Idiot's guide to a self build battery

[marshman]

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[marshman]

Trying to upload the EVE 280K data sheet to the group
But it said the PDF is too large to upload
If anyone in need of the data sheet
Can reach out to me anytime

EVE 280Ah , 304AH 230Ah or any battery data sheet if we have
Thanks

Here is a link to the battery datasheet Colin was referring to. Has a couple of sections on "compression"

Deriy EVE LF280K SPECIFICATION - PDF

[Caesium]

As I said earlier I went for the laminated copper flexible busbars which are nickle plated. Expensive, but I am very happy with them compared with the solid ones.

Do you have a link to these? I've been considering replacing the stock ones as it can be quite hard to get a decent low-resistance connection with them.

[marshman]

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[robl]

Read the section from the EVE spec that I posted earlier. It states:

Place the cell (~40%SOC) covered with blue film (material: PET, thickness 0.1mm) and top film (material: PC, thickness 0.3mm) in the middle of the clamp, and the initial compression force is (300 kgf±20kgf).



So SOC = 40% and compress with 300kgf, which equates to a pressure of roughly 12lb/sq in or a total of about 660 lbs which spread over the four M6 bolts I used is 165lb per bolt. Torque them to around 0.8Nm and you won't be far off.

I think the intended torque is higher than that:
300kgf is equivalent to 3000N
So that’s 750N per bolt, if 4 bolts.
Then the Engineering toolbox calculates the torque to be 5.4Nm

[marshman]

Read the section from the EVE spec that I posted earlier. It states:

Place the cell (~40%SOC) covered with blue film (material: PET, thickness 0.1mm) and top film (material: PC, thickness 0.3mm) in the middle of the clamp, and the initial compression force is (300 kgf±20kgf).



So SOC = 40% and compress with 300kgf, which equates to a pressure of roughly 12lb/sq in or a total of about 660 lbs which spread over the four M6 bolts I used is 165lb per bolt. Torque them to around 0.8Nm and you won't be far off.

I think the intended torque is higher than that:
300kgf is equivalent to 3000N
So that’s 750N per bolt, if 4 bolts.
Then the Engineering toolbox calculates the torque to be 5.4Nm

6mm == 0.006m NOT 0.06mm

So I think my torque figure of around 0.8Nm is correct for DRY threads. 5.4Nm may damage the cells as it is a factor of 10 out !!!

[MrPablo]

If we really wanted accurate compression of these cells, we'd have to start looking at using something like disc springs with an extremely rigid assembly and plate.
That way you're no longer relying on torque on a bolt. Perhaps one for someone to try out if they're inclined.

[marshman]

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[Jinx]

Anyone tried these.
Flexible copper braded connector. LIFEP04


The link went to my account. Removed it.

4PCS 73mm Pitch Screw 6 Flexible Copper Braid Lithium Battery Connector Bus Bar For DIY LiFepo4 Lithium Cell Solar EV Marine UPS

These are standard issue (and have been for many years now) by Yuasa on some of their UPS range of SLA batteries and are generally no issue at all. I wouldn’t hesitate to use them.

[robl]

So I think my torque figure of around 0.8Nm is correct for DRY threads. 5.4Nm may damage the cells as it is a factor of 10 out !!!

Thanks Marshman!

Noted that that datasheet asks for a given compression at 40% SOC, but a rigid structure - so the wanted compression may be higher when fully charged (I think that’s when cells are most likely to expand).