DIY 550Ah Lithium Battery Bank

[cargovanconversion]

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After top balancing the new Lithium battery cells, I will put the two 12V - 272Ah batteries together. A box from plywood without sides will hold the batteries with four threaded rods as enforcement. The battery cells are connected with double bus bars, BMS leads and six BMS power leads. The BMS is placed above the cells, next to a fuse holder and two battery terminals.
Van Williams

[Buc22]

Nice project and very informative. I have 16 272AH Lishen cells on order and waiting patiently to get started. What are the dimensions of your compression plates?

[cargovanconversion]

Originally Posted by Buc22

Nice project and very informative. I have 16 272AH Lishen cells on order and waiting patiently to get started. What are the dimensions of your compression plates?

Wish you well with your adventure in Lithium
I used 3/4" plywood for the side panels. Because I have a very limited area to store the batteries, I kept the dimensions to a minimum. The width of the panel is the width of the battery plus twice the diameter of the washers used for the threaded rods. This makes the rods fit snug alongside the batteries.
The height is the height of the batteries including terminals plus about 2-1/4"; that supports a 1/2" bottom plate, about 1/2" above the terminals and about an inch for the BMS and fuse. Without storage size restrictions, I would add another inch to the width and about 1-1/2" to the overall height. That makes life a lot easier!
I started with the box, while waiting for the batteries, but over-sized all the panels; only when I had the actual cells, I cut them all to size.
Van Williams

[Buc22]

Thanks for the info

[Winston]

Got a chuckle watching you measure the individual cell voltages of cells connected in parallel! Cells, in parallel, of course, all are at the same voltage.

On another matter, we're not familiar with the cells you're using. Could you let us know where you got them? Thanks.

[GeorgeRa]

Originally Posted by Winston

Got a chuckle watching you measure the individual cell voltages of cells connected in parallel! Cells, in parallel, of course, all are at the same voltage.

On another matter, we're not familiar with the cells you're using. Could you let us know where you got them? Thanks.

Hilarious indeed, but, these equalized batteries are equal now, GOOD job. Luckily these batteries didn’t go ballistic.

[cargovanconversion]

Originally Posted by Winston

Got a chuckle watching you measure the individual cell voltages of cells connected in parallel! Cells, in parallel, of course, all are at the same voltage.

On another matter, we're not familiar with the cells you're using. Could you let us know where you got them? Thanks.

Of course, this shows my level of electrical knowledge But this was after top balancing; I started off with one cell, just a bit off.
These are 3.2V - 272Ah LiFePo4 Lishen cells (similar to EVE cells). There are multiple source for this type of cell, but I got them at Alibaba.com from Shenzhen Xuba Electronic Trading Co., Ltd. Their email contact is Pina Long. I have more rescources on my website/page: CargoVanConversion.com. My total cost for 8 cells was ~$750.00 including shipping, tax, handling, import fees. It takes about 6 - 8 weeks from China to the US.
Van Williams

[cargovanconversion]

I continue with the assembly of the Lithium battery by inserting the threaded rods, that will hold the four cells together, while preventing unwanted bulging of the cells. Install and connect the BMS (Battery Management System), fuse box, positive and negative terminals, temperature sensor and bluetooth.
Finally, I test out the Bluetooth connection with the included app and make some prefered changes to the settings.


YouTube Video Link



Van Williams

[markopolo]

Just an FYI - The accuracy spec of your Klein MM400 is listed as ±(1.2% + 3 digits).

If the actual voltage being measured is a true 14.000V for example then the MM400 could display plus or minus 0.17V so 14.17V to 13.83V and still be within spec. (0.34V range)

Apply this to the 3.650V you previously focused on for example:
1.2%*3.65+3*0.001 rounds to 0.046V - the Klein MM400 could display 3.604V to 3.696V (14.42V to 14.78V pack equivalent) and still be within spec.

You might want to consider getting a meter with much better DCV accuracy specs for the 2V to 15V range applicable to a project like this.

[booster]

Originally Posted by markopolo

Just an FYI - The accuracy spec of your Klein MM400 is listed as ±(1.2% + 3 digits).

If the actual voltage being measured is a true 14.000V for example then the MM400 could display plus or minus 0.17V so 14.17V to 13.83V and still be within spec. (0.34V range)

Apply this to the 3.650V you previously focused on for example:
1.2%*3.65+3*0.001 rounds to 0.046V - the Klein MM400 could display 3.604V to 3.696V (14.42V to 14.78V pack equivalent) and still be within spec.

You might want to consider getting a meter with much better DCV accuracy specs for the 2V to 15V range applicable to a project like this.

X2. We are starting to see this more and more on the forum with the higher required accuracy needed to work properly with the lithium batteries. Accuracy that is good enough for lead acid just doesn't make it for a lithium setup procedure.


As always, the caution is that just because a digital meter displays a lot of digits doesn't mean they are valid. Be in electronic measuring or digital calipers or any other display, be sure to look up the actual resolution and accuracy. Also be sure to read the the accuracy numbers thoroughly as things like 1% of reading are a whole lot different than 1% of full scale.


Repeatability is usually, but not always, better than true accuracy with meters so comparison readings of the same parameter are likely to be better than the number itself.


High accuracy meters are not inexpensive, and really should be recalibrated regularly which is also a bit of cost plus you need to find a standards lab that deals over the counter.

[markopolo]

To further illustrate the need for accuracy, the 0.34V voltage range mentioned above represents 80% of my LiFePO4 battery's capacity. What's in play here for cargovanconversion is half of that - the plus or minus 0.17V (at 14V example) but that could still mean the battery is actually at say 20% SOC when cargovanconversion thinks it's at 60% SOC or vice versa.

100% SOC for LiFePO4 is given as 3.65V until the residual current is C/30 or alternately, some manufacturers say 3.65V and 2% of the batteries capacity tail current. You have to know that your 3.65V is accurate in the first place though.

The BMS app interface will help if a coulomb counting discharge test is undertaken and recorded. The rested voltages at 80%, 60%, 40% & 20% SOC are required for that BMS to utilize the Reset Capacity ( https://www.classbforum.com/forums/f...tml#post121662 ) option if the reported SOC becomes inaccurate do to periods of non-use, limited use or the effect of really small currents that escape measurement. 24hrs rest at each step down seems to produce a stable voltage. Winston's data (prismatic cells): https://www.classbforum.com/forums/f...tml#post103586 & my data (cylindrical cells) https://www.classbforum.com/forums/f...tml#post107776