DIY case for 12V 11-Ah pack from pouch cells

spinningmagnets

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This isn't necessarily the best way for me to do it, or even a good way for anyone to do it, but here it is...

I acquired some high-amp LTO cells. This chemistry has a low 2.4V nominal voltage so it takes 5S X 2.4V = 12.0V. I am using 6S so in case of the failure of a BMS, I can charge the cells directly from a car's 14V alternator with no BMS during an emergency.

This chemistry provides an exceptional number of cycles, measured in the thousands, and it also performs well in very cold weather (it snows here in Kansas). It is also known to be able to be drained down to near zero volts, and it can still be charged up with confidence, without fear of a Lithium fire.

These are from Kokam in South Korea. Asia is experiencing a surge in the purchase of electric buses and also hybrid buses. The hybrid cells must provide the full vehicle amps from a smaller pack (compared to a pure EV vehicle), so they are all very high C-rate. Even when the cells are not fully loaded to their max ability, the highest C-rate construction allows them to run cooler under all conditions.

Having multiple internal tabs of the thickest construction will take up some of the room that could be used to fill the cell with more active material, so these cells give up some capacity in exchange for very high current, without getting too hot.

Anybody can order pouch cells in any size, shape, or chemistry...along with the highest possible C-rate. All you have to do is pay up front for $500K's worth. Fortunately, an existing size fits my application, so I only needed to buy six.

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In the pic above, the white board underneath is a plastic kitchen cutting board that is 9mm thick (a hair under 3/8ths inch), made from High Density Poly Ethylene / HDPE, 15-inches by 20" / 38cm X 50cm ($13 at Walmart).

The positive tab on the cell has a section of plastic ziplock bag over it, and held in place by low-stickiness blue painters tape (doesn't leave a sticky residue).

The Cardboard Aided Design shape helps me calculate the sizes I need to cut to make the case. The battery tabs will slide through thin slots I will cut into the head-board. The aluminum bar is for making the tab clamps, 1/2" X 3" and a foot long ($15 on ebay).

BatteryPouchCase2.png

The pic above shows me cutting 1.5mm thick plastic cell separators/insulators from the sides of a plastic storage tub.

The flat lid will be used as the plastic bench cover for the pack assembly.
 
Sounds like a fantastic car battery replacement. Or a UPS battery that works in -100f.. :lol:
Will be watching the build
 
I have a 100W solar panel in my closet for power outages, and 12V is good for keeping my phone, laptop and 18650-cell flashlights charged up during a disaster. The solar panel puts out 15V to feed the 12V charger, so 6S can take-in the solar panel output or a 14V car alternator output.

2.6V [max] X 6S = 15.6V, so there is no chance of an accidental overcharge from 14V-15V sources...

It's sometimes a bad idea to try and get one design to accomplish several functions, but...as long as it was only a little more cost to get high-amp cells, I am also making this pack so that it should be able to jump-start a car.

Plus, my kWeld can run off of 12V, so that will be handy.
 
Made a few minutes of progress today...

In the pic below, I am using dirt-cheap drywall screws, Philips-head. The small drill bit makes a pilot hole, about 2/3rds the diameter of the screw-threads OD. The large bit is what I used to slowly and gently carve-out a chamfer-recess so the metal heads of the screws will sit slightly below the surface. Since they are metal and conductive, I will also cover them with PET-tape insulation (similar to Kapton).

The wood corner braces are just soft pine 2X4 scrap that I cut down on a table saw by eye, to roughly the width of my thumb.

I am happy to report that HDPE kitchen cutting board cuts easily with a coarse-tooth table-saw blade, the standard type for cutting wood (although a fine-toothed blade would work too). After setting the table-saw fence, I ripped the four side-pieces and the four wood-braces to the same width.

The HDPE rectangle in the middle is a side-compression plate. If you look closely you can see a dark plastic 2mm thick shim along side it, so that when the four sides of the case are secured to each other (and the shim is removed), the compression-plate will have some "slop" to allow it to slide easily inwards when compressing the cells.

BatteryPouchCase1.JPG

The compression-plate and the dark plastic shim are shown as a stand-in for the cells. The center clamp holds it all together at the correct distance, and the other clamp holds the wooden brace in the joint while I drill the pilot hole, chamfer the screw-head location, and then insert the drywall screw.

BatteryPouchCase2.JPG

If you look closely, the head-plate has six slots cut in from the right side, and six slots cut in from the left side. The center of the head-plate is solid. The width of the cut that this particular table-saw blade makes (the "kerf") is 2mm wide. The remaining head-plate material between kerfs is about 8mm wide between each cut. The cells are 7.4mm thick, and the plastic sheet separators are roughly 1.4mm thick.

BatteryPouchCase3.JPG

Notice the screw locations are slightly offset, rather than symmetrical. This way the vertical screws and the horizontal screws do not interfere with each other. Once I am happy with the way it turns out, I will loosen all the screws, squeeze-in some clear Gorilla glue, then tighten the screws back in. This new glue has a one hour primary set time, and 24 hours for a full cure. the one hour set allows me time to move things around a bit so I don't have to be in a hurry, or precise in the initial assembly.

I suppose I will find out tomorrow if this works well on HDPE and wood.
 
Most glues don't stick well to HDPE. Sanding the surface helps. Thermal welding works well with the right equipment.
The wood and screws alone should be pretty good.
 
Yup, this Gorilla glue doesn't work on HDPE. As you said, Richard, the wood and screws feel strong and stable.

I'm sure there is something somewhere that would work on kitchen cutting boards. I will keep looking because these are so cheap and available

edit: just tried "JB Weld for Plastic" and it seems to be working OK so far.

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I am curious too regarding these for the spotwelder. Have you made anymore progress on this ? Tried the build with the Kweld yet?
 
I have made some progress but haven't posted pics yet. I figured I was close to finishing and was going to do it all at once. Of course, I am easily distracted.

On my day off from work I accompany my wife when she likes to shop at antique junk shops (she doesn't ask for much, so....why not). I am annoyed by "decorations" that don't do anything. For instance, she found a very good price on an old 1930's typewriter and camera, very cheap. They look cool, and collect dust just as good as much more expensive antiques....

I stumbled upon a non-working railroad lantern for $8. It normally used a disposable 6V battery that is the shape of a large cube, and a 6V 1930's car accessory light. I converted it to a 12V LED, and the battery is a 4S 18650 made from the Nishi kit. I would have used a Vruzend kit, but I had the Nishi's handy.

She likes it, and I like the fact I have a cool looking dust-collector that is actually useful in a power outage (I am in tornado country). Its a Volkano model 151 (here's a random link from ebay)

https://www.ebay.com/itm/VINTAGE-IN...429395?hash=item2ad2fd1b53:g:g2wAAOSw9TFdFsXu
 
Sounds familiar! Just spent a weekend trip with the wife looking at things (and buying some) that I wonder how that adds value to life ...other than it puts a smile on her face. But I guess we all can use a yin to our yang. Keep us posted on this project ...I am especially interested in how they perform with the welder.
 
How about fiberglass? Use a HDPE or cardboard box as a form, layer with fiberglass inside or outside.
 
I have some similar cells. I found they fit nicely in a MTM .30cal plastic ammo can. I used aluminum bar stock for terminals. I figure I can jump start a car with it, but haven't had a dead one to try it on yet. It did not do well as a source for my spot welder.

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I use a waterproof guncase which houses 3S3P 12V 24AH pack build for my E-kayak project.
https://www.amazon.com/gp/product/B00JVA7UGM/ref=ppx_yo_dt_b_asin_title_o07_s00?ie=UTF8&psc=1
It houses the BMS and speed-control/throttle for the brushed trolling motor also.
This doubles as my power source for my spotwelder.....works great for both.
Toggle switch is forward/reverse, the bar is the throttle (rotate forward to increase speed).
Terminals are stainless wing screws for quick hookup to motor.

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