Some LiPo rules were broken, help! (pics + explanation)

[markw]

Hi guys,

Recently completed my bike build (post incoming! ) and started some tests. Took it on it's longest journey to date today and something bad happened.

Bike ran out of juice. Ffffuuu--- . Should have checked the voltages more closely before leaving to go home. I pedaled home (10 minutes) and got the batteries hooked up to the charger in parallel via a balance board. Here's some stats to help unnastand the picture.

5s Turnigy Softcase LiPo 3s2p

After recording voltages for each pack I found that pack #2 might be suspect. Cells 1-5 as follows 2.8v / 2.7v / 2.06v !!!!! / 2.95v / 2.96v.

I did not heed some of the advices from this post http://endless-sphere.com/forums/viewtopic.php?f=14&t=52240&hilit=lipo+rules --- none of the cells were individually balance charged and I think this was probably my huge blunder. For SHAME! I know *bows head in shame.*

All cells are currently parallel balance charging and afterwards will be individually charged to 4.10 and then I intend on throwing them back on the wheels for discharging/fun/monitoring. Unless:

Please advise. Should I just dispose of pack #2 right now? Is there hope for its recovery after respecting it a bit more? It cell 3 in pack #2 was far below safe voltage... for nearly 20 minutes only. When I run my fingers down the top/flat sides of the pack it doesn't feel puffy or bulgy.

http://i.imgur.com/hKOlheD.jpg (pictures of the packs and my charging setup :s )

http://i.imgur.com/7YKLSol.jpg (pictures of current charging stats.)

Thank you ES!!

 

[markw]

Update:

Balance charged to 3.77v each pack individually. Discharged on bicycle. Pack #2 has cell voltages everywhere and cell 3 (the trouble cell) has incredibly low voltage. I'm assuming that this pack is just a huge dud. Or --- did I screw it up some how?

Pack #2 RIP. How do I dispose of this pack? It now is bulging and I'm uneasy with its place in my residence. There's a firepit I'm going to hide it in until you guys advise.

Until then, I'll keep my 5 decent packs in storage mode until a new 5s pack arrives at my door.

 

[spinningmagnets]

Plug the dud pack into any resistive load (a 12V car bulb?) and let it run down to nothing. Then, at that point, it is safe.

 

[dogman dan]

The dud is ruined, safely dispose of it as explained above. Replace it.

You ruined it, but it might have survived if cell 2 was better. Live and learn. The big mistake was not so much less balanced, as simply running it till it mattered so much.

The other packs also got a deep discharge, which may result in a shorter lifespan a year from now. But for now, they are ok to use as long as they stay balanced and don't puff huge.

 

[parajared]

You can bring overdepleted (even 0 voltage) cells back to life if you charge them up immediately after your ride, but I have heard that they will refuse to rise from the grave after a few hours or so.
Be sure to charge them somewhere where its ok if they light on fire from you charging them. I have a pack that I call my "zombie pack" that I keep a close eye on after it hit 0 volts, but it works just as good as the rest of my packs.

Flite Test has an awesome video on how to build a cheap lipo bunker for the firey little rascals:
[youtube]gobFcNzGG9I[/youtube]

 

[markw]

Thanks for the replies everyone!

@dogman i am happy to report that the rest of the cells in my other packsonly depleted to around 3.35v, not great but did receive charging 20 minutes after depletion. With greater respect the dud could have survived as i am understanding. I have one of those small units that plugninto the balance chargers... When riding should i keep it plugged in to the weakest cell as a warning? I dont have a cycle analyst... Yet.

@parajared this is really good information and i thank you for dissecting my post and finding the answers i was looking for. Its good to know that the length of time undercharged has some significance to the health of the battery.

@spinningmagnets nice! I will do just that.

More on my setup for your very valued advise to come. Thanks again everyone.

 

[dnmun]

you mean that the cells rebounded to 3.35V after sitting. if they ended up that low they were pulled down to 2.5V and the other cells you have that show 2-2.7V resting may have gone down to almost 0V.

it doesn't help to leave them sitting for a long time over discharged like that but if you recharge them then you can use a bulk charger to charge and then use that as a way to evaluate the internal resistance.

measure the cell voltages first and then put the pack on a bulk charger and then measure the cell voltages multiple times as the pack recharges using all of the cells that you have so then you can compare the voltage across each cell as it is recharging and this will give you a first order estimate of the damage done and you can use that information to evaluate the internal resistance and your ability to make the pack balance. you have to actually write down the voltage values so you can go back and create a graph showing how the voltage across the cell changes with time as it charges up and compare the graphs of each cell to make final determination.

if you use a balancing charger then why didn't the cells balance on the charger? this could never happen with a BMS installed to protect the pack.

 

[markw]

To clarify, all packs with the exception for suspect dud pack never went below 3v when i was on my tet run and power was cut to the motor. Dud pack, number 2, had cell 3 well below healthy voltage while other packs were within the 2.7v and greater voltage range - but luckily for only 20 minutes.

After noting this i did indeed balance charge all cells to 3.77v. Then, on my test run, it was noted that pack 2, cell 3 had again depleted even further below healthy voltage. Thus it was decided that pack 2 has a faulty cell and should be retired. Pack 2 also is noticeably puffy and i assume it is from gas released.

All packs were balance charged before the run, but not individually as the post that i mentioned suggested. Before the first test journey they were parallel charged and then tested to be within .02 volts balanced.

There is not a pack bms but everything is done with a balance charger, supervision, and monitoring/recording of all voltages! With this is mind, @dogman's post, is user error still fairly egregious?

 

[dnmun]

3.77V is not charged. why doesn't your charger charge them up to full charge?

 

[Hillhater]

More to the point, you cannot balance a pack at 3.77 volts !!
Remember, you are trying to "balance" (match) the CAPACiTY , not the voltage.
At that voltage you could have cells at greatly different levels of capacity still even though they all read near 3.77.
Balancing has to be done at either near the max voltage (4.0v +), or arguably at the bottom of the capacity range (-3 v ?)
In these areas, the voltage/capacity ratio is very different and gives a much more accurate means of cell capacity matching.

 

[markw]

Thanks for the continued input guys. I think we've reached one of many root problems in my LiPo learnings. I had been under the impression that voltage and capacity are directly linked. IE charge a battery to 4.1v and it's at or near full capacity. I'll read more on how the two variables effect one another.

@dnmun It does! But because of my aforementioned misconception on capacity and voltage (or voltage being the tell for battery capacity) I did not charge them to full.

@Hillhater Your post especially helped clarify things for me. I need to read more on this relationship between voltage and capacity.

I read up on this via the wiki and a lot of my confusion was put to rest. Thanks to all for steering me in the right direction and for being so patient!