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272Ah Lifepo4 battery with DIYBMS on 3d printed cradle

Hi folks, thanks to the brilliant work by Stuart and plenty of help on here I have my battery built and BMS mounted.

In the end I build a base from aluminium extrusions that has a heater pad built in that holds the 4 cells together. I then designed and 3D printed a cradle for the DIYBMS and relay board that snuggly sits over the top of the cells.

Finally I added a webbing strap that can be used to pick the battery up with.



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Hi Ian,

great work! :grinning:

Lishen cells?

Would you be so kind and share the .stl and .dxf files of the cradle?

Then I could just redesign your idea for my 280 Ah EVE cells in this or other orientation.

Cheers

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Thanks,

Yes the 272Ah Lishen cells. I’ve attached the 2 top cradle STL files. Battery Top Cradle STLs.zip (535.6 KB)

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Looking great!!

I don’t see any clamping force on the sides of the cells.

That’s highly recommend by Eve and Lishen to prevent delamination.

Look at it as a phone book on its side.
That won’t hold long, while together it’s strong enough to stop a bullet.

Many people use plywood or acrylic sheet and threaded rods to compress.

For more information:

If you look carefully at the bottom frame you will see that the long bars are shorter than the cells. I have tapped the ends of these bars so that I have been able to apply torque to the fasteners, which in turn clamp the cells.
After this is done I then tighten up the fish plates on top of the bars to hold it all rigid and lock it down in place. Also the top cap is a ‘snug’ fit, this along with the bolted down busbars will resist the cells ‘opening’ at the top.

he’s not talking about holding the bottom or the top together, he’s talking about the sides.
Think of each plastic encased cell as a rubber balloon which is currently prismatic but when there’s any pressure on the large long sides, such as when charging, each cell wall will push against the next and start to bulge outward. This deforms the laminations internally and weakens the chemical reactions.

So you want to put a piece of 1/2" or 3/4" plywood on each large side and use long bolts to hold them together so they too won’t bulge outward when the cells try to expand.

Good question, thanks. I’ve now been and done some further reading.

It does look like adding some compression could increase the number of available cycles. But I’m not sure how tangible that will be. If can increase the life by 1.6X which sounds a lot, but this is based on higher C rates. And whilst the system is all geared around producing 270A without an issue, I’m not sure that this will happen very often (I’ll have to try and think this through).

So I will look into it, but the cost/benefit of replacing the cells after 10 years rather than 15 years may not be there. Especially since a lot of what I was reading looked at adding spring systems, these soon add up in price.

As far as I have read there any no short term risks with having little/no compression, so this is a gradual thing, like changing the oil on your car after 10000 miles, rather than 7000 miles.

I just thought I’d share my progress on here. The system is now up and running and I’m really over the moon with it. I have an issue with one of my cells, that my supplier in China needs to replace. In the mean time I’ve been able to ‘turn the system down’, basically everything is set to max out at about 13.65V and it’s golden.

I have done a few videos about it, but some people on here might find our most recent one interesting, as it shows how we’ve integrated the BMS relays into our Victron equipment to give us full control over the system.

Looking good!

For the compression…
Yes supposingly you are able to increase the cycle life.
That’s just one added benefit.

I have over 80 cells, 32* 280 52x 152Ah that I started with and like you are, naïve.

I didn’t clamp the 152’s and after a few months of usage with solar and low capacity setup (S16, 51.2v) almost all the 152 are (slightly) bloated.

Never over charged,
Never over discharged,
Never beyond 0.1C rate.

The 152Ah seems to be little more prone to bloating, too much sheets in the housing, as the same housing is also used for 120Ah.

A bit like the 310Ah now who have the same size as 272/280.

Fact stays…
They bloated.
Only because I didn’t clamp the wide sides.
It doesn’t have to be a crazy tight fit.
10mm plywood is strong enough.
It just needs some additional help keeping the thin aluminium walls in place.

Official (Eve) build has aluminium casing that is laser welded around the cells while being compressed.
And laser welded busbars.

https://youtu.be/xdl5a2iyPYU

Please do watch this video to understand how the cells are intended to be used.

We are playing with half fabrication product, that needs further assembly as shown in the video.

As most of us don’t have a laser welding system, we use alterative.
Like drilling holes and tapping threads. (Done by your seller to make it more accessible for wider public, NOT the factory!!!) (except CALB)
That’s just one part of the process.

Anything we do different/ less is outside the specifications of the factory and will have negative impact on the lifecycle.

Did it hurt? The bloating?
After a year of usage, I did capacity test of all cells, 142-151Ah
Daily cycles.
Most ended around 145-148

So yes, it hurt, a bit.
Supposed is 30% rest capacity after 10 years.

With my speed of decay…
4% in a year…
You can do the math.

They are now clamped.
You can compress the bloating a bit, and tightening it more over time as the pressure will reduce some in a month.
Once released from clamping, the bloated quickly back to “original” shape.

I re-tighten not to de-bloat the cells, but to keep even tention on the sides.
6 * 1/4 inch threaded rods and little over hand tight with pipe wrench.
That’s all it takes.

Just don’t complain after a year or so when you see the cells bloating.
You now know the fix to prevent further damage.

Thanks for taking the time to share your experiences, that’s really useful.