nashvillecactus

iTrader: (3)

I have a Turnigy 2s 5200 mah 30c hard case lipo that I bought less than a month ago, have ran at most 6 times, and now one of the cells appears to be bad. When I hook up the balance lead, and set the charger to balance charge, one of the cells will barely take charge, but the other one does. So what happens is one cell gets to 4.2, but the other one can't really make it past 4V. The charger is set to cut off after 2 hours regardless if it's done or not. I've set this to cycle a couple of times, so in 4 hours it's not able to bring this other cell up to 4.2. I've tried discharging and then charging again, and that doesn't seem to work. The pack doesn't look puffed as far as I can tell, but certainly something is off.

Does anyone have any suggestions before I soak it in saltwater etc?

Duster_360

iTrader: (21)

I would charge the weak cell directly using the balance connector. They make chargers that charge this way, but you can rig something up pretty easy to ID the weak cell and charge it directly.

I've had several lipos do something like this and charging the prob cell either resolves the prob - some permanently and some for just a while or confirms that its time for a new lipo.

nashvillecactus

iTrader: (3)

Before I read your response, I decided I just didn't trust the battery any more so I cut the deans and balance plug off to reuse later, popped the case off just to take a peek inside. The cells weren't at all puffy, but the soldering job was a mess inside. Gobs and gobs of solder everywhere.

So anyway, after reading your response, I tried charging the weak cell, it took a charge, all the way to 4.2V. So I took the opportunity to swap out the 8AWG wire with 12AWG (it's way overkill for a 2s and I hate soldering it), clean up some of the messy soldering and put on some new 22awg servo wire in place of the original balance wire (the original wasn't really long enough), then spliced that back to the bits coming from the balance plug I had cut off earlier. I had broken the case when I took it apart, so now it's gorilla-taped back together. If you look up ghetto lipo in the encyclopedia, there should be a pic of this guy Maybe it will hold up. Or maybe it'll cause a fire... Time will tell I guess.

Duster_360

iTrader: (21)

Sounds like the wiring/soldering was a mess and that was preventing that cell from charging all the way. If the resistance that the charger's balancer 'sees' is not equal one cell to the other, then the charger may think the cells are at same voltage when they're actually not.

I agree about the 8ga wires - complete overkill, no one likes or needs that heavy of a wire. Hopefully, one day they'll exhaust their supply and we'll get reasonably sized main power wires.


Bet you now have a decent lipo....

nashvillecactus

iTrader: (3)

well, the battery still doesn't quite want to charge properly, the other cell charges, just a lot more slowly than the first one, and I guess my charger isn't so smart as to figure out that it needs to concentrate more charge to the weaker cell. It appears as though it just applies current to the charge leads, and then when it sees the first cell is at 4.2 it goes to discharge mode briefly, and then goes back into charge mode again, the first cell takes the charge more quickly, gets to 4.2, etc. Is this the way most lipo chargers work in balance mode, or is this just specific to the Thunder AC6? Or am I off base on what's actually going on?


In the mean time, I've decided that I'm going to rig up a little switcher so that I can easily charge one cell at a time using the balance plug. I've found some balance leads on ebay, going to put a dpdt toggle switch in a little project box so I can switch between cell 1 / cell 2, and have a lead coming out the other side to hook up to the charger. Even though I'll probably toss the battery soon, it should be generically useful I'd think.

cweaver19

iTrader: (1)

i have a had many problems with turnigy batterys and the only reason i bought them was because there so cheap so i wouldnt even bother with them anymore,better off with a different type of pack i think.

nashvillecactus

iTrader: (3)

I'm waiting for hobbypartz to get some more stock on gens ace and I'll order one of those to try it out. Also thinking about getting a scooter motorworks since they're so lightweight, someone at my local track recommended them to me, but they're nowhere near as affordable as the gens ace or turnigy packs. So far I'm pretty happy with my Common Sense RC pack, but it was $65 and not ROAR approved so I'm not sure I'd buy another one.

Duster_360

iTrader: (21)

For these kinds of probs, I have a charger that charges each individual cell directly and independently. I just wait until the lights for all cells change from red to green and its charged, all to 4.2. If a red light doesn't change to green, that cell is damaged and beyond anything but replacement which is generally not worth the time and trouble at these prices. I knew with HK lipos there would be probs and thats the reason I have this type of charger, its paid for itself saving lipos.

Not sure exactly what kind of logic a balancer uses, but chargers do just apply voltage and watch response, they have no ability to concentrate on one cell vs another. Some chargers seem to handle having a cell at 4.2 easier than others, but thats just an observation. Remember, the AC6 is a cheap charger and its intended for use on good lipos.

Sal Bandini

That would just make it pointless to even have a balance tap, now wouldn't it.

With balance charging the charger is controlling the charge current of each individual cell. Even the lowly AC6 does that.

Meradin

iTrader: (19)

Not true, when balance charging the charger supplies engergy through the manin charge leadn and continues to do so as the charger enters the balance phase. The balance tap is only used to bleed off excess energy. When one cell reachers 4.2 volts the charger lowers the charge rate and discharges that cell while charging the other cells. When all cells reach 4.2 volts the charge is finished. There is a bit more that the charger calculates to determin the end but that is basically it.

When shopping for a charger, take a look at the current drain for balancing spec. that is a good indicator of how fast a charger will be able to balance a battery. My iChargers have a current drain of 350ma for balancing. Not the best but they do a great job. I have seen some that will drain up to 500ma and I am sure there are more.

Sal Bandini

My manual states:

"In this mode, the charging process will be different from ordinary charging mode. The internal processor of the charger will monitor the voltages of each cell of the battery pack and controls the charging current that is feeding to each cell to normalize the voltage."

so I think this is different than a balancer only. Plus, from my experience, when I charged a 2S with cells out by about 0.3 to 0.4V, they started to normalize well before the higher one hit 4.2V.

trickedout

iTrader: (31)

hey duster could you link me to the charger you have than can charge per cell, seems like a very useful charger if needed.

Duster_360

iTrader: (21)

Can do - it comes setup for plugging into a cig lighter, I just replaced that with the usual 4mm bullets -

http://www.hobbyking.com/hobbyking/s...idProduct=2055



I was reading in their forums and HK said they use this charger to rescue returned lipos they get sent back. Its come in handy, makes it easy.

trickedout

iTrader: (31)

Thanks!

nashvillecactus

iTrader: (3)

http://www.radioshack.com/product/in...lterValue=DPDT

Picked one of these up today, and ordered some balance extension plugs off ebay, one of which will get sacrificed to making my little rig to allow my charger to charge a single cell through the battery's balance plug. I guess something like this or this would be more generic if I needed to handle > 2s packs, but I don't, so a dpdt should work just fine.