.5 Amps over 1C, charging Li Poly bad?

Not recommended for the life of the pack or for safety.

Mik

-- pda4yo

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| I have been using a Triton charger for a little over a year, and | charged my 3S3P Kokam packs at 2.5 Amps (maximum on this charger for | Li Poly). I usually got 12.60V when fully charged. But it took 2:10 | hours if the battery was discharged on flight.

You forgot to mention the capacity of your battery. 4500 mAh?

| Now I have a new Astro 109 charger. Not wanting to wait the 2 hours, I | charged at 5 Amps instead of the 4.5 recommended. Now the same battery | is fully charged in about 45 minutes at 12.69V. | | I liked the shorter charge time, but is the "slight" over voltage bad?

The `slight' over voltage is probably not related to your higher charge rate. 12.69v is very close to the suggested cut-off of 12.60 volts -- I'd say it's probably ok.

Still, if your pack is 4500 mAh, I'd suggest charging at 4.5 amps, not

5 amps. The odds of this causing a problem are small, but accidents are expensive.

| How about my 3S Thunderpower Li Poly battery reaching a 12.75V, | charged also at .5 Amps over the recommended 1.5 Amps for the Astro | 109?

.5 amps over 1.5 amps is 33% too high, so you're charging at 1.33 C instead of 1 C? It may work, but I wouldn't risk it.

12.75 volts is still pretty close to 12.60 volts. But it's getting high enough that I wonder if your charger doesn't need some adjustment. I'd measure the voltage with a voltmeter, and if the actual figure is *any* higher than that, I'd send it in to be repaired.

| I had been charging with my Triton at 2.5 Amps for both types of | batteries before. Would this practice (higher than 1C charging) | shorten the useful life of my batteries?

Probably, to a small degree. But the bigger danger is causing a fire ... while going slightly over 1C isn't likely to cause this, I certainly wouldn't risk it.

I think these batteries have proven to everyone that a very strict charging and storage routine HAS to be the rule of the day. Charge at 1C and no more. Even if a little more won't hurt, it's just a better bet to have a firm rule, and never waver. Lipolys have a way of punishing those who are loose with the rules, and sometimes even those who are not. I hope these cells become much safer in the future somehow. As for now, I treat them the same way I would treat a little stick of dynamite, and that's unfortunate. BTW, is there any truth to a story I heard the other day about a guy why shorts a pack with his wedding ring and loses his finger?? I figure it's an urban myth but I thought I'd ask?

| As for now, I treat them the same way I would treat a little stick | of dynamite, and that's unfortunate.

I don't believe you :)

I'll bet you'd treat dynamite by not even picking it up :)

| BTW, is there any truth to a story I heard the other day about a guy | why shorts a pack with his wedding ring and loses his finger?? I | figure it's an urban myth but I thought I'd ask?

Wearing jewelry while working with machinery is a well known and well understood risk. A wedding ring can easily get caught in a band saw, for example, and where flesh would just cut and let you go, the ring will not and you'll get pulled in.

With car batteries, what will happen is a short will be created with the ring being part of the short. Suddently hundreds (literally!) of amps are flowing through the ring, and it is almost immediately red hot ... and yet still on your finger, and impossible to remove. It's not pretty.

That part is no urban legend -- it's happened, several times, and I can certainly see somebody losing a finger to it very easily. A R/C pack could cause that, though the whole process would be much slower.

I'll bet what you heard about was a car battery ...

Here's some pictures :)

... though this was a very mild case. Consider what happens if the ring gets stuck in the short circuit ...

Okay I'll give you that one...except when I was in my teens, then I probably WOULD have picked it up, an that would be just to start with. Ahh the stupidity of youth.

Yes, I forgot there are different capacities to various packs. My pack of 3S3P Kokam is 4500 mAh.

They can be very expensive. I've been lucky so far. I did cause an accidental overcharge by inadvertenly turning the Amp dial when I returned to continue charging. I believe I posted this some time ago in this Usenet. Lucky it was the 3S pack instead of the 3S3P.

The battery became bloated and had to be disposed.

Now that I have the Astro 109 charger, I probably would not be charging at that rate anymore.

I really don't think there is anything wrong with my charger. It's just that it is brand new and the first time I used it. Still, I have more confidence now then before I have the new Li Poly dedicated charger.

Thanks, Doug. I will take this under advisement.

Wan

Hey guys,

Look Wan I'm not trying to tell you what to do but I recomend yo follow the rules with lipo's very closely and double check yoursel every time. It only takes one time to burn your house down. I've rea countless stories where real people have become complacent and charge or discharged lipoly's at rates they were not intended and the resulin fire is sometimes life threatning.

-If you charge over 1C your pack will vent flames.

-If you discharge over 10C (on the first generation lipo) your pac pack will vent flames (5C is reccomended)

-If you overcharge by 1/2 volt your pack will vent flames and possibl explode.

I say charge and store in a fire prof box like a $15 Brinks money bo from an office supply store. Try a search on RCGROUPS.com for lipol fire and you'll gain a healthy respect for this new and unprotecte technology.

I use only Lipo and I love them, but I did read alot before gettin them. There is alot of good info on the site I recomended. Hopefull you will read the one about the Astro charger lipo fire before you fire. Good luck ...Momcr

-- Major Mom Cr

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May, no will. In reality its far more likely that at the worst, its life span is reduced, and at the very worst, ultimately you get a puffed cell.

99% of pack failures are 'reduced capacity', and 99% of the rest are 'puffed pack'

Fires are extremely rare, but potentially very destructive.

May. Almost certainly won't. To get a fire you need very high pack temperatures internally. Internal shorts caused by pack deformation as the thing puffs up are the usual cause it seems.

However pack heating seems to follow square law, so only a little too much current over the max can destroy the pack.

Also prolonged running in confined spaces with no airflow is lethal - even WELL below manufacturers ratings. Well below. Helicopters seem to wreck packs at far lower currents than aircraft do.

I would say you should not discharge a pack faster than 6C continuously, and then arrange some cooling.

Almost true. It will almost certainly puff, it may vent and it may explode.

Sound advice.

Nothing is foolproof. Which is why charging in a safe environment is highly advisable.

Even under an upended flowerpot on a concrete slab in yer bedroom is better than nothing.

Its unlikely that you will have a problem, and even more unlikely that it will result in a major fire.

But the possibility is there, and its happened. Make sure that the pack cannot do total damage to you or your car or your house if it ever does.

That's all.

It can be. LiPolys should NEVER read at more than 4.2V per cell. Anybody that tells you "a little bit is okay" does not know what he's talking about.

Don't come crying here when your house burns down because you can't follow instructions. Charging at too high a rate with the Astro 109 can and will cause it to incorrectly detect the number of cells in the pack. If the 109 detects a 3S pack as a 4S, it will try to overcharge it to 16.8V. The pack will swell up, and could vent flames.

It will not only shorten the batteries' useful life, it may also shorten YOURS!!! The fact that the 109 is overcharging the packs tells me that it's detecting the wrong cell count. One of these times it will literally backfire on you. Please RTFM and FTFI.

Overvoltage protection circuits designed for lipoly charging use 4.35 volts as the point at which they dump the charge. I would suspect the point at which the cells puff is considerably higher. This would put the danger point above

13 v for a 3s pack. Your experience of 12.75 v charge is well within the nominal range. I'm sure the pack settled down to a resting voltage of 12.6 shortly thereafter.

No manufacturer recommends charging above 1c, so I wouldn't do it. Fred Marks of FMA is working on a 20 minute charging system for lipolys, so it looks like the 1c charging barrier will soon be a thing of the past.

Wan

U don't need to charge 100% to get full power out of a LIPO. 90 charge will be more than adequate.

I slow charge at the office at 200 ma for a 2S1P tp 2100 mah using th Hobbico Mark II and I don't see any difference in power and duratio using AFI 109 at 2.1 amp ,just less charge time which I do on weekends out at the flying field.

SLOW charging will help equalize the cells in a LIPO pac

-- hall wo

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I got the message. Just about everyone tells me not to charge above the mfg. recommended rate. I will not do so in the future.

But I think I know what RTFM > means but Mathew, please what does mean? Those are your expressions.

Wan

Mike,

I vowed not to charge above 1C.

I read your post earlier, but I forgot to ask you about Fred Marks developing a 20 minute charging system. No doubt it will be for Li Poly. I wish I had known this may be coming, then I would've waited for it.

As it was, I waited three months before I found an Astro 109 from LightflightRC. The Astro 109 took about 45 minutes to charge a 3S3P, compared to 20 minutes.

I wonder if I could afford the one by Fred marks? Would you have anymore information on the cost?

Wan

RTFM - read the fine manual FTFI - follow the fine instructions

| > No manufacturer recommends charging above 1c, so I wouldn't do it. | > Fred Marks of FMA is working on a 20 minute charging system for | > lipolys, so it looks like the 1c charging barrier will soon be a | > thing of the past.

Personally, I wouldn't belive it until it's actually done and tested by many people who know what they're doing.

| As it was, I waited three months before I found an Astro 109 from | LightflightRC. The Astro 109 took about 45 minutes to charge a 3S3P

1C = it will take about an hour to charge a fully discharged battery.

With LiPos, you don't usually fully discharge your battery (if you're smart) so it takes less time. But beyond that, I don't see how you're going to do it in 20 minutes unless your battery is only 1/3rd discharged.

My Triton starts slowly, then ramps up to the full charge rate you've programmed in, the slows down as it approaches full charge when charging LiPo and Pb. So even if you set it at 1C, the average charge rate is a good deal lower than that.

(In contrast, with NiCd and NiMH, it starts out a full speed, but occasionally stops to give the battery an opportunity to peak again in case it missed it. This slows things down somewhat, but does help prevent frying your pack.)

But the *only* way to charge a battery in 20 minutes that is mostly discharged would be to charge at approximately a 3C rate. With the manufacturers saying only to charge at 1C, I don't know how much I'd trust tripling that.

(Of course, when a manufacturer says their NiCd cells can be fast charged, they usually mean they can be charged at C/4 to 1C, and yet we'll push them at 2-3C and things generally work ok, and my LiPo packs barely get warm at 1C, so maybe they really can handle 3C. But I won't be doing it anytime soon.)

| I wonder if I could afford the one by Fred marks?

If you're in this hobby, even the most expensive chargers (like the $300 Alpha) probably cost less than one good plane, so if you're willing to give something up, sure! (No idea on the price of the charger though.)

| Would you have anymore information on the cost?

So go straight to the source ...

click on `Contact'.

I believe you're right about the higher voltage. Somewhere in my travels I read of people charging LiPolys up to 5 Volts per cell. It didn't do the cells any good as far as longevity, but it did prove possible, and as I recall the cells were on the bleeding edge of catastrophic failure.

That's not the point here, though. The fact that the Astro 109 is overcharging AT ALL is very worrisome. A 3S pack "hot" off the 109 should read 12.60 Volts. That means that at some point, it's detecting the 3S pack as a 4S. If the 109 decided to stick with the 4S setting right to the end, you're charging a 3S pack to 16.8 Volts, well over 5 Volts per cell!

Either this particular 109 is defective, or Wan's running at .5 Amps over 1C caused the pack to be misdetected.

That would be insteresting. I'd like to see how he manages to up the current without upping the voltage. Unless the cells' internal resistances are REALLY low, there's no way to exceed 1C without exceeding 4.2 Volts per cell. It's physics.

BTW, charging at over 1C using contemporary constant-voltage/constant-current charging technology will only make a few minutes' difference in the charge time. Once the pack reaches 4.2 Volts per cell, the laws of physics prevent the charger from maintaining the 1C current without raising the voltage. Since the charger can't raise the voltage without risking catastrophic cell failure, the current naturally drops off. You only gain a couple of minutes during the initial constant-current portion of the charge cycle. Most of the cycle time is spent in the constant-voltage mode (or burst mode on the 109, which is very similar in the end result).

| That's not the point here, though. The fact that the Astro 109 is | overcharging AT ALL is very worrisome.

To be fair, 12.75 v (or 4.25 volts/cell) is close enough to 4.2 volts that maybe they just decided to go a bit higher to get a bit more charge into the pack.

| A 3S pack "hot" off the 109 should read 12.60 Volts. That means that | at some point, it's detecting the 3S pack as a 4S.

I suspect that you're wrong here.

| If the 109 decided to stick with the 4S setting right to the end

And you think it changes it's mind mid-charge? No, it almost certainly detects it properly, and just thinks it's safe to go a bit over 4.2 volts/cell.

| Either this particular 109 is defective, or Wan's running at .5 Amps | over 1C caused the pack to be misdetected.

I doubt it's defective. This is probably by design.

| That would be insteresting. I'd like to see how he manages to up the | current without upping the voltage. Unless the cells' internal | resistances are REALLY low, there's no way to exceed 1C without | exceeding 4.2 Volts per cell. It's physics.

The internal resistances are really low. Especially if the cell is mostly discharged, if you take one of the modern 10C or 20C discharge rate cells, you could probably pump in 3C without exceeding 4.2 volts for a while. I'm not saying this would be smart, only that it's possible.

| BTW, charging at over 1C using contemporary | constant-voltage/constant-current charging technology will only make | a few minutes' difference in the charge time.

It would depend on your cell.

| Once the pack reaches 4.2 Volts per cell, the laws of physics | prevent the charger from maintaining the 1C current without raising | the voltage.

Actually, once the pack reaches 4.2 volts per cell, the laws of physics prevent the charger from charging at all without risking overcharging the cell -- because it's generally considered fully charged.

The charge voltage is *not* the same as the pack voltage while charging, and the difference will be the {internal resistance} * {the amperage}. The {internal resistance} will include the cell's internal resistance, the resistance of the wires and the connectors, but it can be calculated easily enough.

A charger could safely put put more than 4.2 volts into a LiPo cell as long as it stopped charging every few seconds to make sure that the cell itself wasn't above 4.2 volts yet. They could use the difference between the two voltages to calculate the internal resistance and use that. I don't know of any chargers that do this yet but it's certainly possible. It's also a tad more risky than the current setups, so I don't know if the extra speed is worth it.

| Since the charger can't raise the voltage without risking | catastrophic cell failure, the current naturally drops off. You only | gain a couple of minutes during the initial constant-current portion | of the charge cycle. Most of the cycle time is spent in the | constant-voltage mode

In my experience, most of the charge time for an almost fully discharged LiPo pack with my Triton charger is spent in the constant-current mode. It spends a few minutes ramping up at the beginning and around 10 more minutes ramping down at the end, but as long as the battery is mostly discharged when I start, over half of the time is spent at the charge rate (1C usually) that I told it to do.

Of course, the batteries I use the most are designed for high discharge rates -- up to 10C. So they would have low internal resistances, and would probably charge faster than batteries designed for slower charge rates. But even the other batteries I have spend most (60% or so) of their time at the full charge rate if almost fully discharged when I start.

Wan.

I can solve all your problems

Buy some 3000mA/h cells and stick a label on them saying 1000mA/h.

You now have cells that will discharge at 30C, hold their voltage incredibly well doing it, and will recharge in 20 minutes at 3C.

What more could you ask for?

:-)

BTW there are signs that the vendors are in fact doing precisely the above...

yes.

No...see below...

Oh yes there is mate! simply set the charge current to something dramatic. The packs are charged at coinstant current, and the voltage slowly rises towards teh 4.2v per cell, at which piuint the charger starst to pulse charge them - by then its 90% done, but can take anorther 20 minutes to shove the last few electrons in.

On some packs with higher internal resistance I get faster charging using a LOWER charge current - stops the Astro detecting 4.2v per cell untl they are more nearly full.

But in any case, I often pull them off the charger once over about 4v per cell anyway. That's full enough for me. No need to squeeze the last drop out of a LIPO pack when there is so much in hand anyway.

I generally fly for about 15 minutes and charge about 20. The packs are seldom more than half empty.

Astro is faster to absolutely full charge.

Ive seen peak voltages a fair bit higher than 4.2v /cell while it does it tho. 4.3 or more is not unusual.