Understanding Lithium Polymer batteries

[gomotomoto]

The discharge system would be another great group project build (hint hint) anyone want to tackle the process and show how they go about building one?


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[jbrumberg]

My method was simple... I had my wife back my truck up into a tree breaking the plastic rear light assembly unit. In my truck's case it comes as a complete all enclosed unit. I replaced the plastic light assembly and had the leftover wiring harness available. I put it to good use after I got the idea to use it as a battery discharger from the internet. I really do not understand all the science behind it, but I know those three lights (backup, brake, and running) allow for a controllable, slow discharge of the battery. I do not recommend my method- it was kind of expensive.:black_eyed:

 

[phantom_alex]

So please can someone recommend a first battery for use with a dji naza 450 kit. Do I need 3s or 4s. I'd like around 15 minutes or more if possible!!

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[gomotomoto]

So please can someone recommend a first battery for use with a dji naza 450 kit. Do I need 3s or 4s. I'd like around 15 minutes or more if possible!!

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Bart has recommended a 4S 3500 - 5000 mah and around 30c. I'm in the process of choosing one myself.


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[phantom_alex]

What do you think would be the difference flight time between a 6200mah 3S and 4S 35C. The 3S is about 150g lighter than the 4S

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[PeterLester]

A good question that is best answered by means of using eCalc for Multirotors. A wonderful way to gain valuable insight into all such options.

What do you think would be the difference flight time between a 6200mah 3S and 4S 35C. The 3S is about 150g lighter than the 4S

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[Will]

Thank you Bart for putting together such a comprehensive & easy to understand guide. It's an awesome reference!

However, I still have some really basic questions that I just can't find the answers to anywhere (I've read the entire thread, browsed the newbie area, searched the site, used Google/YouTube, etc - nothing).

Most pressing is this...

PART 3

STORAGE, INSPECTION, AND DISPOSAL


If your LiPo batteries are going to sit on the shelf for a while, they are happiest if the cells are at about 3.7 to 3.8 volts each...

How long is "a while"? A day, 2 days, 3 days, a week? I've seen countless warnings, threads, & videos showing how these things can puff up and spontaneously ignite if they're left either fully charged or empty and I want to make sure I'm not sharing my house with a handful of little bombs that could go off while I sleep (I don't have a fire-friendly place like a garage to store them).

At the moment I charge them in the morning and fly in the afternoon but I now need to charge my batteries the night before a planned flight so that they're ready for an early start (balance-charging 5x 4s 5000mAh packs takes about 4 hours). Is it safe to charge them the night before and not worry about them puffing/burning overnight? What if I didn't use all the batteries that next day and didn't have time to discharge them? Would it be safe sleeping next to them for a 2nd night? Are the fully-discharched batteries a danger too if not given a storage charge quickly? Worst-case, what if I 'lost' a fully-charged LiPo around the house - would I have to spend 24 hours tearing my place apart to find the ticking time-bomb?

Sorry if this sounds like a panic - it's not, but I've seen videos of them burning on YouTube and spotted a few hundred warnings from manufacturers and multirotor-pros like this ( http://www.multirotorforums.com/sho...l-charge-warning&highlight=store+charged+lipo ), coupled with the fact that members here seem divided with some saying it's fine and others saying you're asking for trouble (note: I don't mind the batteries going bad, I just don't want them going 'bang'). I can't find a clear answer and it seems like a pretty important question. Any help would really be appreciated.

 

[kloner]

i've dealt with a few lipo fires now..... there really tame, only problem is if something else ignites..... theres no bang, it's like a road flare

being stored means within days. every second makes a difference, it's alot like heavy metals in a body, the damage accumulates. when the damage gets too high it'll show in loss of volume, early voltage drops and heavy voltage sags..... they all make it come down sooner than you thought it should...

 

[Motopreserve]

Will,

I've been doing the same as you - charging the night before and then flying the next day. I always keep them in a "bunker" I built using a metal box and sand. This way, worst case the sand extinguishes the flames. Then I make sure that I fly through all the batteries by the end of the day - that way the storage discharge doesn't take quite as long.

do you have a storage function on your charger?

I've read some good papers/posts about batteries, and began with similar concerns as you. I check the batteries for puffing each time I touch them.

THIS has some good info.

 

[gomotomoto]

I took a metal toolbox (smaller one) and lined it with fiberglass blankets, picked them up at harbor freight on the cheap, I also store inside that - in a LiPo bag. Not sure if that's the best solution but it's what I do. I've also gone to great lengths to learn how to discharge if I can't fly the battery. Still trying to figure best practices out.


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[jbrumberg]

I have to find the article to provide the link, but the research seemed legitimate. The basic premise and the research test results confirmed the hypothesis that charging a battery to 4.1V/cell instead of 4.2V/cell significantly lengthened the lifespan and number of cycles of the batteries tested in this experiment, especially when stored in the manner described in the article previously mentioned and linked. It does make sense on an intuitive level. Now I have to find that article.

 

[kloner]

you want to contain the flare, but you don't want the box on anything flammable, keep it away from walls, trash, etc and do not seal it..... if you do, it can make more problems than venting the smoke....

The main damage from these is smoke damage unless it ignites something. It's a plasticy most likely unhealthy smoke..... they don't need air to burn, seen em going underwater, etc.

 

[Motopreserve]

I took a metal toolbox (smaller one) and lined it with fiberglass blankets, picked them up at harbor freight on the cheap, I also store inside that - in a LiPo bag. Not sure if that's the best solution but it's what I do. I've also gone to great lengths to learn how to discharge if I can't fly the battery. Still trying to figure best practices out.

I forgot to mention that I also grabbed some of the Lipo bags. So actually, the batteries go inside the bags, and then the bags go inside the bunker.

 

[Dezy]

I measured the Internal Resistance of my 4 cell 4000mAh batteries that had just a couple flights on them with my 208B iCharger. One had 22 mOhms and the other had 24. Using the formula found earlier in this thread: (12000 / C rating of battery) (number of cells). Using this formula my batteries would be (12000 / 4000) 4 = 12 mOhms. So, if my math is right:nevreness: my batteries are about twice as should be, after only a couple flights with no crashes. How much of a percentage change from normal is acceptable? Or do I have the math wrong........

 

[PeterLester]

IR varies by manufacturer. If you measured them when new and the new readings are very close to orig.... Then no issues. And 22 milliohms sounds reasonable from my perspective.

 

[kloner]

22-24 is excellent,,,,, you will notice that rises as you go and will be acting up by 40-50. storing them in the right environment/state, no over discharging, no over amp the charge rate all keeps them healthy

 

[Benjamin Kenobi]

22-24 is excellent,,,,, you will notice that rises as you go and will be acting up by 40-50. storing them in the right environment/state, no over discharging, no over amp the charge rate all keeps them healthy

Really, 22-24 is excellent? Mine are all around 2milliohms which means they are super awesome!

 

[kloner]

that sounds like your reading off each cell, in which case 0-3 is great, 4 and up is leaving ya,,, over 8 on a 6s is sucking wind..... the cells as a whole was how i read his numbers and that includes the plug the power goest through.... i don't even look at the balance plug cause i'm monitoring it at the power plug, when that goes up i'll take a look at the balance plug to see what it has to say about the situation.... i charger will read either or.....

the way he does his math isn't how you want to monitor these.... when you get new packs, put your plugs on and read to ir, write it on the pack, go fly, recheck, monitor, etc....

 

[Benjamin Kenobi]

Ah, that makes more sense! Yes, I read per cell, always. I'm looking for bad cells rather than the overall lipo. So I'm on 12 per lipo which still sounds very good. My year old lipos are still the same as the brand new ones! Hence why I've stuck with the GensAce brand, they seem to just last.

Cheers mate!

 

[kloner]

you want to look at the main plug as the pilot, lets you know if it isn't making good contact, if carbon build up is making an issue, if flux is on the connectors, etc.... when that number jumps up that's when you look at cell, if that is still low, then it's the plug...