PDA

View Full Version : What is coming out of my Headways?



moon
29 May 2012, 0811
Sorry if this is long-winded, skip to the red part for the actual question.

So I'm doing a full pack breakdown balance charge after the initial shakedown runs. I stressed the hell out of some of the pack to the point of failure and lost 7 cells total. Out of 24s4p (96) cells I'm chalking it up to a (expensive) learning lesson. :( My bad, live and learn, right?. This time I will be nicer to the pack. Going to wire up the MiniBMS and perhaps get some CellLogs to monitor everything. I will make a graphic showing the distribution of voltages when I took the pack apart but essentially one half of the pack was more stressed than the other half.

Anyway, that's the background, here's the issue:

I'm doing bulk charging 4 cells at a time, with the 4 paralleled cells charging in series on a nice quality hobby RC charger at 6 amps to a pack voltage of ~14volts. I was having success getting the cells to all charge in series without having to do much or any individual charging. If my technique/procedure is wrong there hasn't been an issue until now...

This morning I went to check on the charged set and swap it out for another set before work. Unusually, the charger was not showing the completed indication and there was the smell of acetone. One of the cells had popped the burst disk! Sure enough, a quick voltage tests showed that one cell was at 1.1V and there was a good amount of fluid surrounding the cell. Now, I've smelled that smell and seen the fluid after I dropped a cell on its end, I'm guessing that is was the electrolyte leaking out. Why I'm concerned, is that this time I considered these cells to be 'good', as in, they were of a good voltage before charging (3.2V) and they were in a portion of the pack where all the cells were of good health.

>>>Is it 'normal' for healthy(ish) Headways to occasionally leak fluid(electrolyte?)? Is this fluid dangerous? Why did it happen? How can I prevent it and should I discontinue unsupervised charging?

liveforphysics
29 May 2012, 1025
You should never charge LiFePO4 from unknown states of charger in series without balance taps. It's virtually impossible to know the state of charge on LiFePO4 until you're beyond 3.4v or below 3v resting voltage).

You likely had one cell at perhaps 80% SOC, with 3 others at perhaps 20% SOC, (all reading nearly identical voltages), stuck them on the charger, the 80% cell reached 100% while the 3 others reached 40%, which would mean the charged cell is going to be getting driven to ~4.5v and held there while it's trying to finish the charge on the other cells, which it may or may not be able to complete depending on how fast current drops off in CV mode. The burst seal and liquid you're smelling is the organic solvent that disassociated into off-gassing from electrolysis. That cell is destroyed.

Bulk charge unknown SOC headways always in parallel. Can't really go wrong that way. :-)

Allen_okc
29 May 2012, 1054
:cool: forgive my ignorance liveforphysics - parallel charging?

:D i use the ED method of charging, individually charge. but curious about the parallel charging...

moon
29 May 2012, 1126
Good information LFP, thanks!

I was individually charging the undervoltage (2.2-2.8V)cells but it was taking way too long. At 2.5hrs per cell it took me the better part of a week to get through a quarter of the pack. I figured that taking the >3.2V cells that were in parallel groups and putting them in series would at least make them close in SOC. Yet another lesson learned...

My charger (http://www.horizonhobby.com/products/super-cub-dsm-rtf-THP610) does have balancing capabilities but I don't have the leads to connect to the balancing board.

EVcycle
29 May 2012, 1511
"Is it 'normal' for healthy(ish) Headways to occasionally leak fluid(electrolyte?)?"

No....never... they are now paperweights. I have a few myself only because I over discharged them drag racing.

EVcycle
29 May 2012, 1513
:cool: forgive my ignorance liveforphysics - parallel charging?

:D i use the ED method of charging, individually charge. but curious about the parallel charging...

Step away from the parallel charger..... :)

moon
29 May 2012, 1540
"Is it 'normal' for healthy(ish) Headways to occasionally leak fluid(electrolyte?)?"

No....never... they are now paperweights. I have a few myself only because I over discharged them drag racing.

Haha, well..yeah, I suppose it was a dumb question. :o

EVcycle
29 May 2012, 1614
Haha, well..yeah, I suppose it was a dumb question. :o

No dumb questions here....you never know until you ask!! :) :)

Skeezmour
29 May 2012, 1731
Think I ask dumb questions everyday.

Allen_okc
30 May 2012, 0558
Step away from the parallel charger..... :)

OK...

your method works perfectly for me Ed, and ive been able to charge my 48 volt pack within 20 minutes with each cell evenly charged.

i did use the 48 volt smart charger i got from Frodus about five times in between, then individually charge the cells every sixth time, every cell is still working perfectly. No Leaks...

and i'll probably do the 72 volt pack 24S3P the same way...

the only problem i have, individually charging the cells in my headway 4S 12 volt pack is, they wont top out... im sure its because the alarm system and the GPS tracking system is running while charging the cells, which cant be shut down or everything will have to be re initialized...

Allen_okc
30 May 2012, 0601
:eek: if my motorcycle gets stolen, it will go screaming and telling the police where it is... they would have to totally dismantle the motorcycle before they can kill it...

moon
30 May 2012, 1833
I went to the local hobby store and picked up a set of balancing lead connectors, so now I'm one step further in trying to treat my cells right. Funny, now that I can see what's going on in each charging cell, it makes perfect sense why blind serial charging is a Bad Thing™. I'm all for learning about these batteries and their care but I'm growing more concerned about the number of cells I probably killed with my over excitement when the bike(and pack) had just been thrown together. So, perhaps my job here is to show new electric conversion enthusiasts how not to break in batteries. :(

Nah, I'm just getting all my mistakes out at once.
;) :D :D :D