DIY Lithium Packs, Proposal and Discussion

rollerbearing

Well-known member
Not trying to belabor any of this - just followed a few more links and thought some of the content was useful. These high current, low voltage drop SOPs are new ground for me. Semi pun there was not intentional.


Copper busbar surface prep and contact characteristics:

Some more on Belleville washers:

Aluminum busbars:
 

vanski

If it’s winter, I’m probably skiing..
Thanks for showing our Sprinter community the way here MWD!!! I took my education from your thread(s) along with working with some great fabricators (LOL) who produced some 4 cell and 8 cell clamping systems to produce this bad boy (please note these are not completely installed for prime time, just bolted in for testing and some initial light use). This is in a 118 high top t1n bolted to the wall with the custom clamps and a some additional steel members for additional support):

E9B4EB64-D148-49EA-9194-F70DA2AA7EF2.jpeg
CD5BCA32-730C-4149-98CB-D85C19F60F12.jpeg
70A7FBAF-3498-463F-9324-D113372E3FD0.jpegE9B4EB64-D148-49EA-9194-F70DA2AA7EF2.jpegCD5BCA32-730C-4149-98CB-D85C19F60F12.jpeg70A7FBAF-3498-463F-9324-D113372E3FD0.jpeg
 

Midwestdrifter

Engineer In Residence
Thanks Vanski!

If anyone is interested a friend of mine will be offering the clamping plates and hardware for sale in the near future. The plan is to add coil springs to the assembly to ensure consistent clamping force and maximum cycle life.

With all the parts and tools making one of these 560AH packs can be done for less than 1,900$ DIY. Obviously you need to source your own cells from China unless you known someone stateside that resell gray market A- or B+ grade cells.
 

RVBarry

2023 AWD 170 DIY CamperVan
Hi, with the clamping plates, are prismatic cells still recommended?

I notice non-prismatic cells can be much cheaper. Someone posted here yesterday that they can get 8x 280aH cells (13V, 560aH) for under $900USD shipped from China. A link to a vendor was not included.
 

Midwestdrifter

Engineer In Residence
You could possibly use pouch cells, the springs for clamping would absolutely be required though. Some additional padding might be called for.

My 8x280AH cells were about 900$ delivered, so the pricing is pretty competitive. If you already have the tools to balance a pack, and crimp terminals, etc, it can be fairly cheap to make your own even with BMS.
 

PaulDavis

Member
Thanks Vanski!

If anyone is interested a friend of mine will be offering the clamping plates and hardware for sale in the near future. The plan is to add coil springs to the assembly to ensure consistent clamping force and maximum cycle life.

With all the parts and tools making one of these 560AH packs can be done for less than 1,900$ DIY. Obviously you need to source your own cells from China unless you known someone stateside that resell gray market A- or B+ grade cells.
What's the status on your friend's offerings?

It seems that along the way, you needed to fabricate some small electrical components too. For me personally, this is intimidating (more so than fabricating the rest.

(I have 7-year old Lifeline AGMs that are now becoming less and less usable, and am looking at Li as the replacement)
 

blutow

Well-known member
I'm currently installing 4 x 272Ah DIY batteries in my 2021 170. I welded up some custom battery boxes to compress the cells and protect everything (see pic of one battery below).

Also, with these larger prismatic cells, most recommend that they be installed sitting upright rather than on their side. For my Lishen cells, the spec sheet specifies that they should be installed upright. I've seen people install them on their side and they certainly work, but I personally wouldn't do it in a high vibration environment like a van or boat.

The 16 cells cost right at $1600 delivered and I have close to $2500 into them with the BMS's, cabling, boxes, etc. They all tested over 280Ah, so that's about 1,100Ah for a fraction of the cost of off the shelf options. It's a bunch of work and can be dangerous if you don't take precautions, so not something to be taken lightly in my opinion. Doing all the balancing, testing, fabrication, etc. kept me busy for at least a month while I was waiting on my van to arrive. Fun stuff if you like tinkering with high power things.

IMG-0518.jpg
 

calbiker

Well-known member
The fun begins when building your own bms. You get exactly what you want.

BMSgen3.jpg

BMSgen3B.jpg

ESP32 processor with WiFi
Current granularity down to 9.2 mA with a 300A shunt
SD card datalogging as well as data display on iPad
Board, cell and ambient temperature measurement
High & low voltage disconnect signals
Charge chassis bat from house bat when chassis b. is below a programmable threshold and house b. is above a programmable threshold
16-bit adc
 

rollerbearing

Well-known member
Ahhh - memories of 1" bits of Kynar insulation embedded in the carpeting back during the wire wrap days.

You must have a good magnifier.
 

Zoomyn

Member
Looks great yet it reminds me to share my wish list… PWM resistance heater pad controller, something that is not wham bam thermostat controlled, something able to ‘learn’ ambient vs. cell core temperature and continuously ration 4x 12w outputs etc. just enough to keep coldest cell above 35 or 38f…

Also speed controlled cooling fan, yet something smart enough not to push hot stagnant air from RV or Van interior over (relatively) cooler cells, attempt to maintain 78 or 80f or proportional limited charging until cells have cooled - to stop generator charging etc. when folk return to sun baked oven campers etc.
 

Airtime

Well-known member


This method is a bit labor intensive, so I am not sure if I would repeat or not.
Great build thread on your lithium pack! I built one with same 280Ah cells last summer. At the time I did solid bus bars but looking at more flexible options since I'm now using springs for compression. You said not sure if you would repeat this DIY approach? If doing it now, what would you do?
 

Midwestdrifter

Engineer In Residence
Great build thread on your lithium pack! I built one with same 280Ah cells last summer. At the time I did solid bus bars but looking at more flexible options since I'm now using springs for compression. You said not sure if you would repeat this DIY approach? If doing it now, what would you do?
Good heavy wall lugs and cable on my hydraulic crimper? If I could source some Calb style busbars in the right size, I might go that way.

If I was ordering cells again today, I would get cells with laser welded studs instead of threaded holes. It gives you a lot more tolerance for non-flat or non-perfect busbar connection points.
 

jmole

Active member
Wanted to add a sneak preview of my build - 16 cells in 4s4p, packed in like sardines with all my other electrical stuff. You can just barely see the wheel well behind the trays for the DC components.
78476C4D-07BF-4AC4-AB3F-53E9718FDAC6.jpeg

DIY box w foam compression & 1/2” thick aluminum busbars. Metal compartment on the end houses BMS, contactor, fuses, etc.
49BDC8C8-EA29-446C-B66F-C779B7CF6C6A.jpeg
 

jmole

Active member
If I was ordering cells again today, I would get cells with laser welded studs instead of threaded holes. It gives you a lot more tolerance for non-flat or non-perfect busbar connection points.
I ordered with welded studs and I wish I'd have gotten cells without them. The studs on mine were like +/- 0.1" vs the actual terminal positions, and the laser cut busbars I made didn't always align, so I had to ream out the holes to make them fit.

Before studs were popular, most people were using red loctite with M6 set screws (grub screws) as makeshift studs, and I imagine that those would be much more dimensionally accurate than the studs I got.
 

rollerbearing

Well-known member
Will that foam maintain compression over years?
Yes - that was my question too - Does the spring constant remain stable over years? Initially looking at the data my first impression was that it does - but I want to give it a harder look. Especially since it is an open-cell foam.

From the Manufacturer Lit:

  • PORON EVExtend maintains constant pushback force, allowing designers to meet both beginning and end of life limits despite pouch expansion
If it does then that is quite the find - thanks jmole!

I suppose one could similarly implement this in the plate/all thread design by putting die springs on one side between the plate and the all thread end-nuts. Then tighten all thread nuts until die spring compression gives correct PSI for plate contact area.
 
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