Spot-Welding a123 Prisimatic tabs

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oatnet   10 MW

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Spot-Welding a123 Prisimatic tabs

Post by oatnet » Jul 17 2011 2:14pm

I've built a few packs from the prisimatic a123 cells by folding the tabs together 3 times around a balance wire, crimping it flat, and sealing it with a dab of solder at the end.

With most mechanical joins, the contact area is only on the side where the tabs overlap, and if the fastener holding the tabs together comes loose, the tabs separate/arc. With my technique, BOTH sides of each tab become contact areas, and it takes a great deal of force to unroll the folds. The folds are further secured by a layer of heat-shrink (that oozes adhesive all around the join), a plastic clip, and a layer of fiber tape. I got some skeptical opinions at the time, but I've pulled 100 amps through this termination without any sign of heating. However, I also recognize that at some point, despite being sealed in the amber of heatshrink adhesive, the tabs could oxidize, and add resistance, so bonding the metal is also desireable.

I saw some footage of an a123 factory, which shows them laser-welding the pouches, and it stuck in my brain. I don't have a laser welder, and while I could probably tig-weld the tabs together, they would get very hot which would trash the cells. Spot-welding is out, because the battery tabs are thin and made of low resistance metal that won't heat up when the welder's current goes through them.

Then I had the idea to put a thin strip of steel on either side of the weld, making a sandwich with thin steel strips on the outside, and the battery tabs on the inside. When I zapped the sandwich with the spot welder, the steel on either side had enough resistance to get hot, which melted the battery tabs, and welded them together.

I use 3 vice-grips to hold the sandwich together, exposing only the section of steel strip I am about to weld. The vice-grips help dissipate the heat, and I have a wet paper towel resting on top of the tabs. I hear water sizzle when the weld happens, but by the time I shake off a glove and grab the tab it is ice-cold again, so I don't think the cells are getting heat at all.

This is Harbor Freights $160 "115v spot-welder" I could have purchased the same product on ebay for $35 less, but I wanted to be able to return it. Anyhow, on to the pics...


[attachment=3]00_cutting strips IMG_5994.jpg[/attachment]

[attachment=2]01_cutting strips IMG_5993.jpg[/attachment]

[attachment=1]02_stack of strips IMG_6045.jpg[/attachment]

[attachment=0]03_Balance Charge Cells IMG_0201.JPG[/attachment]
Attachments
00_cutting strips IMG_5994.jpg
As with any weld, surface preparation is essential. I did my initial testing on tabs from dead cells; they were wrinkled and covered with

junk, and the welds did not hold well. I clean the battery tabs with a paper towel and alcohol, polishing them until they shine like mirrors.

I thoroughly wire-brushed both sides the sheet steel before I cut it into strips. Use weldable steel not galvanized steel, which is plated with zinc. Zinc fumes are hazardous, and the plating does wierd things to the weld. I got this 22ga sheet from Ace Hardware for $5, only used 1/8th of it.

I used shears for a while but my cuts were not consistant, and it was a pain. I got this paper cutter at a swap meet for $5, it did a great job of cutting strips. Although it could only cut half way through...
00_cutting strips IMG_5994.jpg (113.48 KiB) Viewed 8565 times
01_cutting strips IMG_5993.jpg
... it was simple to flip the sheet over, line up the cut edge with the table, and finish the cut.
01_cutting strips IMG_5993.jpg (134.09 KiB) Viewed 8560 times
02_stack of strips IMG_6045.jpg
Here is a stack of strips, long as the tab is wide, and just big enough to accomodate the weld head.
02_stack of strips IMG_6045.jpg (57.88 KiB) Viewed 8565 times
03_Balance Charge Cells IMG_0201.JPG
Preparation - here I am balance charging a stack of 8 cells to make a 24v pack. I charge them up, let them self discharge while clamped together, and repeat a few times to give them the best possible initial balance. I also prep-cook the operation by cutting a stack of balance wires, heat shrink tubing, plastic clips, and strips of fiber-backed tape, so that I can just grab them during the build.
03_Balance Charge Cells IMG_0201.JPG (77.1 KiB) Viewed 8560 times
Last edited by oatnet on Jul 17 2011 2:48pm, edited 1 time in total.
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Performing the Weld

Post by oatnet » Jul 17 2011 2:14pm

Here is the actual Weld process. Note that picture #5, showing the inside of a weld, needs to be clicked on to be viewed in a new page. Most of the pics need to be clicked on just to open full size. :roll:


[attachment=8]1_tabs and strips clamped IMG_0206.JPG[/attachment]

[attachment=7]2_closeup of one weld IMG_0207.JPG[/attachment]

[attachment=6]3_welded tab IMG_0209.JPG[/attachment]

[attachment=5]4_closeup of 2 weld spots IMG_0248.JPG[/attachment]

[attachment=4]5_Opened Weld IMG_0264.JPG[/attachment]

[attachment=3]6_Lay In balance wireIMG_0218.JPG[/attachment]

[attachment=2]7_First Fold IMG_0217.JPG[/attachment]

[attachment=1]8_two more folds IMG_0219.JPG[/attachment]

[attachment=0]9_crimp IMG_3123.JPG[/attachment]
Attachments
1_tabs and strips clamped IMG_0206.JPG
Note the weld tips on the right side of the picture!

Tape on tab condoms (unshrunk heatshrink) to avoid a short. Tape a pair of cells together so that the exposed tabs line up, press the tabs together at the base. Put a pair of steel strips on either sides of the tabs, as close to the end as you can get it. Clamp it with vicegrips so that just the area to be welded is exposed. This is tricky, I use a small vice-grip on top of the weld area to jockey them into position, before I put this large vice grip on to hold everything together, then I take off the small vice-grip to expose the weld area.

Clamp with the welder tips, and zap it for just an instant, the steel will glow, and melted metal will gush out of the weld.
1_tabs and strips clamped IMG_0206.JPG (45.53 KiB) Viewed 8563 times
2_closeup of one weld IMG_0207.JPG
Here is a first weld. It is fragile at this point, and the steel strips can rotate around the weld spot and break it. I carefully put the small vice-grips right on top of the weld (not too tight, or you crush and break the weld), them move the larger vice-grips over enough to expose the next weld area. Repeat until you have 5-6 welds on the tab, make each weld outside the metal blued by the last weld.

The tabs must be clamped everywhere but the spot you are about to weld, or the steel strips will creep apart and tear the other welds. 3 vice grips are sufficient.
2_closeup of one weld IMG_0207.JPG (48.1 KiB) Viewed 8558 times
3_welded tab IMG_0209.JPG
The rightmost weld was done for too long, 3rd to the left is perfect, 4th/5th/6th wasn't zapped long enough.

If you don't hold the current long enough, the steel strips don't get involved with the weld, and fall off. The weld is much more stable if the steel strips are melted together.

If you hold the current too long, the metal of the tabs evaporates out of the weld, and the rest of the tab gets brittle and breaks on the first fold.

You only get one shot at each weld. If you try to weld it again, the tab gets too brittle to fold. If your weld was too short, the other welds will pick up the slack, so move on and do a better job on the next one.
3_welded tab IMG_0209.JPG (37.89 KiB) Viewed 8563 times
4_closeup of 2 weld spots IMG_0248.JPG
Here is what they look like up close. Note the oozed metal, I clip this off before folding.
4_closeup of 2 weld spots IMG_0248.JPG (128.59 KiB) Viewed 8563 times
5_Opened Weld IMG_0264.JPG
On the left is one steel strip pried off so you can see the involvement of the metal below.
5_Opened Weld IMG_0264.JPG (302.57 KiB) Viewed 1155 times
6_Lay In balance wireIMG_0218.JPG
The balance wire is laid in before the first fold is completed. It will be secured by clamping force and final spot welds, and if it is pulled hard enough to tear it out, I'd rather lose the balance wire than rip the tabs off. :D
6_Lay In balance wireIMG_0218.JPG (20.93 KiB) Viewed 8558 times
7_First Fold IMG_0217.JPG
I use wide vice grips to start the first fold evenly, over the balance wire.
7_First Fold IMG_0217.JPG (119.06 KiB) Viewed 8558 times
8_two more folds IMG_0219.JPG
Then I fold it two more times...
8_two more folds IMG_0219.JPG (15.1 KiB) Viewed 8558 times
9_crimp IMG_3123.JPG
... and crimp it flat as I can with giant pliers. Then I spot-weld the whole package 4 more times along the strip (need a picture of this), which melts everything inside. These welds generate a lot of heat, so I pause between each weld and cool the tab down.
9_crimp IMG_3123.JPG (43.59 KiB) Viewed 8563 times
Last edited by oatnet on Jul 17 2011 3:19pm, edited 4 times in total.
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Finishing up the Tabs and the pack

Post by oatnet » Jul 17 2011 2:15pm



[attachment=9]a_heat_shrink IMG_0220.JPG[/attachment]

[attachment=8]b_plastic clip IMG_3032.JPG[/attachment]

[attachment=7]c_profile of plastic clip IMG_0274.JPG[/attachment]

[attachment=6]d_clips sourced from IMG_6220.jpg[/attachment]

[attachment=5]e_fiber tape IMG_0223.JPG[/attachment]

[attachment=4]f_ assembled 24v IMG_0238.JPG[/attachment]

[attachment=3]g_3 sheets of newspaper IMG_0271.JPG[/attachment]

[attachment=2]h_newspaper installed IMG_0276.JPG[/attachment]

[attachment=1]j_stacked in case IMG_0268.JPG[/attachment]

[attachment=0]k_ case 27.4 on scale IMG_0270.JPG[/attachment]
Attachments
a_heat_shrink IMG_0220.JPG
I use heatshrink (2") that is stiff with adhesive. WHen melted, it flows an amber-like substange over the tab area and into the rolled ends of the tab, making a solid stiff unit. I've pulled this off of dead cells, it was everywhere and it was tough.
a_heat_shrink IMG_0220.JPG (29.66 KiB) Viewed 8560 times
b_plastic clip IMG_3032.JPG
Then I slide a plastic clip over the end. This applies tension holds the base of the tabs together, and supplies a hard surface over the shrinkwrap.
b_plastic clip IMG_3032.JPG (49.87 KiB) Viewed 8560 times
c_profile of plastic clip IMG_0274.JPG
This is what the clip looks like in profile.
c_profile of plastic clip IMG_0274.JPG (44.6 KiB) Viewed 8555 times
d_clips sourced from IMG_6220.jpg
I got the clips from this. I cut each spine into 4-5 clips as wide as the tabs.
d_clips sourced from IMG_6220.jpg (82.19 KiB) Viewed 8555 times
e_fiber tape IMG_0223.JPG
Fiber tape maintains the clip's tension and holds it together even if the clip is broken. I make the tape tight at the base of the tab, which makes the ends of the tape cross over each other when folded.
e_fiber tape IMG_0223.JPG (36.68 KiB) Viewed 8555 times
f_ assembled 24v IMG_0238.JPG
Here is a 24v16ah pack assembled.
f_ assembled 24v IMG_0238.JPG (84.2 KiB) Viewed 8555 times
g_3 sheets of newspaper IMG_0271.JPG
I separate the cells with (3) sheets of newspaper. It looks sort of ratty, but they act as an insulator and a wear barrier, one sheet for each cell and one to wear between them. I cut a chunk out of the top where the cells are welded together, and the remaining bit fits between the taped clips to keep them separated.
g_3 sheets of newspaper IMG_0271.JPG (57.71 KiB) Viewed 8560 times
h_newspaper installed IMG_0276.JPG
Here is a pack with the newspaper installed.
h_newspaper installed IMG_0276.JPG (75.16 KiB) Viewed 8560 times
j_stacked in case IMG_0268.JPG
Three 24v cells sitting in the Pelican case that will be mounted to the forks of an upcoming project.
j_stacked in case IMG_0268.JPG (109.3 KiB) Viewed 8560 times
k_ case 27.4 on scale IMG_0270.JPG
The case, 24s16ah a123 pack inside, and 8 clamps that will mount it to RockShox Boxxer Forks, weighs 27.4 lbs, not bad for 1.42kw. Each clamp will support only 3.42 pounds - including its own weight.
k_ case 27.4 on scale IMG_0270.JPG (84.7 KiB) Viewed 8560 times
Last edited by oatnet on Jul 18 2011 7:35pm, edited 2 times in total.
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Re: Spot-Welding a123 Prisimatic tabs

Post by Doctorbass » Jul 17 2011 8:55pm

Nice work!

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Re: Spot-Welding a123 Prisimatic tabs

Post by BLUESTREAK » Jul 18 2011 7:54am

NICE WORK OATNET. would it help if instead of mildsteel strips you used stainless steel strips?. I am partial to stainless steel for everthing. 8) 8)

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Re: Spot-Welding a123 Prisimatic tabs

Post by regmeister » Jul 18 2011 9:48am

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Last edited by regmeister on Aug 06 2011 10:22am, edited 1 time in total.

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Re: Spot-Welding a123 Prisimatic tabs

Post by oatnet » Jul 18 2011 10:16am

Thanks Doc!

Thanks Bluestreak! You can spot weld some varieties of stainless, some other you can't. Since this is sacrificial metal, not structural, mild steel was enough for me, cheap, and readily available. :D

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Re: Spot-Welding a123 Prisimatic tabs

Post by neptronix » Jul 18 2011 1:00pm

Great info, oatnet. Thanks for the post.

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Re: Spot-Welding a123 Prisimatic tabs

Post by EBJ » Jul 18 2011 3:47pm

looks good. I like the clamping method.

Has anyone actually tried tig welding the tabs?

I would be willing to bet you could weld with less heat tig welding than you can with spot welding.

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Re: Spot-Welding a123 Prisimatic tabs

Post by oatnet » Jul 18 2011 7:25pm

Thanks for the kind words, guys! :D

I would love to tig them but I'd think the process would dump a TON of heat into the cell and I'd expect damage. :( Ever touch a small piece of 1/8" after doing a 1" seam? HOT! I did a lot of 1/8"
aluminum in class, but nothing thin as the foils these tabs are made of, so they could require less heat. Maybe you could penetrate a puddle before the tab heats up, and "spot weld" it that way, but I am skeptical. :D

The TV show I mentioned, about a123 manufacturing the prismatics and packifying them, showed cells being joined and the process described it as laser-welding. IIRC, the cell zipped past a device and then two pieces of severed tab fell away... I guess that happens FAST, and doesn't dump heat. Surely amongst us battery geeks, we have some laser geeks who have the hardware and skills and want to give it a shot! :lol:

Now I need to work a new termination method for the packs. I used to crimp and solder an 8ga wire on there, but after dissecting solder joins made by myself and others, solder doesn't seem to stay bonded long-term. It gets up into the ends of my crimped/rolled tabs and keep them in place, but I can't count on it for actual conduction.

I am thinking (4) 14ga wires, each terminated in a 45a Anderson, for a total 180a rated throughput, and well able to handle 240a (15c). That is futureproofing, the max I would choose to run this chemistry at, but for right now it will be driving my Methods Controller @100a peaks. Anyhow, I thought I'd crimp in the wires with slivers of steel and some sacrificial aluminum, zap it and see if I can melt it solid. Hmm, wonder if solder would bond to the tabs while they are molten, if I used that instead of aluminum.

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Re: Spot-Welding a123 Prisimatic tabs

Post by oatnet » Jul 18 2011 7:32pm

regmeister wrote:Wow oatnet, that's great info.

I was thinking fish paper might work well in the place of your newspaper. I had a link to a really inexpensive source for it, but unfortunately can't find the link.

http://search.digikey.com/scripts/DkSea ... e=560GC-ND
http://www.polymerplastics.com/composite_vulcan2.shtml

probably a bit too expensive for the application though.
I just realized I missed this post - thanks for the comments, and I'll look into those alternatives!

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Re: Spot-Welding a123 Prisimatic tabs

Post by texaspyro » Jul 18 2011 10:14pm

Even posterboard would be orders of magnitude better than newspaper... fish paper or other phenolic based material would be even better.

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Re: Spot-Welding a123 Prisimatic tabs

Post by 999zip999 » Jul 18 2011 11:04pm

Hay Oatnet, I can use stuff as a heat sink between the tabs and cell. You could make a jig as to take the heat. I don't know the best thing. But it can be a toothless aligratetor clip or something parelle jaws ? It's beatiful. Good work.

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Re: Spot-Welding a123 Prisimatic tabs

Post by EBJ » Jul 19 2011 12:29am

oatnet wrote:Thanks for the kind words, guys! :D

I would love to tig them but I'd think the process would dump a TON of heat into the cell and I'd expect damage. :( Ever touch a small piece of 1/8" after doing a 1" seam? HOT! I did a lot of 1/8"
aluminum in class, but nothing thin as the foils these tabs are made of, so they could require less heat.

-JD
Yeah, 1/8" thick aluminum requires a lot of amps. But that thinner stuff would require a lot less. (general rule in my classes were 1 amp per .001" thickness. +15% for aluminum)
I imagine a weld w/ no filler right on the ends would work on those tabs, or you should be able to do just as you mentioned... just use the tig to do some no-filler tac welds. Agreed the heat-sink would be a good jig.

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Re: Spot-Welding a123 Prisimatic tabs

Post by 999zip999 » Jul 19 2011 1:48am

I think a heat snink is very good plus it will hold the tabs together.

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Re: Spot-Welding a123 Prisimatic tabs

Post by nechaus » Jan 08 2012 4:00am

very good, i think i will use this method when i get my a123's

I have seen a guy mig weld around a coke can, pretty remarkable

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Re: Spot-Welding a123 Prisimatic tabs

Post by oatnet » Mar 26 2012 9:19pm

Been seek for a few days, bad for getting projects done but but gives me a chance to get around to things like trimming the pics for this post on how I addressed terminating the cells.

While spot welding is a great way to join the tabs on a123 prisimatics, it was not effective for connecting power leads to the pack. Instead I put a pair of copper straps on either side of the a123 tab, soldered wires to them, and screwed the straps together.

[attachment=18]00_IMG_1504.jpg[/attachment]

[attachment=17]05_IMG_1505.jpg[/attachment]

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[attachment=1]85_IMG_2004.JPG[/attachment]

[attachment=0]90_IMG_2001.JPG[/attachment]
Attachments
00_IMG_1504.jpg
I cut the copper straps to length, and drilled (2) holes to solder the power wires, and (3) holes for the screws. The ones on the bottom have been tinned to avoid oxidation.
00_IMG_1504.jpg (51.2 KiB) Viewed 7621 times
05_IMG_1505.jpg
To create a mechanical join, I put one wire on each side of the strap, and feed half of its diameter through the hole. The half that remains behind, gets soldered to the half of the other wire coming through the hole. With solder through the wires and through the holes, it is pretty solid.

This gives me the low resistance of 8ga throughput, with the the thin profile and flexibility of (4) 14ga wires. The rule of thumb is that a pair of wires is the equivalent to a wire 3ga lower. Each strap has (2) 14ga wires soldered to it, which are equivalent to 11ga. I put a strap on either side of each battery tab, so the (2) 11ga are equivalent to 8ga.
05_IMG_1505.jpg (36.08 KiB) Viewed 7621 times
10_IMG_1506.jpg
Looks like I only took pics at this stage of the first one I did, which was my crappiest of some crappy jobs, but you get the idea.
10_IMG_1506.jpg (38.74 KiB) Viewed 7621 times
15_IMG_1955.JPG
Here is a completed tab. Wierd how the tinning looks so ripply in the pics.
15_IMG_1955.JPG (53.42 KiB) Viewed 7621 times
20_IMG_1955.JPG
Left, a stack of finished straps.

Center, a strap as it will be used on a single a123 cell tab. The pair of red wires gets cut in the middle, to give 2 wires on each strap.
Right, a pair of straps bolted together, ready for an a123 cell tab.
20_IMG_1955.JPG (61.09 KiB) Viewed 7621 times
25_IMG_1956.JPG
8 sets of power takeoffs built up for (4) packs. On the lower right, you can see a disassembled power takeoff.
25_IMG_1956.JPG (67.53 KiB) Viewed 7621 times
30_IMG_1956.JPG
The 'sandwich' is stacked up in this picture:

(3) stainless Bolts
nickel strip
(future, folded-over a123 cell tab-end)
tinned copper strap
(future, main a123 cell tab)tinned copper strap
Nyloc nut

The nickel strip is from my spot welding stash, it isn't very thick, but it helps keep the folded a123 tab-end in place. The holes in the straps get threaded by the bolts on first insertion, which takes a little effort. The nyloc nuts allow for a lot of torque, and the abundant adhesive from shrinkwrap helps keep them from loosening.
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35_IMG_1967.JPG
Clamp the straps around the a123 tab's base; leave clearance such that the tab does not short out against the body. A misappropriated wood auguer easily perforates the cell tab for the bolt. I tried to do both the main tab and the fold at the same time, but too many parts were in motion for it to work out.
35_IMG_1967.JPG (53.45 KiB) Viewed 7621 times
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with all three bolts firmly in place, I fold the tab halfway over the straps.
40_IMG_1969.JPG (62.05 KiB) Viewed 7621 times
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Back out the two outside bolts as much as possible, while still holding the sandwich in place. Remove the center bolt, fold the cell tab over the rest of the way, and auger it through center hole. Because this techninique dictated the direction of the fold, the nickel strip ended up on the bolt side as pictured.
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Once the center bolt and nickel strip are on, the other two are easy.
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A finished join.
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On the left, a lug has been added for the balance wire. Note the nickel strip under the nuts, holding the folded cell tab against the tinned copper strap. Say that three times fast for a gold star.
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2 pieces of heavy-adhesive heatshrink will seal the whole thing in amber.
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A wide piece fits over the whole sandwich. It is tapered to make a completely encapuslate the right side, but fit under the power wires on the left.
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Another view of the wide heatshrink before shrunk.
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Shrunk, ready for the next piece.
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The second piece slides down the red power wires on the right, encapsulating the copper straps all the way up to the cell tab. Cut this piece at an angle, so the point covers the seam of the first piece of heatshrink. The balance wire emerges to the left.
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Another, darker view, but you can see how the point in the second piece of heatshrink covers the seam in the first piece of heatshrink.
90_IMG_2001.JPG (27.3 KiB) Viewed 7621 times
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docnjoj   100 GW

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Re: Spot-Welding a123 Prisimatic tabs

Post by docnjoj » Mar 27 2012 6:56am

Thanks oatnet. I was thinking about something similar using copper strips but now I don't have to think as hard! :) This seems like a pretty foolproof way of connecting pouch a123 cells. What sizes are the nuts and bolts?
otherDoc
E-bike stable at our house

Steintrike Mad Max full suspension trike rear Cute 100H going on: Whoops, Cute wheel broke but I fixed it.
Sun USX delta trike EbikeKit small geared front wheel sort of front suspension for wife

Agniusm/A123 AMP 20 36 volts on the Steini has been taken off.
2x16000 Multisport from HK now gone as they died after 2 years
New Luna 10S bottle battery 13.6AH now on mine
Relatively New 10S4Px2 for wife's bike giving 20ah @ 40 volts home made Panasonic from Tumich. BMS's rule.

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oatnet   10 MW

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Re: Spot-Welding a123 Prisimatic tabs

Post by oatnet » Mar 27 2012 10:38am

docnjoj wrote:Thanks oatnet. I was thinking about something similar using copper strips but now I don't have to think as hard! :) This seems like a pretty foolproof way of connecting pouch a123 cells. What sizes are the nuts and bolts?
otherDoc
I think the bolts were 6/32 x 3/8", I realized I needed more length and went to a larger size so I don't remember clearly. I'm sure a lot of folks have thought of doing something similar, I hope this gives them ideas on what they would like to do (or not do! :shock: ). Mostly I hope I've shown that these cells are pretty easy to work with.

-JD
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dnmun   100 GW

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Re: Spot-Welding a123 Prisimatic tabs

Post by dnmun » Mar 27 2012 10:56am

your stuff is inspirational. you do such good and thoughtful layout and then you have the good sense to do it right the first time.

you are right, this is how 'engineers' learn to do stuff. the right way.

better than learning from mistakes, like the current blowout on the total platform in the north sea. more bad engineering there.

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oatnet   10 MW

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Re: Spot-Welding a123 Prisimatic tabs

Post by oatnet » Mar 30 2012 12:43pm

dnmun wrote:your stuff is inspirational. you do such good and thoughtful layout and then you have the good sense to do it right the first time.
Thanks dnmun, that is nice of you to say! :mrgreen:

-JD
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Re: Spot-Welding a123 Prisimatic tabs

Post by oatnet » Apr 21 2012 7:48pm

I bought (110) cells from Victpower, thanks to Doc Bass for pointing that deal out to me. I tested them all for volltage, most were around 3.27v, 2 were 3.24v. I noticed (1) with a misaligned tab, it jumped out at me, if there are others I didn't notice them on this quick check.

I also have a few cells from the cell_man era, in the 16ah and 20ah flavors, so I thought I would compare and contrast. I noticed right away that the foil used on the new USA cells feels thicker and more solid, more puncture and flex resistant. Both 20ah cells are exactly the same dimensions, and tabs line up in the same spot and are the same dimensions. The new USA cells weigh 6.7% more, which I would attribute to the thicker foil.

I think it would be really hard to counterfit these cells, and have the same dimensions, really similar weight, and have identical tab placement and construction. They look clean and new and unused.
boxed_IMG_2964.jpg
(8) boxes of cells!
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compared_IMG_2986.jpg
On the left, a new USA 20ah cell from Victpower. Center, a cell_man 16ah cell. Right, cell_man 20ah cell.
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head to head 1 IMG_2987.jpg
One side of 20ah victpower vs cell_man
head to head 1 IMG_2987.jpg (63.23 KiB) Viewed 7423 times
head to head 1 IMG_2988.jpg
the other side of 20ah victpower vs cell_man
head to head 1 IMG_2988.jpg (60.52 KiB) Viewed 7423 times
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comparing the tops
top_to_top IMG_2989.jpg (45.67 KiB) Viewed 7423 times
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The edges
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USA_20_494g_IMG_2993.jpg
The USA 20ah cell weighs 494g, 6.% more than the original unlabeled cell_man 20ah cell.
USA_20_494g_IMG_2993.jpg (52.37 KiB) Viewed 7423 times
UNKNWN_20_466g_IMG_2994.jpg
The cell_man cell weighs 466g
UNKNWN_20_466g_IMG_2994.jpg (37.97 KiB) Viewed 7423 times
KOR_16_399g_IMG_2995.jpg
The 16ah cell weighs 399g.
KOR_16_399g_IMG_2995.jpg (37.72 KiB) Viewed 7423 times
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Re: Spot-Welding a123 Prisimatic tabs

Post by docnjoj » Apr 22 2012 8:24am

Thanks oatnet for that timely information. My order of 14 is on it's way fromVictpower. They seem like a class operation so far.
otherDoc
E-bike stable at our house

Steintrike Mad Max full suspension trike rear Cute 100H going on: Whoops, Cute wheel broke but I fixed it.
Sun USX delta trike EbikeKit small geared front wheel sort of front suspension for wife

Agniusm/A123 AMP 20 36 volts on the Steini has been taken off.
2x16000 Multisport from HK now gone as they died after 2 years
New Luna 10S bottle battery 13.6AH now on mine
Relatively New 10S4Px2 for wife's bike giving 20ah @ 40 volts home made Panasonic from Tumich. BMS's rule.

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oatnet   10 MW

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Re: Spot-Welding a123 Prisimatic tabs

Post by oatnet » May 28 2012 9:54pm

Someone asked for this a while ago, I got around to cutting open a dead 16ah a123 prisimatic, that had previously been used for my spot-welding testing. There was a chemical smell, but no juice or powder flying around. Like any prisimatic, the layers of subcells are stacked on each other like a book. Enjoy! :D

-JD
0 new cell IMG_2236.JPG
0 new cell IMG_2236.JPG (238.27 KiB) Viewed 7275 times
1 unfolded IMG_2237.JPG
1 unfolded IMG_2237.JPG (235.39 KiB) Viewed 7275 times
Image
3 tab IMG_2244.JPG
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5 tab IMG_2245.JPG
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Image
7 tab side IMG_2246.JPG
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8 tab top IMG_2248.JPG
8 tab top IMG_2248.JPG (117.19 KiB) Viewed 7275 times
Image
Attachments
2 opened IMG_2239.JPG
4 tab full IMG_2244.JPG
6 open like a book IMG_2242.JPG
9 bare tab IMG_2250.JPG
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Re: Spot-Welding a123 Prisimatic tabs

Post by oatnet » May 30 2012 9:57pm

In this thread dnmun speculated on spot-welding cotter pins to join a123 packs. Today I tried it out, and I like it. :D :D :D It does not shift around like the two steel plates used to so it is easier to setup. I don't have to adjust the two pairs of vice grips for each weld, just clamp it on one side with vice grips and zap zap zap down the row, it is much faster. This is a simple, effective method for welding cells together in high-quality join, without heat-damaging them.

I used stainless steel 1/8" x 2" cotter pins, .65 each from my local Ace hardware. The rest of the technique is the same stuff I have been posting here for two years.

[attachment=10]IMG_4290.jpg[/attachment]

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[attachment=7]IMG_4295.jpg[/attachment]

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Attachments
IMG_4290.jpg
Position the pin. The tough part is getting the round end of the pin over the tabs, it is quite tight there.
IMG_4290.jpg (138.96 KiB) Viewed 7234 times
IMG_4291.jpg
First weld completed, spot welder still in place, and the vice grips where they stayed for the whole operation.
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IMG_4294.jpg
A completed weld - note how the entire edge of the tabs are melted, welded together.
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IMG_4295.jpg
The 18ga balance wire doesn't carry much load, so it just rests the middle of the roll. I make it a little long, and bend the end up into the next fold, so it doesn't pull out.
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IMG_4296.jpg
like this, on the next fold.
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IMG_4297.jpg
Last fold complete, and the whole mess crimped with electrician's pliers. The round cotter pin keeps it from crimping as flat as it did with my folding method, but between the weld, and both sides of both tabs being in full contact with each other, it just isn't an issue.
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A layer of adhesive heat shrink to seal it in amber
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Heat shrink folded over at the top
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Sliide on one of the plastic report clips I use (bought more at staples today!)
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A layer of fiberglass-reinforced tape to keep the plastic clip from stretching out.
IMG_4302.jpg (100.15 KiB) Viewed 7234 times
IMG_4303.jpg
The whole assembly from the side.
IMG_4303.jpg (133.85 KiB) Viewed 7234 times
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