Idiot's guide to a self build battery

AE-NMidlands
Posts: 2011
Joined: Wed Jun 02, 2021 6:10 pm

Re: Idiot's guide to a self build battery

#721

Post by AE-NMidlands »

Stinsy wrote: Sun Apr 09, 2023 12:43 pm 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?
2.0 kW/4.62 MWh pa in Ripples, 4.5 kWp W-facing pv, 9.5 kWh batt
30 solar thermal tubes, 2MWh pa in Stockport, plus Congleton and Kinlochbervie Hydros,
Most travel by bike, walking or bus/train. Veg, fruit - and Bees!
marshman
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Re: Idiot's guide to a self build battery

#722

Post by marshman »

AE-NMidlands wrote: Sun Apr 09, 2023 5:10 pm
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.
Last edited by marshman on Sun Jun 11, 2023 1:07 pm, edited 1 time in total.
AE-NMidlands
Posts: 2011
Joined: Wed Jun 02, 2021 6:10 pm

Re: Idiot's guide to a self build battery

#723

Post by AE-NMidlands »

exactly... you are pre-compressing the cells, so you are not really applying "initial tension."
2.0 kW/4.62 MWh pa in Ripples, 4.5 kWp W-facing pv, 9.5 kWh batt
30 solar thermal tubes, 2MWh pa in Stockport, plus Congleton and Kinlochbervie Hydros,
Most travel by bike, walking or bus/train. Veg, fruit - and Bees!
marshman
Posts: 614
Joined: Thu Jun 17, 2021 7:58 pm

Re: Idiot's guide to a self build battery

#724

Post by marshman »

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Last edited by marshman on Sun Jun 11, 2023 1:06 pm, edited 1 time in total.
MrPablo
Posts: 273
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Re: Idiot's guide to a self build battery

#725

Post by MrPablo »

MrPablo wrote: Thu Apr 06, 2023 7:44 pm A little more progress this evening, balance leads are now done.
Image

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.
10x 405W JA Solar panels (4.05kWp) @ 5 degrees
3x 405W Longi panels (1.22kWp) @ 90 degrees
16.5kWh DIY LifePo4 battery
Solis inverter/charger
0.6kW Ripple WT
64kWh Kia E-Niro
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Colin Deng
Posts: 199
Joined: Mon Nov 21, 2022 8:33 am

Re: Idiot's guide to a self build battery

#726

Post by Colin Deng »

It looks great !
First 17s build
Colin Deng(Batterycolin)
Battery supplier for battery cells and pack
Email:guohed070@gmail.com
https://www.linkedin.com/in/colin-deng-2b4277238/
marshman
Posts: 614
Joined: Thu Jun 17, 2021 7:58 pm

Re: Idiot's guide to a self build battery

#727

Post by marshman »

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Last edited by marshman on Sun Jun 11, 2023 1:01 pm, edited 1 time in total.
ALAN/ALAN D

Re: Idiot's guide to a self build battery

#728

Post by 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
Image
Tinbum
Posts: 1112
Joined: Mon May 31, 2021 9:55 pm

Re: Idiot's guide to a self build battery

#729

Post by Tinbum »

ALAN/ALAN D wrote: Mon Apr 10, 2023 3:56 pm 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
Image
I was also looking at those.
85no 58mm solar thermal tubes, 28.5Kw PV, 3x Sunny Island 5048, 2795 Ah (135kWh) (c20) Rolls batteries 48v, 8kWh Growatt storage, 22 x US3000C Pylontech, Sofar ME3000's, Brosley wood burner and 250lt DHW
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Colin Deng
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Joined: Mon Nov 21, 2022 8:33 am

Re: Idiot's guide to a self build battery

#730

Post by 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
Colin Deng(Batterycolin)
Battery supplier for battery cells and pack
Email:guohed070@gmail.com
https://www.linkedin.com/in/colin-deng-2b4277238/
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