Limn Probs! - RC-Monster Forums

nbcaznmaster · **Limn Probs! -** 12.09.2006, 03:33 PM

My limn seem to have gotten bigger. I cant really tell. I tested out the LVC with a foward/brake. Before, my lvc woudl throw my revo into full reverse when the voltage got low. So i put brakes, and now ti didnt work at all. I drove it till the batts at were 2.9v. I tried to bump them back up by hooking up the packs in parrelel. They seem fine, but it seems as if one of the packs gotten bigger. I was having trouble balencing the pack that grew. it wouldnt seeem to work with my balencer. After bringing them up, i had 3.86v for one cell and the total was 7.67. Thats a .06v diff betwen cells. WOuld that explain? My temps are fine on them, not warm or anythign. I was only chargint that at 250mah too. Are these packs gargabe? Theres no way for them to blow up correct, cuz they limn?

zeropointbug · 12.09.2006, 06:15 PM

Are you saying your Lithium Polymer pack got bigger? If this is the case, than you are in a dangerous situation, when they swell up like that, they are very sensitive to anything, if you pock them, or anything they might explode.

Does Limn mean Li-Po? Or are you talking about Lithium Manganese?

nbcaznmaster · 12.09.2006, 06:42 PM

lithim manganese

BrianG · 12.09.2006, 07:23 PM

Any battery will have a limit as to how many amps it can supply on a continual basis without overheating. AFAIK, LiMn was "safe" against explosions from puncturing, but you can still pull more current than the C rating and ruin them. Even though they aren't Lipo, they still have a C rating you have to follow.

You can measure the voltage on each cells in a pack by using the balancer connector. Just measure across each pair of wires. For instance, let's say you have a 2s pack; it will have three balancer wires. Let's call these wires wire1, wire2, and wire3. You can measure one cell by measuring across wire1 and wire2, measure the other cell across wire2 and wire3, and the whole pack by measuring across wire1 and wire3 (or the main power connector).

What do you mean it won't work with the balancer? Does the balancer display some type of error or something? What happens if you try to hook the suspect pack on a charger without the balancer (just as a test)?

I suppose you could measure both packs with a micrometer or precision ruler and compare the dimensions.

BTW: Before you hook up any battery pack in parallel with another, you really should make sure they are the exact same voltage. If they aren't the same, or very very close, you will have a potentially high current flow between the two packs, which could cause problems.

nbcaznmaster · 12.09.2006, 07:40 PM

they had same voltage. The balencer is a inline one. it would balence, but it wouldnt say CHARGE on teh apache. The other pack can charge. I think the other pack might have grew, not exactly sure though. It still charges without the balencer.

BrianG · 12.09.2006, 07:53 PM

That's weird. The pack was at 7.67 and there was only a 0.06v imbalance. The balancer should balance it fine. Some balancers have an automatic cutoff when the cells are too low/high, but that doesn't seem to be the case here.

Does your charger have a discharge mode? If so, discharge the "bad" pack at like 2A and while it is discharging, use a meter to measure the voltages on each cell through the balance connector. From what you've said, you've been measuring open circuit voltages. A bad cell can seem OK with no load at all, but as soon as you either charge or discharge, there can be a large imbalance.

nbcaznmaster · 12.09.2006, 07:51 PM

my micrometer measures 21.08mm, the other pack, which i think grew, but not as much is 20.18mm. these results shoudl be pretty accurate.

nbcaznmaster · 12.09.2006, 07:56 PM

the packs grew 2mm larger. I was able to charge the otehr pack. Not sure why, but i think its the balence tabs. I had to move it aroudn till the red CHARGE light on teh apache showed up. It didnt balence compeltely but i didnt want to risk charging it fully, it was already at 4.17v and not finished balencing. Sorry, not discharge. Should i toss the packs or are they still usable?

BrianG · 12.09.2006, 08:04 PM

Honestly, I would contact wherever you got them and explain the situation. It might be under a warranty. You were using both packs in series and one pack went bad. Could be a defect. If they won't help you, then maybe you can try a few things to make them OK again. No sense in doing something they won't cover under warranty. The fact they are bigger and are staying that way is a little troubling...

nbcaznmaster · 12.09.2006, 08:22 PM

well, do limn explode? if theres no fire hazard, ima just run em till they smoke or vent or watever.

BrianG · 12.09.2006, 08:35 PM

Like I said, I think they are safe from puncturing, but not sure if you run with a bad pack...

crazyjr · 12.09.2006, 08:40 PM

Like BrianG says, call where you got them from. You did get them new, didn't you?

coolhandcountry · 12.09.2006, 08:47 PM

I never had a problem with mine. Maybe running them under did something. They don't want you to go under 3v per cell.

crazyjr · 12.09.2006, 10:08 PM

I think he's running a 9l, so, is it possible he went beyond the 76amp(20c 3800)constant and damaged them

BrianG · 12.09.2006, 10:30 PM

I agree with both of you; either ran them beyond the continuous C or set the cutoff too low.

The general consensus for cutoff seems to be to set the cutoff so that after the batteries dump, they drift or "rebound" back to about 3.6v-3.7v after 20 minutes or so. If they only get to say 3.5v, increase the per-cell cutoff in 0.1v increments until they do.