HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Nov 08, 2004, 09:17 PM
Tell that to George Zipp!
mikeb33's Avatar
United States, IL, Inverness
Joined Oct 2000
1,819 Posts
My first lipo problem

BACKGROUND FIRST:
I made 2 4S2P 5200 packs of 8 iRate 2600 cells(16 cells total). First I checked that all voltages were equal and then soldered pairs of cells in parallel mode. Then I soldered 4 in series to make my packs. I charged them on my Orbit Pro 6.3 at 1 amp. Both packs worked fine for a few months, probably 15-20 flights each. The max I ever used them was about 40A static and I would guess lower in flight. They were never flown to LVC, which was set at 12V.

PROBLEM: Yesterday, I put one of the packs in and ran the motor up and it started cutting out right away. I always charge my packs after use and this one should have been full. I put it on the Orbit and set it for 1A. It charged for hours and showed over 4000ma! So I decided to discharge it and start over. I set it for 10 cell discharge(12V). It only discharged 1200ma and stopped. Then I started charging again at 1A and it took 3000ma before I stopped it. Some of the cells seem a little puffy to. If you look at he picture, it seems pairs 1 and 4 are puffed and maybe pair 3 too. Could pair 2 have died and the other 3 were absorbing the voltage and were ruined by overcharging? Any other ideas what happened? There doesn't seem to be any physical damage to them.
Where do you dispose of old liPos?
A little disappointing financially. This packs is coming in at about $10 per flight
mikeb33 is offline Find More Posts by mikeb33
Reply With Quote
Sign up now
to remove ads between posts
Old Nov 09, 2004, 05:56 AM
Registered User
Mr DIY's Avatar
South Africa
Joined Aug 2003
587 Posts
mikeb33 ... are you pulling 40 Amp from each pack of 8 cells or is that 40A from the full quota of 16 cells.

Secondly, how have you joined your tabs togethor. Did you solder them directly to each other and then smear with silicon?

Brian
Mr DIY is offline Find More Posts by Mr DIY
Reply With Quote
Old Nov 09, 2004, 07:43 AM
Tell that to George Zipp!
mikeb33's Avatar
United States, IL, Inverness
Joined Oct 2000
1,819 Posts
It is 40A from each 4S2P pack. I fly 1 pack at a time. This is a bench testing number, so it should never be higher in flight.
I soldered the tabs together then smeared silicon on them to avoid shorting out.
mikeb33 is offline Find More Posts by mikeb33
Reply With Quote
Old Nov 09, 2004, 08:26 AM
Registered User
Mr DIY's Avatar
South Africa
Joined Aug 2003
587 Posts
Quote:
I soldered the tabs together then smeared silicon on them to avoid shorting out.
Thats what it looked like to me, but had to check.

Quote:
It is 40A from each 4S2P pack
So that makes it 20A /cell

My personal experience in playing with the Irate 2600 cells (the slightly older ones) is that when making up a pack like you have done, you must use small PCB material to solder your tabs on. I am not sure which cells you are using though. When were they purchased?

I ran a pack with my finger placed on a tab soldered together like you have done mikeb33. At 10 Amp, it was already getting unpleasantly hot. At 20 Amp, it is way too hot for my liking.

If tabs are soldered to a small PCB, the copper on the PCB helps draw away that heat and dissipate it. At 20 Amp, I could feel a big difference in temperature and made me feel far happier to run cell at 20A.

At 20 Amp, your heat is being dissipated back into the cell and its surrounding seal. My guess is that that heat will eventually cause the seal to break down and produce a leak that will in turn cause cells to balloon. I suspect the silicon will not help the situation ether.

What I have noted may not be your problem though. It is purely speculation on my part. It is worth taking note that your pack construction is not ideal though.

Just my 2c

Brian
Mr DIY is offline Find More Posts by Mr DIY
Reply With Quote
Old Nov 09, 2004, 07:25 PM
Tell that to George Zipp!
mikeb33's Avatar
United States, IL, Inverness
Joined Oct 2000
1,819 Posts
I bought the cells sometime this summer. They are 2600 cells good for 10C or 26 amps. I joined pairs of these cells so I thought they were good for 52 amps. The tabs were soldered well and when I did my testing at 40 amps, they never got hot. I hadn't covered them with silicon yet.
I don't really think the tabs played a part in this deal, but I don't know what did. I liked making my own Nicad packs, but I may stay away from lipo building. I saved a few bucks, but have no recourse or warranty right now.

What about disposal of the old cells?
mikeb33 is offline Find More Posts by mikeb33
Reply With Quote
Old Nov 09, 2004, 07:46 PM
Permanently Banned
San Jose Ca / RSA flyer
Joined May 2003
8,030 Posts
If the packs never got hot, then U may have picked up some cells that got sick from "micro shorts", that's my best guess
hall woo is offline Find More Posts by hall woo
Reply With Quote
Old Nov 09, 2004, 11:31 PM
Registered User
mattk17's Avatar
Dallas,TX
Joined Jul 2001
1,656 Posts
Mikeb, sorry to hear about your pack failing. I have read what is recommended on disposing of bad cells but since some of your cells are ballooning, I am leary to recommend anything. I'm sure one of the more li-po educated readers will give you the low down on how to handle disposal.

I think we have the discharge rates on the li-poly good enough and it is time to work on 3 other areas that need to be addressed:
1. safety of cells when charging - looks like that is in the works
2. price per cell - lower would be better
3. durability of cells/packs -

I don't think anyone would argue that li-poly are not nearly as robust as nimh or nicad cells. The risk of a hard landing/crash ruining a $30 2 cell li-poly pack is one thing but losing a Many li-poly cells pack that can cost $200 or more is a big hit on our fun budgets!
2.
mattk17 is offline Find More Posts by mattk17
Reply With Quote
Old Nov 10, 2004, 01:21 AM
Registered User
Mr DIY's Avatar
South Africa
Joined Aug 2003
587 Posts
Quote:
I bought the cells sometime this summer. ....... The tabs were soldered well and when I did my testing at 40 amps, they never got hot
You must have the newer cells then.

As long as you did not damage the cells when doing the soldering, I am at a loss.

Other thoughts are that the internal cells in middle of pack could overheat. You do not have spacers between them to allow for airflow. From what I have deduced, most heat seems to be generated as cell closes in on it discharge state. If you charge a fresh charged pack and then test it at 40A for a short while, it may look good and stay cool. You need to run the cell down longer to see any temperature effects.

Quote:
What about disposal of the old cells?
Well, from one of the stickies on this thread …Ultimate Guide to Lithium Polymer Batteries

Point 7 says.

Quote:
7. If a cell balloons while charging DO NOT puncture the cell while it is still hot. Put the cell/pack in salt water and wait until the cell has cooled. Once it is cool gently puncture the pack's outer casing and put it back in the salt water. After this the cell is safe to throw in the garbage.
My understanding of this is that the salt will increase the conductivity of the water and create a load for the cell to discharge into. I do not understand why the cell must be punctured though. The construction of the cell makes it difficult for the water to penetrate all the internal plates. You would have to leave it in the solution for days?

Some other tips from Ultimate Guide to Lithium Polymer Batteries

Quote:
5. General usage tips.
1.Lithium batteries don't work well in cold air. If you are flying in the winter keep the batteries in your car for best performance.
2.Don't let the batteries overheat. Try and keep them under 140-160 degrees F. This will prolong your battery life.
3.Don't push the batteries past their rated maximum C rating. This will damage the battery and the apparent capacity of the batteries will drop. If when you recharge you are only putting ½ to ¾ of the rated capacity back into the batteries you are probably pushing them too hard.
4.If your building your own cells then put spacing between each cell in the pack to help cooling of the pack. This is most important when building packs larger than 2 cells.
hall woo said...
Quote:
If the packs never got hot, then U may have picked up some cells that got sick from "micro shorts", that's my best guess
We were talking about the tabs hall woo, not the cell itself.

Brian
Mr DIY is offline Find More Posts by Mr DIY
Reply With Quote
Old Nov 10, 2004, 07:14 AM
Tell that to George Zipp!
mikeb33's Avatar
United States, IL, Inverness
Joined Oct 2000
1,819 Posts
Quote:
Originally Posted by Mr DIY
You must have the newer cells then.

Other thoughts are that the internal cells in middle of pack could overheat. You do not have spacers between them to allow for airflow. From what I have deduced, most heat seems to be generated as cell closes in on it discharge state. If you charge a fresh charged pack and then test it at 40A for a short while, it may look good and stay cool. You need to run the cell down longer to see any temperature effects.

Brian
You can't tell from the picture, but I did put a piece of thick double sided tape between each cell to hold them together, but not actually touch each other.
One last question. If I take this pack apart and find a pair that aren't damaged, can I reuses them? I was thinking of adding a pair to my other pack to make a 5S2P pack. To minimize the stress of the tabs, should I separate all the cells and make 2 5S1P packs and then connect them in parallel with a Y cable?
mikeb33 is offline Find More Posts by mikeb33
Reply With Quote
Old Nov 10, 2004, 08:26 AM
Registered User
Joined Jan 2002
6,588 Posts
Is anybody interested anymore in how to avoid ruining multiple cells in a large LiPo pack when one or more individual cells and/or connections goes bad?

If so, I'll post a link to the general procedure (again).

- RD
RD Blakeslee is offline Find More Posts by RD Blakeslee
Last edited by RD Blakeslee; Nov 10, 2004 at 08:31 AM. Reason: correct spelling
Reply With Quote
Old Nov 10, 2004, 05:33 PM
Tell that to George Zipp!
mikeb33's Avatar
United States, IL, Inverness
Joined Oct 2000
1,819 Posts
I am interested.
mikeb33 is offline Find More Posts by mikeb33
Reply With Quote
Old Nov 11, 2004, 12:41 AM
Registered User
Mr DIY's Avatar
South Africa
Joined Aug 2003
587 Posts
Quote:
One last question. If I take this pack apart and find a pair that aren't damaged, can I reuses them?
If they look 100% I would use them ... but not in another multiple cell pack. The cells may differ in condition to your other cells. I would use them in a smaller pack ... but that is just my thoughts. Maybe somebody could add to this.

Glad to see you did use some form of spacer.

Just as a last thing, while ripping your pack apart. Look closely along all the cell seams. See if you see any 'foreign' substances that have appeared anywhere along any seam. I have had a cell with tiny tiny leak that caused ballooning like this. Worth a look just to try and see if you can still find cause of your problem.

Quote:
Is anybody interested anymore in how to avoid ruining multiple cells in a large LiPo pack when one or more individual cells and/or connections goes bad?

Yes RD. Seems I might have missed that thread.

Brian
Mr DIY is offline Find More Posts by Mr DIY
Reply With Quote
Old Nov 11, 2004, 08:18 AM
Registered User
Joined Jan 2002
6,588 Posts
Simply charge your LiPo cells in parallel and connect them in series for flying only!

http://www.rcgroups.com/forums/showt...91#post2883691

You can use the good cells from your failed pack with similar new cells, if you construct your pack using the parallel charge - series discharge strategy.

Imbalance caused by mismatched cells is automatically corrected with each charge.

But don't mix cell generations - the internal impedance mismatch is too great and can cause some cells to overdischarge.

- RD
RD Blakeslee is offline Find More Posts by RD Blakeslee
Reply With Quote
Old Nov 11, 2004, 03:29 PM
Registered User
vintage1's Avatar
East Anglia, UK
Joined Sep 2002
29,705 Posts
Mike. I'd double check your charger The original post looks like a cell failed and the others all overvoltaged or maybe the charger overvoltaged in the first place..

I think the whole pack is toast probably.

Heartbreaking.
vintage1 is offline Find More Posts by vintage1
Reply With Quote
Old Nov 12, 2004, 09:20 AM
Tell that to George Zipp!
mikeb33's Avatar
United States, IL, Inverness
Joined Oct 2000
1,819 Posts
Quote:
Originally Posted by vintage1
Mike. I'd double check your charger The original post looks like a cell failed and the others all overvoltaged or maybe the charger overvoltaged in the first place..

I think the whole pack is toast probably.

Heartbreaking.
I have a Orbit Pro with V6.3 software. How would I "double check your charger"?
I took the pack apart and that double sided tape is so tough that I had to use a heat gun(carefully) to soften the tape and pry and pull them apart. The only cell that looked good had the tab break off. There is nothing left useable and it is "heartbreaking". Nearly $200 for the pack, about 15 flights and it is junk. I never crashed them and was always carefull when charging, I feel like I don't deserve this loss
I don't think I will buy or build any 2P packs anymore.
mikeb33 is offline Find More Posts by mikeb33
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Question Considering my first LIPO...which do I need? miamiquasar Batteries and Chargers 19 Dec 21, 2004 09:42 AM
I want my first LiPo Willie Levi Batteries and Chargers 39 Dec 19, 2004 01:53 AM
My First Lipo, Need Help, Whats with the two wires? Photo Attached for reference ontheweekend Batteries and Chargers 8 Sep 10, 2004 09:47 PM
help save my first lipo philip frank Batteries and Chargers 3 Aug 20, 2004 01:25 AM
Help! My first Lipo pack death! EABiker Batteries and Chargers 7 Apr 29, 2004 02:26 PM