases with age, which leads to more voltage sag.

 

[neptronix]

I came here to say how overrated the cheap lipo is with regards to it's C-rate, but damn! The abuse you put it through, and you still got 15000km?! That's pretty great if you think about! Your sag will increase over time though. Ri increases with age, which leads to more voltage sag.

The cool thing about lipo is that it has a ton of internal resistance to spare. Even the more expensive stuff can be quite overrated though.

I am surprised that aaronski's lipo even lasted more than 2 cycles, lol.

 

[auraslip]

The cool thing about lipo is that it has a ton of internal resistance to spare. Even the more expensive stuff can be quite overrated though.

I am surprised that aaronski's lipo even lasted more than 2 cycles, lol.

Nep, your charger can calculate the Ri of batteries right?

I want to create a calculator that shows power loss from I^2R... I mean I already made one for calculating power loss from wiring, but I'd like to add batteries to the calculator....
It'd be cool to get all the popular battery choices in there; headway, ping, a123, and the different lipo too..

 

[neptronix]

The cool thing about lipo is that it has a ton of internal resistance to spare. Even the more expensive stuff can be quite overrated though.

I am surprised that aaronski's lipo even lasted more than 2 cycles, lol.

Nep, your charger can calculate the Ri of batteries right?

I want to create a calculator that shows power loss from I^2R... I mean I already made one for calculating power loss from wiring, but I'd like to add batteries to the calculator....
It'd be cool to get all the popular battery choices in there; headway, ping, a123, and the different lipo too..

Yeah, it can calculate RI but i don't get a decimal reading.. :|
Here's what i'm seeing on two packs that stay quite balanced:

20C turnigy:

2, 2, 2, 2, 1 - pack 1
2, 2, 4, 4, 1 - pack 2

Avg resistance: 2.2 mOhm
20C zippy:

10, 11, 8, 9, 9 - pack 1
9, 10, 9, 7, 9 - pack 2

Avg resistance: 9.1 mOhm

Woah O_O.. BIG difference..
Now, the zippys i measured are 5 months older than the Turnigy, but that is a huge difference.
Zippy pack #2 only had 2 cycles on it.

By the way, calculating power loss is going to be difficult.. voltage sag is apparently not linear at all :/

 

[auraslip]

By the way, calculating power loss is going to be difficult.. voltage sag is apparently not linear at all :/

By taking a the difference between Ri at lvc voltage and nominal voltage it shouldn't be that hard to make a logarithmic function to predict Ri at different SOCs
Using ohms law, the selected amp draw, and the logarithmic internal resistance/SOC function you could find I^2r power losses.

I'm not totally sure of the math, and it won't be super accurate, but for just giving a ballpark number itshould be useful enough to make to show how different batteries will have different power output in different situations