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Discussion Starter #21
My post and that of eq1 crossed as I was trying to be as careful as possible with cautionary wording.
 

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Discussion Starter #22 (Edited)
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.
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.

The adhesive between the separator and either cell wall is very strong stuff, as indicated earlier.

Splitting off individual cells is probably impossible with any degree of success.

The entire operation is pretty tricky and all the procedural steps though successful are doubtful.

edited
 

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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.
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.

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.
 

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Discussion Starter #24
Perhaps removing the intercell strap on top of the pack at the split line eliminates the danger of the cell short. I have to think this through a bit and look more carefully at the pack.

In any case, I did successfully split off 5 cells. Maybe I got lucky. PROCEED AT YOUR OWN RISK - NOT FOR THE FAINT OF HEART.
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...
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.

FYI, this means that the voltage between successive cells in a stack is equal to one cell voltage, and that is where one of the major risks arrises.
 

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Discussion Starter #25
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.
Yes, strap=busbar.

How deep can the tap hole be drilled?
 

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Yes, strap=busbar.

How deep can the tap hole be drilled?
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.

I'm slowly adding to my solar array with more LTO packs so if I find a bad cell that's shot anyways I'll drill through and let you know how deep the terminal runs.
 

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^ 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:
85769
 

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Discussion Starter #28
+1. Nice data, but not encouraging from a utility viewpoint. All the taps I own have a taper end so the first few threads are undersize and therefore useless. I guess Toshiba might cut threads, but no home hobbist. On top of that, the threads are soft, as indicated above, and probably unreliable for automotive use. I think that the most promising approach to using individual Fit cells, even if they could be reliably separated, would be to saw the bus bars in half and then use a spot welder to reconfigure buses as desired. Four spot welds per conductor vs. two:(

I have on occasion created shallow blind threaded holes by using a two step process. One can create an untapered tap by grinding off the first 1/4" or so. Used in conjunction with a regular tapered tap, it sometimes works, but not likely in soft metal.
 

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Ever heard of a "bottoming tap"... Jime?
 

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Discussion Starter #30
^ Nope. Give us a ref to those, if you have one.
 

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^ 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
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.
 

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^ Nope. Give us a ref to those, if you have one.
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.

That being said I think for automotive you are correct all that vibration there is likely not enough strength in that few threads for that use. For me it just sits on a shelf for solar so I don't need as much strength. If you want I think I have an aluminum bar somewhere that I can drill to those specs and see what torque value it strips out at.
 

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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.
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'):
85773
 

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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
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.
 

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^ 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?
 

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Discussion Starter #36
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?
 

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^ 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?
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.
 

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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?
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:

-the car needs to be in auto-stop*
-the DCDC needs to be in low power mode, i.e. not kicking-in until voltage falls to about 12.2V (probably about 12.5-6V on OBDIIC&C)...

'12V' will show you when the DCDC is in low power mode, simply by not being the normal power mode voltage, which I gather in your setup should be 13.85V actual, probably more like 14.0-14.3V on OBDIICC.

Under these conditions, the 12V battery will supply the full 12V system load, so long as the battery can uphold a voltage above 12.2V. This is when you need to be watching 'Bam' - IMA battery current - and secondarily watching IMA pack voltage (just knowing about what it is is fine, you don't need to 'watch' it very actively)...

Bam will be zero if the 12V battery is sourcing the full 12V system load; anything under zero is the amount that the DCDC is needing to pull from the IMA pack via DCDC to supplement the 12V battery if it can't supply the full load itself. This is the key to it all.

For example, if Bam is -2.6A and pack voltage is 150V, then 390W need to be pulled out of the IMA pack in order to uphold 12.2V under whatever 12V system load is going on. The thing is, 'Eld' doesn't include the 12V battery load itself. If discharged, the 12V battery becomes a load rather than a source, and the only way you know how much of a load the battery has become is by subtracting an 'Eld' and '12V' based metric of 12V load from an IMA-based 12V system load.

If 'Eld' is 15 (amps) and '12V' is 12.2V, the 12V system load excluding 12V battery is 180W.
If 'Bam' is -2.6A and pack voltage is 150V, total 12V system load, including 12V battery, is 390W.

390W minus 180W = 210W, 210W is the amount of power your 12V battery is consuming. I.e. 210W / 12.2V= 17.2 amps -- your 12V battery is charging at about 17 amps...

In reality you'll only see such extreme values under even more specific circumstances - and this, too, is a key thing to watch for.

When the DCDC has been in low power mode for relatively long stretches - that is about the only time your 12V battery sees a lot of action. Your battery sees an honest-to-goodness discharge, rather than being floated at 13.85V. AND, when your DCDC comes OUT of low power mode - that's when you actually see your 12V battery getting charged! That's when you're likely to see very high charge rates, or at least, that's when charge rates will be the highest they will ever be...

When the DCDC toggles out of low power mode, going from 12.2V to 13.85V, how discharged the battery is will determine how much current is needed to bring voltage up to 13.85V. If your battery were really discharged, I imagine the LTO would sink a massive amount of current. But I don't think it will ever get that discharged in the car, as the lowest voltage it will see is 12.2V, or 2.44V per cell on average. And that's probably not very discharged, maybe 50% at 10-20 amps? But in any event, toggling out of low power mode is a key key juncture to watch.

Take-aways:

-Watch for negative Bam in DCDC low power mode: zero means battery can uphold 12V load on its own, going negative means battery is needing to be charged to uphold ~12.2V.

-Watch for when DCDC toggles out of low power mode, and watch for how negative Bam goes. The more negative, the more your 12V battery is needing to be charged to reach 13.85V.


I hope this helps. Like I said, it's tricky to get a handle on. It has become second nature to me, so I actually find it hard to explain in writing what I actually look at and do, and how it all works...

* You don't actually need to be in auto-stop, it's just that low power mode gets enabled when you go into auto-stop more than at anything other time, plus you kind of need to be stopped in order to size-up all the parameters, plus it becomes much easier to calculate stuff in your head when you have a known, fixed 12V system load - which can happen in auto-stop, unlike when you're driving and the ignition becomes a 12V load that's hard to pin down... No accessories ON, in auto-stop, is about a 10 amp load, give or take (for me that includes DRLs on, high beams at half power).
 

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Discussion Starter #39 (Edited)
Thank you for the detailed explanation.

The "new" 12V Battery parameter is now called "12V Comp Value" I think. It is Peter's attempt to compensate for the wire harness losses to get a more accurate 12V display. We'll see how that works out.

I'm going to set that and "eld" into my gauge to "try" to monitor.

I thought cutting the red/yellow wire would "peg" the dc-dc output at 13.85V, but apparently it just eliminates the "cold start" 14.8V phase.

"You're a better man than me Charlie Brown." I could not get that pin to release from the plug, even tinkering with good light on my kitchen table. You'll have to show me one day in person. ;)
 

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Depending on what firmware you are running the 12v can be monitored from the OBDIIC&C by selecting either

Msv (MCM System Voltage) or
Esv (ECM System Voltage) as a parameter.

The "12V Comp Value" in the main menu is a byte value 0-255 (0-25.5V) added to Msv and Esv to compensate for voltage drops. 1 would add 100mv to the reading, 20 would add 2V.
 
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