Splitting off several cells at an end, if done correctly will result is the cell separator acting as a "wrap" for the "good" part resulting in a complete plastic wrap. The "donor" half will be left with a bare cell wall.Also after getting the individual cells did you wrap them? I remember testing the bare aluminum case and terminal to case had a voltage so it seemed like each one needed to be re-wrapped after splitting.
Ok that's in line with my experience. I was hoping you had found a better method or solvent or something else that made this easier or repeatable. For my use case I needed to make the pack parallel not series connection so I just ran the wires to a fuse block to do that once I realized that getting individual cells out and flipping them was not going to happen.Well. I'm going to start with a caution: ATTEMPTING TO SPLIT ONE OF THE FIT LTO SUBPACKS IS EXCEEDINGLY DIFFICULT AND PERHAPS PERSONALLY DANGEROUS. THE PRACTICE CAN ALSO EASILY RESULT IN DAMAGE TO ONE OR MORE CELLS. USE OF METAL TOOLS HAS A HIGH RISK OF SHORTING TWO CELL OUTER CASES, WHICH ARE ELECTRICALLY HOT.
Now, I first cut the plastic around "divide" line with a Dremel rotary saw blade. It is important to stay slightly off the exact divide line between cells so that the metal saw blade only lightly touches the metal outer case of ONE cell.
The spot weld on the stap between the cells must be driled free at one end. I was very careful to use the very minimum drill depth. Only a little drilling is necessary to free the strap. The strap makes a convenient, though somewhat flimsy, terminal.
All the cells are separated by a single layer polyethelene (?) plastic separator. One wants to retain the undamaged separator with the cell(s) to be used and not those to be discarded. As a separation tool, I used a sturdy but thin paint scraper. The tool needs to be sharpened on one side in a bevel manner like a wood chisel. In this way it can be driven with a hammer between the two cells being split and still follow the wall of the discard cell, saving the single layer plastic separator for the usable cell(s). It requires careful attention and some skill. There is a chance that the metal tool will not follow a true course and will contact both cell walls at the same time, creating a short between two cases, and that will I believe cause a positive to negative short of one cell - probably damaging one cell, and potentially creating a fire. One should be prepared to protect self and property. I did the final separation operation on a concrete slab outside my garage , because of risk to property.
Bottom line is that I successfully separated 5 cells, but I don't recommend the practice because of the danger involved. Obviously this account is my personal experience and does not constitute a recommendation to others to do the same.
I believe your assumption about the electrolyte being in contact with the case is correct. The "half voltage" measurements which I had also observed would thus be explained.I gather that the electrolyte must be in contact with the case ('can'), as the pos terminal-to-case circuit and the neg terminal-to-case circuit seem to reflect half-reaction voltages, i.e. the potential between pos electrode and electrolyte, and negative electrode and electrolyte, I think... Add them up and you get the cell voltage. As I recall, when you short between terminal and case you actually start to discharge that electrode - or at least the voltage goes down... I don't really understand it well, if at all...
Yes, strap=busbar.When you talk about the strap do you mean the busbars? I think what you were saying there is to free the end from the donor pack so that the end has the busbar hanging off. If thats what you meant, drilling works as does prying it up with a flat head screw driver. I've experimented with this part and the busbars are .5mm and seem to be nickel plated. I can definitely solder or spot weld to them without issue (the busbar not the terminal). If you remove them completely I've also tapped a few which also works fine.
Thanks for responding.
I never wasted a cell to find out when it punctures through and lets out the gas. I went fairly shallow basically just enough so I could put a little torque on a ring terminal . The terminal is aluminum anyways so even if it runs fairly deep which I doubt the threads aren't going to accept much torque before stripping.Yes, strap=busbar.
How deep can the tap hole be drilled?
Thanks for this. I realize this is for the 2.9AH cells but I have a feeling the 20AH ones in the fit packs are pretty similar if not the same. While the side that the terminal is on is not quite double the size if you look at the photos and compare the visible part of the terminal looks almost the same size only the gap between the 2 terminals seems to have gotten larger. Obviously it might be a little bigger but going from the photos I don't think it's double like the dimensions would suggest. Your info likely applies to the 20AH terminals as well.^ This might help a little. I have measurements and made a model of a tapped 2.9Ah SCiB cell terminal. At least for the small cells, the terminals aren't very deep at all. The terminals for the larger cells might be similar, only scaled larger, of course...
Here's an image:
View attachment 85769
These are the ones I used since I drilled out 10-24 threads. IRWIN Tap Set for Machine Screws, High Carbon Steel, 10-24 NC, 3-Piece (2528):Amazon:Home Improvement but taper, plug, and bottoming tap sets are pretty common. The shape at the end allows the threads to be usable to the bottom on a bottoming one.^ Nope. Give us a ref to those, if you have one.
Not sure I follow what you're describing here. The 20Ah cell terminals are thicker, wider - the girth is obviously bigger than the 2.9Ah cell terminals. But the depth, the length, probably isn't much deeper than the 2.9Ah - now that I think about it.Thanks for this. I realize this is for the 2.9AH cells but I have a feeling the 20AH ones in the fit packs are pretty similar if not the same. While the side that the terminal is on is not quite double the size if you look at the photos and compare the visible part of the terminal looks almost the same size only the gap between the 2 terminals seems to have gotten larger. Obviously it might be a little bigger but going from the photos I don't think it's double like the dimensions would suggest. Your info likely applies to the 20AH terminals as well.
I was specifically talking about the terminals comparing the photos on the scib product page. While the batteries are larger the terminal looks to be about the same (the length is longer as you mention but the other dimensions look the same). Thanks for all the info.Not sure I follow what you're describing here. The 20Ah cell terminals are thicker, wider - the girth is obviously bigger than the 2.9Ah cell terminals. But the depth, the length, probably isn't much deeper than the 2.9Ah - now that I think about it.
For both size cells, the terminals just need to be long enough to pass through the top of the 'can' and interface with a thin aluminum busbar with a hole in it. I can't see any reason to scale the 2.9Ah terminals in the length direction as much as they are scaled in the width direction, i.e. they make the 20Ah wider, but not longer, wider handles more current, longer doesn't do anything, expect perfrom mechanical fastening. The busbar in the cell is probably bigger in the 20Ah than 2.9Ah - and so the terminal would need to be bigger/longer to accommodate that. But beyond that there isn't a reason to make them longer...
Here's a pict of the interface between the terminals on the inside of the cells (still 2.9Ah of course. Image credit goes to the guy I bought these from, 'twejacky'):
View attachment 85773
It's 7mm x 14mm at the longest parts since it's more of an oval shape. The 14mm is what I thought you meant by length (obviously it depends on the orientation of the battery). The "width" is the same and we don't for sure know about the depth. That being said I could easily see the depth being the same but I won't know for sure unless I come accross a bad cell I don't mind drilling into.^ No, the 20Ah terminals are much larger - they have a much larger surface area than the 2.9Ah, which suggests a much larger 'girth'/'width. I'm saying the length - how deeply they penetrate the can, is probably similar.
The surface area of the 2.9Ah cell terminal is about 7mm X 7mm (both the raised pad and the little bit that sticks out beyond that pad). Maybe go measure one of your 20Ah cells?: How does it compare to that?
Not sure how much useful 'performance' data you'd get from the OBDIIC&C parameters... 'Eld' (12V system current) and '12V' (voltage) or whatever the more modern versions are, will show you the load on the 12V system. Based on OBDIICC data, the only meaningful metric for judging the performance and state of the 12V battery is a little tricky to get a handle on. It depends on a few parameters and works only under specific circumstances:I'm just about finished with the install and car mods. @ eq1, which OBDII C&C parameters would you suggest as most useful to monitor the performance of the battery and the dc-dc converter?