Need help designing triangle pack, 18650 cells.

[spinningmagnets]

Ebay vendor supowerbattery111 is selling 18650 size cells with the NCA chemistry. DocBass has said he will test those cells, and if the performance is OK, I would like to make a triangle pack out of them. That particular vendor will spot-weld strips on parallel cell groups, which would eliminate about 2/3rds of the pack-building hassles. Still not "easy", but certainly more doable. I would prefer fatter cells, but 18650's are what has the NCA chemistry right now (for cordless tools). This pic is not NCA chemistry, but is a sample of his spot-welding.

http://endless-sphere.com/forums/viewtopic.php?f=14&t=48074&start=25#p708027

The cells are listed as 2900mAh, so assuming they have a real-world capacity of 2800mAh, then a parallel string of 5 would supply 14-Ah? twelve of these cell groups in series (12S/44V) would be 60 cells. At $13/cell which includes tab-welding its $780 (plus shipping)

I have a 100W soldering iron, any advice is appreciated to help me avoid any big mistakes. If the cells were oriented on their sides, My initial sketch is this (The red cells are simply in a 3/2 block instead of 5-inline):

OOOOO OOOOO OOO
OOOOO OOOOO OO
OOOOO OOOOO
OOOOO OOO
OOOOO OO
OOOOO
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OOOOO OOOOO OOOOO OOO
OOOOO OOOOO OOOOO OO
OOOOO OOOOO OOOOO
OOOOO OOOOO

edit: If we allow 20mm of space for each 18mm cell, this configuration would be 260mm / 160mm (10.3 X 6.3 inches). If I went to 6P in each string for 16.8-Ah, this configuration would be 320mm X 160mm (12.6 X 6.3 inches). 16-Ah at 3C is around 48A. 13 X 7 inches in a triangle....nice.

edit: With the new cells as of July 2015 (10A/3500-mAh) the 12S / 5P packs configured above would be small, and also provide 44V @ 50A with 17.5-Ah.

 

[docnjoj]

That seems like quite a clever approach, SM. Even moreso since they will provide the welding to your specs. Do these cells self balance like my Konions do?
otherDoc

 

[spinningmagnets]

Its my understanding that they self-balance, but a real-world test is called for. It has some cobalt in the cathode for dense energy (not as compact as LiPo which is actually LiCo, but better than LiMn). The problems with cobalt are better known now, and the addition of nickel and aluminum in a certain amount improves a variety of characteristics (or so the sales literature says). NCA sounds good on paper. Everything about LiMn is great, that is why ebikes.ca sells a lot of those, but...LiMn (like Konions from Makita packs) don't have as a good a C-rate as NCA. They claim 5C for NCA, so I'm guessing 3C, but...the final word will come when DocBass beats them like a rented mule.

The Samsung NCA cells have identical specs, and are only $9 each, but that price does not include spot-welding tabs to 5P strings. If I was going to make a bunch of these packs, I would consider using the Samsung cells and make one of those DIY $100 spot-welders.

 

[e-beach]

Have you contacted the vender and asked what they recommend besides welding the tabs?

(edit) See if they will leave an extra unwelded tab hanging off end of every strip for you to solder to the next group of batteries.

 

[mistercrash]

What's the dimension of your triangle? Maybe you don't have to join the cells in a triangular shape which would make the job easier and simpler. If you go with 12 string of 5P all welded together in straight lines and join them like this

ooooo ooooo
.ooooo ooooo
ooooo ooooo
.ooooo ooooo
ooooo ooooo
.ooooo ooooo

the pack would have a rectangular shape and be under 200mm long by 100mm high and it would be as thick as the cells plus the bus bars and maybe some wires so let's say under 75mm thick.

 

[spinningmagnets]

I'll be getting a bike to fit the battery and kit, but I agree its an option to have a different shape. Perhaps half-square, half triangle?

00000 00000 00000 000
00000 00000 00000 00
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If we allow 20mm of space for each 18mm cell, this configuration would be 360mm / 80mm (14.2 X 3.2 inches). If this turns out to be very small (once the wires and case, etc, are added), I could even go to 6P to get 16.8-Ah, which would be 480mm X 80mm (19.0 X 3.2 inches).

Part of the reason I am interested in a triangle pack (even if a rectangle would fit the middle of my frame) is that they are hard to find anymore, and I think there is a pent-up demand for them. By making one, I want to show how someone can make their own (with actual numbers concerning what the real-world result will be) and if there is enough interest to make a few for sale, I want to know exactly how to copy a working pack that is optimised for a triangle.

There is a growing trend in DH bikes being used as a basis to build an E-bike, and their frame-triangles are consistently smaller than average. Here is the style of frame that I am personally drawn to: full-suspension, round cross-section tubing on the seat-tube and down-tube for easy clamping solutions, horizontal shock frees up seat tube for attaching experiments...

 

[e-beach]

Part of the reason I am interested in a triangle pack (even if a rectangle would fit the middle of my frame) is that they are hard to find anymore, and I think there is a pent-up demand for them. By making one, I want to show how someone can make their own (with actual numbers concerning what the real-world result will be) and if there is enough interest to make a few for sale, I want to know exactly how to copy a working pack that is optimised for a triangle.

I think you are right about the the need for triangle packs. Last April I was trying to get Paul from emissions free to build me a custom A123 triangle pack to my configurations. It was just a little too far outside his normal packs and it didn't work out.



The problem I see with building triangle packs is that every body has a different shaped triangle as almost no two custom e-bikes are the same.
In my case, Paul's final suggestion was that he could make me strips of cells and I could configure them any way I want. Logic has brought you to the same conclusion.

I am not familiar with the "18650 size cells with the NCA chemistry" batteries above, but all the batteries I have ever soldered together needed to be soldiered fast! Keeps them from burning up. I always found soldering tab to tab hard to do, but multi-stranded copper wire to tabs can sometimes be done. Tin the tab, let it cool while tinning the wire, solder them together.....no doubt you know how to do it already.

Getting a $100 battery tab welder sounds better and better.

 

[etriker]

This
http://www.endless-sphere.com/forums/download/file.php?id=98637

From this thread.

http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=28285&hilit=makita+building#p407778

 

[etriker]

I have not used a battery cell spot welder but from the videos I have seen they get the end of the cell red hot ?

As the tips wear they will also put extra heat into the cell during the welding process ?

In the USA we can still buy low temp solder.

It may not be PC to put lead on these green cells but soldering may put less heat on the cell than spot welding if done fast ?

 

[spinningmagnets]

Thanks, etriker. Those links are quite useful, and I have been recently collecting links that apply to this kind of project.

The problem with lead is when drinking water passes through old lead pipes, or chldren eat lead-based paint chips (I've also read about people breathing-in lead dust). When the industry insists on lead-free solder, I believe it was being unneccesarily over-cautious. If I happen to find out that I have accidentally used some lead-solder, I would not be concerned about it.

edit: if you work around molten lead, there is a very real danger in breathing lead fumes. Civil-war re-enactors often melt lead to cast their own lead bullets in the field. If you solder in a well-ventilated area and only solder a few things each year, I doubt you will inhale any lead fumes.

 

[migueralliart]

Get the tab welder ... then I can send you hundreds of cells and you make money out of it?

 

[etriker]

Get the tab welder ... then I can send you hundreds of cells and you make money out of it?

There is a big price difference between them. Good ones cost a lot.

http://www.batteryspace.com/Welding-/-Soldering-/-Shrinking-and-Packaging.aspx

I would rather use a good soldering iron than a cheap spot welder.

Cheap welders of any kind are a pain to use.

The more packs I solder together the faster I get and the better they look.

 

[999zip999]

I was using these u-shape flat rails and 18650 or konions can snap right in they come with the vertical blinds from lowes, it's the throw away part. And double wall strong bottom plastic. With the slot enbetween you can insert a L - bracket or at 38 degrees ect. A plastic pipe u- clamp or metal on the top bar.

 

[999zip999]

But it also a snap tight fit for 12s A123 20ah pouches with the tupperware sides as you can see yes a 12s in the triangle. Thats what the cut out inthe bottom is.

 

[Popstar]

Cellman now has a Samsung 18650 14S9P NCM triangle pack on his site: http://em3ev.com/store/index.php?route=product/product&path=35&product_id=123

It seems impressive that can get 48V 18ah inside a small triangle, maybe even a larger full suspension. I have a pack on order along with a MAC from Paul.

 

[pwbset]

OOOOO OOOOO OOO
OOOOO OOOOO OO
OOOOO OOOOO
OOOOO OOO
OOOOO OO
OOOOO
OOO
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Looking to re-do my triangle pack this summer and will be following this thread. I had a hell of a time last summer with my 18s konion triangle pack. It was just not built that great design-wise so I'd have strings fail a few times. I didn't do much capacity/IR matching though. This summer should be better providing the cells are still good. I dislocated my shoulder last summer hitting deep gravel so haven't ridden since and it didn't heal well so we'll see how it goes. Cell_man's stuff is looking better all the time.

Frame size...

*barf* Meh.

Almost done.

Looked okay all duct taped up. Hah! Kicked out gobs of power at least and handled great.

 

[999zip999]

Pwset I don't like to see so much extra tab on the pos. end. This is where a short can happen with the extra pos. tab hitting the neg. case. Docbass had wrote about these in his pack build thread on konions. Did you see this plastic rail I got from vertial blinds from lowes. The konions snap right in and could be fixed to the down tube from support of the pack.