# how to hold Li cells together?



## tomofreno (Mar 3, 2009)

Hi Dan,

The copper straps have a slight bend in them to provide the flexture for movement between cells. The cells don't swell unless you greatly overcharge them. It is not an issue generally. I just used the ss threaded rod and end brackets shipped with the cells for clamping. Haven't had any issues. Cell terminals are always cool after a drive.


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## dtbaker (Jan 5, 2008)

hhhmmm, ok. Seems like a bend in strap would help w/ cells moving together/away, but not in shear. I guess you just have to trust the all-thread and clamps hold everything together tightly. Did the straps come with cells as well? how wide/thick are they?


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## madderscience (Jun 28, 2008)

at least some of the resellers supplying LiFePO4 are doing so with the cells pre-banded into 12V modules (4 cells each). My understanding is you MUST keep the cells supported to keep them from swelling over time, even in normal use. The bands I have seen consist of stainless straps across the cells and heavy aluminum plates on either end.

Of course, I am still just dreaming about the day I go Li.


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## dimitri (May 16, 2008)

If you go with ThunderSky cells, they come strapped in groups of 5, not 4.

Its best to use them with straps they come with, unless your pack configuration requires restrapping in different group sizes. TS straps are pretty good quality and fit into battery boxes pretty well. You'd make your life a lot easier if you can use original straps in groups of 5 cells.

Hope this helps.


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## O'Zeeke (Mar 9, 2008)

dimitri said:


> If you go with ThunderSky cells, they come strapped in groups of 5, not 4.
> 
> Its best to use them with straps they come with, unless your pack configuration requires restrapping in different group sizes. TS straps are pretty good quality and fit into battery boxes pretty well. You'd make your life a lot easier if you can use original straps in groups of 5 cells.
> 
> Hope this helps.


Dimitri, could you give an approximate dimension the end plates add? I am waiting for TS 160's and want to start on the boxes. Thanks


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## dimitri (May 16, 2008)

O'Zeeke said:


> Dimitri, could you give an approximate dimension the end plates add? I am waiting for TS 160's and want to start on the boxes. Thanks


Sorry, mine are sunk in the battery box without immediate access with measuring tools. Those 8 I have under the hood have been restrapped, so I can't use those for measurements. I would recommend to wait until you have them sitting in your garage, so you can physically place them together and measure. I left 1/8" spacing around cells just in case, you can always fill that with a plywood or some shims.


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## RKM (Jun 9, 2008)

O'Zeeke said:


> Dimitri, could you give an approximate dimension the end plates add? I am waiting for TS 160's and want to start on the boxes. Thanks


I had to reassemble my TS cells into larger groups. I have spare end plates in the shop. I'll calliper and get back to you on the thickness. My memory is that each plate is .370 inches thick. I'll double check that. 

Rob


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## O'Zeeke (Mar 9, 2008)

RKM said:


> I had to reassemble my TS cells into larger groups. I have spare end plates in the shop. I'll calliper and get back to you on the thickness. My memory is that each plate is .370 inches thick. I'll double check that.
> 
> Rob


Thanks Rob,


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## azdeltawye (Dec 30, 2008)

RKM said:


> I had to reassemble my TS cells into larger groups. I have spare end plates in the shop. I'll calliper and get back to you on the thickness. My memory is that each plate is .370 inches thick. I'll double check that.
> Rob


Remember to add the height of the screw heads which attach the banding straps to the aluminum plates ~ 1/8".

The overall length of a 5-pack of TSLFP160AH cells measures 14-7/8" long. This includes the end plates and screw heads.

The width is 7-3/16".


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## RKM (Jun 9, 2008)

O'Zeeke,

I have spare end plates in the shop, but can't locate them!! My notes show an allowance of .750" for the pair of plates, so I expect .370" per plate to be correct.

Darren makes an important point to allow for the strap and screw. Some of the straps on my packs had several spacer washers between the end plate and the folded end of the strap, to take up slack. This could add as much as .250", including the screw head. 

Rob


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## GizmoEV (Nov 28, 2009)

dtbaker said:


> Which also begs the question WHY go with rigid straps? Seems it would be easier on the terminals to use flexible cable... or is it because the distance between cell posts is too short to use lugged cable?
> 
> Lastly, if straps are the best choice to use between cells, are there any tricks to build in a little compliance so that vibration is not so much of an issue? Or, are the straps too thick to allow any 'spring'? How thick do they need to be to carry 1000 amps?


I went to a friends house and took some measurements of the straps which came with his TS-LFP100AHA batteries from EVComponents. There were two types, one with 4 laminations and one with 5. It doesn't show in the picture but the 5 lamination version was 0.098" thick.


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## dtbaker (Jan 5, 2008)

thanks for pix! Interesting that they use heat shrink to hold to gether the laminations, but leaves me wondering WHY not use a single strip .1 or .125 thick?


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## GizmoEV (Nov 28, 2009)

Using multiple strips allows it to flex more so it doesn't put as much strain on the battery posts with the slight movement the batteries may go through. Much like the difference in stiffness of solid wire vs. stranded wire. That is also why there is a bend in the middle.


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## dtbaker (Jan 5, 2008)

so... why not go with stranded cable?


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## MJ Monterey (Aug 20, 2009)

Cost. You can machine cut those copper plates for very close to zero compared to the cost to crimp cables.


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## Guest (Jan 8, 2010)

Shrink tubing is also for looks and protection from dropping things in bad places.


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## etischer (Jun 16, 2008)

Electrons travel on the surface of the metal, there is more surface on a laminated bus bar compared to a solid bar. The laminated bar can carry more current



GizmoEV said:


> Using multiple strips allows it to flex more so it doesn't put as much strain on the battery posts with the slight movement the batteries may go through. Much like the difference in stiffness of solid wire vs. stranded wire. That is also why there is a bend in the middle.


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## Lordwacky (Jan 28, 2009)

etischer said:


> Electrons travel on the surface of the metal, there is more surface on a laminated bus bar compared to a solid bar. The laminated bar can carry more current


While this is technically true. There is essentially no difference with DC current, or low frequency AC. Also with DC current the laminated straps will essentially act as an equivalent solid bus bar. 

The main reason for lamination that I can think of is for mechanical reasons.


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## GizmoEV (Nov 28, 2009)

dtbaker said:


> so... why not go with stranded cable?


Primarily cost. The straps came with my batteries any way. I would prefer braided connections because they are more flexible still but as others have pointed out, they would cost more.

For DC current the shape of the conductor doesn't matter much because the electron flow is nearly consistent throughout the conductor. Remember we are talking high current, not static or HF AC. My rough measurements show the cross sectional area of the straps to be a little less than my #1 welding cable. My Gizmo came with #4 which would be slightly warm after climbing my hill. The #1 cable I replaced it with feels the same temp as ambient after the same climb. I haven't checked but I suspect the straps are probably close to #2 cable. If after I get my LiFePO4 pack installed I'll check the temperature of the straps to see if they warm up. I figure I can easily add one or two laminations to them if I wish.


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## wejank (Jan 6, 2010)

Maybe cable was lead to shot circuit easily when hit the copper located in the two sides on each cell.
I have ever saw the process of assembling the whole battery.
First,connect every cell tightly by welding,then band them with tape to prevented they were loosed like vibrated phnomenon in the way of transportation,
The last step,cover the battery pack with heat shrink.


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## Overlander23 (Jun 15, 2009)

Looks like the battery boxes I built for my TS160 cells aren't quite big enough to handle the cells plus the generous end-plates that Thundersky provide without some serious box modifications.

Anyone have an opinion on losing the stock TS banding hardware and going with something like multiple bands of poly or steel strapping? The kind that is used to contain crates, etc?

Or will this idea still allow for too much end swelling? I just need something a little more low profile.









Edit: Looks like I'll either have to add reinforcement to the box sides (possible) and allow the box to do the containment or figure out a thinner but rigid enough end-plate system.


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## GizmoEV (Nov 28, 2009)

I don't know how much stretch those bands will have compared to the SS bands that TS uses but I think if you don't have some sort of rigid end plate you will get bulging on at least the end cells. I had to rebundle my TS100s in sets of 10 cells so I just had a local sheet metal shop cut some SS straps for me and I drilled and bent them to use the TS end plates. If you are using two strapped bundles end-to-end you could maybe do the same thing I'm doing.

David Nelson


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## Lordwacky (Jan 28, 2009)

This what I'm doing. I'm not sure how well it is going to work, but I think it will be sufficient. I cut pieces of 0.06" diamond plate for end caps then just used the packing strapping you show above. It seems to work ok, but the cells are still pretty slippery and will slide up and down and left and right, which causes problems when the notches line up (very frustrating). What I did to prevent left and right slipping is I cut strips of (1/8", I think) lexan and drove them down inbetween adjacent batteries. This does a nice job of locking them in place, kinda like legos. 

If I had to redesign what I'm doing. I would not use the braided strapping, I would go with some kind of solid strapping material (probably solid plastic, metal makes me a bit nervous). I would definitely not use the stupid buckles either I would go with a crimp on clip. 

edit: Oh and I wouldn't use Diamond plate either I would use flat Al plate and chamfer the edges, the braided strapping doesn't like sharp edges.
hope this helps


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## dtbaker (Jan 5, 2008)

I like the idea of a strip down one slot to keep them aligned, but would leave most open for cooling. If you are that close on ends of your box.... can't you just drive in some rigid shims on the ends? smooth AL plate, or plywood? No straps required! Leave a hook or hole at top edge to grab and pull out!


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## Lordwacky (Jan 28, 2009)

I only put in two strips, one on each side... most of the holes remain open


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## Amberwolf (May 29, 2009)

dtbaker said:


> I like the idea of a strip down one slot to keep them aligned, but would leave most open for cooling.


If you wanted to use strips for alignment/locking *and* improve cooling, you could use aluminum strips that are long enough to stick up beyond the tops of the batteries far enough to act as radiator fins. 

They may not help, and if there is sufficient air gap between them and the cells over their length it's possible they'd even hinder cooling compared to having holes in the bottom of the battery boxes that line up with the gaps, and simply allowing (or forcing) airflow in the gaps instead.
________
Live sex


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## pm_dawn (Sep 14, 2009)

Overlander23 said:


> Looks like the battery boxes I built for my TS160 cells aren't quite big enough to handle the cells plus the generous end-plates that Thundersky provide without some serious box modifications.
> 
> Edit: Looks like I'll either have to add reinforcement to the box sides (possible) and allow the box to do the containment or figure out a thinner but rigid enough end-plate system.


I would say reinforce the outside of the box on one side and then drill holes directly into the box. Used threaded rods (like 6 or 8 mm SS rods) make sure they follow the lines in the cells. They will take almost no space inbetween the rows of cells. Then cut a large endplate at the other end that you put inside the box. That way you both secure the cells in the box and keep them compressed. I think a diamond plate like lordwacky had would do.
I think three rods in the ends and two between each row will be good enough. 

This is what I would do. And WILL do this summer when I rebuild my boxes.

Best Regards
/Per Eklund
Sweden


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