2D Bi-Bore + 2S2P 18650: Additional Mods Required?

[adamlau]

Will a 2D bi-bore take a 2S2P 18650 pack w/o a spacer, PVC tubing, custom tailcap, or any additional modifications?

 

[mdocod]

Provided the cells were made up into some sort of actual "pack" with end caps and a button top to make contact with the tailcap spring and switch assembly then it should work, but that custom pack design is what would be the most limiting factor. It would need to have those end caps be pretty thin, probably spot welded to the cells. a lot of additional "pack style" shrinkwrapping and it probably wouldn't fit even in the bi-bore.

If you don't mind me asking, why not just use a pair of Emoli or A123 systems 26650/26670 type cells and a piece of PVC, or a pair of 32600 LiFeP04 cells from batteryspace.com,

Keep in mind that the normal length of 2D cells is 120mm, so 2 18650s end to end would be 130mm, My 6AA>2D battery packs are about 126mm long and they fit fine with a more compressed tailcap spring, I have no idea if there would be room for another 4+mm, I'm thinking maybe not. (edit in: a pair of 26mmx70mm cells can be made to fit as I understand because they will fit down into the tailcap. where as a pair of 18mm cells size by side can't do this)

 

[adamlau]

Thanks for the needed info, mdocod. I plan on using a Moli IMR-18650E 2S2P to drive the 64623, and a 2S3P for the 64655.

 

[mdocod]

yea I think you would be better off with a pair of 26670 cells instead. Much less complication.

 

[mdocod]

to drive the 64623, and a 2S3P for the 64655.

wait.... for the 64655 I'm pretty sure you mean 6 cells in series. It's a 24V lamp right?

The 64623 is a 12V.... 2 Moli cells in series will only be ~7.4V, that won't work either...

The 64623 might work reasonably well on 3 Moli cells in series, but probably won't be as bright as possible, I would guess that 4 LiFeP04 cells would be much better.

The 64655 Might work on 6 Moli cells in series, but again, I think it would be better on 8 LiFeP04 cells in series.

 

[adamlau]

The 64623...4 LiFeP04 cells would be much better.

2S2P and 2S3P refer only to how the cells are to be packed in order to fit into a 2D and 3D host as they are to be run in series. I should have been more specific and mentioned that. 2S2P does indeed refer to four cells.

The 64655...would be better on 8 LiFeP04 cells in series.

My justification for running the 64655 off of six cells and not more is posted towards the end of What is missing? and essentially states that:

Six IMR-18650E cells at 3.8V (manufacturer rated) at rest ought to give us 22.8V. The HyperBlaster runs off of 21 x 1.1V (accounting for just 0.1V sag) for 23.1V, whereas the Mac Elephant runs off 20 (assuming Elite 1500) x 1.1V (accounting for just 0.1V sag) for 22V. Even at 3.7V nominal, six IMR-18650E cells would offer 22.2V.

 

[mdocod]

seems to me that to run the 64655 effectively you need to get at least 24V to the pins, but maybe I'm wrong? By my calculations 26V would be the place to shoot for.

 

[adamlau]

You are likely correct, it is just that LL and Mac appear to have also underdriven 64655. Unless of course, the Elite cells actually perform at 1.2V under load, which would mean a slight overdrive of 25.2V for LL and 24V for Mac, not taking into account resistance losses.

 

[mdocod]

in studying discharge graphs, if the cells were "heated" fresh off the charger they might be seeing over 24V at the pins for a short time, within a few (maybe 30-60) seconds the voltage would probably drop to about 1.1V per cell or so. Idduno, I've never worked on a mod that big.