Lost one cell in my 4 cell pack-what happened?

[Loneflier]

Hi all,

I was flying my FMS P-40 this afternoon, all was going well, when I noticed a loss of power. I was nowhere near my timer limit, but I started to circle to come back around and land. I had just dropped my gear when all power stopped. The prop quit moving, and I lost all control. Fortunately, I was over some fairly tall grass, and was in level flight. She just glided in with a slight nose down attitude. I kept trying to pull back on the elevator to level out, but I had no control. Luck was with me, it didn't hit hard, and only popped the landing gear loose on one side. Didn't even break a prop.

Once I got back to the bench, I checked the battery and had no reading at all on my battery analyzer. I could plug in a fresh battery, and everything came back to life. On further analysis once I got home, I could determine that one cell of the 4 went completely flat. The other three were at 3.91volts each.

So, I am pretty sure it was the battery that failed, and I see nothing from the plane that could have caused a drain on only one cell. If there was a problem, it should have drained the battery equally I would think.

Does anyone out there have any ideas what happened? I have several more of the same batteries and am wondering about them now. I always balance charge, and checked this one before flight and all cell voltages were close. Not exact, but close, and the battery was at 97% capacity.

Any thoughts or suggestions would be appreciated.

[Konrad]

RE: Lost one cell in my 4 cell pack-what happened?

Hi all,

I was flying my FMS P-40 this afternoon, all was going well, when I noticed a loss of power. I was nowhere near my timer limit, but I started to circle to come back around and land. I had just dropped my gear when all power stopped. The prop quit moving, and I lost all control. Fortunately, I was over some fairly tall grass, and was in level flight. She just glided in with a slight nose down attitude. I kept trying to pull back on the elevator to level out, but I had no control. Luck was with me, it didn't hit hard, and only popped the landing gear loose on one side. Didn't even break a prop.

Once I got back to the bench, I checked the battery and had no reading at all on my battery analyzer. I could plug in a fresh battery, and everything came back to life. On further analysis once I got home, I could determine that one cell of the 4 went completely flat. The other three were at 3.91volts each.

So, I am pretty sure it was the battery that failed, and I see nothing from the plane that could have caused a drain on only one cell. If there was a problem, it should have drained the battery equally I would think.

Does anyone out there have any ideas what happened? I have several more of the same batteries and am wondering about them now. I always balance charge, and checked this one before flight and all cell voltages were close. Not exact, but close, and the battery was at 97% capacity.

Any thoughts or suggestions would be appreciated.

The battery probably developed an internal short, an insulator failed. These usually happen near the edges of the cell as these are the easiest to damage (distort).

Another strong contender for the problem was that the lithium matrix wasn't applied evenly to the copper or aluminum plates allowing them to come in direct contact with each other in the cell, again a  high resistant short.

Better modern lipos are now made with automatic processes to cut down on this variability. 

These are just 2 possibilities with the data you supplied. There are a myriad of reasons batteries die.

All the best,
Konrad

[Loneflier]

RE: Lost one cell in my 4 cell pack-what happened?

Hi all,

I was flying my FMS P-40 this afternoon, all was going well, when I noticed a loss of power. I was nowhere near my timer limit, but I started to circle to come back around and land. I had just dropped my gear when all power stopped. The prop quit moving, and I lost all control. Fortunately, I was over some fairly tall grass, and was in level flight. She just glided in with a slight nose down attitude. I kept trying to pull back on the elevator to level out, but I had no control. Luck was with me, it didn't hit hard, and only popped the landing gear loose on one side. Didn't even break a prop.

Once I got back to the bench, I checked the battery and had no reading at all on my battery analyzer. I could plug in a fresh battery, and everything came back to life. On further analysis once I got home, I could determine that one cell of the 4 went completely flat. The other three were at 3.91volts each.

So, I am pretty sure it was the battery that failed, and I see nothing from the plane that could have caused a drain on only one cell. If there was a problem, it should have drained the battery equally I would think.

Does anyone out there have any ideas what happened? I have several more of the same batteries and am wondering about them now. I always balance charge, and checked this one before flight and all cell voltages were close. Not exact, but close, and the battery was at 97% capacity.

Any thoughts or suggestions would be appreciated.

The battery probably developed an internal short, an insulator failed. These usually happen near the edges of the cell as these are the easiest to damage (distort).

Another strong contender for the problem was that the lithium matrix wasn't applied evenly to the copper or aluminum plates allowing them to come in direct contact with each other in the cell, again a  high resistant short.

Better modern lipos are now made with automatic processes to cut down on this variability. 

These are just 2 possibilities with the data you supplied. There are a myriad of reasons batteries die.

All the best,
Konrad

Thanks Konrad-I really wanted to make sure it couldn't have been anything in the plane that caused the problem, and I don't see how it could be. Now my concern is that I have 5 more of these same batteries and wondering if they are "time bombs" waiting to happen too. They are new batteries, less than a year old most with less than 10 cycles on them. Always balanced charged, at only a 1c rate. Hopefully, this was just a bad one in the bunch.

[Konrad]

RE: Lost one cell in my 4 cell pack-what happened?

"Thanks Konrad-I really wanted to make sure it couldn't have been anything in the plane that caused the problem, and I don't see how it could be. "


I don't think I'd go that far. ANYTHING THAT ROTATES CAN INTRODUCE A VIBRATION. Vibrating is the killer of many things. Are your props balanced?


I dirty little secret about liops. They are only "good" for about 2 years. That is the chemistry in the cells will break down just sitting on the shelf. After 2 years at room temperature most Lipos will not take much more than 80% of their original charge (energy).


Balance charging is the best way to charge. Do not let the cells get more than 0.2V out of balance.
I have seen NO data that support 1C charging as being advantages. My time is worth a lot more than the battery. I like to charge at 3C plus if the battery will support those charge rates.

[Loneflier]

RE: Lost one cell in my 4 cell pack-what happened?

Yes, checked the props before assembling and they were perfectly balanced. Even ran it up afterwards to make sure there was no shake, and it still runs smoothly. Just a bad battery I guess.

[Konrad]

RE: Lost one cell in my 4 cell pack-what happened?

Just being picky here, but there is no such thing as being in perfect balance when it comes to rotating machinery. How are you balancing the props? You are aware that a balanced prop will stop in any position (360°). A prop on the balance machine that stops with the blades close to horizontal or in the same spot each time is way out of balance.

I have yet to find an FMS/ROC prop that was well balanced out of the box.

After any prop strike the prop will be out of balance. While I don't balance my props after each landing, I do balance each prop at the end of the day, or should :rolleyes: .

[Pheonix]

RE: Lost one cell in my 4 cell pack-what happened?

You are right one here.  APCs are supposed to be balanced from the factory, so they say.  I balance anyway and found that most are out of balance.  Three and 4-blace props are always out of balance.  This is the method I choose to balance these:

1. I weight them so ensure the same weight;
2. I then balance using a Great Plane CG machine;
3. I balance after each flight;
4. If a prop is out of balance, I use clear tape on the lighter blades until balance

It is a good idea to take extra, balanced props to the flying field.  Nothing worse than having a prop strike and no extra, balanced to continue flying.
This is probably nothing new to most. 
[hr]

Hi all,

I was flying my FMS P-40 this afternoon, all was going well, when I noticed a loss of power. I was nowhere near my timer limit, but I started to circle to come back around and land. I had just dropped my gear when all power stopped. The prop quit moving, and I lost all control. Fortunately, I was over some fairly tall grass, and was in level flight. She just glided in with a slight nose down attitude. I kept trying to pull back on the elevator to level out, but I had no control. Luck was with me, it didn't hit hard, and only popped the landing gear loose on one side. Didn't even break a prop.

Once I got back to the bench, I checked the battery and had no reading at all on my battery analyzer. I could plug in a fresh battery, and everything came back to life. On further analysis once I got home, I could determine that one cell of the 4 went completely flat. The other three were at 3.91volts each.

So, I am pretty sure it was the battery that failed, and I see nothing from the plane that could have caused a drain on only one cell. If there was a problem, it should have drained the battery equally I would think.

Does anyone out there have any ideas what happened? I have several more of the same batteries and am wondering about them now. I always balance charge, and checked this one before flight and all cell voltages were close. Not exact, but close, and the battery was at 97% capacity.

Any thoughts or suggestions would be appreciated.

The battery probably developed an internal short, an insulator failed. These usually happen near the edges of the cell as these are the easiest to damage (distort).

Another strong contender for the problem was that the lithium matrix wasn't applied evenly to the copper or aluminum plates allowing them to come in direct contact with each other in the cell, again a  high resistant short.

Better modern lipos are now made with automatic processes to cut down on this variability. 

These are just 2 possibilities with the data you supplied. There are a myriad of reasons batteries die.

All the best,
Konrad

Thanks Konrad-I really wanted to make sure it couldn't have been anything in the plane that caused the problem, and I don't see how it could be. Now my concern is that I have 5 more of these same batteries and wondering if they are "time bombs" waiting to happen too. They are new batteries, less than a year old most with less than 10 cycles on them. Always balanced charged, at only a 1c rate. Hopefully, this was just a bad one in the bunch.

I recently found one of my batteries with one completely dead cell.  I was able to recharge this cell only by first using the NiMH function to get some power. I then charge the dead cell only with a chargng lead that I made.  Here is a great link on the balancing issue:https://www.youtube.com/watch?v=wIbHLacozFo .  I hope this helps.  I have saved a few batteries using this method in both balancing discharging.  Of course I am ready to land quickly if a particular battery cell fails using this method. So far so good.

[Konrad]

RE: Lost one cell in my 4 cell pack-what happened?

Be aware that a Dead (Zero voltage) cell will never rebound to full capacity. The plates will be come etch resulting in a much higher internal impedance. Measuring the internal impedance (not voltage) will show that the cell is permanently damaged. This also happens if you leave the battery fully charged, which plate gets damaged the fastest depends on the charge state. The storage charge tries to balance this decay across both plates. Please be aware that the plates will deteriorate just sitting. This is why lipos have a shelf life of about 2 years.

If you do try to recover dead (zero voltage) Lipos this way please make sure you are not using the battery to power your on board radio (No BEC). Use a separate good battery to power your RX and servos.
Safety first!

[Pheonix]

RE: Lost one cell in my 4 cell pack-what happened?

Be aware that a Dead (Zero voltage) cell will never rebound to full capacity. The plates will be come etch resulting in a much higher internal impedance. Measuring the internal impedance (not voltage) will show that the cell is permanently damaged. This also happens if you leave the battery fully charged, which plate gets damaged the fastest depends on the charge state. The storage charge tries to balance this decay across both plates. Please be aware that the plates will deteriorate just sitting. This is why lipos have a shelf life of about 2 years.

If you do try to recover dead (zero voltage) Lipos this way please make sure you are not using the battery to power your on board radio (No BEC). Use a separate good battery to power your RX and servos.
Safety first!

Roger and thanks.

[Loneflier]

RE: Lost one cell in my 4 cell pack-what happened?

Thanks for the inputs guys. I did weigh each prop prior to installing them on the hub, then balance checked it. It was as close to perfect as I could make it, and runs smooth.

As for the battery, there had to be a failure from the cells to the main connector. When I check using only the red and black wires going to the T connector, there is no voltage at all. The only way I can see the cell levels is by using the balance charge leads.

I don't plan to try to revive it, and certainly wouldn't trust this one in my plane again. I am guessing this is just a strange anomaly and hoping I won't experience it again!

[Capt. Crunch]

RE: Lost one cell in my 4 cell pack-what happened?

I also have a 4 s battery with a dead cell. I noticed it when I hooked it up to the charger. The charger kept giving an error alarm. Tried it on another charger and it did the same thing. Checked the voltage and 3 cells have 3.82 and one reads zero. This battery is only a month old. I wonder how rare this anomaly is.

Jeff

[Loneflier]

RE: Lost one cell in my 4 cell pack-what happened?

I also have a 4 s battery with a dead cell. I noticed it when I hooked it up to the charger. The charger kept giving an error alarm. Tried it on another charger and it did the same thing. Checked the voltage and 3 cells have 3.82 and one reads zero. This battery is only a month old. I wonder how rare this anomaly is.

Jeff

I don't know, but it would stand to reason that the more cells you have in a battery, the more likely one is to fail. Just more connections and internal pathways that could fail.  Yet another reason for me to stick to 4 cells and less, besides the extra cost of 5 and 6 cell batteries. If only I could quit looking at some of those planes that need a 6 cell battery!!

[Capt. Crunch]

RE: Lost one cell in my 4 cell pack-what happened?

Ha! I hear you on that one!

Jeff

[Konrad]

RE: Lost one cell in my 4 cell pack-what happened?

I also have a 4 s battery with a dead cell. I noticed it when I hooked it up to the charger. The charger kept giving an error alarm. Tried it on another charger and it did the same thing. Checked the voltage and 3 cells have 3.82 and one reads zero. This battery is only a month old. I wonder how rare this anomaly is.

Jeff

I don't know, but it would stand to reason that the more cells you have in a battery, the more likely one is to fail. Just more connections and internal pathways that could fail.  Yet another reason for me to stick to 4 cells and less, besides the extra cost of 5 and 6 cell batteries. If only I could quit looking at some of those planes that need a 6 cell battery!!

The flip side is that for any given power the strain on the batteries and associated components is less as the amp draw is lower. I for one like High Voltage set ups. As most ESCs and Chargers can now deal will 22.2V systems I really see no need to stay in the 3 to 4 cell trap.

[Capt. Crunch]

RE: Lost one cell in my 4 cell pack-what happened?

I don't really consider it a trap. If the batteries only have a 2 year life span, that's all the more reason to stay in the 3 to 4 cell range to keep it affordable for me.

But as addicting as this hobby is, I'm sure I will eventually end up with a couple 6s planes!

Jeff

[Konrad]

RE: Lost one cell in my 4 cell pack-what happened?

The trap comment was referencing the old days when we flew Sanyo cells Nicads. The low car cell count of 6 or 7 cell meant that charger and ESC were plentiful for the 7.2V to 8.4V systems But if you wanted to go with higher voltages you were trapped as the upgrade to 10, 12 , 16 or 27 cells, usually meant a huge financial out lay or making the components yourself.

But today there really is no need to stay with 3 or 4 cells for most sport flying. With 6 cells you gain all sorts of advantages and yes even the cost comes down as you can use smaller cells for the same amount of work (time and power).

As most ESC and charger can handle 22.2 volts there really in little reason not to go to 6 cell systems.

Sorry I don't follow the 2 year logic reasoning to stay away from 6 cells.

Bringing planes out of the ashes of defeat since 1969.
Konrad

[Capt. Crunch]

RE: Lost one cell in my 4 cell pack-what happened?

All I meant was that if Lipo batteries only last 2 years, then I would rather have to replace a 20 dollar 3s battery versus a 100 dollar 6s battery when the 2 years comes due. I'm still a newbie here, only having a little over a year into this hobby and am going off what u said about the dirty little secret with lipo batteries only lasting 2 years. Theres no reason for me not to trust your knowledge since I haven't even hit the 2 year mark yet, you've been in this hobby since the year I was born, and you clearly have a good grasp of the electrical side of things.

Jeff

[Konrad]

RE: Lost one cell in my 4 cell pack-what happened?

Nothing to trust, It is in the numbers Volts x Amps x Time.

Now a 6 cell $100 battery will have the same energy as a $100 3 cell. The difference is that the 6 cell will have half the capacity, Amp Hour rating but double the voltage of the 3 cell. But the cost will be close to the same for the same amount of energy.

Staying on this site (MotionRC) you can see that both batteries cost the same when looked at as far as the energy they hold. Sorry this is the best I could do yes the 6 cell has twice the energy as the 3 cell and it costs twice the cost.

http://www.motionrc.com/admiral-3300mah-6s-22-2v-30c-lipo-battery/
http://www.motionrc.com/admiral-3300mah-3s-11-1v-30c-lipo-battery/

To make a 6cell have the same energy as the 3cell we would need to find a cell that was half the size (1650 mAh). And then it would actually cost the same in dollars, and still have the same cost as to energy content

Only lasts 2 years means that they will only take about 80% charge at the end of that time period. Also their discharge rate will be down. But they are still usable for most sport application.

If you have a choice always go for the higher voltage system. This is assuming your charger can handle it. The lower current draw will pay dividends in less line losses (more flight time), and less stress to the electrical switches, Mosfets (longer lasting ESC and motors).