diy solar

diy solar

Best practice for 300kgf ‘fixture’ 280Ah cells

In another thread I implied that the torque we're looking at is so small that the margin for error is large, meaning that A) confidence levels are questionable and B) it doesn't take much to be off. Of course, I was talking about the torque on the terminals, but now I'm thinking the same thoughts may be appropriate for clamping.

Get the compression snug enough that you can lift the battery by the threaded rod with no cells falling out. If a cell falls out, it's too loose. :)
Clamping something without compliance that is going to expand is like freezing a glass bottle of water that doesn't have any air in it. Enjoy picking the glass shards out of your freezer.

Springs provide both compliance and an easy way to set the preload. Both of which are absolutely required if you intend to do this.
 
I have no way of working in Psi. My torque wrench goes down to 1Nm and supposedly accurate to 4%(iirc)
So i was thinking(as an approximation) 300kgf = 29.4Nm divided over 6 rods = 4.9Nm. Now the washers i have on order are 1mm thick, but total height of 1.4mm(giving a deflection of 0.4 mm. The cells expand/contract approx 0.5mm each, so over 8cells in line = 4mm=10washers.
So 10 washers tightened flat to 4.9Nm when at 100% soc, would hopefully be in the ballpark(I'd probably drop back to 4.5Nm for margin of safety). However, presuming at 30%soc, the washers would have 'released' back to close on zero Nm being applied??? Thus i was wondering, and soon to experiment once i recieve my washers, if i doubled them up, could i still manage to torque them to 4.5Nm at 100%SOC and still be left with a reasonable compression at 30% soc. Early days in my thinking, but experimentation should be illuminating. ;):ROFLMAO:
If you ordered enough springs, send me a set and I will see if they are close to being correct. If they can work, I will even measure what preload (turns from finger tight) you should set them to.

There is nothing magical about the disc springs I ordered, I ordered a pack of every disc spring in 5/16" ID that McMaster Carr had in stock that had a reasonable working force rating. This particular one works sufficiently well to satisfy me.

If it turns out I need more compliance, I could just add more of the same spring in series, although I think I will probably add some lighter springs to give me a progressive spring rate. I tested that concept when I was looking for 3mm of compliance and was able to find a combination that worked (min pressure was 50 kg, max 94 kg)
 
If you ordered enough springs, send me a set and I will see if they are close to being correct. If they can work, I will even measure what preload (turns from finger tight) you should set them to.

There is nothing magical about the disc springs I ordered, I ordered a pack of every disc spring in 5/16" ID that McMaster Carr had in stock that had a reasonable working force rating. This particular one works sufficiently well to satisfy me.

If it turns out I need more compliance, I could just add more of the same spring in series, although I think I will probably add some lighter springs to give me a progressive spring rate. I tested that concept when I was looking for 3mm of compliance and was able to find a combination that worked (min pressure was 50 kg, max 94 kg)
Thanks for the offer HaldorEE, but i think i will be lucky to have 10 spare. The other thing i thought of doing was to attempt to distribute them evenly at either end of the pack....not sure if this would have any influence whatsoever on the compressibility of said spring washers...but i feel better balanced....lol.
 
Everybody, forget PSI. Think what force is the spring going to exert on an individual threaded rod as the cells expand from 0 to 100% SOC.

Assuming you have 4 threaded rods:

Target pressure is 75 kg. This equates to 300 kg total force or 12 PSI
Max pressure is < 108 kg. This equates to 432 kg total force or 17 PSI
Min pressure is > 50 kg. This equates to 200 kg total force or 8 PSI.

If I have to give anything up it is going to be on the minimum pressure. I would not be happy exceeding 100 kg rod force to be honest. My max target is 94 kg.
 
Everybody, forget PSI. Think what force is the spring going to exert on an individual threaded rod as the cells expand from 0 to 100% SOC.

Assuming you have 4 threaded rods:

Target pressure is 75 kg. This equates to 300 kg total force or 12 PSI
Max pressure is < 108 kg. This equates to 432 kg total force or 17 PSI
Min pressure is > 50 kg. This equates to 200 kg total force or 8 PSI.

If I have to give anything up it is going to be on the minimum pressure. I would not be happy exceeding 100 kg rod force to be honest. My max target is 94 kg.
I'm six threaded rods, so at least it is distributed more evenly, target pressure of only 50Kg

ps...i'm not an engineer of any description, so all this is a bit over my head, whilst i fumble my way along. :ROFLMAO:
 
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Bumping thread back to the top.....
Went with a variation on a theme with regards to using the belville washers.
My washers were spec'ed such that at 60% deflection they were loaded at 243N. At 20% deflection, they were loaded at 117N
The distance between the two 0.24mm.
Thus a single part threaded bolt with 17 washers in series gives:
17 x 243 = 4131N = 17.3psi @ 100% SOC
17 x 117 = 1989N = 8.3psi @ 30% SOC.
Total dist travelled = 17 x 0.24mm = 4.08mm over 8 cells = 0.5mm/cell as per datasheet.
Washers are distributed on a part threaded rod, so no threads to bind the washers movement. Only one cental point of contact, so no uneven pressures applied to one side if a washer got bound up etc. The plate at the cell face is free to move and is held in place only by the force applied by washers.
My intention is never to charge to 100% SOC anyways, so never reaching the 17.3psi maximum. Winter storage at 44% SOC = 30% deflection = 11.43 psi.
Hardest part is final adjustment of the washers at 100% soc, to be very accurately measured.

Seemed like a reasonably good compromise????

using washers 1.jpg
 
Bumping thread back to the top.....
Went with a variation on a theme with regards to using the belville washers.
My washers were spec'ed such that at 60% deflection they were loaded at 243N. At 20% deflection, they were loaded at 117N
The distance between the two 0.24mm.
Thus a single part threaded bolt with 17 washers in series gives:
17 x 243 = 4131N = 17.3psi @ 100% SOC
17 x 117 = 1989N = 8.3psi @ 30% SOC.
Total dist travelled = 17 x 0.24mm = 4.08mm over 8 cells = 0.5mm/cell as per datasheet.
Washers are distributed on a part threaded rod, so no threads to bind the washers movement. Only one cental point of contact, so no uneven pressures applied to one side if a washer got bound up etc. The plate at the cell face is free to move and is held in place only by the force applied by washers.
My intention is never to charge to 100% SOC anyways, so never reaching the 17.3psi maximum. Winter storage at 44% SOC = 30% deflection = 11.43 psi.
Hardest part is final adjustment of the washers at 100% soc, to be very accurately measured.

Seemed like a reasonably good compromise????

View attachment 36428
Very nice. So you’ve used your threaded rods to position a fixed surface against-which the Belleville washers are pushing a calibrated force against an end-plate - I’ve thought about doing the same.

Here are some things to keep in mind that I hope you’ll be able to confirm soon through your own measurements;

You designed for 0.5mm per cell ‘per datasheet’ but the datasheet indicates nothing by +/-0.5mm on the width, totally unrelated to SOC. This is a total delta of 1.0mm/cell, not 0.5mm.

The one member who has completed a 300Kgf fixture, used it and made measurements reports a 4mm travel between 0% SOC and 100% SOC, so your design should actually be OK (though your travel will be as much as twice that over the first couple of cycles, so I’d advise you to monitor closely and adjust springs as needed, especially to assure you don’t run into the stops and exceed 17psi on the first couple charge cycles.

I like that your using non-threaded rod for your secondary apparatus holding the Belleville washers - that solves one of my biggest issues with them.

I think you have the math wrong though. Force dies not multiply in series, deflection does.

So 17 washers in series will provide you 4.08mm of deflection from a force of 117N to 243N or 26.3lbs to 54.7lbs. This means your single spring is applying 40.5 lbs +/-14.2lbs.

We’re aiming for 660 +/- no more than 330lbs (12psi +/-6psi max).

So you’ll either need a total of 16 springs like the one you’ve built, or you’ll need to use 177 Belleville washers like the one you have in a 4P7S configuration, or you’ll need to get another Belleville washer which applies more force.

Or you can go to Lee Springs and find a single spring you can place on your unthreaded rod that will do the job. At worst you’ll find a spring that means you’ll need to double-up or triple-up the number of pressure points...
 
Have a look at LHL 200A 04: https://www.leespring.com/compression-springs

609 lbs at solid.

300lbs per inch.

1 of these would give you 11.2 psi @ solid (100% SOC) and 10.3psi after 4mm expansion (0% SOC).

Or with two, you could compress by 2.2” at 50% SOC for exactly 12.1psi and you’d then compress 2mm for 100% SOC @ 12.5psi or decompress 2mm for 0% SOC @ 11.7psi...

There are other options that may be a better fit depending on how much space you have and whether you’re going single-post or double-post, but if I had already invested in the design you have, I’d strongly consider finding a single or doubles compression spring that fit my specs (and budget).
 
Very nice. So you’ve used your threaded rods to position a fixed surface against-which the Belleville washers are pushing a calibrated force against an end-plate - I’ve thought about doing the same.

Here are some things to keep in mind that I hope you’ll be able to confirm soon through your own measurements;

You designed for 0.5mm per cell ‘per datasheet’ but the datasheet indicates nothing by +/-0.5mm on the width, totally unrelated to SOC. This is a total delta of 1.0mm/cell, not 0.5mm.

The one member who has completed a 300Kgf fixture, used it and made measurements reports a 4mm travel between 0% SOC and 100% SOC, so your design should actually be OK (though your travel will be as much as twice that over the first couple of cycles, so I’d advise you to monitor closely and adjust springs as needed, especially to assure you don’t run into the stops and exceed 17psi on the first couple charge cycles.

I like that your using non-threaded rod for your secondary apparatus holding the Belleville washers - that solves one of my biggest issues with them.

I think you have the math wrong though. Force dies not multiply in series, deflection does.

So 17 washers in series will provide you 4.08mm of deflection from a force of 117N to 243N or 26.3lbs to 54.7lbs. This means your single spring is applying 40.5 lbs +/-14.2lbs.

We’re aiming for 660 +/- no more than 330lbs (12psi +/-6psi max).

So you’ll either need a total of 16 springs like the one you’ve built, or you’ll need to use 177 Belleville washers like the one you have in a 4P7S configuration, or you’ll need to get another Belleville washer which applies more force.

Or you can go to Lee Springs and find a single spring you can place on your unthreaded rod that will do the job. At worst you’ll find a spring that means you’ll need to double-up or triple-up the number of pressure points...
Thanks for this...i had assumed that two washers in series, both compressed to 60% would both provide an equal force....back to drawing board....lol.
 
Watching Wills teardown on the SOK and BigBatteries recently I noticed they seemed to have some play in the tolerance between the cells. The batteries appear to be fixed inside by a removable bracket but once that was removed he was able to slide them out pretty easily. I wonder if they can get away with that because they only have a small number of cells inside the pack? Do the larger packs need tighter compression?
 
Watching Wills teardown on the SOK and BigBatteries recently I noticed they seemed to have some play in the tolerance between the cells. The batteries appear to be fixed inside by a removable bracket but once that was removed he was able to slide them out pretty easily. I wonder if they can get away with that because they only have a small number of cells inside the pack? Do the larger packs need tighter compression?
I doubt they are compressing at all. At the time those batteries were designed, EVE had not yet even put out any information indicating that compression was beneficial to extended cycle life.

Those batteries are probably designed so that there is enough space for 100% SOC (possibly with some modest level of compression) and then ~0.5mm of space opens up between cells as they are discharged to 0%.

That’s perfectly fine - it just means those batteries are more likely to deliver the base level of 2500 cycles to 80% capacity versus the new and improved 3500 cycles to 80% capacity (which requires a 300Kgf fixture).
 
Thanks for this...i had assumed that two washers in series, both compressed to 60% would both provide an equal force....back to drawing board....lol.
Yeah, 2 washers in series (cone-to-cone) provide double the range for identical force.

2 washers in parallel (cone-nestled-in-cone) provide double the force over identical range.

It takes 4 washers in series-parallel configuration (parallel pair positioned in series’s meaning outside-cone against outside cone) to deliver twice the force over twice the range...
 
Have a look at LHL 200A 04: https://www.leespring.com/compression-springs

609 lbs at solid.

300lbs per inch.

1 of these would give you 11.2 psi @ solid (100% SOC) and 10.3psi after 4mm expansion (0% SOC).

Or with two, you could compress by 2.2” at 50% SOC for exactly 12.1psi and you’d then compress 2mm for 100% SOC @ 12.5psi or decompress 2mm for 0% SOC @ 11.7psi...

There are other options that may be a better fit depending on how much space you have and whether you’re going single-post or double-post, but if I had already invested in the design you have, I’d strongly consider finding a single or doubles compression spring that fit my specs (and budget).
Ok, latest incarnation =
A series/parallel stack thus ((()))(((()))((())) x 23pairings.
This equates to 3 x 1181N(3543N) at 75% deflection and 3 x 505N(1515N) at 30% deflection with an overall travel dist of 4.14mm.
I believe this equates to a range of roughly 15psi - 6psi

orrrr...

I might decide just to run three seperate rods/stacks in vertical orientation???
 
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Ok, latest incarnation =
A series/parallel stack thus ((()))(((()))((())) x 23washers.
This equates to 3 x 1181N(3543N) at 75% deflection and 3 x 505N(1515N) at 30% deflection with an overall travel dist of 4.14mm.
I believe this equates to a range of roughly 15psi - 6psi

orrrr...

I might decide just to run three seperate rods in vertical orientation???
You didn’t indicate the force at 75% deflection, but this will give you 3 times the base force for 3 times the deflection.

You originally stated that 60% deflection amounted to 243N, so 30% deflection cannot be less than that (and thus cannot be 505N).

3 rods with ((())) each will provide 3 times the force but only 1/3 the range of ((()))((())))((())) but 3 rod with ()( each will give the same force over the same displacement as ((()))((()))((())).

Oh, and 3x3x2 = 28 washers total, not 23...
 
You designed for 0.5mm per cell ‘per datasheet’ but the datasheet indicates nothing by +/-0.5mm on the width, totally unrelated to SOC. This is a total delta of 1.0mm/cell, not 0.5mm.
When i looked at the datasheet, i read it somewhat differently from yourself. The thickness (30% SOC) figure at 71.5mm. The thickness (100% SOC) figure @ 72mm = 0.5mm difference due to state of charge. You also get +/- 1mm on the accuracy of the cell thickness measurement due to tolerances, not SOC. 8 cells in series for my 24V = 8 x 0.5mm = the 4mm range i was looking for total. If it is less than this after a few cycles, then even better.

Just one more way of viewing things, plus i felt that some of Cinergi's work seemed to confirm this.
I'm really only primarily concerned with the maximum force applied at 100% soc and making sure i dont exceed this. (y)
 
You didn’t indicate the force at 75% deflection, but this will give you 3 times the base force for 3 times the deflection.

You originally stated that 60% deflection amounted to 243N, so 30% deflection cannot be less than that (and thus cannot be 505N).

3 rods with ((())) each will provide 3 times the force but only 1/3 the range of ((()))((())))((())) but 3 rod with ()( each will give the same force over the same displacement as ((()))((()))((())).

Oh, and 3x3x2 = 28 washers total, not 23...
yes, this is using the different double thickness washers and different deflection criteria to meet the spec.
 
When i looked at the datasheet, i read it somewhat differently from yourself. The thickness (30% SOC) figure at 71.5mm. The thickness (100% SOC) figure @ 72mm = 0.5mm difference due to state of charge. You also get +/- 1mm on the accuracy of the cell thickness measurement due to tolerances, not SOC. 8 cells in series for my 24V = 8 x 0.5mm = the 4mm range i was looking for total. If it is less than this after a few cycles, then even better.

Just one more way of viewing things, plus i felt that some of Cinergi's work seemed to confirm this.
I'm really only primarily concerned with the maximum force applied at 100% soc and making sure i dont exceed this. (y)
I must have an old datasheet since mine does not have those figures. Can you post a link?

Yes 0.5mm of compression ~30% SOC and ~100% SOC closely matched what Cinergi reported, but he also experienced more than 0.5mm / cell over his first couple cycles.

As long as you assemble your pack and calibrate your force near 100% SOC, you should safely stay under 17psi.

I’t’s calibrating at 0% or 30% SOC and planning for 4mm of expansion that can get you into trouble...
 
I must have an old datasheet since mine does not have those figures. Can you post a link?

Yes 0.5mm of compression ~30% SOC and ~100% SOC closely matched what Cinergi reported, but he also experienced more than 0.5mm / cell over his first couple cycles.

As long as you assemble your pack and calibrate your force near 100% SOC, you should safely stay under 17psi.

I’t’s calibrating at 0% or 30% SOC and planning for 4mm of expansion that can get you into trouble...
If one of three single stacks is compressed 6.9mm at 100% soc, what does it matter if it 'relaxes 2mm or 4mm, you are still in the range above the 30% defl value. Now, if it 'relaxes' 5mm, then you might drop down to between the 10 - 20 % values, but you will still be in some degree of compression. I dont see it relaxing by 5mm myself but i might be wrong. I'm waiting for a repair stud to be manufactured and delivered and its driving me crazy...cant do any testing on my pack.....covid delays...:cry:

edit....obviously if i go the route of series/parallel single stack, that pushes me out to a total of around 76mm on the rod....which would mean a bit of redesign work...will weigh up the options.
 
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