How to Kill LiMn- Or, the devils review of Konions

[aaronski]

Hi guys, I've done over a year of LiMn testing on bosch fatpacks. and now, not one pack works at all. I know DrBass says their bulletproof, and he's mostly right, but even they have their limits.

for about a year I rode various configurations of 6 fatpacks.

1. the sag hammer- one pack, 72v, 2.2ah probably 50 cycles like this. pulling 50-60 amps, or 25-30c out of 5c rated cells, I managed to sag them from 80v hot to 55v under load. it got worse as the SoC dropped. after this, they still had no appreciable ah loss. I got 2.2 ah from this config.
2. gotta... get...home..... 10 cycles of 100% DOD, I pulled the cells down to 20v on a 72v pack. at full throttle I'd only get 100 watts.
3. Oops. Left batts on controller over weekend, come home to 0v. also, repeatedly left packs lying around dead.
4. 72v,6.6ah 60 amps max- about 100 charges like this. worked like a charm. was still pulling 10c out of 5c packs, but the sag was about 10v. untill....

5. Finally killed them. - wore through the tape harness I made for one half of the pack, and dead shorted various cells to the bike frame. black goo seeped out of various cells. took about 2 weeks to realize this. meanwhile, I'm charging the pack to 85v hot, and likely only on 36v of cells, so doubling their voltage?? seemed saggy to, as I was dropping it from 84v to around 40 at first touch of the throttle.

results:

out of 6 fatpacks, I have 2 that still work, marginally, around 2.0 ah from them at 5c, but sag to 28v pretty quickly. the other 4 packs are not recognized by the charger at all.I've tried just various cells, no love. one charger says no connection. the lead acid charger doesn't respond to plugging them in.

 

[miuan]

Great effort dude! Now man up and do this to LiCo

 

[Ratking]

If that is their limit, I will gladly use them.
I think your abuse of the batteries can be compared to trying to put a flame near gasoline and except the gasoline to work in a engine afterwards.
So the fatpacks only have 5c discharge?
I am using the cells from makita packs, I hope they are as robust.

 

[kfong]

Good job torturing them, no fires to boot. Going past 5C is a good way to shorten the lifespan. Too bad the fat packs are now over $100 new. I wish there was a cheap source for new cells.

It's good idea to check the wiring and batts once in a while as well. I like the silicone wires from hobby king, but they are the worse for abrasion resistance. My tire went through a set and I had wiring short out in my rear rack bag due to all the movement. Luckily it just kept vaporizing each strand as they made contact. I no longer use silicone wire in certain abrasion prone areas.

 

[neptronix]

Great effort dude! Now man up and do this to LiCo

Well, he already did kill some RC lithium polymer ( lico ) doing the same thing.

aaronski, i don't know what you're trying to prove here. Any battery ran at it's absolute maximum, or above will not live long.

My "5C" headways sag like mad and get hot at 3C constant. My 20C RC lipo will sag quite a bit ( half a volt per cell, which is awful ) and get warm at 10C constant load. A 1C laptop cell will sag like crazy at 1C and produce a ton of heat.

C rates are generally very optimistic. The maximum cycle life of lithium cells are typically rated at 1C or far below. You'll never see a rated cycle life at the maximum C rate.. you know why? because it's atrociously low. Then they couldn't advertise inflated specifications.

 

[aaronski]

Not trying to prove anything. If you're asking why, psychologically, it's likely justification for my impulsiveness and lazyness. I'll get bored halfway though building a pack, and just run half the pack for a bit, then poof! Besides, I think people enjoy reading it.

Now about those laptop cells... I have 1kwh of them sitting in my garage. Gonna make a 36v, 27 ah pack from it, and limit the draw to 15 amps. Should get good range/ low speed. Wondering what the sag will be at .5c

 

[neptronix]

Now about those laptop cells... I have 1kwh of them sitting in my garage. Gonna make a 36v, 27 ah pack from it, and limit the draw to 15 amps. Should get good range/ low speed. Wondering what the sag will be at .5c

I am glad the cell abuse has ceased. I was about to call the lithium protection services on you and have all your batteries confiscated and put into a foster home where they'll only be used to run 250w geared motors in europe.. :wink:

 

[miuan]

Was testing my new 4S hardcases yesterday, unfortunate enough to get them down to under 1 volt at 8C discharge. First cycle ever, so stupid. One of two serial strings disconnected while riding. Didn’t notice that and kept on riding on 5Ah instead of 10Ah. There was a slow section near the end of my ride, and I didn't notice the lower power from my motor because I didn't use WOT anyway. Then when I needed it, there was suddenly no power at all.
Got home on the second 5Ah string, then looked at the damage. No swelling thanks God, all cells sprang back to 1.7 - 2.7V, so I charged them up and they seem to hold voltage and balance reasonably well today. These are tough cells! Granted, I did a full balance charge yesterday morning so they fell down together nicely. Doing this to an unbalanced pack would definitely kill some cells.
What I learnt from this accident is DON'T RELY ON RC PLUGS alone and add some retention support like duct tape or epoxy to prevent them from falling apart. I noticed these new hardcases came with a different plugs to my older (but otherwise identical) Turnigy 4S 20C hardcases.

 

[SamTexas]

Now about those laptop cells... I have 1kwh of them sitting in my garage. Gonna make a 36v, 27 ah pack from it, and limit the draw to 15 amps. Should get good range/ low speed. Wondering what the sag will be at .5c

I tested the Panasonic CGR18650E cell:
05% sag at 0.5C. A 4.00V cell will be at 3.80V under that load.
09% sag at 1.0C. A 4.00V cell will be at 3.64V under that load.
15% sag at 2.0C. A 4.00V cell will be at 3.40V under that load.

What's the sag for your LiMn cells at those loads?