Lifepo4 battery characteristics

[johnnyz383]

I want to run by something for the readers of this forum. I had a 48 volt system consiting of 18650 lifepo4 1400 mah batteries. I wanted to increase the voltage to 72 so bought 96 lifepo4 batteries from china. I finally hooked everything up and the sag was incredible....(i have a Crystalyte hs3540 hub motor on a custom trike)...nominal voltage was 72 volts....at full throttle, it sagged to 59 volts....after a couple of minuets of testing something happened and i was now down to 67 volts nominal. I took it apart and 16 of the group of batteries were down to about .3 volts.

Earlier when charging the whole battery pack using a singalab bms, it would immediately go past 4 volts only on a specific series of batteries (the new ones). I initially thought there was something wrong with the BMS so bypassed it and simply hooked up a 84 volts charger to neg and positive and again this row spiked in voltage and the others stayed the same so now im thinking that in fact there was something wrong with some of these junk batteries. When it did go past 4 volts i heard a faint popping noise. I initially inspected the batteries but they appeared fine. Voltages checked out too..after this ride i find that after taking them all apart they are leaking something, and voltages near zero. When i go to charge individually they initially come up to 3 volts but off the charger immediately start going down in voltage to almost zero HERES THE QUESTION....if a battery is shorted would it display this behavior?...and if there was something wrong with them maybe the BMS simply couldnt bleed off the high voltage fast enough and the battery kept rising in voltage while the others remained the same??

Thanks

John

 

[Hillhater]

18650 Lifepo4 cells in what pack configuration ? ...how many in series , ? ..parallel ?
...how are they connected ( soldered /welded ?)
What brand/ type of cell ?
Are you sure they are LiFepo4 ?
If they are , why are you charging them to/past 4.0 volts ?

 

[johnnyz383]

18650 Lifepo4 cells in what pack configuration ? ...how many in series , ? ..parallel ?
...how are they connected ( soldered /welded ?)
What brand/ type of cell ?
Are you sure they are LiFepo4 ?
If they are , why are you charging them to/past 4.0 volts ?

The original battery was arranged in cells of 16(3.2x16 =51.2 volts) x (1100 mag x 18=20 amps). I added another 96 cells rated at 3.2 volts and supposedly 1400 mah. The originals were machine welded. The new added cells were soldered by me .
I didn't overcharge them...this is what I'm getting at...the BMS began charging but the first time it went way over 4 volts and this must have ruined them. I attempted to revive them but they just "bucked" the charge Iwas giving them so iI replaced these with some others I had lying around a
and all seemed well until I tried charging again. Once again a specific row of 16 cells approached 4 volts and the red led came on the board signaling they were full and trying to bleed the voltage off but the cell kept rising...no change in the other cells.
I've never heard of a lifepo4 cell leaking and being destroyed by going to 4.2-3 volts. I'm wondering if they're real...

John

 

[DAND214]

Do you know what brand cells and from which vendor

What BMS did you get from where?

If you soldered directly to the cell you might of cooked them.

Do you have a link where you bought the Batts? Either you cooked them or they are not what you needed to use.

Dan

 

[dnmun]

i have overcharged lifepo4 to 4.2V but i drained it off immediately. they never puffed or exploded, but it was only a few mAh.

 

[johnnyz383]

I bought the cells off of a vendor on Alibama..they were from Optimum Battery Company and were advertised as lifepo4 3.2 volts 1400 mah. When i recieved them, there was not indentifying marks on the battery which made me a bit suspicious, but she assured me that the factory simply must have forgot to print the identifiying marks on the battery. As Dmnum says, they shouldnt have been ruined by going to 4.2-4.3 volts as i took them off right away. My question is why did the BMS, a signalab immediately go for the same set (16) cells and rapidly raise the voltage and the other voltages did not rise...to test this i then bypassed the BMS and simply hooked up the Charger to pos and neg and bingo....the same set of cells began rising to over 4 volts while the others remained the same....why?. In an earlier post Dmnum had been helping me try to figure out the BMS but im now thinking its not the BMS but something inherit in the battery itself.
By the way soldering will not cook the battery, if done properly, ive done many many cells and never destroyed one yet.

John

 

[Gregory]

...to test this i then bypassed the BMS and simply hooked up the Charger to pos and neg and bingo....the same set of cells began rising to over 4 volts while the others remained the same....why?.

Did you start with cells that were all well balanced? It sounds like these new cells were already the most full cells. Otherwise you can expect the full cells to shoot up fast when bulk charging. Bulk charging only works with balanced cells.

 

[johnnyz383]

Yes they were all around 3.2 volts...the new ones were 3.3 and most of my old ones were around 3.25-3.3.
You said that bulk charging only works with balanced cells...but how to explain why the signalab BMS shot these particular group of cells up way past 4 volts and the others didnt move..i thought it was the BMS and got another one and it did the same thing, only this time the cells are ruined as they all dropped to near zero volts.


John

 

[johnnyz383]

The story gets worse...about 43 out of the "new" 96 cells were ruined. I dissasembled the battery completely and had tested each one. The remaining cells that were ok i put aside. 5 hours later...another 10 have dropped to near zero!!! I have never seen anything like this before...before i actually say where i bought these pieces of trash has anyone ever seen anything like this?...alot of them appear to be leaking something as well...the ones that have very low voltage like .9-.1.4 volts..when i put the voltmeter on them they immediately begin dropping in voltage untill they get to about .2 volts....


?????


John

 

[d8veh]

If the new cells had lower capacity than the old ones, they'd reach 3.65v sooner. If the BMS doesn't shut off charging when they reach that voltage, continuous charging will make them rise rapidly, but 4v shouldn't damage them. Normally the pack voltage would be high enough that the charger eventually switches off before any damage is done. What's the maximum cell voltage that your BMS allows. I think Signalabs can go quite high.

 

[dogman dan]

I think they were lower capacity, likely lower because they were reject cells. So they never had much capacity, and even less c rate.

I doubt good cells would have been ruined quite so quick. Basicly, you just got burned on the purchase. The bms did not cause the cells to overcharge, no doubt it was discharging them all it could. They were just a horrible mismatch with the original cells.

 

[johnnyz383]

I think they were lower capacity, likely lower because they were reject cells. So they never had much capacity, and even less c rate.

I doubt good cells would have been ruined quite so quick. Basicly, you just got burned on the purchase. The bms did not cause the cells to overcharge, no doubt it was discharging them all it could. They were just a horrible mismatch with the original cells.

THANK YOU!!...i Contacted the company and they are blaming me and saying that mixing new and old cells caused this catastrophic damage to their excellent cells. Absoloute rubbish!! I initially blamed the BMS but i now know they are junk cells or are faulty. If they do not give me a refund im going to tell everyone who it is that i bought these cells from.


John

 

[johnnyz383]

OMG it gets even worse!!!
I left the "new cells on the table all disconnected. I put aside the cells that have been reduced to near zero volts. All the others were tested to have between 3.2 and 3.2 volts. This was yesterday. I woke up and viola!..another 8 cells have died. Down to almost zero volts!!!...Has anyone ever seen anything quite like this?....i obviously know they are faulty...just wondering if anyone has had similar experiences



John

 

[doovalacky]

You have never mentioned how much charge/amps you were throwing at them?

 

[dogman dan]

Well, you could have also made them die sooner. But for sure, they weren't up to what you did. Whether they should have held up or not remains uncertain till you show us the specs they claimed.

 

[johnnyz383]

You have never mentioned how much charge/amps you were throwing at them?

They were suppose to be lifepo4 3.2 volt 1400 mah batteries. I have a Lyen controller set to a max of 40 amps but i didnt go anywhere near this as i was only testing them. Besides at 20 amps( the total amperage of the battery) that shouldnt have hurt them.

John

 

[fechter]

I've seen some pretty severly abused A123 cells but never observed anything like that.

Most likely they are just defectively built.

Possibly they can't handle the discharge current placed on them and they were toasted.

Possibly soldering them damaged the cells.

 

[dnmun]

i don't think there is any way to know about the history of these cells so there is no way to form an idea of what caused the failure described. when they are discharged below LVC then the pressure inside can blow the pressure relief valve in the top and that may have killed them. but no way to know how high in voltage they were charged up to.

too bad since you even had the signalab BMS to protect them. maybe you can sell the BMSs to someone else there in britain. if you were in the US it would be worth the shipping cost to get them.

 

[johnnyz383]

i don't think there is any way to know about the history of these cells so there is no way to form an idea of what caused the failure described. when they are discharged below LVC then the pressure inside can blow the pressure relief valve in the top and that may have killed them. but no way to know how high in voltage they were charged up to.

too bad since you even had the signalab BMS to protect them. maybe you can sell the BMSs to someone else there in britain. if you were in the US it would be worth the shipping cost to get them.

Yes, i was blaming the BMS but in fact it appears the BMS couldnt drain off the voltage fast enough...the fact that they had no markings what so ever when i got them immediately made me suspicious. Ive been going back and forth with the vendor from China and NOW theyre saying theyre going to look into it, because they yet have answered my question about why theres no identifying marks on the batteries not to mention the catastrophic failure. Thanks Dnmun for all your help with the BMS, but im going with headway cells this time.

John

 

[dogman dan]

8p of 1.4 ah cheap lifepo4? That's only 11 ah. It should have died even at 20 amps discharge, but that was really fast. If you never gave it 40 amps, how did you know the sag at full throttle?

Clearly they couldn't handle even 2c let alone the 4c to 6c spike. But no way that was going to last with 40 amps, unless they were some really good stuff.

One possibility is simple, the cells were made years ago. That would explain the quick death.

 

[johnnyz383]

This is really unbelievable. The jerk at OPTIMUM BATTERY comapny where i bought these junk fake batteries is telling me that it was my fault that they died. UNREAL!. I want everyone on this forum to be aware of this situation and how you really have to do due dilligence in order not to be taken advantage of. Heres a copy of what he sent me.

Dear John,

I checked all order information.

I check the email record between you and White Zhang. You only mentioned the cells is for
"airsoft gun", but you never mentioned the cells is for EV with other batteries.

All the cells are tested at 1C, the cells capacity is around 1400mAh to 1500mAh,
If we do it at 0.2C according to IEC standard, the capacity will be at least 50mAh more
(it means at least 1400mAh to 1550mAh at 0.2C according to IEC Standard).
So the cells is very common cells for small electronic toys, but not for EV with other
old cells from other company. 3.5V means the cells are charged to 80%-90%.

As for the PCM/BMS board, you also didn't do it in a scientific way.

The cells are defective because of abusing use. I can not help you to apply for
a refund. Sorry.

Please tell the whole process to the professional people. And tell them how many
testers you have used for the cells packing. The professional people is the only
choice to explain the problem for us.

Even if we buy the Li-NCM cells from Samsung or Panasonic and put them with the
old Samsung and Panasonic cells directly just like your way, the new cells will still be ruined
by the wrong connection.

Best Regards

Rocky

LOL first of all i didnt mention that the cells were for an "airsoft gun"...what the heck is that?....they know why i wanted the cells...incredible. Please all reader read this ridiculous answer and judge for your self. He wont answer my questions, as to why there was no markings on the cells themselves as i found out it is mandatory by law. Anyway, im pursuing this further.

John

 

[johnnyz383]

Heres a copy of my email i sent to these bozos when i recieved these "lifepo4 cells" and their answer...


Hi there, i recieved the batteries, thank you. There is no identification on the outside of the battery like i normally see..I cant remember , what is the Amp rating of these cells?

Thanks

John


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sales1
To Me
Oct 29, 2013

oh, sorry,John . May the sample studio forget it . real capacity >1400mah.
thanks

White Zhang

OptimumNano Energy Co.,Ltd

Optimum Battery Co., Ltd

AdptimumNano ,No.68,Lanjing North Road

Pingshan District ,518118,Shenzhen, China.

T:86-755-84630787 I F:86-755-84630785

E:sales1@optimumchina.com

Skype: optimumnano11

www.optimumnanoenergy.com









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[doovalacky]

. Besides at 20 amps( the total amperage of the battery) that shouldnt have hurt them. John

Something is not adding up to me. You were adding 24V to the pack, brought 96 cells@ 1400mAh.
I assume therefore a 8Sx12P arrangement. Assuming claimed rating of 1400mAH is correct that's only 16.8Ah max.
1C tested apparently, no idea if can handle higher.

I don't doubt they might be low quality and less than claimed specs. But is sounds like you have thrown to many amps at an unbalanced pack and the BMS has not been able to keep them within limits.
The ones shooting up to 4v or higher were "full". The others didn't move as they still were discharged. The voltage stays very stable right to the last few percent.

 

[johnnyz383]

Please re-read the posts. I added 19.2 volts (6 x 3.2)
They were not unbalanced. All cells were between 3.25-3.3 volts. The inclusion of a battery in series would not account for what happened. I have had lifepo4 batteries and used them under horrific conditions, short circuited, heated, frozen, pulled 4 c and more and they never died and never experienced what these cells did and considering i only did a test run and they failed this quick is illogical for a quality cell. I have also put unbalanced cells with good cells and after re-charging they were fine. The Signalab BMS works by bleeding off the voltage of a group of cells once they reach a certain limit in this case 3.65 volts. Thsi works when the cells are balanced as PER THE AMPERAGE..obviosuly they were not close to 1400 mah and much less otherwise the BMS would have been able to work as intended, besides after they spiked to 4 volts i took them off the charger. And ive never heard of a lifepo4 cell completely discharging ITSELF once at 3.2 or 3.3 volts have you??



John

 

[dogman dan]

Still wondering how you know what that sag at 40 amps was,,,,, unless you gave them 40 amps. That could have killed em, but they should have stood it a bit longer.

Did you solder those cells?

That email just called em 1c cells.

You disbalanced the pack, then put it on a bulk charger naked rather than balance it manually, one parallel group at a time. That popping sound was the cells death scream.

They may have sent you poor stuff, but you sure can't prove that now, without changing your story.

Time to dial 911.