# Life04 battery straping/tieing together how many is the max



## evnz (Jul 24, 2010)

If i stap together to stop bolaging am i best to have them in 4,5,6 cell packs i need 6 to fit across the deck if not adviserable i will rethink setup before it is to late
Thanks
Owen


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## Ziggythewiz (May 16, 2010)

Whatever you can easily lift in case you need to remove and restrap.


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## onegreenev (May 18, 2012)

You can't stop bulging by strapping. Strapping only hides bulging and bulging is a result of overcharging, overdischarging or leaving your cells to bake in the hot sun for hours on end. The last being the least to worry about. You only strap them to hold them from moving. Nothing else. If you overcharge or over discharge you will swell the cell but being strapped tight you will not notice but the cell is still damaged and swollen. Just because you don't see it does not mean it is not swollen.


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## skooler (Mar 26, 2011)

onegreenev,

I think you are wrong, cant find the source but....

I was always under the impression that less electrolyte is damaged when the cells are strapped or clamped as the electrolyte has less room to move around and expand meaning that the plates / foils inside the cell do not move apart. 

Hence why cells such as the A123 pouch cells with no propper casing need to be clamped down.

I'm not arguing that overcharging, overdischarging or letting them cook will damage the cell. Just that it is less damaged when strapped or clamped under these conditions.

Happy to do some testing to confirm!

Cheers,

Mike


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## Ziggythewiz (May 16, 2010)

Simple physics says stuff stays in solution better at higher pressures. Obviously if you mistreat your cells they will suffer no matter what you do, but since the manufacturers recommend clamping, I'm sure there is at least a small window where damage would be prevented or lessened by clamping vs no clamping.

If you don't mistreat them at all, I don't think clamping would have any effect either way. Much of what the manufacturers say stems from our (primarily Jack R) reported experience. They keep lowering recommended peak charge voltages, and the latest specs recommended staying out of the top and bottom 10%. I wonder if they even do any cell testing or if they just have some tech and pump it out of the factory AFAP to let us find out what it is capable of.


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## onegreenev (May 18, 2012)

No, not so. I have been sitting on a batch of cells that have been under high pressure within the battery case since 2008. These cells looked perfect with no bulging or venting. These cells were damaged by over discharging but you would never know by looking. I wanted to put them back into service but when I pulled them and released the clamping pressure these cells just bloated instantly into a pile of fat little piggies. I have already posted the photos and said what happened already. Clamping does not make help. It only hides a problem. Clamping is only to hold your cells. ONLY. 

When the cell swells the gas produced will not go back into solution and IF the cell were under enough pressure to cause that, the co2 is not part of the electrolyte. Then once you release the pressure it pops right out of solution anyway . Sorry but keeping them under pressure is total BS.


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## dougingraham (Jul 26, 2011)

skooler said:


> Hence why cells such as the A123 pouch cells with no propper casing need to be clamped down.


They don't need to be clamped down. If they puff from overcharge or undercharge they are damaged. Clamping the pouch cells will not prevent this at all. You cant clamp the edges so if you manage to clamp the flat faces well enough to prevent the bulging you will blow a seam seal or the seal around one of the tabs.

If they bulge from external heating they will probably recover when the temperature goes down unless they vent and lose the part of the electrolyte that boiled off. In that case clamping would be exactly the wrong thing to do.

In normal operation these cells do not change geometry. If they change geometry it is because something is wrong.


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## skooler (Mar 26, 2011)

I'm going to offer to do something testing on this to get a definitive answer.

I think the issue is not the buldging of the cells causing the breakdown of electrolyte, but the fact that the plates/films/foil inside the cells are not distorted from it's flat shape while it is clamped. Meaning there are not any internal shorts until the cells is allowed to expand.

The need for compression may not even be related to the overcharge/discharge issue

To be clear, I am not arguing that overcharging or discharging damages the cells.


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## onegreenev (May 18, 2012)

The gassing of the ruined cells is just that. GAS. Under pressure it will cause the plastic case to swell. Kept strapped it will only hide the fact that they are damaged. Once released from compression the cells swelled up even after 4 years of solid compression. The cells were cold and still expanded. The swelling of damaged cells within the plates won't be helped either by compression. The cells will still swell. Period. Compression won't stop or prevent damage. The outgassing is the RESULT of damaged cells not the CAUSE of damaged cells. Case swelling IS caused by OUTGASSING of electrolyte. Damage and swelling of the anode/cathode IS the RESULT of overcharging or over discharging. No compression will stop or make less the damage that results from over charging or over discharging. NO MORE TESTING IS REQUIRED. IT IS NOT A MYTH. IT IS OBSERVABLE FACT AND HAS BEEN SHOWN MANY TIMES. 

Sorry you don't believe the truth. 

Pete 

My posting is a direct RESULT OF ACTUAL DAMAGE. EVEN AFTER 4 YEARS THE ISSUE IS STILL THERE AND NO AMOUNT OF COMPRESSION HELD BACK THE DAMAGE. 

It only HID the problem for 4 Years.


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## EVfun (Mar 14, 2010)

onegreenev said:


> The gassing of the ruined cells is just that. GAS. Under pressure it will cause the plastic case to swell. Kept strapped it will only hide the fact that they are damaged. Once released from compression the cells swelled up even after 4 years of solid compression. The cells were cold and still expanded. The swelling of damaged cells within the plates won't be helped either by compression. The cells will still swell. Period. Compression won't stop or prevent damage. The outgassing is the RESULT of damaged cells not the CAUSE of damaged cells. Case swelling IS caused by OUTGASSING of electrolyte. Damage and swelling of the anode/cathode IS the RESULT of overcharging or over discharging. No compression will stop or make less the damage that results from over charging or over discharging. NO MORE TESTING IS REQUIRED. IT IS NOT A MYTH. IT IS OBSERVABLE FACT AND HAS BEEN SHOWN MANY TIMES.


Did you test the internal resistance of the cells before and after you unclamped the cells? The old Thundersky documentation indicated that overcharging caused the cells to gas and the internal resistance to increase. Keeping the cells clamped tightly minimized the loss of contact between the thin plates and separators and so minimized the increase in internal resistance. Capacity loss by overcharging was not supposed to be helped either way and is permanent. Thundersky even had a tool to re-compress a mildly bloated cell.


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## onegreenev (May 18, 2012)

No I did not test the resistance because it is not important. If the damage and loss of capacity has been done then checking resistance is moot. I would agree that you could keep some of the resistance down because the distance between the plates is kept to a minimum but the bloating is mostly outside the package. The plates are packaged tightly inside the cell and there is no indication that the gas bloating is causing any problem. The separation is caused because of mechanical changes within the anode/cathode and has nothing to do with gassing. Gassing is an indication you have screwed up. What I am going to do is take my most bloated cell from that pack that had been held tightly for 4 years and reclamp it and then open the top to release the gas and then tighten it back up and release the pressure again to see if the cell remains flat. 

I do not know how to check resistance. If I can do that I will check before I reclamp and again after as long as the cell takes a charge. That I can and will do. Can you help me with what is needed to check resistance? 

Pete


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## Ziggythewiz (May 16, 2010)

onegreenev said:


> Can you help me with what is needed to check resistance?


Check voltage drop at a known current.


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## dladd (Jun 1, 2011)

onegreenev said:


> I do not know how to check resistance. If I can do that I will check before I reclamp and again after as long as the cell takes a charge. That I can and will do. Can you help me with what is needed to check resistance?
> 
> Pete


You have a Powerlab 6/8, right? That will measure resistance for you.


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## EVfun (Mar 14, 2010)

The quickest way to check resistance would be a load test. The catch being you need a pretty good load (1/2C to 2C recommended) and it has to be repeatable. So many loads have drift, which could mask changes.

An accurate load about 1/2C for 10 seconds with the voltage recorded right before load cut-off would discharge the cell so little that you should be able to check again, after clamping and giving the cell time to flatten, without needing to charge the cell. The SOC change would only be 0.2%. Of course, that would only work if the SOC was somewhere in the 30% to 70% SOC range where the discharge curve is quite flat. 

These are some short quotes from the 2008 Thundersky document. For some reason I can't search, or copy, material from the it:

"Please use jigs and straps to fix the single cell or battery pack to avoid swelling for normal use!"

"The battery swelling usually happens when it is overcharged or over discharged."

"Discharge the battery pack to its standard minimum voltage and release the straps to replace the cell with new one of same capacity."

"Please use the renewer as the picture shows to make the case back to normal shape." 

This is a pair of plates, heavier than the standard plates they shipped with, with threaded rods to pull the cell thickness down. It wouldn't fix swelling on the short ends or top or bottom. If the plates the cells shipped with are in place I'm not sure how one could swell. When would this clamp would be needed? This is an old document, so sometimes the translation leaves a bit to be desired. 

This is an old document so some of the instructions are a bit excessive, belt and suspenders approach. We know now the cells are quite a bit tougher if you don't let them go over 3.8 volts or below 2.0 volts under load or 2.8 volts no load or allow them to get to hot. Still, my cells are strapped with the Thunder Sky hardware. It is a handy way to hold the cells down in the EV. When I re-bundled them I added threaded holes in the end plates (in case safe locations) so I could attach the blocks of cells by the end plates.


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## onegreenev (May 18, 2012)

So once you collect the information then what formula is used to plug in the numbers? I am also aware of the manufacturers thinking for strapping but once the damage is done its done. Strapping really only does COVER/MASK the resulting damage. It is NOT a fix or preventive measures. To keep from swelling you stay off the top and bottom. That is the only way to prevent swelling. Once swollen the damage is truly done and clamping does not change that fact. 


I'd like to see the cells vacuum packed within the plastic case and if any is left behind it should be nitrogen which is inert to help prevent any corrosion and to hold all internal things tight. A-123 pouches are vacuum packed. Vacuum compressed. Any gassing will puff them like a little puffer fish.


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## EVfun (Mar 14, 2010)

Resting cell voltage minus loaded cell voltage will give you the voltage drop. The voltage drop divided by current will give you the cell resistance. It actually varies slightly at different loads because only one part of the sag is actual resistance. That is why a consistent load is needed. 

As an example, my cells are right at 2.78 volts at 360 amps. 

3.3 - 2.78 = 0.52 volts.

0.52 / 360 = 0.00144 ohms, generally referred to as 1.44 milliohms.


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## bga (May 25, 2009)

The LFP cells are filled with an organic solvent in the electrolyte. At elevated temperatures, it has significant vapor pressure, so will swell the sides of the cells, particularly in the larger sizes.

The solvents are things like ethylene carbonate, dimethyl carbonate, diethyl carbonate. See http://en.wikipedia.org/wiki/Lithium-ion_battery#Electrolytes for more info.

They smell a bit like ether and have lowish boiling points, hence the need to physically contain the prismatic cells.


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## skooler (Mar 26, 2011)

bga said:


> The LFP cells are filled with an organic solvent in the electrolyte. At elevated temperatures, it has significant vapor pressure, so will swell the sides of the cells, particularly in the larger sizes.
> 
> The solvents are things like ethylene carbonate, dimethyl carbonate, diethyl carbonate. See http://en.wikipedia.org/wiki/Lithium-ion_battery#Electrolytes for more info.
> 
> They smell a bit like ether and have lowish boiling points, hence the need to physically contain the prismatic cells.


Just gave you positive rep for that 

Thankyou!


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## Jesse67 (May 12, 2009)

Back to the original question....

I have my cells strapped in groups of 6 and have noticed no problems so far, I can lift the groups out without much trouble but you have to make sure they are clamped tight to keep the middle cells from slipping out if you give a jerk on the handles! 
The only tricky part is making up new straps and finding a way to tighten them, mine were shipped in groups of 4. I made up straps that wrap right around the cells and the end plates and tighten with a 1.5" machine screw and nut pulling one end of the strap to the other. I tighten the bolt so the strapping all plays about the same note, nice and snug. With a good clamping system I wouldn't hesitate to clamp 12 cells together, they just get heavier to move and harder to get lined up initially.

And the excellent debate,

Everything I've read about clamping the cells is to prevent the plates from separating due the gasses produced during overcharging or abuse, you will still damage the cell and possibly reduce it's capacity but if you can keep the plates from separating the internal resistance will not increase as much and the cell should still be usable. High internal resistance causes excessive voltage sag and increased cell heating. 

This is one reason why cylindrical cells can generally take much higher current draws, the cylindrical shape is incredibly resistant to expansion due to the high tensile strength of the material and it's inherent shape, internal pressure puts the case in tension vs. mostly bending forces that are applied to the flat face of a prismatic cell under pressure.

In fact this discussion has made me realize that I have two cells which have higher internal resistance than the rest (more sag under heavy current draw than the average) I think I'll try tightening up those packs to see if I can bring them back down. I haven't noticed any swelling but perhaps some extra pressure will help out a bit. 

Jesse


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## EVfun (Mar 14, 2010)

Jesse67 said:


> Back to the original question....
> 
> I have my cells strapped in groups of 6 and have noticed no problems so far, I can lift the groups out without much trouble but you have to make sure they are clamped tight to keep the middle cells from slipping out if you give a jerk on the handles!


I have my 60 amp hour Thundersky cells banded in groups of 8. The bundles are tight enough that no cell from the center will even move. Each bundle weighs 40 lb. They have worked out well so far.


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