Sony US26650VT Li-ion Cells - Need More info

[lincpimp]

Looks interesting, How are you attaching the cells end to end?

You do need to test these, if they are ghood for 15-20c discharge rates, they would be a good solution. Are they available online for sale?

[sikeston34m]

Originally Posted by lincpimp

Looks interesting, How are you attaching the cells end to end?

You do need to test these, if they are ghood for 15-20c discharge rates, they would be a good solution. Are they available online for sale?

I don't like the idea of straight soldering cell to cell. There's ALOT of heat involved with doing that. It might be ok for Nimh or even A123, but I don't feel like it's a good idea with Lithium Ion.

You can solder to them, but you gotta get in and get out quickly. Afterwards, I like to quickly cool the solder with a wet cold cloth. It sucks the heat right outta there.

On the 18650 and smaller cells, there is a neoprene gasket under the positive end. If too much heat is applied, this will melt and then leak electrolyte. Not good. So much care needs to be taken. I'm not sure if the 26650 cells have this same gasket, but I'm not taking any chances on that.

First I scuff the ends lightly with a Dremel tool.

See the copper jumper bars? I solder each end of a jumper to a cell. Then I carefully fold it over until the cells are end to end, taking care to make sure they are square. This also provides a nice convenient solder spot to attach balance leads.

I then apply 1 layer of heat shrink, attach the power lead, then go back and put one more layer of heat shrink on. Double heat shrunk for toughness.

I'm hoping these will make for some good bashing packs. They not be the best for all out racing, but I think they "might" do.

I do know where a few are. PM if you want more info Linc.

[sikeston34m]

Captain! We're ready to give her all she's got!

Now if this nasty weather would just clear up.

[lincpimp]

Well that is certainly the quick and dirty way to get them to fit! Good thing those cells have metal cases!

Time for some good testing. Do I need to send you a hacker c50l of the apropriate kv so that you can load them heavily? Seems like the inrunner motors can produce higher amp spikes than the outrunners, bad for running but good for testing.

[othello]

I don't use the Sony 26650VT but the smaller 18650vt (1100mAh -> 9s2p in my truggy). Those have the same characteristics but feature a lower Amp rate due to their smaller size. First off you won't need any balancing cable. This cells do remain perfectly in balance. Charge them up to 4.1 or 4.2V per cell and you are good to go. I don't use an LVC since summer 2007. Capacity hasn't changed noticeably still 2200mAh can be charged back.

Their weakest point is a constant drop in voltage during discharging (your car gets slower and slower) and when it comes to power density A123 cells are superior, as they can deliver up to 100A per cell in a 1p config (1 A123 cell delivers up to 220W burst but may drop voltage down to 2V). At 50A the sony 26650 will drop below 3V per cell and at the end of discharge even lower so you might get up to 130-150 Watt per cell. If you don't expect lipo or A123 performance than you won't be dissapointed as those cells are very reliable and uncomplicated when it comes to handling: good bashing cell for a milder setup.

[sikeston34m]

Thanks for the input Othello. I was hoping you would join in here.

I just finished with the 1st test run. It is true that the voltage drop curve is different. I noticed that.

1st part of the run was awesome. It would jump out the hole like gangbusters. I had to watch that itchy trigger finger or it would land on it's lid from a backflip. These cells do deliver good amperage. They didn't even get warm with this setup. As the run progressed, the urge to flip or do wheelies slowly "went away".

I had my LVC set at 3.0 volts per cell. Should I lower that some? Sony says these can be discharged to 2.5 volts per cell. What got me was, these packs didn't just dump like lipo's at the end of the run. It would still go, but I could tell it was definately on the LVC, so I just stopped. I ran it hard and the run lasted 25 minutes. I'm charging them back up now, so I'll see how many mah my superbrain puts back in them. I don't feel as if 5000mah was discharged this round.

From the looks of things, these make GREAT bashing packs. They are tough. They are somewhat heavier than Lipo, but they do deliver.

[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