Best practice for 300kgf ‘fixture’ 280Ah cells

[Luthj]

Some of the research I have read indicates that any reduction in capacity due to clamping is reversible with a couple charge discharge cycles unloaded, I will try to dig up the study.

 

[Solar123456]

Yes, whatever spring solution you elect, you will need sufficient range for full deflection.

Lee Springs LHL 2000AB 01 delivers 679.1 lbs at solid (12.2psi) and has a rate of 693 lbs/inch so if gives up only 109 lbs after 4mm of decompression (meaning 10.1psi at 0% SOC).

It has a free length of 2.5” and a solid length of 1.52” (smaller than the 76mm you are considering to accommodate your Belleville washers...).

What was the end result of your build? If you pursued this, I'd love to see how this turned out?

 

[fafrd]

What was the end result of your build? If you pursued this, I'd love to see how this turned out?

I ended up getting different springs from another outfit (Dayton Lamina) but am pretty happy with the end result.

Here is the full Dayton Lamina spring catalog: https://www.daytonlamina.com/pdf/DS117_DieMax_XL_Springs.pdf

And here is the springs I used: https://www.dgisupply.com/product/LAA9120411/

I made a single-row fixture clamping 16 280 Ah cells from wooden end pieces reinforced with what Home Depot calls ‘Punched Square Tube’, secured by four 4’ long 5/16” threaded rods, each secured with two of the 8 springs (one at either end).

I got the battery close to ~50% SOC and tightened each spring the number of turns to apply 37.5kgf (82.5 lbs of force) which, since those springs apply 32 lbs per 1/10th inch of compression, translated to a hair over 1/4” of compression per spring.

Calibrating the compression was easy using the threaded - rod: I just calculated the number of turns needed for 1/4” based on thread pitch.

I’ll eventually recalibrate and check compression both when the cells are fully discharged and fully charged, but for now, everything seems to be working well (been letting it settle in for a little over a week now).

Once you’ve gone through 5-10 cycles, I can confirm observation by others that there is very little expansion/contraction but I have not yet bothered to measure the delta I’m getting (partly because I still need to disassemble and reassemble for other reasons).

 

[Solar123456]

I ended up getting different springs from another outfit (Dayton Lamina) but am pretty happy with the end result.

Here is the full Dayton Lamina spring catalog: https://www.daytonlamina.com/pdf/DS117_DieMax_XL_Springs.pdf

And here is the springs I used: https://www.dgisupply.com/product/LAA9120411/

I made a single-row fixture clamping 16 280 Ah cells from wooden end pieces reinforced with what Home Depot calls ‘Punched Square Tube’, secured by four 4’ long 5/16” threaded rods, each secured with two of the 8 springs (one at either end).

I got the battery close to ~50% SOC and tightened each spring the number of turns to apply 37.5kgf (82.5 lbs of force) which, since those springs apply 32 lbs per 1/10th inch of compression, translated to a hair over 1/4” of compression per spring.

Calibrating the compression was easy using the threaded - rod: I just calculated the number of turns needed for 1/4” based on thread pitch.

I’ll eventually recalibrate and check compression both when the cells are fully discharged and fully charged, but for now, everything seems to be working well (been letting it settle in for a little over a week now).

Once you’ve gone through 5-10 cycles, I can confirm observation by others that there is very little expansion/contraction but I have not yet bothered to measure the delta I’m getting (partly because I still need to disassemble and reassemble for other reasons).

Awesome, thanks for the quick reply. Do you have any pictures you’d be willing to share?

I am leaning toward the spring route for my 8s 280ah set up for my camper.

 

[fafrd]

Awesome, thanks for the quick reply. Do you have any pictures you’d be willing to share?

I am leaning toward the spring route for my 8s 280ah set up for my camper.

No, and I’m leery of posting any pics until I understand how to strip out the geotag info…

It’s still a work in progress and ‘under construction’, but once it’s finished, if I find an easy way to sanitize some pics, I’d consider posting a few…

 

[Hedges]

No, and I’m leery of posting any pics until I understand how to strip out the geotag info…

You just need to figure out how to spoof them?

I open with Paint, crop unneeded background, save as a new file.
One can paste bitmap image directly into the forum, but file is bigger and upload slower.
So I save as a .jpg and upload that.

There is a way to make thumbnails which can be expanded, a courtesy to members with low bandwidth.

 

[HRTKD]

No, and I’m leery of posting any pics until I understand how to strip out the geotag info…

It’s still a work in progress and ‘under construction’, but once it’s finished, if I find an easy way to sanitize some pics, I’d consider posting a few…

I use the tool IrfanView to do batch conversions of images. There is a feature in that tool to not keep the EXIF data during the batch conversion process. I haven't used that feature myself.

 

[fafrd]

I use the tool IrfanView to do batch conversions of images. There is a feature in that tool to not keep the EXIF data during the batch conversion process. I haven't used that feature myself.

Thanks, sounds like that might be the tool I’m looking for. I just want to strip all metadata from any pics before posting them (so will also want a viewer to confirm metadata has been stripped).

If you go a screen capture of a displayed picture, does that image contain any metadata?

 

[HRTKD]

Thanks, sounds like that might be the tool I’m looking for. I just want to strip all metadata from any pics before posting them (so will also want a viewer to confirm metadata has been stripped).

If you go a screen capture of a displayed picture, does that image contain any metadata?

I verified that IrfanView knows about the location data. I have one image with it and one without. It presents more options when the geo info is there.

I did a capture of a displayed picture that did have the EXIF data. The captured image did not have one bit of EXIF data.

 

[Solar123456]

Thanks, sounds like that might be the tool I’m looking for. I just want to strip all metadata from any pics before posting them (so will also want a viewer to confirm metadata has been stripped).

If you go a screen capture of a displayed picture, does that image contain any metadata?

I ended up getting different springs from another outfit (Dayton Lamina) but am pretty happy with the end result.

Here is the full Dayton Lamina spring catalog: https://www.daytonlamina.com/pdf/DS117_DieMax_XL_Springs.pdf

And here is the springs I used: https://www.dgisupply.com/product/LAA9120411/

I made a single-row fixture clamping 16 280 Ah cells from wooden end pieces reinforced with what Home Depot calls ‘Punched Square Tube’, secured by four 4’ long 5/16” threaded rods, each secured with two of the 8 springs (one at either end).

I got the battery close to ~50% SOC and tightened each spring the number of turns to apply 37.5kgf (82.5 lbs of force) which, since those springs apply 32 lbs per 1/10th inch of compression, translated to a hair over 1/4” of compression per spring.

Calibrating the compression was easy using the threaded - rod: I just calculated the number of turns needed for 1/4” based on thread pitch.

I’ll eventually recalibrate and check compression both when the cells are fully discharged and fully charged, but for now, everything seems to be working well (been letting it settle in for a little over a week now).

Once you’ve gone through 5-10 cycles, I can confirm observation by others that there is very little expansion/contraction but I have not yet bothered to measure the delta I’m getting (partly because I still need to disassemble and reassemble for other reasons).

Why did you go with 8 springs ( 4 each side if I understand correctly) instead of just 4 stronger ones on 1 side?

 

[fafrd]

I verified that IrfanView knows about the location data. I have one image with it and one without. It presents more options when the geo info is there.

I did a capture of a displayed picture that did have the EXIF data. The captured image did not have one bit of EXIF data.

Cool. Well that’ll be my low-tech backup then…

 

[fafrd]

Why did you go with 8 springs ( 4 each side if I understand correctly) instead of just 4 stronger ones on 1 side?

At least with the Dayton Lamina stings, 8 shorter springs worked out to being pretty much the same price (and length) as 4 longer ones…

Especially with 16 cells in a long line, I felt better about the idea of symmetric force from either end (minimized movement of the threaded rods in the punched square tube (50% on either end versus 0% on one end and 100% on the other end).

 

[Solar123456]

At least with the Dayton Lamina stings, 8 shorter springs worked out to being pretty much the same price (and length) as 4 longer ones…

Especially with 16 cells in a long line, I felt better about the idea of symmetric force from either end (minimized movement of the threaded rods in the punched square tube (50% on either end versus 0% on one end and 100% on the other end).

Got it thanks. I was hoping you or someone might be willing to double check my math. I am planning on using 8 cells but building two separate compression builds of 4 each because of space constraints.

The plan is to use 4 rods for each and have 1 spring on each rod all on one side so 4 springs per 4 cells on on side with 5/16 threaded rod as well as using the punched square tube as you mentioned.

If I understand things correctly the expansion per cell is approximately .5mm and for 4 cells are approximately 2mm which translates to hair under .08 of an inch

The two springs I am looking at have the following specs:

Option A) Model 1 9-1204-21 3/4 inch hole diameter and 3/8 inch rod with 1 inch free length

• 51.5lbs per 1/10 inch
• 127lbs at 0.25 inches
• 152lbs at 0.30 inches
• 190lbs at 0.37 inches
• 208lbs at solid 0.40 inches

If my median target is 165lbs and .08 inches of compression with this spring is approximately 41.2lbs (51.5 x .08). Then I'd want my max compression at 100% SOC to be 185lbs = (165 + 20.6 which is half of 41.2). Then my min compression at 0% would be 144.4lbs =(165 - 20.6).

That would mean I'd want to compress the springs at approximately .36 inches at 100% SOC to get the 185lbs of pressure.


Option B ) Model #1 9-1604-11 Size 1 inch hole diameter and 1/2 inch rod with 1 inch free length

• 61.2lbs per 1/10 inch
• 151lbs at 0.25
• 181lbs at 0.30
• 241lbs at 0.40
• 296lbs at solid 0.48

If my median target is 165lbs and .08 of compression with this spring is approximately 48.96lbs (61.2lbs x .8). Then I'd want my max compression to be 189.48lbs = (165 + 24.48 which is half of 48.96) at 100% and my minimum compression to be 140.52lbs = (165 - 24.48) at 0%.

This would mean I'd want to get a hair over .3 inch to get the 189lbs compression at 100%.

Question 1:
Does my logic check out?

Question 2:

Which option would you go with?
My concern for option A is that it is awfully close to solid which shortens the average lifespan of the spring.

Option B is larger made to fit 1/2 rod size but if I am using 5/16 threaded rod would that cause any concern?

 

[fafrd]

Got it thanks. I was hoping you or someone might be willing to double check my math. I am planning on using 8 cells but building two separate compression builds of 4 each because of space constraints.

The plan is to use 4 rods for each and have 1 spring on each rod all on one side so 4 springs per 4 cells on on side with 5/16 threaded rod as well as using the punched square tube as you mentioned.

If I understand things correctly the expansion per cell is approximately .5mm and for 4 cells are approximately 2mm which translates to hair under .08 of an inch

The two springs I am looking at have the following specs:

Option A) Model 1 9-1204-21 3/4 inch hole diameter and 3/8 inch rod with 1 inch free length

• 51.5lbs per 1/10 inch
• 127lbs at 0.25 inches
• 152lbs at 0.30 inches
• 190lbs at 0.37 inches
• 208lbs at solid 0.40 inches

If my median target is 165lbs and .08 inches of compression with this spring is approximately 41.2lbs (51.5 x .08). Then I'd want my max compression at 100% SOC to be 185lbs = (165 + 20.6 which is half of 41.2). Then my min compression at 0% would be 144.4lbs =(165 - 20.6).

That would mean I'd want to compress the springs at approximately .36 inches at 100% SOC to get the 185lbs of pressure.


Option B ) Model #1 9-1604-11 Size 1 inch hole diameter and 1/2 inch rod with 1 inch free length

• 61.2lbs per 1/10 inch
• 151lbs at 0.25
• 181lbs at 0.30
• 241lbs at 0.40
• 296lbs at solid 0.48

If my median target is 165lbs and .08 of compression with this spring is approximately 48.96lbs (61.2lbs x .8). Then I'd want my max compression to be 189.48lbs = (165 + 24.48 which is half of 48.96) at 100% and my minimum compression to be 140.52lbs = (165 - 24.48) at 0%.

This would mean I'd want to get a hair over .3 inch to get the 189lbs compression at 100%.

Question 1:
Does my logic check out?

Question 2:

Which option would you go with?
My concern for option A is that it is awfully close to solid which shortens the average lifespan of the spring.

Option B is larger made to fit 1/2 rod size but if I am using 5/16 threaded rod would that cause any concern?

I only perused your math quickly but it seems like you know what you’re doing.

My goals were to keep above ~8psi at 0% SOC and keep below ~12psi at 100% SOC.

You are below 12psi at 100% SOC, so I think you need stronger springs.

In general, you want to stay as far away from Solid as you can (subject yo space constraints).

And the larger the play you have between spring opening and rod diameter, the more likelihood you have of the spring getting hung up by the rod threads, though I found it pretty easy to keep my springs centered once compressed and in the worst-case, you just need short pieces of 3/8” stainless tubing the shield the springs from the 5/16” rod…

 

[Solar123456]

I only perused your math quickly but it seems like you know what you’re doing.

My goals were to keep above ~8psi at 0% SOC and keep below ~12psi at 100% SOC.

You are below 12psi at 100% SOC, so I think you need stronger springs.

In general, you want to stay as far away from Solid as you can (subject yo space constraints).

And the larger the play you have between spring opening and rod diameter, the more likelihood you have of the spring getting hung up by the rod threads, though I found it pretty easy to keep my springs centered once compressed and in the worst-case, you just need short pieces of 3/8” stainless tubing the shield the springs from the 5/16” rod…

Thanks for the help, great idea with the stainless tubing.

You mentioned I am below 12psi at 100% SOC so I am wondering where I might of went wrong.

I thought 12 psi was approx. 672lbs / 4 rods which would be 168lbs per rod. My 100% SOC with option 2 would be approx 190lbs per rod which would be 760lbs at 100% and 562lbs at 0%.

Am I missing something?

 

[fafrd]

Thanks for the help, great idea with the stainless tubing.

You mentioned I am below 12psi at 100% SOC so I am wondering where I might of went wrong.

I thought 12 psi was approx. 672lbs / 4 rods which would be 168lbs per rod. My 100% SOC with option 2 would be approx 190lbs per rod which would be 760lbs at 100% and 562lbs at 0%.

Am I missing something?

I probably took the wrong number or multiplied by 8 instead of 4..,

You want 300Kgf nominal (660 lbs of force at the midpoint, or 165 lbs/spring at the midpoint).

You want a range of no more than +/- 50% at the endpoints, so no less than 82.5 lbs/spring at 0% SOC and no more than 247.5 lbs/spring at 100% SOC.

I did plan for 0.5mm / cell maximum range and it seems to have worked well for me so if you plan for a spring with less than 165 lbs per 2mm or 130 lbs/0.1” you should be good.

Just be aware that your cells will start out bloated by closer to 2mm or 1/8” when you first place them in your fixture, so you’ll likely need more range in your springs or an adjustable rod solution that allows you to first engage the springs further out ABV tighten down as the cells settle in over multiple charge/discharge cycles…

 

[Solar123456]

I probably took the wrong number or multiplied by 8 instead of 4..,

You want 300Kgf nominal (660 lbs of force at the midpoint, or 165 lbs/spring at the midpoint).

You want a range of no more than +/- 50% at the endpoints, so no less than 82.5 lbs/spring at 0% SOC and no more than 247.5 lbs/spring at 100% SOC.

I did plan for 0.5mm / cell maximum range and it seems to have worked well for me so if you plan for a spring with less than 165 lbs per 2mm or 130 lbs/0.1” you should be good.

Just be aware that your cells will start out bloated by closer to 2mm or 1/8” when you first place them in your fixture, so you’ll likely need more range in your springs or an adjustable rod solution that allows you to first engage the springs further out ABV tighten down as the cells settle in over multiple charge/discharge cycles…

Thanks again for the speedy response and all the help! Good to know I am on the right track, took a bit to comb through so much info.

One thing that I am realizing that I did forget to account for is which actually might throw quite a bit off, is the two of my cells are lower capacity. I am in the process of the whole dispute but thats another thing. The 8s24v 280 pack tested at 237ah instead of 280 because two of the cells triggered low voltage disconnect early.

If I do end up using these cells, it will lower the overall capacity of the pack to 237 meaning 6 of the 8 cells will only every get to approx 84% of full charge.

My thinking is that this would lower the 2mm of expansion if its linnear to about 1.68mm. Which I think should still be good because it would just mean a lower overall fluctuation in pressure so instead of jumping between 10 and 14 psi it might only go between 11-13. Is this the correct way to think about it? (i just randomly made those last numbers, they arent the actual corresponding psi just wanna know if I am thinking about this right

 

[fafrd]

Thanks again for the speedy response and all the help! Good to know I am on the right track, took a bit to comb through so much info.

One thing that I am realizing that I did forget to account for is which actually might throw quite a bit off, is the two of my cells are lower capacity. I am in the process of the whole dispute but thats another thing. The 8s24v 280 pack tested at 237ah instead of 280 because two of the cells triggered low voltage disconnect early.

If I do end up using these cells, it will lower the overall capacity of the pack to 237 meaning 6 of the 8 cells will only every get to approx 84% of full charge.

My thinking is that this would lower the 2mm of expansion if its linnear to about 1.68mm. Which I think should still be good because it would just mean a lower overall fluctuation in pressure so instead of jumping between 10 and 14 psi it might only go between 11-13. Is this the correct way to think about it? (i just randomly made those last numbers, they arent the actual corresponding psi just wanna know if I am thinking about this right

I doubt the ~15% difference in ‘empty to full’ capacity will make any noticeable difference at all in the expansion range you’ll see / have to deal with.

A more important issue will be building a fixture with enough range to engage your uncompressed cells and tighten along with them as they settle.

If you’ve got long enough threaded rods to engage compression nuts with you current uncompressed cells, you are good to go (just tighten the nuts as the cells settle/compress.

I didn’t want long extensions of threaded rod sticking out at the ends of my pack so I went to the trouble of getting 2” long 5/16” coupling nuts and 5/16” bolts for my ‘ends’ so that I could tighten into the coupling nuts as I needed more compression.

 

[Solar123456]

I doubt the ~15% difference in ‘empty to full’ capacity will make any noticeable difference at all in the expansion range you’ll see / have to deal with.

A more important issue will be building a fixture with enough range to engage your uncompressed cells and tighten along with them as they settle.

If you’ve got long enough threaded rods to engage compression nuts with you current uncompressed cells, you are good to go (just tighten the nuts as the cells settle/compress.

I didn’t want long extensions of threaded rod sticking out at the ends of my pack so I went to the trouble of getting 2” long 5/16” coupling nuts and 5/16” bolts for my ‘ends’ so that I could tighten into the coupling nuts as I needed more compression.

Interesting. Is the 5/16 bolt at the end for extra strength to prevent the coupling nut from moving? (as opposed to using something like two 5/16 nuts instead of the coupling +bolt)

 

[fafrd]

Interesting. Is the 5/16 bolt at the end for extra strength to prevent the coupling nut from moving? (as opposed to using something like two 5/16 nuts instead of the coupling +bolt)

My battery will be 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…