Pack / Cell compression Optimized By Using Springs.

[Capt Bill]

I wonder is somebody with flexible bus bars on 280Ah Eve cells in compression mode have done any testing on expansion and contraction vs SOC and various high Amp Charge n Discharge Cycles ... I wonder if solid bus bars might be OK with Compression, or really NOT OK (via putting stress on those battery terminals ????

 

[S Davis]

I wonder is somebody with flexible bus bars on 280Ah Eve cells in compression mode have done any testing on expansion and contraction vs SOC and various high Amp Charge n Discharge Cycles ... I wonder if solid bus bars might be OK with Compression, or really NOT OK (via putting stress on those battery terminals ????

I have my cells in a compression fixture at about 640lbs per square inch and they do move, they expand about half of the figure on the EVE data sheet. This is on the older version the LF280N. I ran my buss bars at a diagonal to reduce the direct pressure on the terminals.

 

[Capt Bill]

I have my cells in a compression fixture at about 640lbs per square inch and they do move, they expand about half of the figure on the EVE data sheet. This is on the older version the LF280N. I ran my buss bars at a diagonal to reduce the direct pressure on the terminals.

wow ... There is a figure for this??? "expand about half of the figure on the EVE data sheet.? I am going through a phase of being critical of these EVE Cell being supplied with those solid bus bars while also recommending (or not ???) Compression for longer life expectancy ... If Compression makes a difference, I think Flexible Bus Bars would be a very good idea, to supply with these LiFePO4 cells !!! My Two Cents

 

[CB-OTB]

Where’s the manual for the Eve cells?

 

[cinergi]

I wonder is somebody with flexible bus bars on 280Ah Eve cells in compression mode have done any testing on expansion and contraction vs SOC and various high Amp Charge n Discharge Cycles ... I wonder if solid bus bars might be OK with Compression, or really NOT OK (via putting stress on those battery terminals ????

Like S Davis, mine expands & contracts with SoC. No so much with temperature or C rate that I've observed. And I've now observed that rigid bus bars are a BAD idea in this configuration (resistance between bus bar and cell terminals have crept up and were fixed by re-seating; and when I went to check, I had to PRY the bus bar off the cells because they no longer properly fit).

 

[CharlesK]

Where’s the manual for the Eve cells?

Here is one in the Resources section.

EVE LF280 (3.2V 280Ah) Product Specification (Version E)-2019.7.5

Most recent Spec Sheet for the 280 LFP cells as provided directly by EVE March-14-2020.

diysolarforum.com

This is for EVE LF280-72174. If you go to Section 3. Drawing, you will note that they list two different thicknesses.
Thickness (30% SOC) 71.5+-1.0mm
Thickness (100%SOC) 72.0+-1.0mm
That would lead me to believe that the cells are expected to expand as they are charge, then contract as they are discharged.

The datasheet for LF280K-72174 can be found at:

Eve LF280K data sheet

This is the latest version of the Eve 280 amp hour cell. March 23, 2021

diysolarforum.com

Section 3. General Technical Parameter includes a chart with dimensions.
They list Thickness with different amounts of compression. (Too detailed to list here. A diagram in Appendix I is also referenced in the datasheet.)
Section 5.1 Electrical Performance is a chart that talks about cycle life at different ambient temperatures. The point to note is that the testing was conducted with the cells in compression as noted in Measuring Procedure.

There may be other data sheets for other EVE 280AH cells. These are just two that I found quickly.

 

[Gazoo]

But a box without springs provides no working length at all. When the cells are too "shrunk", the pressure is very low (and the cells may even flop around, rubbing against each other in an uncontrolled way).

That's very true and another reason it's recommended to put a spacer between the cells even if using springs. If using in a stationary environment like I do one doesn't need to be too picky although since watching my cells expand and contract, I have always recommended using braided bus bars no matter how the cells are mounted. I am happy Cinergi has posted his experiences and agrees

Of course, if using in a mobile environment, then one has to be more careful to keep the cells from flopping around. However there are a few on this forum who have compressed the cells with no springs and are using in a mobile environment with good results so far.

 

[Capt Bill]

That's very true and another reason it's recommended to put a spacer between the cells even if using springs. If using in a stationary environment like I do one doesn't need to be too picky although since watching my cells expand and contract, I have always recommended using braided bus bars no matter how the cells are mounted. I am happy Cinergi has posted his experiences and agrees

Of course, if using in a mobile environment, then one has to be more careful to keep the cells from flopping around. However there are a few on this forum who have compressed the cells with no springs and are using in a mobile environment with good results so far.

Gazoo; Question (or anyone with experience in this arena of examine and shared learning): In watching your cells expand and contract under compression, ... using braided bus bars: Have you notice slight bulges in you battery cells flattening out? Did you have slight bulges on the sides of your LiFePO4 cells? What Amp/hr cells are we talking about in your story? ... Asking Question like this for the educational benefits ;+)

 

[Gazoo]

I have the older 280ah cells and they are kinda like what was explained here. I did slight compression with a full SOC. I have not tried to flatten them out and I have not installed my braided busbars yet. Having said that I have noticed the cells expand while charging and contract when discharging. Keep in mind my cells are in a stationary environment and I am floating them at around 3.385 volts per cell as they are used with a UPS I ordered from China

 

[Capt Bill]

As I consider if I will compress my 280Ah cells or not, while noticing some slight bulges on sides of my mixed ages of cells from recent to two years old; ... I searched outside this forum on LiFePO4 Compression, and found this info recommending compression sooner vs later for LiFePO4 cells: I generally take everything I read as the opinion of the writer until I see more references: from: a Summary at https://batteryfinds.com/should-i-make-lifepo4-battery-compression/ (I have no other experience with linked website/ just included as my search reference for what I copied and pasted below ??? )
??? " ... LiFePO4 battery compression is an operation that should be done at the beginning of the purchase of the battery, and if the LiFePO4 battery pack after a period of use wants to make up for it, it is actually too late, because, ... ... each battery cell was deformed to varying degrees, and it was no longer suitable for compression at this time. "???

??? WONDERING: What Opinions from within the DIYSoalrForum might be on that ???

What I am really wondering about is IF I could get my 280 Ah Eve cells that have slightly wavy sides to go flat ... by switching to flexible bus bars, and applying compression. Might have to just go for it, and see what happens after other priorities are accomplished.

 

[Capt Bill]

Just saw good deal price for flexible braided copper bus bars on Docan Power's website (though says 32 min. order/ when I tried order; ... looks like it might go through w a battery order/ or explore via asking Docan for DIYSolar support for solo sample type order :

Gold M6 Size Flexible Busbar CAN BENT LiFePO4 Battery cells 280Ah 302Ah 304Ah 320Ah Metal Connector

ModelM6 size copper Flexible Busbar(Gold M6)Load current300AApply to Lifepo4270Ah, 280Ah, 302Ah 304Ah 310Ah 320AhMaterialCopperNormal torque＜0.7N.mSize190*20*2mm for 270Ah, 280Ah, 302Ah 304Ah 310Ah 320AhSize2Baided busbar 90*20*4mm for 270Ah, 280Ah, 302Ah 304Ah 310Ah 320AhSize379*20*2mm for 100Ah 10

www.docanpower.com

... I only need 28 for my 2 x 24v 280Ah LifePO4 Battery Banks. It looks like the 50mm wide braided is rated for 200 amps in China on Alibabaexpress. .. I was considering doubling up the Docan bus bars on my 280 Ah Eve Cells to make sure they could handle a 1.0C ... 280 Max Amp Flow to match the 300 Amp Breaker Fuses of each battery bank (for safety ... even though I likely not see that high of amperage).
The Amp specs are missing at Docan (so far) for mm2 vs; ... but here is some info from alibabaexpress; w the 50 mm2 rated for 200 amps, and wider 75 mm2 braided bus bars rated for 400 amps.

 

[HackNFly]

These springs are ~$4 each and easy to get.

Pack / Cell compression Optimized By Using Springs.

If each pack has independent plates on either end, you will get expansion/contraction on both ends even if the springs are only one end (so the center cell or two will be stationary with a small amount of expansion / contraction on either end of the pack). With a common plate on one end, both...

diysolarforum.com

I installed some of those springs in my new case, I see a closed height of 1.86 in and an open height of 1.43 in with force varying from 200 lb -> 125 lb. I figured half way would be roughly close enough so I compressed my 4 springs down to 1.6 in. Is that correct? I thought I saw that mentioned somewhere but can't find it again.

 

[100 Proof]

I installed some of those springs in my new case, I see a closed height of 1.86 in and an open height of 1.43 in with force varying from 200 lb -> 125 lb. I figured half way would be roughly close enough so I compressed my 4 springs down to 1.6 in. Is that correct? I thought I saw that mentioned somewhere but can't find it again.

That's the neighborhood. I think mine are at 1.7" at 80% charge.

 

[cajocars]

Thanks for the props Bob! Here's some screen shots for people interested.
View attachment 27693View attachment 27694
View attachment 27697

where has this file been posted?

 

[Saltyoldcruiser]

I installed some of those springs in my new case, I see a closed height of 1.86 in and an open height of 1.43 in with force varying from 200 lb -> 125 lb. I figured half way would be roughly close enough so I compressed my 4 springs down to 1.6 in. Is that correct? I thought I saw that mentioned somewhere but can't find it again.

I've been trying to find an actual link to springs someone has used. I just ordered 4 of these for a 4s EVE 280 AH build. They are a lot smaller in diamater and have a 3/8 ID. https://www.grainger.com/product/44...gucid=EMT:10339122:Item:CSM-323&emcid=NA:Item

 

[S Davis]

I've been trying to find an actual link to springs someone has used. I just ordered 4 of these for a 4s EVE 280 AH build. They are a lot smaller in diamater and have a 3/8 ID. https://www.grainger.com/product/44...gucid=EMT:10339122:Item:CSM-323&emcid=NA:Item

These are what I used in seven 4s 280ah EVE cell packs.

Associated Spring Raymond 3/4" Hole Diam, 3/8" Rod Diam, 1-1/4" Free Length, Blue Die Spring 160 Lb Max Deflection, 0.63" Max Deflection, Medium Duty, Chromium Alloy Steel 103-405 - 07660590

Offering a huge selection of industrial tool sales online. Find over 100,000 metalworking products, precision measuring tools, power tools & accessories.

www.penntoolco.com

 

[Saltyoldcruiser]

I received the granger springs in the comment above. They'll work, but there's more to it than the spring rate. Those springs have a rate of 150 pounds, which means that they'll exert 150 pounds of force when compressed an inch. That's cool, except that they won't actually compress a full inch. I believe that parameter is called the "range" and it's actually only about 3/4 of an inch with that spring. I tested this by putting the spring on a bathroom scale and compressing it with my hydraulic press until the scale reached it's rated 150 pounds. at that point the spring was completely compressed with barely any space between the coils. Unless I'm calculating wrong, the area of a EVE 280 ah cell is 56 square inches. If we're looking to achieve 12 psi 672 pounds of pressure. That 672 divided by 4 equal springs is 168 pounds per spring. A 150 pound rated spring gets you in the ball park but it's a little light. And, the above springs which I bought will be nearly fully compressed. I think a more appropriate spring would be one with the same specs as the Granger one in the comment except at least a half inch and probably an inch longer. I'm going to go with what I've got and compress them to about 130 pounds each which will be about 9.28pounds per square inch. That's a bit short of the theoretical 12 pounds everyone is saying they need but it is what it is. Appreciate any thoughts.

 

[Zwy]

A scale like the bathroom scale measures weight on the platform, not ppi. PPI is spring rate, pounds per inch.

You need a tester like the one shown in this video.

 

[Saltyoldcruiser]

It's measuring the pressure on it's surface. One inch of compression of the spring shows 150 pounds on the bathroom scale, exactly the value of the spring rate.

 

[justgary]

It's measuring the pressure on it's surface. One inch of compression of the spring shows 150 pounds on the bathroom scale, exactly the value of the spring rate.

Buy two more springs and use six in your build.