Inside Lipo failure

[DaFF]

Hi all,

Just wanted to share with you my experience with the Lipo.

So far, 2 battery packs failed on me for different reason.

1- Flight Power Lipo: 2 pack ( in serie ) 2S2P 7.4 volt 3200 mA ( only one pack failed )

Operating pack temp under race condition: 45 deg C or 113 deg F

What happened: Battery pack gave up suddenly. After investigation, 2 cells out of four where down to 0.01 volt and had expanded ( bulge on the face of both cells )

Root cause: slightly smashed cell corner

2- Poly Quest: single pack 2S2P 14.8 volt 2600 mA

Operating pack temp under race condition: 50 deg C or 122 deg C

What happened: Battery pack gave up suddenly. Voltage of pack was O volt. after investigation, all four cells where intact and still in good working condition ( 3.89 volt on each )

Root cause: cell tab failure

FYI: Max recommended temp for Lipo is 70 deg C or 118 deg F.

I am showing pictures of both pack that I completly took apart

First pic: Overview of the PolyQuest Pack took apart

You can see:
- The four bare cells still in working condition
- The PCB board where the cell tabs are welded. You can see as well my batt conector and the special Poly Quest connector that allow to tap into each cell for equalization purpose
- The red heat shrink
- a sample of the foam on which the pack was enclosed ( only one piece of foam showed, the other pieces where not saved )

DFF

[DaFF]

The flight power packs taken apart:

- left side, the pack that is still intact and in good condition ( with the Pro4 sticker )

From the second pack that failed:

- on right bottom, 2 of the cells that failed ( watch the wave on the cells )
- on right top, the 2 cells ( with wire ) that are still working and could be saved

DFF

[DaFF]

Flight Power cause of failure:

Watch the corner that was smashed on the top cells... and see how the top of the cells has waves ( from internal over pressure )

I guess because they were both hooked in parallele, when one failed, the other followed.

DFF

[DaFF]

Flight Power failed cells:

Side view showing how the failed cells on top expanded. you can see there is no more space between the failed cells, while the pack that is intact has a gap in between cells.

This space between the cells is to my opinion needed, has it allows for air flowing around the cells, thus less temp and less chance of failure.

( The Polyquest do not have this feature, all the cells are stuck together. As a result of my testing, the pack sure was warmer. On top of this, the foam and the heat shrink do not help either on keeping the temp low )

DFF

[DaFF]

Close view of the Power Quest board

This is a good addition to the lipo, as it allow for tapping into each cells.

( This is feature lacking on the Flight Power pack )

DFF

[DaFF]

Power Quest failure:

On top, you can see the Flight Power ( wide ) tabs

On bottom, you can see the Power Quest smaller tabs.

If you look on bottom left, you can see that the tab is side way. This is the reason why the batterie pack failed, because there is no more contact between the cell and the tab.

I prefer as well the Flight Power wider tab, as it allows for more tab material, thus lead to more Amp going through it before failure.

also, note that the Fligth Power pack has, to my opinion a better way of welding the wire to the cells. The cell tab kind of wrap around the wire and would lead to better contact.

On the Power Quest, the tab is welded to the PCB board...

Both tab welding has pro's and con's, only do I prefer the wider tabs of the Flight Power because there is less chance of tab failure.

DFF

[DaFF]

Conclusion:

I still have faith on the lipo for my car.

I know this is the best solution to send high volt to the controller / motor and keep the amp draw to a minimum while delivering a lot of rpm and power. It is also the best solution handling wise as it decrease weight a lot and gives unbelievable handling on my pro4.

I am more inclined to use the 2500 mA pack, because it is less weight than the 3200 mA. For me, it is of high importance since I need to have a good right to left balance and do not want to had too many ballast.

I had enough track time today before the Power Quest failed ( around 3 full packs ), so that I know that with the right balance my car is on rail ! I was also able to give it full power right from the beginning and this thing has unbelivable low grunt, it can burn all 4 tires easy.

The Power Quest failure showed me that eventhough the 2500 are more stressed than the 3200 ( less continuous and peak Amp rating ), it is enough for my Pro4. The fact the cells were still intact proves that those cells are tough enough and can handle the Amp draw.

On a side note, the continuous ( average ) Amp draw is minimum, for example, after I runned my car for 8 minutes under race condition, I used-up only 710 mA ( that's what my charger told me ). It means that even with only 2500 mA, the run time is well over the 15 minutes marks.

Now, I sure need to try an other type of 2500 mA cells because the Power Quest tab are the weak link.

I would like to test try the 14.8 volt 2500 mA Tanic pack, but since I don't know how wide the tabs are and how they are welded ( PCB board ?), I think I'll pass on this one !

I am not giving-up and I'll look into the Flight Power 2500 mA pack...

DFF

[starluckrc]

The Tanics went to wider tabs to get the 12C discharge ability.
Packs are now being built at the factory. I'll have to see if I can get
some more info on the buildup.

[TheSteve]

DFF,

Thanks for sharing the info - real shame you didn't get more use outta the packs. Hope you haven't exhausted the RC bank yet :) I'm working on getting a LiPo myself, only 7.4 volt though for my xxx-s. If it works out then I'll find something for the RC10L3t

[DaFF]

Starluck,

Yes, I'll be interrested to now more about the Tanic packs, namely what are the tabs width, if they have a PCB board and how the tabs are welded to it.

Please keep me posted ( BTW, if you look for a lipo tester, your quest is over, send me a pack and I'll torture it nicely for you LoL )

The Steve,

No, my RC bank account isn't exhausted yet, only might I have to delay some purchase until the account ressuscitate at the end of the month :)

You know Steve, when like us you venture into territories where no bobody have ever been before, you should be ready to drop some serious coin. I am sure the end result of this will be equal with the time, effort and money I spent on this project.

The smile on my face when I pass nitro guys at my track is priceless :p

Please, keep me posted on the result of your first Lipo try !

Anyway, thinking again at my last Poly Quest tab failure, I suspect it might be also on the way I strapped the pack to the chassis.

I am using high strenght batterie tape and might have done the straps too tight. By doing that, I might have put too much pressure on the front of the batt, thus leading to put excessive load on those tiny tabs.

Since the failure occured after 3 or 4 full packs of driving, I guess the acceleration / braking had put more load on the batt tab and that's when they gave up...

The more I look into lipos, the more I feel those cells needs to be handle with extreme care because they are way more fragile than anything I've tried before. Take this into account when you try the lipo, Steve.

For my next batt pack, I'll find a better way of tightening the batt to the chassis :D

DFF :p

[Rotary Rocket]

Daff,

Thanks for taking the time to take pics and sharing your experience.

I also run LiPos, but I am a lot more conservative than you.

I run 2 sets of 4S4P 8000 pack on Hacker C50 12S (two motors) on my scratch built 1/5 scale rally, 2 packs of 2S4P 8000 (in series) on Starluck 8L in an E-maxx, 2S4P 8000 pack with Hacker C40 7t in 1/10 TC3, 2S and 3S 1320, and 3S 1900 mAh packs in 1/18 M-18 (Hacker B20-22S), and RS4 Micros. All my packs are Thunder Power (TP).

I have had very good luck with this company. They have an excellant manufacturing process in which they "match" the cells in pack, it results in cooler packs in use, better output, and packs stay in balance.

So far I only "puffed" one 3S 1900 pack. Thunder Power actually mentioned some "bad" cells got out early in their Gen2 (10C) manufacturing. They promptly replaced it for free.

My oldest pack, a first generation 2S4P 8000 mAh pack has gone through three really HARD crashes (I have over 40 runs on this pack). This pack had three crushed in corners, one from each crash, but it was still performing perfectly. I sent it in when I sent in the puffed pack. TP checked it out, and it was still perfect. :)

I wonder if your pack failures are due to the low mAhs in the packs!

You should try a Gen 2 (10C) TP next. I think you will like their quality control and performance.

[Shawn Palmer]

I'd look into Apogee as well - www.pfmdistribution.com

I'm doing some things with them on 10th after TONS of testing proved them superior in 18th scale over other brands.

2s2p 2080's (maybe) or 2s2p 2500ish cells (can't remember exact mah) should do it for you nicely. Big wide tabs, and well soldered construction.

Shawn

[DaFF]

Thanks a lot Shawn for your help !

I'll look after the 2480 mA cells, they seems to be very well suited for my project being narrow ( 45 mm wide ).

I will call Apogee to see if they can build a 4S - 14.8 volt pack with those 2480 mA cells. I'll see with them also if they have connector to tap into each cell individualy for cells voltage balance...

Thanks rotary as well, I might also try the TP later on.

DFF