Turnigy nano-tech round cells.

[x88x]

Well, today I finally got the "you weren't home so we'll try again later" note. So that's 14 days from arrival at "sorting" at my zip code to delivery. I can only assume that the majority of that time was spent in customs.

Unfortunately, I won't be able to pick it up from the post office until Thursday, but once I do I'll post pics/measurements/etc.

[Trackman417]

Strange, I always thought shipping battery's from Hongkong to US would be a couple month wait time. I guess not!

[x88x]

Got the cells in today. Not quite thrilled with them, I have to say.

Images (camera can't seem to focus well):



Construction:
Appears to be standard cylindrical wrapped cathode/anode layers, encased in the same sort of foil material as the pouch cells. Ok, I'm guessing on the wrapped layers, but that's what it feels like, based on how solid it is.
Because of the foil material used for the shell, there is a small ridge along each side of the cell, where the foil is joined together.
About the same diameter as a AA, but about 5mm longer.

Termination:
One tIny 2mm wide tab at each end, each about the thickness of the tabs on the pouch cells.

Actual density:
I laid them out, comparing against a 5S 5Ah 20C pouch cell pack. It looks like I could fit 18 of these in about 1.2 times the space of the 5S 5Ah pack. With termination bars/etc, I would say optimistically about 1.5x.
That brings us to 115.44Wh for these, vs 138.75Wh for 1.5x the 5S5Ah pack. Of course, you would also have extra space taken up by whatever termination system you use for the pouch packs...I'm gonna say optimistically you would probably end up breaking even.

So to sum up, I think that for building a large pack these are out of the question. If they had a more solid termination, maybe they could be feasible, but like with 18650 cells, it would still probably require a large amount of engineering work to get them into a usable module. Interesting, and they seemed like a good prospect, but let's just say I'm glad I only got 10. I'm sure I'll find some use for them, but it looks like my original thought of combining the energy density of 18650 cells with a fairly high discharge capability is a bust.

If anyone has any questions or anything they would like me to try with these cells, let me know and I'll see what I can do.

First on the list is some discharge tests.

[neptronix]

Aaaahhhh.. i figured that was the case..

BTW, how are you getting the 138whr/KG figure? Did you know that this RC Lipo is actually 3.8v nominal? were you using 3.6 or 3.7v as the nominal voltage in your calculations?

[cwah]

Are lipo 3.8V nominal? Because on HK they use 3.7V nominal and the WH you can get out of it should rather be calculated at 3.7 rather than 3.8V

[x88x]

BTW, how are you getting the 138whr/KG figure? Did you know that this RC Lipo is actually 3.8v nominal? were you using 3.6 or 3.7v as the nominal voltage in your calculations?

I used 3.7V. I've never really seen a good justification for any of the quoted 'nominal' voltages for lipo. LiFePO4 makes sense, as the voltage curve levels off at 3.2V for the majority of discharge, but with lipo not really having a level discharge at all, there's no clear point to draw the line.

[neptronix]

Are lipo 3.8V nominal? Because on HK they use 3.7V nominal and the WH you can get out of it should rather be calculated at 3.7 rather than 3.8V

They are if you put a moderate load on them, like 1/4th their rated C, and charge them up to 4.15-4.2v/cell, then yes.



( this image does not fully demonstrate that, since this pack is only charged up to 4.15v/cell. )

I'm not sure why hobbyking rates it at 3.7v nominal. That's probably if you are pushing them really hard, like at their C rate, constant..

[neptronix]

BTW, how are you getting the 138whr/KG figure? Did you know that this RC Lipo is actually 3.8v nominal? were you using 3.6 or 3.7v as the nominal voltage in your calculations?

I used 3.7V. I've never really seen a good justification for any of the quoted 'nominal' voltages for lipo. LiFePO4 makes sense, as the voltage curve levels off at 3.2V for the majority of discharge, but with lipo not really having a level discharge at all, there's no clear point to draw the line.

It's difficult to calculate, but i've noted that about 20% of the rated amp hours are usually left at 3.7v/cell average, and there is a miniscule amount of energy after 3.6v.

Without voltage sag being a factor, the 50% mark for these batteries is actually 3.85v/cell average.

[cwah]

With my 4 pack of 5s8AH 30C zippy, when I charge them to 4,15V and use then up to 3.7V I have around 400wh of power usable at 4C. At 3.7V nominal I should consider that my pack has 592WH of power and I'd use around 2/3 of the battery power with 400wh which is normal.

I wouldn't consider that I could have more energy than that so if I count the lipo at 3.7V nominal that would be more representative of the energy stored. However, it's true that most of the time I'm around 3.8V and I don't like to go lower than that