Wrecked a cell in my battery pack, can i just remove it

[caleb7777]

I got a new LiFePO4 battery pack, 16 cell i believe. I poked the top cell and it burned up last night, literally. I removed the top cell promptly and blew the fire out.

I forgot to put something between the battery and the screw ends in the basket. So I punctured the top cell and kicked myself for it well. Brand new battery.
ugh.
I wasn't too worried about it because i understood I would only need to replace the one cell in the worst case. The internal layers did not appear to be shorting either. The cell still operated, so i though of just filling it up with epoxy so that nothing shorted by movement, which may have worked but that night the little shit lit up and caught on fire at 6 am today. i threw it outside after hearing the fire alarm and just cut the the top cell off right away.

So now I need a new cell for sure, maybe even a few but I may have cut the lower one when i pulled out the top one.

So no more bike for me right now. unless....

OK so i removed the top cell. Now if I attach the main hot to the next cell in series I will have a 15 cell battery which could be charged with charger putting out 55v? Is this right? or would it screw up the BMS if i left the one balancing line that went between cells 1 and 2 unhooked?

Will it damage the BMS?

This might work because of my charger situation. My LiFePO4 charger died, so i grabbed a SLA charger I had laying around for temporary use and it puts out 55v. That would be great for the 15 cell right?

Bottom line. Do I need to wait on new cells or can I just run it with one less. BMS issues?

 

[caleb7777]

subscribed

 

[dnmun]

i need to find a pouch too. 10Ah lifepo4, 7.8mm thick, 80mm wide, 230mm long. lemme know what you find out. i am gonna ask mr ping if he knows who made this one. it has zbikes.com.au printed on it but they never replied to my email.

anybody have good sources for lifepo4 pouches?

 

[caleb7777]

I will get mine from ecitypower as that is where I got the battery and i want matching packs. Quality might be sketchy, I had one bad battery but he took care of it promptly.

See here
http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=9054&hilit=18000w

 

[heathyoung]

The zbikes.com.au is a red herring - they don't seem to have these cells or any LiFePo4 listed.

However - a 10AH cell is available from here: http://www.ev-power.com.au/-DIY-Small-LiFePO4-Battery-packs-.html

LiFePO4 10Ah Pouch Cell
$58 per cell (4 cells)
$55 per cell (8 cells)
$53 per cell (16+ cells)
Lithium Iron Phosphate, safe battery technology.
3.2V nominal, 2.1V minimum, 4.2V maximum, 3.65V fully charged
10Ah capacity
325g
250 x 80 x 8mm
20A continuous discharge, 60A pulse discharge
Solderable tabs for easy cell interconnection

 

[caleb7777]

I don't need a pouch. I want to know if I can get away with using only the 15 cells in series rather than 16 without damaging the BMS if I leave off the one balancing line.

 

[dnmun]

i don't think your capacitive balancing BMS will work without all the cells present. plus it will look like it has a dead cell to the BMS and will shut down for LVC.

 

[swbluto]

Yes, the LVC will shut-down the battery if it doesn't detect a cell. I don't know about charging, however, if it's through a separate FET/connection.

 

[caleb7777]

Here is the current BMS.
I damaged my top cell and had to remove it, want to run just 15s rather than 16s now. Probably will replace cell next season. Need something now.

Top left is Positive Main (1)
Bottom right by shunt is Ground from cells (2)
Top Right is Ground to main connection or bike (3)

I have 50 volts across 1-2 and nothing or very small voltage across 1-3.
I am assuming that the BMS is cutting the power out to bike. Is it because I have only 15s now or because I fried the BMS?
If I solder a jumper from 2-3 it will work but what are the consequences? I pretty much won't have a BMS if I do. Or will it just not LVC and still will balance?
What does it do to the charging circuit?

I am just new to BMS.

I destroyed cell 1.

I want to run the BMS at 15s now.
I got it reattached, sorta without the last cell but the BMS appears to cut the power.
What needs to be done for the BMS to run at 15s if possible?

Other questions: Can I increase the continuous discharge current? Does anyone know what this BMS is rated for continuous. It is different than the first I received and I don't know which is the high output.

 

[swbluto]

Wait, can you be absolutely specific about which cell you burned? Was it "the first cell" or "the last cell" in the chain (as opposed to something in the middle)? If so, you might be able to skip it by "moving" either the main positive or main negative cable up one cell group and leave the sensor wire and damaged cell intact in the pack. I wouldn't actually "move" anything as that could introduce complications, but just solder on new power wires. If it was near the black cable, then you might have some problems. What to do is to use this new soldered on cable for discharge and possibly for charging, although I can't guarantee your charger will work correctly at a lower voltage.

If it's in the middle, you're kind of on the screwed side unless you can swap the "first cell"(next to the main positive cable) and the damaged cell and then do the aforementioned mod. Also, if it was near the black cable("the last cell"), you could just swap it with the cell in the first of the battery pack and do the above mod. That'd avoid some complications with installing a new ground cable.

I ended up skipping the first cell near the main positive cable using the method with my Ping (Totally different purpose - I wanted to reduce the cell count), and then used that for charging and discharging and so on and everything worked fine.

P.S. Who'd you get the battery pack from and what version is it?

 

[caleb7777]

The pack is 48v 15aH from jack Xie at ecitypower

I wrecked the cell on the far left of pic, it is gone now.
That corresponds to the small wire on the far left of plug also.

I moved the main hot down to the next cell and left the sensor/balnce wire unhooked but the BMS won't allow power thru. it is in shut off mode.

 

[caleb7777]

I am building my tab spot welder today

I have the replacement cells for this pack.
The new cells have essentially no charge on them right now and the cells in the original pack I am adding to are charged. Can I add these sells in and just let it balance across the BMS or should the voltages be equal when I add these replacement cells. Should all cells be dead or full or does it matter?

Thanks guys.

 

[karma]

its a good idea to charge the new cell close to what the old cells are before assembly. :wink:

 

[caleb7777]

Any easy suggestions on how to do so?
3.65 v cells lifepo4

 

[karma]

theirs single cell chargers out there. hobby shops etc. i have a few packs on the go im cheap im just using a cell phone charger i monitor the voltage when it hits 3v i remove the power. :wink:

usb charger works well also. you just need to diy your own usb cable.

cheers

 

[caleb7777]

thanks karma

 

[dnmun]

you did not say what the voltage of the new cell is. if you can get alligator clips onto the tabs of the cells that are there, then you could use a jumper to charge the new cell from the others in the pack and pull them down a little each to charge up the new one. do you follow what i mean? you can't make mistakes doing that either. remember that each sequential cell has the polarity reversed and you cannot get away with connecting them + to -.

3 nicads will give you 3.6V. charge them up with the nicad single cell charger and then discharge them into the lifepo4.

remember to always maintain polarity.