Li-Po Batteries, worth the effort?

Trying to decide what replacement batteries to buy Nimh , Li-Po or stay with trusty NiCads, heard that Li=Po are much better for their size and
weight but also they need special charging and are likely to burn if overcharged so what are the benefits and the risks of Li-Po?.
regards, Terry
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Terence Lynock (MSW) wrote:

The benefits are as advertised..the risks are overstated.
The key to using LIPOS is to use them with commoon sense. Run within their limits they are safe. Run outside and you are asking for trouble, possibly explosive trouble.
- don't ever let them get over about 70C...one person left a pack on the front seat of his car in a hot carpark in full californian sunshine. No car now.
- Never let the voltage go above 4.2v per cell, or much below about 3.3v per cell..yes you CAN exceed these limits in SOME cases..but play safe for now. The charger SHOULD take care of the first, and the LVC the second point, but mistakes in setting cell counts are probably the most likely cause of LIPO fires when charging. Even autosensing chargers like the Astro 109 - my definite choice - can be fooled into wrong detection if the current setting, or state of charge are wildly different from whet it expects.
- de-rate the cells to about 70% of manufacturers and vendors claims, unless you have the test equipment to verify them and an application that is trying to squeeze the ultimate out of a pack. I would typically operate a '30A rated' pack at 20A *burst* peak, and much much lower for general flying..and if it says its 2000mAh capacity, try to use never more than 1300-1400mAh. There is an accumulation (sic!) of evidence that packs treated this way last far longer than packs that are pushed..
Using all of the above techniques works really well..if you stop flying well before the packs are flat, and run them cool, they don't overheat,. don't get out of balance and last many cycle. My only three pack failures are due to being stuck in trees..and in one case left switched on for two days in a test rig. In tow of the cases the pack was pretty much showing zero volts but very careful and slow charging was able to restore about half the capacity. I still fly these packs, but they ain't what they used to be. The third did the puffy thing after 2 months up a tree.. and no attempt to revive it worked.
I have momentarily shorted cells and packs when making them up and fitting connectors, with no problems.
All these techniques will reduce the chances of an accident to almost zero. However the consequences of an accident are more severe than for Nickel chemistry, so it pays to treat the things with care. I would say that I trreat my LIPOS about the same as I treat a can of fuel, or a firework. Basically they are safe enough, unless you let them catch fire..then you have a serious prioblem.
Storage in *cool* conditions requires nothing special..lets face it LIPOS are in every laptop and mobile phone, and they do not spontaneously combust.
The three ever present dangers are due to accidental shorting of them while being transported, getting too hot, and being pushed too hard - either when charging or discharging.
For that reason one should never charge then in a flammable situation - inside a fuselage..or on a wooden desk etc - just get a simple sort of fireproof container with a loose lid - a flower pot, or a cooking pot of ceramic is ideal - and put them in that to be safe. I admit I am fairly cavalier about charging, but always keep an eye on them while I do..I watch TV in the same room for example when charging up to go flying..and I know where the window is to toss the lot out if the worst should happen.
If they burn up in the model while flying you probably have a writeoff pure and simple.
That's the risk. However I've only ever had a model fire with a shorted Nicad pack..
Likewise be careful when field charging in dry conditions..if you fly at a club, a fire extinguisher is a sueful thing, as is a fireproof area to charge.
Contrary to myth, there is no lithium *metal* in Lithium batteries...its actually a lithium salt, typically lithium carbonate, and whilst some lithium metal is formed during charging and discharging (I believe) its quantity is very small. The issues with self ignition are far more to do with the possibility of a cell internally shorting die to a localised hot spot under high discharge rates, or breaking down and shorting due to over charging. That so to speak provides the energy to ignite, and what burns is a complex mix of organic chemicals that form part of the electrolyte, and, finally the aluminium electrodes themselves.
In short a lithium battery is about as good at burning as a firework of comparable size. And has enough oxidant inside to do it in the absence of air too. Which means that once its going, it won't go out till its finished. You use the extinguishers to stop collateral damage to property and the environment.
Your focus should be - as with a firework - to prevent it happening at all by correct treatment, and isolate its effect in the very unlikely event it ever does it.
Strangely enough, the frequency of accidents does not seem to have increased with the massive quantities of flight packs sold, so either manufacturers are getting better or people are just learning what to do..or what NOT to do.
So far in the 5-7 years I have been back in this hobby, I have seen one death a year reported on average from an IC model, and probably around 2 fingers a year lost to IC prop's. Yes. electric priops are just as dangerous..but..you don;t need to fiddle with needle valves or flick start them. Although they can occasionally burst into life unexpectedly ;-)
I can recall reports of one burnt out car, and one workshop fairly well gutted, due to LIPO fires, and no personal injuries to date. In the case of the workshop the owner freely admitted he had made a mistake in setting his charger..several planes have burn out though..due to crashing/shorting or being charged as a whole..and I think one small brush fire..
You should put these things in perspective.
Yes LIPOS can be dangerous. So can firearms, eating raw fish, driving a car and fishing with a steel aluminium or carbon pole in a thunderstorm.
Understanding the risk is the key to reducing it.
As far as the advantages go, they simply have turned electric models from short duration overweight underpowered eccentricities, to be in almost every way comparable, and in some ways better performance than IC engines. My models can swing bigger props at less power and often less weight than IC engines can..I get typically on a lightweight sport or scale model more duration than the average tank of fuel..I don't get deadsticks, and I don't have starting problems. I carry NO field equipment except a selection of charged packs - there is no need to even take a charger for a short flying session. LIPS hold charge for typically a year or so..though some of the 'hotter' ones lose their edge after a couple of weeks charged. Those will die if not charged even when not in use..the lower battery weight has implications beyond just a simple weight reduction..less weight means you need less power to stay up, and that means more duration..less battery weight means no massive structure to contain the batteries, so structures get lighter..no big vibration means lighter engine mounts..less weigh means a smaller motor can be used..which means less weight..
When you see a 60" span model flying off a specific power that is about equal to a rather poor 049, at less than 2lb all up weight, you realise that electrics with Lipos is indeed something rather special.
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| The benefits are as advertised..the risks are overstated.
Agreed.
| - Never let the voltage go above 4.2v per cell, or much below about 3.3v | per cell..yes you CAN exceed these limits in SOME cases..but play safe | for now.
Don't exceed the 4.2 volt/cell limit, ever.
3.0 volts/cell is a reasonable cutoff for a high performance plane, as the voltage will go down somewhat while the motor is on. But once the cutoff cuts off once, don't just throttle back and keep flying -- it's time to plan your landing. (As TNP said, don't push it.)
Going from 4.2 volts to 3.0 volts gives you about half your original power, so it should be pretty obvious when the battery is this low, and you want to land before you reach this point.
| - de-rate the cells to about 70% of manufacturers and vendors claims, | unless you have the test equipment to verify them and an application | that is trying to squeeze the ultimate out of a pack.
Absolutely! If you get 20C `rated' cells, don't actually push them at 20C. 10C is much more reasonable, and your cells will last much longer. (And really, 10C still means only a six minute flight.)
The only time you'll really want to push cells as hard as they're rated at is in some sort of serious competition, where having to replace your pack after every few flights is acceptable. And even then it's dangerous if you can't really test things first.
| I have momentarily shorted cells and packs when making them up and | fitting connectors, with no problems.
Ditto, as long as it's quick. But this isn't really any different than NiCd/NiMH cells.
Shorting out cells is bad, be they NiCd, NiMH or LiPo.
| Storage in *cool* conditions requires nothing special..lets face it | LIPOS are in every laptop and mobile phone, and they do not | spontaneously combust.
Actually, they do. But it's rare. And when it happens, it tends to make the news, so we hear about it.
| The three ever present dangers are due to accidental shorting of them | while being transported, getting too hot, and being pushed too hard - | either when charging or discharging.
Actually, TNP forgot one danger of LiPo packs -- physical damage. If you physically damage a LiPo pack, like by dropping it or in a crash, that can cause it to immediately short out with incendiary results -- or sometimes the incendiary results won't happen for a few minutes. So any time you crash your plane, or just drop your pack, take the pack out and put it somewhere safe from fire for a while (an hour or so) just to make sure nothing is going to happen.
In any event, most accidents with LiPo packs ruin the pack themselves and don't start a fire. They are much less tolerant of mistakes than NiCd or NiMH cells, however -- one mistake can easily ruin a LiPo pack entirely, when a similar mistake on a NiCd pack will just cost you like 1% of the capacity (warning: made up figure!)
--
Doug McLaren, snipped-for-privacy@frenzied.us
By the time a man realizes that maybe his father was right, he usually
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Doug McLaren wrote:

That whole "six minute flight" thing is a bit misleading. It's only a six-minute flight if you run at a continuous 10C draw from start to finish. The 20C bashers also say, "Well it only gives you a 3-minute flight!"
Well, okay, IF full throttle current is equal to the 20C rating of the pack, AND IF you fly full throttle for the entire flight. Reality is that the left stick does go up and down, and most people already know how to use it, or will quickly learn when their flights only last 3 minutes.
The truth of the matter is, that it is perfectly safe to match your full-throttle current to the pack's rated capacity, provided that you actually use the throttle! Planes should be set up so that cruise power is around half-stick, give or take. If you're going to go roaring around at full throttle all the time, then yes, I would agree that cutting the packs' ratings in half is a prudent move.

Yup, I've had NiMHs catch fire in the past.

No, they don't spontaneously combust. Some prior damage or abuse has to be present for a pack to combust. An undamaged, properly-built pack will not burst into flames just sitting on the shelf. Drive a nail through it, okay. Set the charger for one cell more than the pack has, okay. Set the charger for more than 1C, okay. Just not sitting on a shelf doing nothing.
The "exploding" packs that made the news were caused by defective construction. Remember the cell phone battery scare a while back? Shoddy workmanship created a situation where the packs were easily damaged or overcharged. Same thing with the Dell batterys of late.
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| That whole "six minute flight" thing is a bit misleading. It's only a | six-minute flight if you run at a continuous 10C draw from start to | finish.
Of course. But when you get a 10C rated pack, that generally means 10C *continuous* -- you can go higher for short periods of time.
But if you push it at 10C *continuous*, that's a six minute flight.
| The 20C bashers also say, "Well it only gives you a 3-minute | flight!"
I've never heard of `20C bashers'. In any event, 20C packs generally have lower internal resistances, so they tend to perform better than 10C packs, even at lower currents. (But often that lower internal resistance comes at the cost of reduced capacity or more weight and usually at higher cost, so it's all a trade-off.)
| Well, okay, IF full throttle current is equal to the 20C rating of the | pack, AND IF you fly full throttle for the entire flight.
Yes. That's one possible meaning.
It could also mean a full throttle current of 30C (which the pack might tolerate for 15 seconds) and 20C being throttled back a bit.
Either way, my point is that if you take a pack rated at whateverC, and you run it at whateverC for the entire flight, it's not likely to last long. Unless you're doing a pylon race or something, I'd instead suggest going for (whatever/2)C -- your pack will last a lot longer.
| Reality is that the left stick does go up and down, and most people | already know how to use it, or will quickly learn when their flights | only last 3 minutes.
Reality is that if you really do push your 20C pack at 20C (or more!) for the entire flight, you'll be replacing it soon. This could be a result of never throttling back, *or* of just not putting a big enough pack in your plane.
| The truth of the matter is, that it is perfectly safe to match your | full-throttle current to the pack's rated capacity, provided that you | actually use the throttle!
Yes, that's reasonable. It's also safe to put your full-throttle current well above your pack's rated maximum continuous capacity -- but you'd better make *sure* you use that throttle appropriately.
(Also, note that the prop will unload in the air, so unless you actually measure the current draw in flight and instead only look at on-ground current draws, you might have over-estimated it. Fortunately, the Eagle Tree logger isn't very expensive, and neither are tools like Motocalc.)
| Planes should be set up so that cruise power is around half-stick, | give or take. If you're going to go roaring around at full throttle | all the time, then yes, I would agree that cutting the packs' | ratings in half is a prudent move.
I don't care what your throttle is set at -- I'm talking about the current you actually use, no matter what throttle setting is needed to achieve that current.
Your pack may be rated at 10C or 20C continuous, but if you actually use 10C or 20C continuous, your pack won't last long. Get a bigger pack, or another pack, or throttle back, or a smaller prop -- or just get used to the idea that your packs won't last long.
| > | LIPOS are in every laptop and mobile phone, and they do not | > | spontaneously combust. | > | > Actually, they do. But it's rare. And when it happens, it tends to | > make the news, so we hear about it. | | No, they don't spontaneously combust. Some prior damage or abuse has to | be present for a pack to combust. An undamaged, properly-built pack | will not burst into flames just sitting on the shelf.
Ok, fine, there's a reason they combust -- it's not spontaneous. But my point is that even laptop and cell phone batteries DO occasionally combust, either due to abuse, or accidents or whatever else. Just like R/C batteries.
| Drive a nail through it, okay. Set the charger for one cell more | than the pack has, okay. Set the charger for more than 1C, | okay. Just not sitting on a shelf doing nothing.
Not very useful sitting on a shelf. | The "exploding" packs that made the news were caused by defective | construction. Remember the cell phone battery scare a while back? | Shoddy workmanship created a situation where the packs were easily | damaged or overcharged. Same thing with the Dell batteries of late.
Yes, I recall the cell phone companies saying that. It was an OEM pack -- our genuine packs would never do that! (Of course, all the evidence was burned up, so we never got to really *prove* where the battery came from.)
Either way, cell phone and laptop batteries sometimes burn, just like R/C batteries do. But not very often, just like R/C batteries. The only reason you hear about it so often is that it's considered newsworthy.
--
Doug McLaren, snipped-for-privacy@frenzied.us
You look like a million dollars. All green and wrinkled.
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snipped-for-privacy@rochester.rr.com wrote:

It will if the shelf is in direct summer sunlight. IF the internal pressure and temperature in the pack is high enough, mechanical distortion and internal shorting are distinctly possible.
Drive a nail

Depends where you live mate. I spent some years designing stuff in Johannesburg..I had temp gauges and all the gear. One day I came in to test my latest design, and was astounded to see that a black heatsink in the sun was at 65C before I even switched the circuit ON..IIRC air temperatures in e.g. the Mojave desert are 130F...over 50C..it doesn't take much direct exposure to sunlight to push an object in those conditions well over 100C. Yes, people can and do fry eggs on exposed sheets of metal ;-)
Care to put a LIPO in a frying pan? Or an oven? And expect it WON'T 'spontaneously combust'
Agreed such conditions are rare in temperate climates..but the possibility exists allright.
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Hi, well, asked for a bit of info and got the grand tour thank you very much and when you have been out of the game for so many years every bit is welcome, for the time being I am only planning on building and flying power assisted gliders of 4 to 6 foot span and building as light as possible because as you point out the lighter the airframe and less wind resistance you generate translates into endurance. The one I am experimenting with is a 74'' span approx 1970's design that used mainly Balsa sheet for the fuse so i have swapped this in some areas for 1/32 ply which is lighter and much less bulky so has allowed me to slim the fuse down somewhat saving more weight, when I come to paint it I will use an airbrush which on a big model can save the weight of a can of paint and so on and with this one if I can have an all-up weight of 40 ounces I will be happy. Thirty years ago free flight gliders used dethermalisers and I see they are still used but now its a bit of string in an ally tube which burns through a little elastic band etc but the ones we used were little clockwork timers that released a pin allowing the tailplane to cock up at 45 degrees and bringing the a/c down, looking at modified kitchen egg timers for that one. Looks like once the decent weather gets here I will be ready to have a bit of fun again, right now though it is a dirty grey day with odd heavy showers and blustery wind so not good flying weather I am afraid, English weather for you.
regards, Terry
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Terence Lynock (CSM) wrote:

I think that is probably achievable, but it will not be overpowered at that weight..the contest gliders I have seen run ridiculously high powers to essentially get a 1000 ft of altitude out of less than 30 seconds 'burn'..my humbler efforts will get about 3-400 feet out of that sort of motor run.

Are you not intending radio control at all? This is possible, but most people strap some servos in..and fly RC....the modern equivalent to a D/T is crow braking..flaps down ailerons up..which gives a very smooth and rapid rate of descent at very little forward airspeed at all.
Good luck anyway..its all different these days but there is still fun to be had.

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Hi, the first one off the stocks is the largest of the two I am building and I am fitting servos to rudder and tailplane with an auxiliary motor and folding prop for the time being but once I am proficient enough to fly without using it i will probably take the motor out and fit a normal nose end which will save weight and drag, one idea I had which is a variation on something I saw years ago is a stop block on the aileron push rod so that when you have 50% up aileron a contact switch connects the motor, a weak compression spring behind the contact allows full travel so you can still go to 100%. The other glider I have an idea for is a 53'' span slope soarer but is so lightly built there is nowhere to fit r/c gear so I was thinking of stepping back 40 years anf building it as it was meant to be with a dethermo unit but finding a clockwork version is not very likely unless I can engineer one from a kitchen timer os something like that.

I am working on two or three projects at the same time at present finishing off the last of the commission models for a L.A client building the first of my gliders and also building something for my new grandson to play with when he is older, I bought a life-sized Mallard decoy duck then cut an access panel in its back so that I could fit a prop shaft and motor and the steering servo and receiver out of one of these cheapo radio controlled cars I bought as a wreck for a few dollars, should keep him amused down the local pond chasing the swans and maybe get him interested in model making and r/c too. It really made that ducks eyes water when I rammed a 3/8'' drill up his rear orifice to make a hole for the prop shaft,
regards, Terry
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| Are you not intending radio control at all? This is possible, but most | people strap some servos in..and fly RC....the modern equivalent to a | D/T is crow braking..
Well, that's one of many.
- There's also spoilers, typically seen on gliders.
- Spoilerons, where you raise your two ailerons.
- Simply doing a `slip', where you turn your rudder one way and use the ailerons to bank the other way, so your plane flies sideways.
- Or just put your plane into a `spin' -- loses altitude fast and normally doesn't stress the airframe too much.
I've seen dethermalizers on R/C planes (gliders) before -- if you moved the elevator too far, the entire horizontal stab would come lose and go up and rotate to a 90 degree angle. I wouldn't want it on my own plane -- I'd rather land it myself normally.
Personally, I would have though that free flight would be dead by today, or only done by kids with toys, but the Model Airplane magazine tells me differently. (I'm guessing that what's really going on is that FF is *almost* dead (at least compared to R/C) and that MA is just showing most of what's going on.)
--
Doug McLaren, snipped-for-privacy@frenzied.us
My inferiority complex is not as good as yours.
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Doug McLaren wrote:

There is a small but extremely active bunch of people who do indeed chuck models up and hope..I must say I am tempted too..
I fly a lot of 'old timer' stuff..basically old FF or S/C designs converted to electric with 3 channel radio..takes a lot of the sting out of trimming them if you have an elevator..and mostly all they do is not fly *away*, and do a lot of climbing and gliding.
It's not ALL I fly, but it has a relaxing and nostalgic quality to it I rather love.
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Hi, as I remember it was great fun and the gliders were pretty easy to build too with no worries about battery charging and so on, presently playing with a Chinese made kitchen timer clockwork movement that is just 2'' diam and 3/4'' thick settable from 3 min to 60 min which may be adaptable quite easily as a dethermaliser and as it is all nylon it only weighs about 20 grams,
regards, Terry
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If you use care and common sense, LiPos are a big improvement. With a good LiPo charger it's close to impossible to overcharge them, although nothing is totally idiot proof. Charge them on a fireproof surface or in a fireproof container and you should be safe. Dispose of them if they get damaged(you'll see literature on how to do that safely)
Start here for info, but you can find a ton of sites with google.... http://www.rcbatteryclinic.com /
PCPhill
I fly strictly LiPo now except for some powered gliders that require NiCd, NiMh to compete...

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| Start here for info, but you can find a ton of sites with google.... | http://www.rcbatteryclinic.com /
To be fair, Red's site barely touches on LiPo cells. It's got good information for NiCd, NiMH and even Pb batteries -- but almost nothing on LiIon or LiPo cells. You'll need to look eslewhere.
| I fly strictly LiPo now except for some powered gliders that require NiCd, | NiMh to compete...
Ditto. (Except that I don't really compete.)
--
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But Dad, you're a very old man, and old people are useless. --Homer Simpson
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In what application? In your transmitter I say no, in a flight pack, it depends. Let us know where you are using them. mk

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Benefits: Low weight/small size compared to same mAh capacity Nimh or Nicad. I fly strictly LiPo in all my electrics these days. My Slow Stick is completely stock other than a 2 cell 2100mAh LiPo pack. Weighs about the same as the 700mAh nicad pack that is the stock pack for this plane. The plane will hang on the prop thruout most of its flight time and flies longer than my neck can take looking up at it. I have an MAE Nemesis running a CDRom brushless motor powered by a 700mAh LiPo pack. Wouldnt fly using the same capacity nicad or Nimh pack due to weight.
Risks are overdraining the packs which can ruin them or overcharging which can explode them. You do need a special charger but many multi chargers will also do LiPos now. I use the original version Triton. Charges nicads, nimhs, LiPos, etc. Also most LiPo packs now come with a "balancing plug". This allows a device to be added which balances the cells while charging or discharging. It keeps some cells from overcharging while allowing the other cells to reach proper voltage. Another advantage is that LiPos dont lose much of a charge sitting on the bench the way Nicads and Nimhs do.
--
Dan
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Fubar of The HillPeople wrote:

Which is why I can't WAIT to have them as standard issue for transmitters..
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