thank you for posting all this!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...
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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...
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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.
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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
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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
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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
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I decided to go with the 'Webber" flexible bus bars however. For a mobile application something flexible seems the way to go.
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.
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? ThanksI 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..,
Inquiring minds want to know?@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?
@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?
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.
My biggest problem with what you are describing is if clamping were only needed ‘during the initial charge cycles’, why wouldn’t that be done by the manufacturer / EVE before shipping (as the final step of manufacturing)?kgf is an informal or casual engineering term and relates to a unit of mass (the kilogram, hence kg. The remainder is f for force. Kilograms force) and should also be accompanied by some other unit of measure such as area, time, etc to provide a specified relationship of work.
Since we are discussing an applied mass force upon a surface area of the battery, the second unit of measure is typically expressed in either mm², cm² or m², etc. If it represented mm², the cells would be crushed if the force applied was equal to 300 kgf/mm² and the cells would also be crushed by 300 kgf/cm². it would be like you standing on a tin can and it buckling under your body wiegth.
300 kgf is the expressed force for the EVE LF line of prismatic batteries and all have far different surface areas, some more than double the smaller LF batteries. But all use the same 300 kgf term without ever expressing the second unit of relational measure. Therefore the reader is forced to engage in some form of rationalized consideration.
The applied force need not be great, these aren't balloons and the gasses will escape through the valve at the top of the battery as they form during the initial charge cycles. Some of the gasses are hydrogen and so forth. It depends on the chemical reaction that's occuring. But all that's needed, is to keep the walls of the batteries flat as possible during the intial charge cycles. Adding too much force can cause the electrolytic compounds to be crushed into thinner layers at the center and becoming thicker about the perimeter of the electrodes, not adding enough force will result in the formation of bubbles within both the region between the electrodes and the electrolytic compounds and the electrolytic compounds themselves. Therefore causing thicker gass infused electrolytic compound layers nearer the center of the electrodes.
You can argue this all you like and swear up and down otherwise but in the end, it is what it is.
This proccedure has nothing to do with restraining batteries in an automobile. This is a wholly seperate matter and is a procedure to degass new lifepo4 prismatic batteries. There's nothing more to it than that. Whether your application is home energy storage, automotive energy storage or you're using these batteries to power your aircraft... Whether you decide to degass them when new or not is up to you and you're free to believe whatever you like, to the contrary or not.
And again, all the EVE manufacturer literature shares the same 300 kgf unit for the entire LF prismatic lineup regardless of amp hrs/size.
I have built batteries with and without compression. Based on what I’ve seen with my own...
I have seven 4S batteries with EVE LF280N that have been under 640psi for almost three years in a mobile application, they aren’t crushed yet;-)
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Yes thanks, typo 640lbs total across the face.Probably a typo ..... instead of PSI .... Lbs?
Is that even a serious question here?I have seven 4S batteries with EVE LF280N that have been under 640 pounds of compression
for almost three years in a mobile application, they aren’t crushed yet;-)
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I was responding to post 242 talking about crushing the cells.Is that even a serious question here?
My 16S 280Ah cells have been in a 300Kgf clamping fixture for over 3 years now with absolutely no signs of crushing…