Uneven Discharge!

[jtrucktools34]

Help!

I have read around the forum horror stories about Li-ion cells exploding and do not want to become another statistic.

Last week I purchased an Xtar D-30 from another forum member. He sold it to me with two "D" size rechargeable Li-ion cells and a "generic" charger. I took the light out of the box and removed the cells to check the voltage before trying the light. One of them was at 3.9v and the other was 3.95. Even though they were slightly differing in voltage it wasn't enough to be alarming. I decided to run the light for a while to check it out before charging the batts.

I was able to run it for about 20min this morning comparing it to some other lights I have when the D-30 began to flicker on high! I assumed the batteries were discharged so I promptly shut off the light and removed the cells. I tested them with my VOM and to my amazement the first cell was @ 3.7v... I thought that maybe there was a problem with the light because the cell voltage should have been at about 25% or so. Then I checked the other cell! It was @ 3.1v. Did this happen because I essentially ran the batteries too low? I have only purchased protected batteries in the past because of the hazards.

These cells are blue wrapper cells that only say 3.7v Li-ion on them. No brand at all except for a logo engraved into the negative terminal. It looks like the Xtar logo I have seen in pictures of their batteries. I am assuming they are unprotected but I really don't know. I have e-mailed the seller to get more info.

I currently have them on the charger but I am watching them like a hawk. I am using an IR thermometer to watch for heat build up and check them with my VOM about every 5 min. They are at 3.8v and climbing but I am very concerned about using them again.

Additionally I found out that Xtar has even discontinued selling the 32650's but they would not say why. ??

Any advice would be much appreciated.

Thanks

Jerry

 

[45/70]

Hi Jerry.

Keep in mind that with LiCo cells, the voltage difference numerically, is quite a bit different at those low voltages, but that both cells are nearly depleted. Obviously the cell at 3.1 Volts is more depleted, but the 3.7 Volt cell is well on it's way out as well. And, yes, it'd probaly be a good idea to figure out how to stop discharging the cells a little bit earlier.

There is some discussion about cells that are closer to the emitter(s)/bulb and light engine, discharging faster than other cells in series applications due to the extra heat. You may want to check the next time and see if the cell closest to the heat generating area of the D30 is always the one with the lowest voltage.

I've never witnessed this phenomenon, perhaps because the series lights that I have, either have more even placement of the cells (not in tandem), or I just don't run them at 100% long enough to have much of an effect. Still, it's quite conceivable that the extra heat could be the cause of uneven discharge. The hotter a cell is, the faster it will discharge. The R/C racing folks like their packs hot for this reason.

Dave

 

[jtrucktools34]

Dave,

Thanks for the insight!

The cells are still on the charger. They seemed to rapidly charge up to 3.9v (two hours) and now have slowed down building voltage. They are currently at 3.99v. I do believe it was the cell closest to the light engine that was more deeply discharged. Would you or anyone else recommend rotating the cell positions alternately each charge cycle? What is the "safe" cut off voltage for these cells? Again, I don't know for sure but I suspect they are unprotected 3.7v Li-Ion.

Should I cut the max charge voltage off before the 4.2v threshold? I checked the charger without any cells in it and its output was 4.135. This is the first time charging.

Thanks again.

 

[45/70]

Alternating cell position would certainly help. I'd say it'd be worth it, as the cells will wear more evenly that way.

The best point to stop discharging LiCo or LiMn cells, is at a point that after the cells have rested a few minutes after use, the voltage reads 3.5 Volts OC (open circuit), or above. The higher the voltage (up to about 3.80-3.85), the longer your cells will last. I try, but am not always succesfull, to replace/recharge my cells when I think the voltage has reached ~3.80 Volts. Also, I store my cells at about this voltage.

I don't know what charger you are using, but 4.20 Volts OC is pretty much the standard charged voltage for LiCo cells. No, you don't want them to go much over 4.20 Volts, but some chargers (the better ones) will read 4.20 Volts while the cell is in the charger, for quite some time, as this is the CV stage of the charge cycle. Some less expensive chargers (most all of them) skip the CV stage and only use a CC algorithm, or a modified variation thereof, and are actually "done" when the voltage reaches 4.20 Volts. With these chargers, it's best to pull the cells when 4.20 Volts is reached, to avoid any possible trickle charge (damaging to cells) that some of these inexpensive chargers have.

Dave

 

[kramer5150]

That doesn't sound too alarming. You did the right thing by immediately terminating the run at visible signs of flicker/dimming. A 3.1V cutoff is a safe cutoff point for Lithium based rechargeable chemistry.

I have never had a perfectly matched pair. A series pack is only as strong as its weakest cell.

You are doing the right thing by monitoring voltage + temperature while charging too.

 

[VidPro]

yup, dont ever push it, when you read a resting 3.1V it had probably been lower than that while discharging. Right thing, pull when the power drops, even earlier than you did.
if it really is unprotected, people will try and keep them topped off more, and not take it to the end.

charging to 4.1 whatever you said would be good for a D, and watch your charge RATE, sure its 1C capable, but i never allow them to be charging 1C 1/2 way through . one person had a HUGE fire out of one from charging at 1C. its not like 2-3 18650s its all in one big ball. respect the power

Low charge or normal , finish the charge with Both of them VERY close to the same voltage. so when you say hey charge to 4.1 cool , ok but have both at the same voltage. that is about all you can do to have them both at closer to the same capacity.
If you have one at 4.1, and the other one got to 4.2, it would be better to start with BOTH at 4.2. they will never end the same, as said, starting the same will help.

they do sell these protected. if protection had kicked in, it is possible that was part of the flashing. Pictures :twothumbs, then we can guess if its a protected or not.

as them blue ones age , they are gonna get very bad, so use meter, check things, if they dont "accept charge" (meaning raise in voltage when charging, or dont act like they are charging) or "self-discharge" quicker they are dying. When they dont "accept charge" that charge power is heat, and we all know what that means

 

[jtrucktools34]

Thanks for all of the good advice. I pulled them from the charger at 4.21 and 4.20v. After resting they ended up both at 4.18. Good enough for me. I still am concerned about the possibility of them being unprotected. I don't plan to use the light a lot so I may opt to continue using these batteries for short periods of time and then top them off again.

Here are some pics of the batteries themselves. I am guessing they are unprotected because all of my protected batteries say they are protected on the labels and these do not. The only indication as to who the manufacturer is is the logo on the negative terminal shown in one of these pics. It looks like the Xtar logo I have seen on other batteries but I'm not sure.


Ok,

It looks like I need a little practice posting pics first. They didn't work out. I will try again later!





I think that's got it.

Moderators please remove pics if there is a problem.

 

[45/70]

I'm not familiar with Li-Ions bigger than 18650's........yet. :naughty: Being primarily a pocket light collector, I really don't have that many 18650's, 14.

Most cells 18650 and smaller have the protection circuit mounted on the bottom of the cell, where it is quite easy to see where the shrink wrap is uneven. With D cells though, I imagine the circuit could be mounted at the positive end, seeing as they are so much bigger, there would most likely be room for the PCB there. Someone more familiar with 26500-32650 LiCo Li-Ion cells may be able to tell you for sure. In the meantime, I would treat them as if they are unprotected cells, just to be on the safe side.

Your cells seem to be in good shape. They charge to 4.20 Volts and after resting a bit, still hold 4.18 Volts, that's good. The way to check the health of a LiCo Li-Ion cell, is to do as you did. Charge to 4.20 Volts, let them rest a while (some say 20 minutes, I let them rest 24 hrs), and then check the OC voltage. Then if the OC voltage is,

4.20 Volts = 100% condition
4.15 volts = 75% condition
4.10 Volts = 50% condition
4.05 Volts = 25% condition
4.00 Volts = 0%

Below 4.00 Volts the cell is ready to be recycled/disposed of, as cells in this stage of their life cycle can become unstable and a possible hazard. Keep in mind that this check applies to the condition of the cell, not the state of charge, although that applies also, eg. a cell that reads 4.10 volts after being charged to 4.20 Volts and rested, is at 50% of it's life cycle, and has about 90% of it's capacity.

I should have mentioned that in case you haven't already, you should read up on Li-Ion cells in the sub forums at the top of this Forum. I'm guessing you are at least somewhat educated about the care and handling of Li-Ion cells. Just the same it's a good idea to keep abreast of things in those threads. I've been using Li-Ion's for about 6 years and I still go through them.

Oh, and also just as info, Xtar doesn't manufacture Li-Ion cells. Like most of those companies (Eagle Tac, Wolf Eyes etc.), they just subcontract out to battery distributors (like xxxxxFire et al, who don't manufacture them either) and have cells dressed up with their logo on them and possibly a protection circuit added.

Dave

 

[kramer5150]

Thanks for all of the good advice. I pulled them from the charger at 4.21 and 4.20v. After resting they ended up both at 4.18. Good enough for me. I still am concerned about the possibility of them being unprotected. I don't plan to use the light a lot so I may opt to continue using these batteries for short periods of time and then top them off again.

Here are some pics of the batteries themselves. I am guessing they are unprotected because all of my protected batteries say they are protected on the labels and these do not. The only indication as to who the manufacturer is is the logo on the negative terminal shown in one of these pics. It looks like the Xtar logo I have seen on other batteries but I'm not sure.


Ok,

It looks like I need a little practice posting pics first. They didn't work out. I will try again later!





I think that's got it.

Moderators please remove pics if there is a problem.

Your cells are fine. 99% of the flame/fire/explosions occur from one of 3-4 root causes:
-Over charging
-Over dis-charging
-Mix old with new
-Mix depleted with freshly charged

High current applications also increase the odds of a flame/fire/vent incident.

 

[VidPro]

thanks for posting the pictures.

still hard to tell. seems like false nipple on top
there might be the conductive strip down the side on one picture. Confirm, is there a very thin "band" from top to bottom that makes a bump under the insulation that is not a Seam of the insulation?

4500 properly rated probable actual capacity, that is a clue that the maker cares a little.

 

[jtrucktools34]

Vidpro,

What is a "false nipple"?

There are three slots at the base of the positive terminal "nipple". They do not really look like the vent holes that are on my protected 18650's though.




As for the "thin bump" in the insulation. There seems to be two wrapper seams 180 deg. apart from each other. In addition to this there is a thin bump (hardly visable) running from the top to the bottom of the cell. I tried to get a pic but they would not turn out.

I also found another interesting dilema.

I have two DMM's I use to test cells. One is a Sears (Craftsman) and the other a SnapOn (BluePoint). One is at work and the other at home. I have been charging the cells at work and monitoring them with the BluePoint. It is with this DMM that I have been reporting voltages here. I decided to take my freshly charged cells (4.18v) and light home last night. I ran the light a total of about 3-4 minutes. Afterwords I took the cells out and measured them with my Craftsman. They read 4.06v! Wow! That was a significant drop for only 3 to 4 min of use. I left the cells out of the light last night just in case the D30 had an issue (high parasitic drain). This morning the cells still read 4.06v. I brought the light and cells to work and was going to charge them up again. I measured them with my BluePoint before putting them on the charger and to my surprise they read 4.14v.

I never new there could be so much variance between meters. It doesn't seem like much but in this case it seems quite important to have accuracy! I am not sure how I will test my meters to see which one is more accurate. The Blue Point is about 6 years old but cost me about $500.00. The Craftsman is almost new but only cost me about $50.00. For now I will trust my BluePoint.

Any thoughts?

I do greatly appreciate all the responses. Thanks to all!!

Jerry

 

[45/70]

Concerning meter readings, yes there can exist quite a bit of difference between them. The Flukes are probably the best. Even the less expensive ones are pretty reliable.

I've been a Snap-on fan for years, of course the guy coming by every week helps. I've always thought that their non handtools were a bit over the top, price wise though. You can usually do better somewhere else.

While one of these days I may get a decent Fluke, in the meantime I use what I have. I have never professionally anyway, needed a meter with all that much accuracy. Most of the time it got used for continuity checks and to find out whether the circuit was 12 or 24 Volts, or something drastically less etc.

As I said, what I do is use what I have, for my hobbies. I do have a friend that works with electronics that I can check my meters against once in a while. He has a high end bench model Fluke that is checked for calibration once a year, and as long as my DMM's checkout reasonably well against his Fluke in the ranges I use the most, I'm happy with that for now. So, if you can check your meters once in a while against a known accurate meter, you can get by that way.

Dave

 

[jtrucktools34]

The best I can do is probably checking against a new Snap On meter on the tool truck. My dealer comes today so I guess I will see if he has a new one I could test against.

I believe the Blue Point I have was built for Snap On by Fluke but I could be wrong. I will ask today who makes the new Snap On meters.

Off topic...

Snap on Rocks in the tool world but you are right that they don't always make even their branded tools and can be overpriced...

I am standing at my TOOLWAGON at the moment surrounded by tools and lights. Not a bad job!

Jerry