AW LiFePO4 - bad cells?

[erich]

Hi all,

So, after having a mediocre experience with some Ultrafires, I did some reading and decided to give the AW LiFePO4 linked below a try, as well as the WF-188 charger with the 3.2v selector. I bought 4 of them, and marked them to keep them paired together. Out of the box they registered ~3.5v. I was running them with either the 3ohm Boge or the 2.5ohm smok Tech Dual coil (dual 5ohm). I would run one pair for half of the day, and then switch them out and recharge the others (with the charger on the 3.2 .

Everything started out great, and then suddenly one of the pairs stopped. I took them out and tested, and one batter was @3.3v, the other 2.3v. The low-registering one won't take a charge at all. The charger goes red then immediately back to green. So, I'm thinking maybe I have a bad battery... but then the next day, the other pair did the same thing. Sudden death in the PV, and one measuring only 2.5v that won't take a charge.

Are these duds or have I done something wrong?

AW LiFePO4 RCR 123
Ultrafire WF-188 Lithium Battery Charger

Smok Tech 2.5 OHM Steel Dual Coil Cartomizer
510 Blank Cartomizers

 

[cappadoc]

The 3.2V can over-discharge in HV use. The WF-188 cannot charge them from that low voltage state. Throw on a 3.7V charger for 10 minutes to kick start them. I don't know how bad this is for the cells, but I do this frequently. It works, and so do the "bad" cells.

 

[emus]

The 3.2V can over-discharge in HV use. The WF-188 cannot charge them from that low voltage state. Throw on a 3.7V charger for 10 minutes to kick start them. I don't know how bad this is for the cells, but I do this frequently. It works, and so do the "bad" cells.

I thought some batts pass the point of no return when over-discharged?

 

[erich]

huh, nifty. In fact, 30 seconds in the WF-188 in 3.7v mode seems to have "jump started" them. I took them back out and switched it back to 3.2v and the light is red, at least.

Is this over-discharge due to overuse? It seems weird that one dropped off so much more than the other... If it is, how can one really know when to charge? Are people testing them hourly or...?

 

[emus]

Over-discharge is running voltage so low batt can't recover.
Can happen to new batt.
Some batts handle over-discharge better than others.

 

[erich]

well, right, but using it for part of a day, and then suddenly it registers 1/3 lower voltage than the one with which it's paired? Something seems amiss...

 

[emus]

Defect is possible also.

 

[hairball]

well, right, but using it for part of a day, and then suddenly it registers 1/3 lower voltage than the one with which it's paired? Something seems amiss...

Anytime you use 2 batteries together, one will always read lower than the other or at least from all the mods I have, this is typical. One thing you need to do is to rotate them. I mark mine with a letter and a number....example: A-1 and A-2. I will put A-1 in first then A-2. After I use them down and recharge, I put A-2 in first then A-1. I hope that makes sense. It allows both batteries equal discharging so that I don't have just one battery in the pair quit and still left with a good one. They last longer by doing this.

 

[Switched]

2 things are happening here.

Because their is no protection on LifePo cells, you need to be cognizant of decreased vaping performance. This will happen way before the low voltage threshold of the battery. Kick starting a battery that is below its LV theshold works but not recommended. Basic to Advanced Battery Information from Battery University

Although the DCs at 2.5 should be fine wrt current draw, try vaping a normal atty in the 3-3.5Ohm range and see what that does.

BTW hairball is absolutely right wrt rotating the batts. The one closest to the load always depletes at a faster rate. By rotating them you insure that the internal resistance to current flow is as close to equal as you can possibly can. Not rotating the batts = the one with the greater IR will die faster as time goes by and will not last as long, not to mention creating a potential problem in a stacked situation.

 

[erich]

Awesome. Thanks for the tip. I'll start rotating.

I'm finding that at 6v I like the single coil 3ohm (measure 3.2-3.3) Boge better anyhow, so I'll probably stick to those.

 

[gorman]

huh, nifty. In fact, 30 seconds in the WF-188 in 3.7v mode seems to have "jump started" them. I took them back out and switched it back to 3.2v and the light is red, at least.

Is this over-discharge due to overuse? It seems weird that one dropped off so much more than the other... If it is, how can one really know when to charge? Are people testing them hourly or...?

When one does this jump start thing, is the light supposed to turn red during the jump start? In my case it stays green. Battery measures 0.92...

 

[erich]

Yeah, it'll turn red. Often you can just wait a while and it'll raise back up enough to charge on the 3.2 mode.

0.92... wow. I haven't seen one that low.

 

[gorman]

Tried, but the light went red for a second or so. The battery is new... Probably it's better to ask for a refund?

 

[erich]

I'm no expert, but sounds like it...

 

[Fabsta]

Good info here. Some people are using the 1.5 ohm dc's at 6 volts. Are there any 16340 3v batts that can safely deliver the 4 amps needed to power these? Will the aw's do it?

 

[erich]

http://www.e-cigarette-forum.com/forum/ikenvape/84144-batteries-safety.html#post1252290

"AW C rating for 16340 is 8C" which should be double what you need.

 

[Fabsta]

http://www.e-cigarette-forum.com/forum/ikenvape/84144-batteries-safety.html#post1252290

"AW C rating for 16340 is 8C" which should be double what you need.

Thanks erich. Even after several hours of searching I never came across that thread. I'm gonna save it for future reference. p.s I think that an 8C rating on a 500mah batt means that it can handle a 4 amp draw but I may stand to correction.

 

[erich]

Radio Control Zone - View Single Post - Li-po Battery 'C' rating?

Looks like I misspoke saying "double". However, by this formula, an 8C rating on a 550mAh battery should be able to do 4.4 amps. I believe it's plenty.