Building my next pack 12S72P (with 36P modules)

[prensel]

Hi all,

I'd like to present my next battery building project which consists of a modular pack having modules each having 36P cells.
The cells i'm using are Samsung 29E, each 2850mAh. So each module will be 3.7V/102Ah.

I previously did build a pack with the same cells for my Vectrix electric motorscooter. That pack was also modular build with 30P cells, 36 modules.
So a serious pack with 150V and 85Ah, maximum current is 240A causing serious thoughts of busbars, connectors etc.

The pack im building now is for my CityEl 3-wheel 'motorcycle' kinda thing...

Design considerations:
The modules will be put in battery size boxes custom-made of RVS steel frames covered inside with lexan plate and insulation.
Size of each box will be similar (or smaller) to 100Ah SLA car batteries like 170mm wide, 325mm long and 210mm height.
My boxes will be a little bit higher then this standard size to accommodate the stack of 12cells high, 250mm.
Each box will have 8 modules like 4S2P so its actually 4S72P and delivers 14.8V and 205Ah. Double the density and halve the weight of the SLA lumbs.
Inside each box will also be a BMS board which communicates over CAN-BUS with the other boxes, dashboard etc.

I will add some pictures and the buildup process next.
Paul

 

[skoleskibe]

Reading the headlines i was thinking about my Ellert, (original City El) which i bought some 20 years ago.
What motor and controller are you using?

 

[prensel]

I have one Basic version with the Thrige Titan motor on 36V (this one is going to the Li-ioned...) and one Fact4 version with the Perm132 motor on 48V.
Both still have their original Curtis controllers and HF chargers.

For the Fact4 im thinking of converting sometime to 72V with an OpenRevolt controller.

 

[mistercrash]

This is going to be great. I loved your previous build for your Vectrix. I did plans for making a 20S27P battery following your method by making 27P modules out of Tesla 18650 cells. But the total cost of the cells and all the materials needed pushed me to get a cheaper alternative. Waiting patiently for pics of this new build.

 

[prensel]

Here's one of the finished modules

 

[prensel]

These 'brackets' are pre-fabricated before welding them to the pack of cells.

Each section of 6 cells is connected by two busbars, one on each side, of 10*0.2mm.
So 6 busbars tacked together into one on each side, 12 in total, with a total diameter of 24mm2, good enough upto 240Amps..or something

They all connect at the top where they are stamped with a 5mm hole for interconnection to the other cells.
Big difference with this setup regarding the pack build for the Vectrix is there is no soldering busbars anymore.
Everything is welded together with just pure nickel.

 

[prensel]

This is going to be great. I loved your previous build for your Vectrix. I did plans for making a 20S27P battery following your method by making 27P modules out of Tesla 18650 cells. But the total cost of the cells and all the materials needed pushed me to get a cheaper alternative. Waiting patiently for pics of this new build.

Ok, according to my calculations my modules are still cheaper then standard/COTS available LiFePo batteries.
I pay about €2,40 per Samsung 29E cell of 2,850mAh.
So a module with 36 cells/102Ah is costing me €86,40 per module.Add some €20 for nickel and brackets and thats it.

Comparable Winston 100Ah LiFePo are about €150 each so i'm way cheaper DIY.
And i can build them any shape and any size i like.

 

[mistercrash]

When I compared the two options I was considering to make a battery, I considered all of the expenses. Cells, wires, Nickel, Copper, lugs, nuts, bolts, washers, heat shrink, shipping charges, customs fees, etc. 18650 cells ended up being more expensive for me compared to Leaf modules so I went with the leaf modules. A battery with 18650 cells would have ended up being smaller and lighter, I just did not have the extra cash.

I see you are making some changes from you're other battery. It looks cheaper to build like you're doing now. How big are the four Nickel strips in which you punched the 5 mm holes in?

 

[prensel]

When I compared the two options I was considering to make a battery, I considered all of the expenses. Cells, wires, Nickel, Copper, lugs, nuts, bolts, washers, heat shrink, shipping charges, customs fees, etc. 18650 cells ended up being more expensive for me compared to Leaf modules so I went with the leaf modules. A battery with 18650 cells would have ended up being smaller and lighter, I just did not have the extra cash.

I see you are making some changes from you're other battery. It looks cheaper to build like you're doing now. How big are the four Nickel strips in which you punched the 5 mm holes in?

Yes i've changed things from the previous build.
Space was the biggest consideration with the Vectrix so i couldnt use the cell brackets im using now but had to glue the cells together.
For the busbars i've also looked at different solutions then.
Using solid copper 16mm2 busbars with the Vectrix build was one option but i never liked it really because it was way to much work with the soldering.
During that build i came up with the idea that the next build totally had to be 'weldable' by hand or even by CNC welding system. Very hard to do for soldering.
The 4 nickel strips (busbars) are made up of 6 specially cut 10mm*0.2mm strips and welded as layers to one busbar. So at the end/connection point it is 12mm2, and there are two for the positive and two for the negative connection so 24mm2 for each connection. Good enough for 200-240Amps. I could have used 10x0.3 strips which would have gave me 36mm2, but i expected that welding 0.3 to 0.3 would be too hard.

Its much faster to process now by hand.
Next build is probably going to be more automated by using a strip-cutting-machine and CNC operated CD welder

 

[mistercrash]

Awesome. Is that a JP Welder you are using?

 

[skoleskibe]

My original "Ellert" did not have a controller. It had a hydraulic operated variable resistor and a relay shorting the resistor once the speed was past 25Kmh as i remember. The motor was the thrige pmdc and the batteries was 3S100ah 12v
Range was 30-40 km and topspeed app 35kmh. Used it for several years driving my small children to and from kindergarden.

Still miss the dang thing.

By the way i do still have the users manual.

 

[prensel]

Changed the design a bit.
Decided to lay the cells flat so all weight is just on the brackets and not on the stacked cells.
Cells are 'cornered' with PVC profiles, every module needs to get shrink-wrapped and then 4 modules will be fitted into one batterybox,



This set of 4 is going into one temperature isolated alloy/ss batterybox with the same dimensions as the SLA lumbs.
Regarding the size: the SLA box will provide double the amount of cells here, this is just a 102Ah pack for testing.

 

[prensel]

Still miss the dang thing.

By the way i do still have the users manual.

 

[gogo]

Can you detect any difference in rollover propensity characteristics with reduced battery weight? Did you convert battery space to cargo space?

 

[okashira]

We're looking into a way to reconfigure Model S modules into 12s37p, might be a cool option