Bad Battery Buzz

[Matt S]

Just to clear any misconceptions up...

Most chargers will charge LiPo (unless you have a 20 year old HiIQ charger of course).  

i have a friend in calgary area who modified his hi-iq to charge AND balance lipo

[dajracer]

As a member of the executive, I still would not endorse the use of Lipo or any other lithium based battery. If we were only club racing, then maybe that is OK. But what happens when we want to go on a roadtrip to race. If the club running the race(eg. Kamloops) does not allow the lipos then that means anybody interested in racing outside our club would either not be able to race or would have to purchase some other type of battery suitable to the host club. Now we are doubling or tripleing our battery costs.
I am not happy with the current situation either because out of the last 28 cells I purchased, I have 12 that are completely gone and probably at least 2 more that probably won't last the weekend.

[Gorden]

So were would someone looking to buy some new cells go? I might want to get a few packs.

[dajracer]

Gord, I still have some packs left, but as you can tell from this thread they aren't exactly the most reliable.

[haddow]

get a lipo and run open mod, lipos are legal in open mod (7.4 volt max is the rule). (for the record lipos were legal when we travelled to Kamloops to race in mod last winter).

Oh, and run Nitro too of course (with a lipo receiver pack, also legal)

peace

cya in nitro and open mod

[gearhead]

WOW!
I guess I am happy I decided to run just Nitro this year  8O

[Grinder]

So our 25 or so races in Touring Car should be dictated by a race or two that some members of the club may attend?  I'd rather be able to race for the rest of the summer than go away to a single race.

I agree that there shouldn't be any change in battery chemisty for the Speed Weekend even if it means I can't race.  I do think we need to address this issue as most of the club is affected.  SMC isn't helping out here and we need to come up with a solution.  This isn't a hasty decision for those of us who have had battery problems for over a month now.

The problem Ken in replacing cells is that they continue to fail.  I may have a pack with one duff cell and racing you with three bad cells - doesn't make for much of a race.

[Grinder]

I've sent an E-Mail to Danny directly as he hasn't bothered to respond to the post on his thread at RCTech.net  Odd since most manufactures watch these forums like hawks not to mention the feedback they get from their cronies....

[Grinder]

So the word on the street is that we need to dead short the cells to bring them back to life.  To do this make sure the pack is completely discharged in a discharge tray.  The tray and the pack should be at room temperature at the end of the discharge before I would even think about shorting.  I personally take a multi meter and measure the voltage on each cell while its in the tray.  If its 0.0xx volts then there the cell is only putting out 1/100ths of a volt and they are ok to short out.  Make sure you measure across the entire pack as well as a double check.  Sometimes a cell isn't connected to certain discharge trays and then it doesn't get discharged properly.  Make sure each bulb is lit, etc to verify that you have a good connection.

I ran a couple of packs that sat in the tray overnight and they didn't dump hard but I was running in 19T so its a little harder to tell if they were up to snuff.  Running stock and some discharge graphs will tell the true tale as I have a baseline for all my packs.  I also didn't give them a true short so I will do that to make sure they get a fair shake.  I'll post the results here.  Full discharge did make a difference so lets see if it brings them back.

[cyrrus]

Kurk,  that is a very interesting find(word on the street.) Please keep up informed on your findings.  I know from the 3300 that dead shorting was okay for them.  but you lose some run time due to it.  With 4200 we can afford to lose a bit of run time if the volt is still good.  

again nice find.

[Grinder]

I'm still in the middle of testing the cells.  It looks like dead shorting is reviving the dead cells but the average voltage has dropped.  I'm doing more testing before I say either way for sure though.

For the LiMn packs which have virtually identical discharge curves at 30 amps of the IB4200.  I found some for super cheap at    Zebra Hobby

Thats about the wholesale cost of two of the cells without them being built into a pack - not sure why these are so cheap!  These would be great for bashing as well if you've got another R/C vehicle or even practice night, etc if you don't want to wear out your NiMH packs as these will give you race condition charges for 100 cycles or more.
 
Apogee LiMn Magnum 3800 mAh 20C 2S1P 7.4V
Apogee Lithium Manganese batteries are specially engineered for the 1/10 scale car market.
High-Output Lithium Manganese Technology
Max Continuous Discharge: 20.0C / 76.0 Amps
Pack Dimensions (LWH mm): 139 x 42 x 19
Weight (w/connector): 236 g
13 guage silicon wire with Tamiya Connector


Regularly: $110.25
On Sale: $44.25

[haddow]

so what is the chemistry behind a dead short relieving an internal resistance problem?

[Grinder]

Drum roll please.... the results are in....



I've used pack 5c as the baseline since this is a curve from the original packs.  As you can see only one pack came back to where it should be - pack 10.  Pack 7 came back with close to the same run time but the voltage is significantly reduced.  The rest of the packs have both reduced run time and reduced voltage.

Dead shorting the cells has brought the dead cells back but the performance and run time have been significantly comprimised.  The difference in run time between cells is 300 mAh in the worst case so they are essentially performing the same now.  The problem now is that ALL the batteries in the packs are significantly reduced in voltage and run time with some packs being worse than others.  For myself I had six useless packs and now I have one good one two that are good for practice but not competative racing and three that have very poor performance.

So what is the next step SMC?

[Grinder]

Oh and I should note that all the packs have virtually the same numbers so one would expect all the graphs should be overlaping each other normally.

[haddow]

So what is the next step SMC?

LiPo