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Here is a reprint of a post i made on evtech list last night. I feel its important enough to double post. If anyone disagrees i'll remove. I have also attached photos showing some of the results. I would greatly encourage anyone who can to replicate these tests so as we get some confidence in the results.

Just prior to the evcomponents meltdown I had purchased and received a
quantity of 10 headway 10ah s cells. I've done a few simple tests with
them over the summer and was quite pleased. Recently I purchased and
tested more samples direct from headway and just this week payed for a
big batch of 16ah cells for my ev. Anyway today I decided to do a few
overcharge tests to see what happens. this is especially important for
myself as i'll not be running a bms or shunt balancer so what would
happen if things got a bit out of hand like a failed charger etc. Not
wanting to waste good cells I decided to use 4 of my much battered
original stock from evcomponents. A 24v 50amp forklift charger provided
the power. At switch on and for several minutes the charger maxed out
and nothing much happened. Then the current fell away and the voltage
leveled out to about 29v. Still not a thing. About 5 minutes later i
decided to test the cell temp with a probe. Just them my phone rang and
i was about a minute on a call. Just as i hung up BAM! One of the cells
went off like a stick of dynamite. Five seconds later BAM! another let
go. Copper foil everywhere. Being of above average intelligence , i
quickly concluded this was bad.

The ends of the 2 cells had launched a good 30 feet away and one of the
cells had uncurled like a roll of toilet paper. This i found strange as
i had assumed (i know i know) that the cells had vents to relieve
internal pressure. Clearly this did not happen in this case. Next move
was to repeat the test. This time i used 4 cells from my newer headway
stock. Same setup. Power on. While i'm contemplating the purchase of a
bomb suit two very sedate pops ensued and current fell to zero. Tiny
whisp of smoke drifted upwards. I left it on for 30 minutes to be sure.
Nada,

First noticable difference was a code on the cell label. The
evcomponents shotgun shells read : JC23 while the newer relaxed versions
read : JG06. Means nothing in itself could just be a batch code or build
data. More significantly however was the postmortem of the positive
end. The JC23 cells have 4 grooves in the positive end but the JG06 have
12. Crucially , the JG06 have a burst disc inside the positive cap. This
had popped on the newer cells but seems to be absent from the older JC23.

Time to prove the theory. Took 2 more of the newer JG06 and wired them
in parallel with a pair of headway 2 cell busbars. on one cell I used
the supplied m6 screw. On the other i used a long m6 bolt and nut and
tightened it down on both positive and negative ends. My working theory
being that the bolt would prevent the burst disc from popping on that
cell. Placed them in a metal box , connected the forklift charger and
hit the power. One minute into the test the cell with the headway screws
pops gently and smokes. 2 Minutes later all hell breaks loose. BAM! ,
smoke and flames. Once things calmed down , i inspected the results.

The cell with the normal screws had popped its disc. The other had not
due to the bolt. Instead it had stretched about a half inch in length
and split its case down the middle , vented and flamed.

The most important lesson for me here is the bolt length when joining
cells. DO NOT impede the bust disc on the positive end or you got a
stick of dynamite.


Finally , I decided to test a 16ah cell. These have no codes and i was
quite concerned as i've just dropped 2 grand on them! One cell on the
forklift charger in the metal box. Power
on.............nothing...............more nothing...........15 minutes
of nothing...............ah crap i need to use the
toilet.................can't hold it.................use
toilet...............much better..............still nothing..........40
minutes passed. Power off and inspect. Burst disc popped. No smoke , no
sounds.

So , check labels , don't overcharge a cell to 29v (duh!) , use
appropriate length screws and bolts for interconnects and ALWAYS use the
toilet before commencing a cell test!!

Damien Maguire
www.evbmw.com
 

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Thanks for the information Jack, that should be useful to those who are also using, or considering, the same cells.

Have you contacted the manufacturers to see what their recomendations would be as to bolt length tollorances?
It would seem that it would be easy for someone to make themselves a explosive pack by accident and a faulty charger set up.

Will you be installing a bms now or still planning on running without?
 

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Discussion Starter #5
I've not contacted headway yet and suspect even if i do i won't get a response. They are not the most verbose people i've ever dealt with:D

Regards the bms my tests have shown that an overcharge will damage a cell , under extreme conditions cause a popped disc and some smoke but thats it. I will certainly MONITOR the cells but i'm not a great believer in shunt balancers or top balancing.

I've looked at the minibms on offer here and its not a bad solution. Any cell exceeds the setpoint charger is disconnected. If a charger failed full on then a 1 amp shunt across each cell will just make a bad situation worse.
 

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Nice tests, Damien. I'll bet it smells like hell also :( How do you dispose of the "tested" cells? I was told to soak them in salt water for a couple of weeks and throw into trash can.
 

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Discussion Starter #7
Yeh the cells have that sweet aroma! Lithium no.5 :D

We have a battery disposal bin where i work so they can go in there. Bet its the first time they will have seen a lithium!
 

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I've looked at the minibms on offer here and its not a bad solution. Any cell exceeds the setpoint charger is disconnected. If a charger failed full on then a 1 amp shunt across each cell will just make a bad situation worse.
Many use the minibms to turn off an AC relay on the power input to the charger on an HCV event. I think Dimitri may even sell a relay for this. You can also purchase the minibms without the shunts.
 

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Many use the minibms to turn off an AC relay on the power input to the charger on an HCV event. I think Dimitri may even sell a relay for this. You can also purchase the minibms without the shunts.
Is he still selling them without the shunts? The website seems to have removed many of the options previously available and the only choice now, at least provided through his storefront site is HVC voltage of 3.6v or 3.8v. No option for one without a shunt, if I remember right I think there was a part that said if you don't want a shunt to remove it. I know back when this was actively discussed in the development thread still, there was talk of a DIY option but I'm not entirely sure if that is still an option.
 

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Is he still selling them without the shunts? The website seems to have removed many of the options previously available and the only choice now, at least provided through his storefront site is HVC voltage of 3.6v or 3.8v. No option for one without a shunt, if I remember right I think there was a part that said if you don't want a shunt to remove it. I know back when this was actively discussed in the development thread still, there was talk of a DIY option but I'm not entirely sure if that is still an option.
You can just clip off the shunt resistors.
 

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Is he still selling them without the shunts? The website seems to have removed many of the options previously available and the only choice now, at least provided through his storefront site is HVC voltage of 3.6v or 3.8v. No option for one without a shunt, if I remember right I think there was a part that said if you don't want a shunt to remove it. I know back when this was actively discussed in the development thread still, there was talk of a DIY option but I'm not entirely sure if that is still an option.
I hate to hijack the thread, apologies to OP in advance.

I no longer offer shuntless to simplify ordering and production process, but I stated in product description that clipping off ceramic resistors effectively kills shunting feature, while leaving red LED function, which can be useful to observe end of charge. AC relay is very effective to prevent rogue charger behavior.

Nice Headway testing, BTW, those poor bastards didn't stand a chance at 24V per cell :D
 

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Thanks for the destruction tests - very entertaining! :D

I had the same explosive results with headway's 18650 cells and a soldering iron.

I've been running a (5p) x 24s headway 38120 pack (10AHr) for a year now with several hundred EV miles on them with no problem. My recommendation: use a high voltage cutoff shunting BMS (mine is set to 3.69v) which prevents over charging of cells. I'm in the process of expanding to (8p) x 24s and will keep the same BMS in place. It's worked well for a year, I'll keep it as long as I can. I really think flying "naked" with no HVC/LVC on these cells is a bad idea. If you read voltages by hand on your cells then ok, but who as the time to do that?!

Thanks again for the forensics on HW cell failure.

Cheers,
--Adam
 

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Discussion Starter #14
Latest tests on some 8ah p cell samples from "ecitypower". Less cell and more mortar tube. Tested 2 just to be sure. More to come ........
 

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Jack,
Do you have any idea how much space is required between the bolt end and burst disc to allow it to operate normally? I will be using slightly longer bolts on mine but still have a small gap. Thanks
 

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Dear Jack,
Thanks for your test.
It looks like a man wants to test a parachute, but if someone lock the parachate-opening deployment parachute, if he jumped down from the airplane with this parachuat, what will happen then...?
OK , it's just for an instance here.
But the same reason, you had used a long bolts, and the bolts had locked the burst disc.
We had done this kind of destructive test already!
The length between the bolt end and burst disc can not exceed 6mm!!

E-mail: [email protected]
MSN: [email protected]
Skype: lorainy0
 

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Thanks Lorraine. I did the long bolt test just to prove the point. Can you please explain the differences in the codes on the cells ie JC23 etc and the revised design of the positive endcap?
 

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Thanks Lorraine. I did the long bolt test just to prove the point. Can you please explain the differences in the codes on the cells ie JC23 etc and the revised design of the positive endcap?
Yes, we had revised the positive endcap, there were 4 holes at the side of the old endcap, it's a little hard to do the holes on the side, even easy to cause out of shape. so we have the holes on the top of the endcap now, there are 8 smaller holes now.
 

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Jack,
Do you have any idea how much space is required between the bolt end and burst disc to allow it to operate normally? I will be using slightly longer bolts on mine but still have a small gap. Thanks
jehan,

Bolt/screw head, spring washer, flat washer, connector plate, then < 6mm of thread into the anode end of the cell. If more than 6mm it will prevent the anti explosion valve from functioning properly.

So in short, the length of the bolt or all-thread should not extend more than 6mm into the anode end of the cell.

Hope this helps!
 
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