Li-Po Battery swells up...

[SkyMaxx]

Here's a bit of irony...I started out my RC hobby in battery powered RCs back in the day when options were pretty much limited to alkaline batteries and some NiMH/Ni-Cd packs. I switched to nitro vehicles, and now find myself wandering back into electrics...making me an electric newbie.

Enough history, now to the problem. I recently bought an E-Flite Blade CP Pro heli. It came with e 3 cell Li-Po rated at 11.1V 800mAh. It also came with a balance charger (EFLC3105). I purchased a wall adapter to plug the thing in vice running it off of another battery to provide source power.

I got tired of running my heli for the length of one charge and then having to wait nearly two hours for the battery to charge up, and bought a second battery pack to alternate between.

The first battery, I dropped onto the charger and then dropped it into my heli and flew it. When I got the battery out of the helicopter, it was warm/hot just like the one that originally came with it. Following the directions that came with the heli, I let it cool down to ambient and then tried to plug it into my charger. I got a charge error. Per the user manual, the charge error indicated points to either the battery being over-discharged or that one or all of the cells in the battery are damaged.

Since I had my other battery and it worked fine, I repackaged up the bad battery to take back to my hobby shop and waited for the original battery to finish...flew the heli one more time on the original battery...and called it a day.

In the morning, I took the bad battery back to my LHS to trade for a new one. The bad battery had one cell that was all puffy. This caused concern, but was suspected that the pack simply had a flawed cell to begin with.

They gave me a new one and all was well...or so I thought...came home...dropped the new pack in the heli...went flying...got done...went to remove the new battery...and it had one cell all puffy (just like the other one I had returned).

Now, I have to bring my heli, charger, and batteries into the LHS for the owner to see in order to get a replacement battery...not an issue...but my question for all you electric Li-Po pros...

What causes a cell to get all puffed up after use?

The flying I am doing is nothing special...basic hover (or attempts to hover) and keep the heli in one relative location and relative height (basically within a ten foot circle below three feet). The electronics on the heli are all stock...and I can't honestly give more than book answers for what that means. I bought it ready to fly...so that I could learn to fly the bugger and perhaps move on to a larger heli in the future.

Any information you might provide is most welcome. Note, I already googled my specific battery for problems and could not find any on the brand, make, model. I also searched this forum and came up with zilch.

Sorry about the lengthy post, but trying to limit the game of twenty questions normally associated with troubleshooting these kinds of things.

Thanks in advance for your help.

-SkyMaxx

 

[Rolex]

That shouldn't be happening, and it's nothing you're doing wrong. There's always the possibility that there was a run on defective batteries, and the recall just isn't out yet. The hobby shop will be able to verify that all is well on your end, replace your batts, and deal with the supplier on their end.

 

[SkyMaxx]

I figured it shouldn't be happening and am hopeful that I do not get too much hassle from the hobby shop. I have spent a little over $600 in the last couple of weeks and have spent over $5000 in the store in the lifetime that I have shopped there. My thinking is like yours...bad batch of batteries. The cell that puffed up on each pack was the same one.

But I am still curious about what might cause these things to puff up...

 

[olds97_lss]

Don't lipo's puff up if they are discharged too far? They do the same when overcharged. There might just be a weak cell in the pack that is getting drained too much.

 

[HeartBreak]

I think Olds nailed it... I have a lipo pack that came with the heli I bought off of the forum... I'm kind of afraid to even touch it, considering the voodoo around lipo's.

 

[Rolex]

These batts are well sealed, since oxygen is the only thing they need to burn rapidly. I'm sure the only thing that can cause them to swell is overheating, and that would worry me.
Perhaps when these packs are put together, each batt comes down a different line, and that's the reason it's in the same position. Just a guess on my part.

 

[SkyMaxx]

Hmmm...interesting. Perhaps it is a bad batch then. As for overcharging...not likely on the charger I have and the fact that it charges the original battery just fine. Overdrawn could happen, as the circuitry in the helicopter does not have a minimum shot off point of any kind that I am aware of. No voltage sensing. According to the user manual, drawing the battery below 3V is bad. So, I basically run it until the main rotor can not produce lift. Then I stop.

The battery is warm/hot, but according to the manual that is normal. The thing is not too hot to touch and never smoking. So I am guessing that I am using it within the design constraints of the battery and electronics on the heli. That leaves me with the only conclusion being that I got batteries from a bad batch.

 

[sweetdiesel]

One other possibility is that your battery is getting a deep discharge at the end of the discharge cycle. A deep discharge is a high amp draw in the neighborhood of your packs burst rating. Let's say you're at the end of your discharge cycle and you know that your pack is low but you try to lift the heli off one more time. It doesn't lift, but the amp draw from the motors is high enough to cause the deep discharge.

A lipo pack should always be under 130 degrees when you are finished running it. Judging a pack temp by touch is a unreliable method, use a temp gun to be sure. Also use a volt meter to check the pack voltage after the run. There is long term test data which shows that discharging to 3.2 volts per cell rather than 3.0 volts per cell is better for the packs and increases the effective cell cycles.

Since your heli's ESC does not have a LVC, it would be a wise investment to get a lipo alarm.

http://pfmdistribution.com/secure/shop/item.asp?itemid=203&catid=48

And even though you follow each and every precaution regarding lipos there is always a possibility of getting a bad cell. You can get bad cell in a nimh pack and lipos are no different.

One last thing, the balancing charger that comes with your heli is not very reliable. The OEM E-flite chargers are known to not fully balance the cells after a charge cycle. Running a unbalanced pack can easily cause an over discharged cell.

 

[SkyMaxx]

Thank you for the excellent information. I will look into alternative manufacturers for my battery needs should the LHS not work this out for me. Since I am the newb in this area, I will rely on your guys input and try and get set up the right way.

My next challenge will be either moving up to nitro helis...or making the one I have brushless. But first I need to get this battery thing sorted out and get more flight time under my belt. Am having fun learning to fly...again.

 

[SkyMaxx]

After a certain amount of incredulity, the owner of the store checked my heli, my charger, my original pack and the two I had returned. Nothing wrong with the heli. Nothing wrong with the charger. Nothing wrong with the original pack. The two fried battery packs had a bad cell in the same loop. In fact they had the same bad cell in the same bad loop.

Conclusion drawn: Two bad batteries with the potential for more in the lot he had in his store.

He gave me a replacement and even took the time to charge it up for me.

I brought it home and flew my heli with it...no problems. In fact got two packs worth of flight in before it got too dark to fly safely.

Alls well that ends well here...