DIY Batteries

[Raul]

How do you compress the cells with your wooden box?

I do not, just very tight snug fit with separators when cells are discharged.
The way I get them in is a 3mm compression on the ends, then a fibre separator between the cells. Working my way towards the middle, the last cell gets pushed in tight with the separators helping to slide in. After first charge, you can turn the box upside down, and they will be snug no falling out.

 

[Gromett]

I do not, just very tight snug fit with separators when cells are discharged.
The way I get them in is a 3mm compression on the ends, then a fibre separator between the cells. Working my way towards the middle, the last cell gets pushed in tight with the separators helping to slide in. After first charge, you can turn the box upside down, and they will be snug no falling out.

Is it necessary to compress those cells? Outside of the unpackaged (pouch) prismatics I didn't think compression was necessary for LiFePO4 chemistry cells?

 

[Revolvor]

I do not, just very tight snug fit with separators when cells are discharged.
The way I get them in is a 3mm compression on the ends, then a fibre separator between the cells. Working my way towards the middle, the last cell gets pushed in tight with the separators helping to slide in. After first charge, you can turn the box upside down, and they will be snug no falling out.

Thanks, that's interesting.

 

[L' Hobo]

As others already mentioned, those are the sensing and balancing wires. By keeping same length, it will have equal resistance and also the ability to re purpose the bms without the wires being butchered, they can be re configured in a different arrangement. So the closer cell to bms ends up with excess wire that i just coil up..
Also for balancing and sensing purposes 0.5mohm difference can trow a false reading. The cells are read down to last mili volt. The original wire measures 0.5-0.6mohm including the ring terminal. If I cut, the wire resistance will be modified and not equal.

I know very little but someone once told me that it was very difficult connecting (soldering) the 3.4 batteries together.
Does one have to have special equipment to do this?

 

[Raul]

I know very little but someone once told me that it was very difficult connecting (soldering) the 3.4 batteries together.
Does one have to have special equipment to do this?

The cells have 6mm studs, and come with buss bar links and nuts. All I needed to link them was a 10mm socket, and tight to 5nm. A multimeter is necessary for testing the wires, etc. The more fancy resistance meter etc. is nice to have, but not necessary for battery diy. I solder nothing everything is crimped and bolted. A hydraulic crimper is a must for the heavy lugs,

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[Raul]

Is it necessary to compress those cells? Outside of the unpackaged (pouch) prismatics I didn't think compression was necessary for LiFePO4 chemistry cells?

Some ppl do compress, it’s suppose to give a slight longer life. The caveat is to apply the right compression force, or, if not possible, leave it alone as it will damage it. Some put them in a fixture like myself, and some even loose on a shelf.
It is very difficult to measure 300 kg force on the side of a cell, so fixture is better than to much compression.

 

[Two on Tour]

Is it necessary to compress those cells? Outside of the unpackaged (pouch) prismatics I didn't think compression was necessary for LiFePO4 chemistry cells?

I can't comment on other cell manufactures, but I do not compress my cells as my CatL cells data sheet states that the inner walls of the cells aluminium container apply 300kgf to the cell contents.
I also confirmed this was the case with the produce description on the CatL website.

Edit: I do bind my cells together with Kapton tape which does restrict the cells expanding, but I applied the tape when the cells were at a fully charge state.

 

[MisterB]

Before assembling my Seplos battery case, I compressed the EVE cells using threaded rods and plywood ends PRIOR to charging initially (top balancing). The Seplos case also allows for compression when assembling.

The only cells that are usually welded together are the small cylindrical cells used in vape machines, which when put together in large numbers are used as home/leisure batteries. I think some power packs also use cylindrical calls.

 

[Gromett]

Just searched through my watch history on youtube to find the video that made me drop the plans for threaded bar technique.

 

[Raul]

This morning weather was a bit more cooler, low 20’s and overcast for the first half of the day. We started with the rest of the panels.

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[Raul]

By midd day we had all the panels up, and I finished the cables in the combiner box.

 

[Raul]

Then we cleared the surrounding near by trees, and the sun made it trough the clouds, just in time for testing the charging.
There are 20x 455w panels, 9100wp, but the air cooling at the back of the panels helped to yield a bit over that. The batteries alone with no loads, copes with the power, no heat and no voltage spike. That’s first sign this cells are more than capable to handle in excess of 0.3C charge rate, impressed so far by envision grade B.

 

[Raul]

These are the houses will be supplied by the system for time being. Still work in progress, and on the left of the pic, next year will be a large car port, or another 20 panels array, east-west. The current ones are south facing.

 

[Spriddler]

Been doing it in India for years.........

 

[MisterB]

Just searched through my watch history on youtube to find the video that made me drop the plans for threaded bar technique.

To be pedantic, compression isn't really compression, it's just to stop the cells from swelling ..... but from what seems to becoming the norm, decent quality cells don't seem to 'suffer'as much ...
One issue with swelling is that the cells then can't be assembled into a proprietorial case as they wouldn't be 'uniform' in size. Stopping them from swelling (using tape is another way) can prevent problems when used in those sort of cases.

Bottom line for me - stop them swelling during top charging, whether you call it compression or not ....

Footnote - the guru to lots of these builds has also suggested that compression isn't required on one of his videos .... So my thoughts might be boll#x ...

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[Gromett]

To be pedantic, compression isn't really compression, it's just to stop the cells from swelling ..... but from what seems to becoming the norm, decent quality cells don't seem to 'suffer'as much ...
One issue with swelling is that the cells then can't be assembled into a proprietorial case as they wouldn't be 'uniform' in size. Stopping them from swelling (using tape is another way) can prevent problems when used in those sort of cases.

Bottom line for me - stop them swelling during top charging, whether you call it compression or not ....

Footnote - the guru to lots of these builds has also suggested that compression isn't required on one of his videos .... So my thoughts might be boll#x ...

To be fair he does state it is fixture not compression in the video itself.

But he also says you cannot stop them swelling and they ALL swell a certain degree as part of the process of charging.

His follow in video covers that bit. This one you may find interesting.

 

[MisterB]

There has been some discussion on using spring compression, so it allows some expansion, but it's something I haven't really looked at properly.... It might be an option?.

On a different note, these might be of interest to anyone looking at installing their own - I don't think it will be too long before a motorhome/camper self builder with weight to spare, considers ex EV batteries as a cost effective option

Thread '9kwh lithium-ion battery packs ready to go. Plug and play' https://diysolarforum.com/threads/9kwh-lithium-ion-battery-packs-ready-to-go-plug-and-play.89770/


coupled up with an inverter/charger it might offer an alternative to a 12v system?

Just for clarity, I am not competent enough to suggest it's workable, feasible, affordable but I do think it's interesting....

 

[tonyidle]

I built my battery from four "lightly used" CALB cells - capacity 210Ah. Each cell is in a hard plastic case.

 

[Raul]

Another order just arrived, this time some eve MB31 cells and some budget grade B 280ah envision cells. I will build a box at the weekend for the grade B's with JK bms, and the mighty MB31's are going into a seplos case with seplos V3 bms, at a different location. The grade B are for me to mess around with for a bit, the price is very attractive, and if they play nice, I will have couple of more orders.
The B's don't look shabby at all, a very small gap 1-1.5mm against each other, the MB31 are just perfectly flat, not even 1/4 of mm, nothing.

Forgot to say, the MB31 are considerably heavier, 5.6kg, they managed to squeeze more stuff inside the same size case, giving a wapping 1kwh per cell; that would give a 16kwh per 48v pack.

 

[68c]

There has been some discussion on using spring compression, so it allows some expansion, but it's something I haven't really looked at properly.... It might be an option?.

On a different note, these might be of interest to anyone looking at installing their own - I don't think it will be too long before a motorhome/camper self builder with weight to spare, considers ex EV batteries as a cost effective option

Thread '9kwh lithium-ion battery packs ready to go. Plug and play' https://diysolarforum.com/threads/9kwh-lithium-ion-battery-packs-ready-to-go-plug-and-play.89770/


coupled up with an inverter/charger it might offer an alternative to a 12v system?
And
Just for clarity, I am not competent enough to suggest it's workable, feasible, affordable but I do think it's interesting....

Do cars use the same Lithium type batteries as our leisure batteries or the more 'dangerous' type used in cameras and ebikes etc?

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