Best practice for 300kgf ‘fixture’ 280Ah cells

[Solar123456]

My battery is non-stationary, so I’m really not worried about vibration.

My 5/16” threaded rods were shorter than I needed, so 5/-6” bolts + long coupling nuts was the easiest way to get the extra length I needed…

Mine will also be non stationary as it will be in my camper van so I was planning to use an anti vibration mat like the one linked below or similar to go underneath them.

For busbars, I ended up making my own out of flexible welding cable to help minimize impact of vibration.

https://www.amazon.com/dp/B06XBVWGS3/ref=cm_sw_r_cp_api_glt_fabc_NZR72FE16T4X1XGGQN34

 

[fafrd]

Mine will also be non stationary as it will be in my camper van so I was planning to use an anti vibration mat like the one linked below or similar to go underneath them.

For busbars, I ended up making my own out of flexible welding cable to help minimize impact of vibration.

https://www.amazon.com/dp/B06XBVWGS3/ref=cm_sw_r_cp_api_glt_fabc_NZR72FE16T4X1XGGQN34

Boy, talk about a typo - I meant stationary (and apparently typed the opposite).

I also made flexible busbars out of 2/0 welder’s cable, but just because I was concerned about the stress caused on the aluminum terminals from solid busbars combined with cell expansion & compression…

 

[Solar123456]

Boy, talk about a typo - I meant stationary (and apparently typed the opposite).

I also made flexible busbars out of 2/0 welder’s cable, but just because I was concerned about the stress caused on the aluminum terminals from solid busbars combined with cell expansion & compression…

Haha, yeah that happens. Thanks again for all your help, I appreciate it. I will post pics once I complete the build.

 

[Solar123456]

@fafrd
Just received all of my components and will start building soon. My goal is to build an enclosure as well for the batteries.

So my build will consist of two compression packs with 4 cells each with 3/4 inch ply each side and springs only on 1 side of each build. Both will be next to each other each having their own springs and 3/4 inch piece of plywood.

I was thinking about having them share plywood on the opposite side that is springless. So I’m that side instead of them having their own separate piece of wood they would instead share a larger piece that is also screwed into the battery box bottom. This would all me to create sides which is almost a whole fixed enclosure with the exception of the sides with springs. Would having them share the side opposite the springs mess up the compression?

Essentially two compression packs that share the same backing plate on non spring side?

 

[onemanvan]

It seems as though there are an infinite number of ways to build a fixture for a 4s 280ah battery.
FWIW this is the approach I took...







This battery is for my van camper which I primarily use during the summer to escape the desert heat of southern Arizona. I wanted to be able to easily remove the battery when the van is not in use for the 8 months I spend at my winter home. During the shoulder seasons the temperature in the van regularly exceeds 100 degrees - which is not good for the battery!

Space constraints dictated the design, in particular the overall length. IMHO this design offers some advantages over other approaches. For example: the threaded rod in combination with the binding barrels reduces the overall length and takes some of the guesswork out of 'fixture compression'. The components I used resulted in about the right amount of compression. IE: After the pack is fully assembled you tighten the binding posts all the way, this puts an equal amount of compression on the pack, no need to guess how much torque to apply to the nuts on the threaded rod. If you need more or less compression simply add or remove some washers.

I felt it was important that the threaded rod & binding posts be manufactured with tight tolerances, which I believe these are. It was not necessary to modify the length of the threaded rods. The 8" x 8" aluminum plate works out to be just the right size. So all you need is a hand drill to make the holes in the end plates and a pair of scissors to cut the foam & neoprene separators.

I read somewhere on this thread that Norseal was recommended to use between the cells. The silicone foam I chose had very similar characteristics to what was recommended at about 1/3 the cost. I placed that material between the cells and placed neoprene on the aluminum end plates. The end result is a fairly compact monolithic block that exhibits no lateral flexing or twisting...





The total cost for this approach is quite high! McMaster Carr sells premium products at a premium price! However - as I said - space constraints forced me to keep the overall length to an absolute minimum. No doubt some of the components could be substituted with something less expensive. I present this BOM as a guide for what to consider when choosing components.

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

 

[mrdavvv]

Minimal and functional, excellent work.

 

[Marinepower]

That is a very nice build! I have never seen the "binding barrels" before and it's a great space saver. Wish I had seen this before making my compression solution.

I decided to go with the 'Webber" flexible bus bars however. For a mobile application something flexible seems the way to go.

Here is my messy setup with the Weber busbars. I am also very space constrained.

I also used 1/4 aluminum for the end plates for the compression, but I vinyl wrapped the end plates so they don't become an electrical conductor from one plate to the other via the threaded rods. I also had an aluminum battery tray fabricated (hard to see in image) , so if the electrolyte in the cells ever leaks, it stays contained for disposal.

MP

 

[curiouscarbon]

It seems as though there are an infinite number of ways to build a fixture for a 4s 280ah battery.
FWIW this is the approach I took...

View attachment 79232

View attachment 79211

View attachment 79212

This battery is for my van camper which I primarily use during the summer to escape the desert heat of southern Arizona. I wanted to be able to easily remove the battery when the van is not in use for the 8 months I spend at my winter home. During the shoulder seasons the temperature in the van regularly exceeds 100 degrees - which is not good for the battery!

Space constraints dictated the design, in particular the overall length. IMHO this design offers some advantages over other approaches. For example: the threaded rod in combination with the binding barrels reduces the overall length and takes some of the guesswork out of 'fixture compression'. The components I used resulted in about the right amount of compression. IE: After the pack is fully assembled you tighten the binding posts all the way, this puts an equal amount of compression on the pack, no need to guess how much torque to apply to the nuts on the threaded rod. If you need more or less compression simply add or remove some washers.

I felt it was important that the threaded rod & binding posts be manufactured with tight tolerances, which I believe these are. It was not necessary to modify the length of the threaded rods. The 8" x 8" aluminum plate works out to be just the right size. So all you need is a hand drill to make the holes in the end plates and a pair of scissors to cut the foam & neoprene separators.

I read somewhere on this thread that Norseal was recommended to use between the cells. The silicone foam I chose had very similar characteristics to what was recommended at about 1/3 the cost. I placed that material between the cells and placed neoprene on the aluminum end plates. The end result is a fairly compact monolithic block that exhibits no lateral flexing or twisting...

View attachment 79213

View attachment 79214

The total cost for this approach is quite high! McMaster Carr sells premium products at a premium price! However - as I said - space constraints forced me to keep the overall length to an absolute minimum. No doubt some of the components could be substituted with something less expensive. I present this BOM as a guide for what to consider when choosing components.

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

View attachment 79217

thank you for posting all this!

looks awesome!! so minimal and looks robust??

 

[onemanvan]

I decided to go with the 'Webber" flexible bus bars however. For a mobile application something flexible seems the way to go.

I agree with you regarding the flexible bus bars. However, my cells came with welded studs. The contact area is very minimal. IE: the studs are 6mm, the contact area is 10mm & the flexible bus bars have an 8mm hole. I tried using washers to help improve the contact area but that introduced a 10 mv voltage drop between each cell. I tried both braided & multi layer copper. I purchased them during my long wait for the cells. That was about a year ago. At that time the only braided or multi layer copper bus bars I could find had 8mm holes. It wasn't until I received my cells that I realized how tiny the contact area was on the welded studs! My 'fixture' should minimize the possibility of the studs moving relative to one another. I'd rather cross that bridge if/when I come to it as opposed to having a 10 mv voltage drop between each cell. NOTE: I measured 10 mv drop between the cells at 30 amp charge/discharge. In this video Ray details how he encountered the same issue, IE: he attempted to use washers to increase the contact area but if anything it made things worse. Thanks for the suggestion regarding the Weber bus bars. Since they have a 6mm hole vs the 8mm hole I may give them a try...

 

[Emporium4579]

For example: the threaded rod in combination with the binding barrels reduces the overall length and takes some of the guesswork out of 'fixture compression'. The components I used resulted in about the right amount of compression. IE: After the pack is fully assembled you tighten the binding posts all the way, this puts an equal amount of compression on the pack, no need to guess how much torque to apply to the nuts on the threaded rod. If you need more or less compression simply add or remove some washers.

Really nice and clean install and thank you for sharing your materials list.

Follow-up question, I'm confused by your description of the compression effect. After reading 12 pages of calculating spring constants and washer stacks, how did you arrive to this compression approach and how did you calculate how many washers are required? It looks like you're just using lockwashers on both ends?

 

[russellribeiro10@gmail]

I know the subject of the 300kgf ‘fixture’ (compression clamp) to extend cycle life of 280Ah LiFePO4 cells manufactured by EVE from 2500 cycles without fixture to 3500 cycles with fixture has been discussed in various threads on other subjects, but I could not find any single thread dedicated to that subject and now that I have my 280Ah cells and am beginning to think about how to assemble my battery, I am interested in current ‘best practices’ on this subject.

I have run my first charge and discharge cycle without any clamp/fixture and the cells do swell quite a bit.

So if the fixture is calibrated to 300kgf when the cells are empty, force is likely to far exceed that level once the cells are full.

And if the cells are filled before the clamp/fixture is calibrated, already-established swelling is likely to distort the battery far more than if a constant force of 300kgf had been applied during charging.

So my current thinking is to calibrate the clamp/fixture when close to empty (at least not yet bulging) and then to recalibrate every 0.1C or so as the battery charges to full.

There will still be less than 300kgf as the full battery dischargres but when bulging gets most extreme, there should be 300kgf in counter force and overall stability of cell position should be good.

Anyone else who has already faced this issues and solved these problems care to chime in?

My current plan is to use two 1/2” ABS plastic endcaps and two threaded rods per side to create the clamp/fixture.

If anyone has found a good solution to putting an entire 8S 24V 280Ah battery into a stock case with a 300kgf clamping fixture solution, I’m also interested in that..,

Hello guys. I read below to learn this issue of 300kgf to be applied to the cells in order to improve their qty of cycles. This is all fine and I think I understood. I am planning to use two pieces of plywood at each side of 4 3.2V cells and thigh them with 4 rods, two at each side. However I am wonder how to measure these 300kgf when using my wrench toll to tight the nuts of the 4 rods. As far as I understand 300kgf is 2942 Newtons. This is a lot of force. I have a digital Torque toll that an measure up to 300N. So my questions is. How do you guys measure these 300kgf? Thanks

 

[Hedges]

Torque wrench measures newton-meters of torque.
Would think simple geometry would translate that to clamping force, but friction plays a big roll. Look up clamping force vs. torque for a given screw thread, also a function of material.

What some people have done is to use springs, which have a particular force vs. displacement. The spring acts as a scale, and provides compliance as batteries swell with charging, shrink with discharging. (some people put a support under the batteries so they don't fall out when lifted.) Given an anticipated amount of swelling, you can select spring length so pressure remains within desired range.

Not everybody is clamping. And I don't think we've seen any commercial designs with springs for clamping.

Search results for query: compression

diysolarforum.com

 

[Tradewinds63]

Uhhh. Big time misunderstandings in here about clamping/fixtures and it's purpose... This is an initial few charging cycles degasing procedure for NEW batteries only.

Firstly, I hope none of you applied 300k force to your battery cells.

300kgf in its expressed context by the manufacturer means 300kgf/m2 (something they need to share for the average person). That translates to 0.0003 k per mm² or 0.427 pounds per inch².
Next step is finding the square area of the batteries planar face you intend to clamp and converting the force accordingly. For an LF105 as an example, the compression plane of the battery is 200.5mm X 130.3mm = 26,125.15 mm².
.0003 k X 26,125.15 mm2 = 7.837545 k force or 17.279 pounds applied force.
That's ONLY 17.279 lbs force applied to the the whole series or a single cell. Like having a 17.279 lb cat sitting on something, compressing it, that's all.
If you have different cell amps... You need to find the plane area of your battery and apply the force as provided in the example above.

You also need to know that this force is applied at 30% soc or roughly 3v per cell. AND this fixture state is used for the INITIAL 3 to 5 charging cycles ONLY!
If you didn't do it to your batteries when new... don't bother now, it wont help. If you didn't perform the procedure when new, the gas bubbles will have already caused the damaging seperations between your cells electrodes and their electeolytic compounds and you can't squeeze them back out now. This proceedure is about not providing them the ability to form the early gas seperations to begin with.

To perform the degassing function upon your new cells after you've applied the clamps with the proper force...
The batteries should be fully charge and then discharged to 30% SOC, 3 to 5 times. Once this has been done, the EARLY excess produced gasses will have been purged through the gas valves and the potential gas seperation between the electrodes and the electrolytic compounds is effectively diminished and your cells will be more efficient and provide more cycles than if the degassing function isn't provided.

The clamping fixture is not intended to be permanent and should be removed after this operational procedure phase is complete, this, to allow some minor cooling space between batteries during the banks service life.

I'll do a video later and provide a link here about how to apply this force using a simple scale and jig and using steel strapping clamps with wood ends. It's actually very simple to perform and can be done in many different ways.

 

[Bob B]

@Tradewinds63
Quite some time ago, one of the forum members ..... @ghostwriter66 ....... had a conversation with EVE engineers who verified the specified clamping force. Going from memory, It worked out around 12- 15 PSI ... You'll probably be able to find posts around that conversation with a little searching of the forum ........ Where did you get your information?

 

[Skypower]

clearly we’ve all been wrong according to tradewinds.

 

[Skypower]

@Tradewinds63
Quite some time ago, one of the forum members had a conversation with EVE engineers who verified the specified clamping force. It worked out around 15 PSI ... You'll probably be able to find posts around that conversation with a little searching of the forum ........ Where did you get your information?

Inquiring minds want to know?

 

[Bob B]

@Tradewinds63
Quite some time ago, one of the forum members ..... @ghostwriter66 ....... had a conversation with EVE engineers who verified the specified clamping force. Going from memory, It worked out around 12- 15 PSI ... You'll probably be able to find posts around that conversation with a little searching of the forum ........ Where did you get your information?

At that time, some of the EVE spec sheets detailed a gain in cycles if compression was properly applied.

Since that time, there has been a LOT of discussion surrounding compression ...... As a practical matter, it seems that calendar aging may override any difference in longevity gained from compression .... and serious attempts to achieve the specified compression has fallen out of Vogue.

 

[HRTKD]

For those of us with LiFePO4 cells in mobile environments, clamping is not optional.

 

[upnorthandpersonal]

Uhhh. Big time misunderstandings in here about clamping/fixtures and it's purpose... This is an initial few charging cycles degasing procedure for NEW batteries only.

No, cyce life is determined with a fixture. Cycle life without fixture is lower than with fixture in place.

Source: EVE, CATL engineers, my test lab.

 

[upnorthandpersonal]

Also, see this:

LFP Aries pack in Tesla. Zoom in on the chart in this video (it's very readable in Highest Definition) at this time stamp:

A little further on in the video (16:00 timestamp) you can see the LFP Tesla pack with prismatic cells in their fixture.