Batteries LiPo Life Expectancy

[Heliman450]

Hi all,

I've not been using 6S batteries very long but I've already scrapped two after only 40 flights each as they seemed likely to burst at any time. I put this down to me having run them too low and not having had a sound management system going during their lifetime. On the other hand, my 3S batteries are still going strong for many years. I didn't even count how many times they've been used.

I'm limiting flight time to three minutes and this brings them in at about 80% capacity. I see videos of people flying their 6S-powered helis for six minutes plus.

Tell me your secrets or are you even aware of how much capacity you're using?

 

[Smoggie]

Phil,

You should get a lot more than 40 flights, I've got batteries with 300+ cycles that are still doing ok. If could be that you just got a couple of bad packs but also it might be the way you look after them.

My battery care regime:

• Charge on day of use, usually right before leaving the house (in order to minimise the time they dwell fully charged).
• Balance charge with a good quality charger (usually at 2C rate, sometime higher)
• I don't fly like a mad-man and so don't overheat the batteries.
• Set flight time so that the battery has minimum of 3.7V per cell, measured after removal from heli
• Store batteries as they come off the heli providing voltage is in range 3.7-3.9V per cell.. otherwise storage charge/discharge
• If I don't use a charged battery but plan on using it the next day I'll stick it in the fridge
• If the charged battery wont be used for a few days I'll discharge to storage (3.85V)
• Store in a cool place, out of direct sunlight etc

This is a pretty 'easy to live with' regime, a lot of it is about minimising the time that the battery spends fully charged. The only thing it demands is a reasonably powerful charger so you can charge up the batteries quite quickly on the day you fly.
Some batteries are more resistant to abuse than others but using the regime above I cant recall the last time I had a lipo 'puff', they just tend to very gradually loose a bit of zip over time.

 

[Heliman450]

Hi Steve, I thought you'd be the first to get back, thanks.

The only query I have from your list is the 3.7V. I have done this and only dipped a couple of times below to about 3.68V. Using my statistics, one of my scrapped batteries went to 3.74V and needed 3804 mAh to bring it back up. On the other hand, since restricting my flight time to around 3 minutes, one of my newest batteries needed only 926 mAh after a flight time of 3.5 mins. This equates to 18.52% of the battery's 5000 mAh capacity.

After a flight of over 6 mins as I've seen in your videos, how many mAh does it take to bring the battery to full charge?

 

[Smoggie]

Bear in mind flight time is highly dependant on headspeed and how hard you fly.

On the 700's typically I have about 3.8V left in the batteries which is slightly over 40% remaining, i could easily fly a little longer. I'd expect to be putting about 2800mAh back but I never bother to record what my charger puts in to be honest. I parallel charge so it's impossible to say exactly how much each individual battery takes anyway. On the 630 and 600 helis I tend to run the batteries a bit lower, they are around 3.7V when they come off and occasionally go a bit lower which does them no harm, 3.68V is no problem at all.

3 minutes is very over cautious in my opinion. Even the hardcore 3D flyers who run screaming headspeeds and thrash their helis mercilessly can fly longer than that.

 

[Admiral]

Hi Phil,

Add into the mix occasionally you get a bad battery or in your case maybe two, I bought 4 identical 1500mAh batteries for my 250 quad, one puffed severely after about 20 flights the other three are still going strong after at least 50 flights each.

I have two batteries from 2010 that I use on the bench for setups and testing, I would not try to fly with them though.

 

[Heliman450]

Hi Keith, Steve,

I suppose it's always possible that 'duff' batteries exist in a supplier's stocks but I've still got two of my original four I bought when upgrading to 6S-powered helis and they are a bit swollen when compared to the original dimensions and have completed 26 cycles since I got them. This is the main reason for me raising this issue to see where I'm going wrong. After Steve's feedback, I can move forward with extending the time I'm using them for and begin to build up my stocks. The plan is to buy in pairs and aim for eight in the first stage during this season giving me four flights with the 700X and the full eight when using only the 550. I'm thinking to visit Hugo and buy a different brand for the next batch of batteries.
If my fleet gets expanded, then I'm interested in Velos Rotors' 880 (also from Hugo). I'd be able to load it up for two flights without buying more but obviously, four flights would be even better I need to get my house in order first though.

I've already dropped my head speeds dramatically without any really significant gain in flight times. I can't say that I have any 'style' at the moment but I'm getting loads of practice in as the winter moves behind us. More batteries will also help on that score, too.
Thanks for the help on this, I'm off to negotiate some space in the refrigerator with she who must be obeyed

 

[Eggy 71]

I've been tracking some things since I started flying my 450L last year. I check the internal resistance before charging and for the last couple months after a charge as well. I check the resistance individually but charge in parallel. It seems performance really varies against the resistance. I guess that makes sense since the resistance just turns energy into waste heat when running. The resistances climb steadily as they are used and as they begin to unbalance things change.
Things I've found that seem to help keep the resistances down. Balance Charge individually or with packs with similar resistances. I've charged @ 1C but am going to try it @ 2C and see if anything changes. Sizes make a difference with resistance but so do brands. I find E-flight is often double of Turnigy or Gens Ace as an example. I have a few Zippy as well, good price fairly good IRs. The act of charging lowers the internal resistance ( I'm guessing current flow removes some oxidization) but a charged battery seems to increase IR over time way more than a a pack at storage or even discharged approx 70%. I calculate that from checking mah charged over total mah of packs from flight time. So for my 450L 4:30 always seems to discharge 70% That's where I leave my packs. The IR seems to stay steady.
I chart the packs from new or from when I started with this, the second to last charge, and the last charge to watch the delta now and the overall deterioration. They all seem to come very close to balanced on each cel. As they go, one cell starts climbing. It increases and starts dragging the other cels higher. If it gets 25%-30% higher on a cel I won't parallel charge it or only parallel charge with other packs in similar condition.
The Gens Ace 850 mah packs for my 230s started around 18 mohms and after 75-80 flights are 22-25 mohms. They may climb into the 30s sitting but charging as explained brings them back down closer to initial readings.
I thing I've just thought about, I'm sure they are but do your packs have a high enough discharge C rating. If they are getting too hot during operation might be stressing the pack a bit.

 

[Heliman450]

Hi Derek, great feedback, thanks. I haven't as yet measured any resistances. I'll need to dig out my multi-meter for that. All the packs are charged as pairs so the older of the four together and the latest together. All batteries are 25C rated. The only time that they've been very warm was during the deepest of discharges but not too hot in my view.

I'll have as look at resistances out of curiosity but for now I'm going to follow Steve's lead on not leaving them under full charge for anything more than overnight and then put them into the fridge to let me get an early start during the summer months to come.

 

[Heliman450]

Hi Derek, I noticed that my two latest batteries are 30C, not 25C as were their predecessors. That'll be an interesting point to watch as their use progresses. They're already at almost 20 cycles (half the old ones) and looking good so far.

In the meantime, I'd appreciate some information on how you're measuring the internal resistances of your batteries. I suspect that I'll have to come up with something that would adapt my multi-meter pins to be able to link up with the balance connections on the cells. A picture or something would be great.

 

[Eggy 71]

I've been checking the resistance with my charger. My old 50w Venom charger had a setting as does the new 306b . It's an awesome 1000w charger I put together for $150 with a power supply. Thanks Tony for that video. They both can measure total and individual cel resistance. I noticed the higher quality charger seems a little more accurate but both give similar readings. As per previous posts, it's not so much what the reading is as how it changes over time. The old charger was reading 14-3-6 consistently and the same battery on the new charger read 8-7-7. Same overall resistance but appears more balanced. If your charger doesn't have that setting it can be done long hand but it's a lot of work. (More than I'm willing to put out). I watched a couple YouTube videos showing how to do it with multimeters . Rcmodelreviews did one on graphene batteries that wasn't bad if you can stand the fellows presentation skills.

 

[Heliman450]

Hi Derek, thanks for that info. I'll have a look at my charger's capabilities first. I haven't checked out all its features yet so now seems like a good time.

 

[Smoggie]

I use my iCharger 4010 duo to measure IR (though it's not something I do very often). iCharger's are supposed to have decent IR accuracy, Powerlab chargers aren't so good for IR and generally report much lower numbers. The battery temperature is very important when you measure IR, the values will be lower when the battery is warmer so you need to test at a standard temperature to get repeatable results.
I've not looked at the video Derek mentioned but I'd guess the 'longhand' way to do it would involve putting the battery under a fixed discharge load and recording voltage drop.. more effort than it's worth IMHO.

 

[D.O.G.]

Since I have a cheesy charger "CopterX B601" should I be checking my batteries after ever flight to see if it reads the same every flight? Rodney "Trainrider 06" mention to me once that I run my batteries to low. On a flight time of 6 mins. on my 500, the 6 cell battery reads 7.5 @ 14%. The battery has about 70 flights and it just started to show a little swelling. The battery is almost 1yr old. I was just wondering and hope I didn't screw up this conversation.

 

[Smoggie]

7.5V for a 6S battery! ... If that's correct then the battery is toast. It wouldn't charge up again because the charger would error on too low voltage. the minimum for a 6S is about 18V (3v per cell). It would normally be impossible to run a battery anything like that low because the ESC would cut out on low voltage long before that point.

 

[Heliman450]

Hi all, I don't want to become too paranoid on this subject, just want to know what's best and here's the best place I know of for some interaction. D.O.G. mentions "the battery", I'm not sure if it's the only one but I'm intending to build up to 8 at the moment to get a decent session at the field. I'm finding 4 too few!

Steve, I'm thinking that the 7.5V is a typo.............. over to you D.O.G.

 

[D.O.G.]

Thanks Heliman.... Now back to our program Yes it's a typo error I need to put my mind in motion before I put my mouth in gear, in this case, finger on keyboard. I meant to say 3.75v . I also goofed up on one of my batteries, I think. I made a mistake and put a non charged battery into the 500 and flew the heli not knowing the battery wasn't charged . Good thing I wasn't to far or to high in the air to bring it back safety. , Is the battery still usable or start slowly storage charge the battery then bal. charge to see what happens? Right now the battery is sitting out for the time being.

 

[Smoggie]

I think most of us have accidentally installed a used battery occasionally.

3.75V per cell is no problem. I regularly fly mine as low or lower than that, it's absolutely nothing to be even the slightest bit concerned about. 3.7V to 3.75V is the ideal voltage range to fly down to. Even going lower once in a while isnt a big deal for the battery, the risk is more about losing power due to the ESC cutting out if you go much lower.

 

[D.O.G.]

That's exactly what happen. The ESC cut out and I floated down. That's cool my batteries are in the ball park then. Thanks again Smoggie for your input. Most helpful guys!

 

[Heliman450]

A little bit off topic......................... but not much

I think I'll need to start looking into parallel charging when I build up my stock (8 6S batteries) so I can turn them around faster. Can someone show me their arrangement? A link will do fine if it's already here somewhere.

 

[Smoggie]

I'll take a photo of my setup tonight. There are a few options for parallel charging, the new style 'safe' parallel boards with individual fuses on each connection are the most fool-proof, but you can use non-fused boards or 'squid' cables too.
Parallel charging is really the only way to go if you have a lot of batteries to charge, which it tends to do once you get into bigger helis as each flight needs two. To take full advantage of parallel charging you do need to have a charger and power supply capable of pumping out lots of amps. Parallel charging on a low power charger doesn't really gain you much.