Idiot's guide to a self build battery

[AE-NMidlands]

There is a lot written about compressing the cells and some people get very tetchy about exact forces. The science isn’t settled however there are a few things that we can be pretty confident about.

- An enclosure that resists expansion is desirable. Some initial tension is beneficial to longevity too.
- The batteries will naturally expand on their largest side. Top/bottom and small-side expansion isn’t as problematic.
- The cells have been manufactured with only an ultra-thin lightweight, casing. You are expected to provide a casing suitable to the application.
- Many link bars have one hole elongated to accommodate expansion however this obviously requires the pack to be isolated and the terminals loosened/retorqued periodically.
- The importance of all this depends on how the batteries are used. The applications discussed on here apply very little stress to the cells. We’re talking 0.25C (16s 280Ah 3.6kW) with most installations I’ve seen discussed here having a much lower “C”.

Does this mean tension in the threaded bars, i.e really meaning initial compression of the batteries?

[marshman]

Does this mean tension in the threaded bars, i.e really meaning initial compression of the batteries?

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 four M6 bolts is 165lb per bolt. Torque them to around 0.8Nm and you won't be far off.

[AE-NMidlands]

exactly... you are pre-compressing the cells, so you are not really applying "initial tension."

[marshman]

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[MrPablo]

A little more progress this evening, balance leads are now done.


I've crimped the lugs on the BMS cables, plus the main positive & negative leads. I'm off to an ale festival tomorrow so no more progress until the weekend but so far, so good.

The DIY battery is up and running, the extra 60% capacity has basically taken away any need for solar forecasting right now.

The JK BMS with the 2a balancing was pretty simple to hook up and configure. I went with this BMS for the balancing current and decent support, but it has an extra bonus.
There's a port which sends out BMS data over 3.3v TTL, making it quite easy to hook up an ESP32 to get remote battery monitoring over WiFi.
This same ESP32 can then translate that BMS info and send it to the inverter over canbus, so no need for custom lead acid profiles.
Right now I have a 17s battery sending status info and requested voltages, etc, all over the Pylontech protocol.

17s voltages have been fine as well, the inverter charged it happily to 100% at 58.2v. The extra power I can get for the same amps is a welcome bonus too.

Just need to 3d a case for the canbus adaptor and then I'll get some pictures and close it all up.

[Colin Deng]

It looks great !
First 17s build

[marshman]

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[ALAN/ALAN D]

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

[Tinbum]

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

I was also looking at those.

[Colin Deng]

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