Pack / Cell compression Optimized By Using Springs.

[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.

Pics of the compression fixture. I made the end plates from some 1/2", 9 ply Birch plywood from Home Depot. This is the experimental version, once I am convinced I have everything figured out I will rebuild it using 1/2" Baltic Birch plywood I have. The end plates are 12" high, because I didn't...

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.

 

[Saltyoldcruiser]

Finally seeing the end of this box build. I'm having a lot of trouble wrapping my head around this much compression on these cells. I've only tightened the 4 150 pound rated springs to half the rate and it's just seeming way too tight to me. Are you guys really doing 600+ psi on these cells? Not sure if I have the nerve to do it.

 

[curiouscarbon]

Finally seeing the end of this box build. I'm having a lot of trouble wrapping my head around this much compression on these cells. I've only tightened the 4 150 pound rated springs to half the rate and it's just seeming way too tight to me. Are you guys really doing 600+ psi on these cells?

hello! disclaimer, i am amateur and don't have special knowledge about springs.

first off, the notch design you have with the compression is really cool in my opinion

600psi+ definitely nobody is doing this. perhaps you mean 600 pounds of force across the entire side?

to figure the pounds of force, multiply the surface area of the side receiving compression by the pounds per square inch (psi)
area * pressure -> force or (square inch) * (psi) -> (pounds)

of course the psi figure should be sourced from the specific cell being used, the manufacturer datasheet. same for surface area.

it looks like the springs are fully compressed? unsure if this poses any issue. i usually try to have a little space left, not really sure why, can't articulate it in a clear engineering way.

hope this helps in some way. nice looking build.

 

[S Davis]

Finally seeing the end of this box build. I'm having a lot of trouble wrapping my head around this much compression on these cells. I've only tightened the 4 150 pound rated springs to half the rate and it's just seeming way too tight to me. Are you guys really doing 600+ psi on these cells? Not sure if I have the nerve to do it.View attachment 137655View attachment 137660View attachment 137661View attachment 137662View attachment 137663

I’m compressing to about 640lbs.

 

[Saltyoldcruiser]

Buy two more springs and use six in your build.

That wouldn't work too well for my case. My box is kind of designed for 4 rods. I've ordered a couple of 188 pound springs a half inch longer than the ones I have. I'm still having trouble wrapping my head around putting over 600 pounds on these batteries.

 

[justgary]

I'm still having trouble wrapping my head around putting over 600 pounds on these batteries.

That's why it is better to just think of it as "only 12 PSI."

 

[Dynoman]

That wouldn't work too well for my case. My box is kind of designed for 4 rods. I've ordered a couple of 188 pound springs a half inch longer than the ones I have. I'm still having trouble wrapping my head around putting over 600 pounds on these batteries.View attachment 137720

This has been posted in other threads and maybe it will help here. Sounds like the cells might be over compressed.

Not using springs in compression fixture. Just using yellow pine wood 1 inch x 10 inch cut to length and four 1/4 inch course threaded rods with 1/4 inch nuts & washers on the 8s Lifepo4 battery banks.

This is Info I used and torqued a little less at 5 Inch Pounds with a torque wrench at about 3.2 to 3.3 volts charge in each cell.

The spec from EVE was 300 KG force which rounds off to 660lbs. Battery face is approx 6.85"x 7.874" = 53.94 sq inches
660lbs/53.94sqin=12.23 lbs per sq inch
Divide 660 by 4 bolts that's 165 lbs Axial (clamping) force per bolt.
Using 4 course 1/4 in threaded rods that should equate to roughly 8 INCH pounds torque per bolt. Realistically, that's a snug twist of the wrist on a regular nut driver for the average build mechanic.

Hope it helps...

 

[SolaroSsaurius]

Buy two more springs and use six in your build.

Actually, EVE's diagram shows 6 compression rods, not 4

 

[Saltyoldcruiser]

Actually, EVE's diagram shows 6 compression rods, not 4

I've never seen any diagrams from EVE. If any exist can you provide a link. I'd love to actually see any fixtures the manufacturers suggest. Both plates on the ends of my cells are a full inch thick quality plywood and my cross bars are reinforced 1"x1" oak. I'm confident that any deflection will be insignificant.

 

[Saltyoldcruiser]

This has been posted in other threads and maybe it will help here. Sounds like the cells might be over compressed.

Not using springs in compression fixture. Just using yellow pine wood 1 inch x 10 inch cut to length and four 1/4 inch course threaded rods with 1/4 inch nuts & washers on the 8s Lifepo4 battery banks.

This is Info I used and torqued a little less at 5 Inch Pounds with a torque wrench at about 3.2 to 3.3 volts charge in each cell.

The spec from EVE was 300 KG force which rounds off to 660lbs. Battery face is approx 6.85"x 7.874" = 53.94 sq inches
660lbs/53.94sqin=12.23 lbs per sq inch
Divide 660 by 4 bolts that's 165 lbs Axial (clamping) force per bolt.
Using 4 course 1/4 in threaded rods that should equate to roughly 8 INCH pounds torque per bolt. Realistically, that's a snug twist of the wrist on a regular nut driver for the average build mechanic.

Hope it helps...

That math works out the same as mine. I do prefer springs to accommodate any expansion that might take place within the cells. I'll be using 4 188 pound rated springs compressed to 165 pounds each.

 

[rickst29]

That math works out the same as mine. I do prefer springs to accommodate any expansion that might take place within the cells. I'll be using 4 188 pound rated springs compressed to 165 pounds each.

Use the compression rating and the spring deflection, the 'torque on the bolts' method is not as accurate. The threads in the bolts and nuts are not completely even and smooth.

 

[Dynoman]

I've never seen any diagrams from EVE. If any exist can you provide a link. I'd love to actually see any fixtures the manufacturers suggest. Both plates on the ends of my cells are a full inch thick quality plywood and my cross bars are reinforced 1"x1" oak. I'm confident that any deflection will be insignificant.

Ran across this EVE LF280K spec sheet with diagrams dated April 2022. The Testing Cell Clamp diagrams are shown. It is interesting that it shows 10mm metal plates 6 M6 bolts on a single cell.

 

[SuperShort]

That spec indicates... "It can be seen from the above table, that the
compression force of the battery cannot exceed 50 kN,
otherwise the battery may be damaged."
A 50kN force is equal to just 7.25PSI - The target PSI I've read on these batteries is 12PSI-15PSI?

 

[Hedges]

Double check the math.
I just used a web site to convert 50kN to 11240 lbs.
173.7 x 204.4 mm = 55 in^2
11240/55 = 204 psi.

Did I get that correct?

 

[S Davis]

That spec indicates... "It can be seen from the above table, that the
compression force of the battery cannot exceed 50 kN,
otherwise the battery may be damaged."
A 50kN force is equal to just 7.25PSI - The target PSI I've read on these batteries is 12PSI-15PSI?

The compression spec is 300 kgf +-20 not 300 kn.

 

[SuperShort]

It's a quote from the eve280k spec posted above.
I guess the assumption of 50kn/m2 but no other denominator makes sense.