Sony US26650VT Li-ion Cells - Need More info

[othello]

Glad to hear that you like your Sony cells. The smaller 18650vt cells 1100 or 1300mAh can be found in Bosch 36v powertool packs (20 cells) quite similar to dewalt 36V packs (10 A123 cells). To compensate for their voltage drop at the end and to give a more comparable power output to my 10s1p A123 packs i went up from 8s2p to 9s2p.

This is one of my last discharge graphs dating a few days ago.


As you have noticed there is no noticeable real end of discharge. Lipos and A123 drop their voltage heavily at the end. Those Sony cells dont. They are slowly getting weaker and weaker. At the end of my run at some amp spike they dropped down to 18.89V which represents only 2.09V per cell. I start at 37,8V and voltage comes down below 28V (-> 3.1V per cell) with no load. I usually finish driving when top speed becomes boring

[sikeston34m]

Thank you for the info Othello. Looks like you're having some pretty good fun with the cells you have.

So are you saying I shouldn't be too concerned with a LVC at all?

[othello]

I never used an lvc with my cells and they do deliver reliably since half a year (i used them as 4s4p, 8s2p and now 9s2p). But i wouldn't dump them up to the point where your car won't move any more.

[lutach]

Originally Posted by othello

Glad to hear that you like your Sony cells. The smaller 18650vt cells 1100 or 1300mAh can be found in Bosch 36v powertool packs (20 cells) quite similar to dewalt 36V packs (10 A123 cells). To compensate for their voltage drop at the end and to give a more comparable power output to my 10s1p A123 packs i went up from 8s2p to 9s2p.

This is one of my last discharge graphs dating a few days ago.


As you have noticed there is no noticeable real end of discharge. Lipos and A123 drop their voltage heavily at the end. Those Sony cells dont. They are slowly getting weaker and weaker. At the end of my run at some amp spike they dropped down to 18.89V which represents only 2.09V per cell. I start at 37,8V and voltage comes down below 28V (-> 3.1V per cell) with no load. I usually finish driving when top speed becomes boring

I have bought a few Bosch packs and I was wondering why did they add a 60A fuse. Now I see why. I have used my packs and they are really powerful for their size. I will use them more often.

[othello]

I just looked through my logfiles and i'm now at cycle 75 with my Sony cells. Still charging back 2200mAh as 9s2p. When i started using them as 4s4p i charged 4400mAh back. So no noticeable capacity drop. I guess they will have a very long life in my setup. Sikestone: With a driving time of 25min they will last even longer with your setup. I'm discharging mine now in 8 minutes. In my buggy they lasted for up 13 minutes.

@lutach
Guess i use them up to their full potential then (didn't notice the 60A fuse). I red somewhere that each cell has some kind of integrated fuse which will render those cells useless when you overwork them. If you push them too hard the fuse will trigger and the cell is at 0V ... this is not reversible.
Edit: found some pics of those cells open -> link

[lutach]

Here are a few pictures of the smaller 36V pack as well as the bigger one and the PCB that hooks up to the charger. I left the 60A fuse when I wraped the smaller pack.