Warning to anyone new to RC and Lipo batterys

[zzlentz]

I'd be broke from donations by now.

See picture at left

[kyleservicetech]

Originally Posted by FLOYD V. ULRICH

A few years back, I put my plane in the top of a 50 foot tree. No way to get it down. Went to the local fire company and they put their big ladder up . one of the fireman climbed up and brought it down. They asked nothing but a thanks. A donation is well worth getting the plane back.

Ouch.
I've made it an absolute rule to never allow my models to fly so low that the model is below line of sight to the background tree line. People don't realize just how far away our models can get during normal flight.

We had one big tree across from our flying field, 600 feet away from the pilot area. That tree has been hit at least twice each flying season, by small models and giant scale gassers. Finally got the city to cut it down. Also had several complaints from home owners about some of our wet turbine models flying over homes and the main road East of our field. One of the people who let us know is an employee of the local Electric Power Company. (He is not the one who called the police) We put spotters out to watch. Complaints were correct. That main road is 2500 feet from the pilot area.

Word to the wise.

[Fishbonez]

Here is a beginner question.
Now that fall is here and winter aroiund the corner for some winter is already here however is there a rule of thumb for temperatures to be to cold for a lipo battery to be used?

[AEAJR]

All batteries work better when they are warm. I keep mine in my pocket till I am ready to use them if it is below 40 degrees.

I have used my lipos at 10 degrees F with no problems. And I have charged them at that temp too. No issue.

Edit: I have used NiMh at 10 degrees F also.

They all work.

[Blik]

LiPos use a chemical reaction to both store and release electrical energy. Cold temperatures interfere with the chemical process, which is why LiPos discharge poorly in the cold and if you try to charge them in the cold you may damage them. If you really want to fly in the cold you can always buy some of those hand warmers and wrap your lipo before flying in the cold

Best way I found to store a lipo is around 3.8v per cell and refrigerate, not freeze.

Cheers
Blik

[AEAJR]

Originally Posted by Blik

LiPos use a chemical reaction to both store and release electrical energy. Cold temperatures interfere with the chemical process, which is why LiPos discharge poorly in the cold and if you try to charge them in the cold you may damage them. If you really want to fly in the cold you can always buy some of those hand warmers and wrap your lipo before flying in the cold

Best way I found to store a lipo is around 3.8v per cell and refrigerate, not freeze.

Cheers
Blik

What does that mean? I store my Radian and its lipos in the Garage. Temperatures get down below freezing. I put the plane in the car, go to the field and go fly. When the pack runs down ( sooner than when it is warm) I charge it and fly some more.

So, what are you saying? Electrics can't be used in the winter up north unless you warm the packs?

[kyleservicetech]

Originally Posted by AEAJR

What does that mean? I store my Radian and its lipos in the Garage. Temperatures get down below freezing. I put the plane in the car, go to the field and go fly. When the pack runs down ( sooner than when it is warm) I charge it and fly some more.

So, what are you saying? Electrics can't be used in the winter up north unless you warm the packs?

I did some testing awhile back on those A123 cells, both at room temperature and at 32 degrees F. Was not much difference in voltage, at least at the 15 Amps or so max capacity of my CBAII battery analyzer.

[Blik]

So, what are you saying? Electrics can't be used in the winter up north unless you warm the packs?

AEAJR, I am not saying Lipos can't be used in the cold but as we all know their performance decreases in colder temps. I agree with you about taking a few extra Lipos with you and change them out. The old school way was to baby your lipos because their cost was ridiculous. Now you can pick up cheap lipos anywhere and abuse the out of them because when they lose their punch just replace them.

Cheers
Blik

[AEAJR]

Originally Posted by Blik

AEAJR, I am not saying Lipos can't be used in the cold but as we all know their performance decreases in colder temps. I agree with you about taking a few extra Lipos with you and change them out. The old school way was to baby your lipos because their cost was ridiculous. Now you can pick up cheap lipos anywhere and abuse the out of them because when they lose their punch just replace them.

Cheers
Blik

I agree that cold weather use of batteries benefits from some extra steps. Their power and capacity does decrease. And warming up before use is a good practice as it help with both power and capacity.

My concern was that the message was a bit black and white and gave, in my opinon, a little too strong of a message. Batteries work in the cold, just not as well as in the warm. Kinda like people.

Some chargers, like the Cellpro 4S, have temperature sensors that know the outdoor temperature. If it is below X degrees they charge to less than peak. It has nothing to do with the use at the time, it has to do with the recognition that when they go back into the warm house the voltage will rise as the battery gets warmer.

If you carge them to 4.2V at 30 degrees, they will likely go over voltage in the house. So the charger only takes them to 4.15V, I think. You can fly all day charging them that way. But when you get home they won't go over voltage.

[nits_physio]

I wonder how much flight time one can get from a NiMH 8 cell, 3600 mAh battery and how durable they are ?

[rcers]

Originally Posted by nits_physio

I wonder how much flight time one can get from a NiMH 8 cell, 3600 mAh battery and how durable they are ?

That depends entirely on how much power you take from the battery.

None of them are terribly durable.

[kyleservicetech]

Originally Posted by nits_physio

I wonder how much flight time one can get from a NiMH 8 cell, 3600 mAh battery and how durable they are ?

My models started off with those RC2400 Nicad batteries some 25 years ago. One of the models had 38 Sub "C" RC2400 cells in it. Those cells dropped down to about one volt at a load of about 30 Amps.

Those Nicad cells as I used them had about 100 flights of lifetime, since they were running so hot they needed a fan to cool them off during the recharge cycle.

Nowdays, with the LiPo and A123 cells outperforming the Nicad cells by several times, the Nicad cells have kind of gone by the wayside for electric powered model airplanes. And, from my experience anyhow, at high currents, the Nih cells were not as good as the old RC2400 Nicad cells.

[Arianna]

Lipo also gets fire if charging element contacts air when the cover breaks for any reason. In this case use any means to to cover the fire and battery to separate them from air.

[nits_physio]

Originally Posted by rcers

That depends entirely on how much power you take from the battery.

None of them are terribly durable.

I am beginner, so I wont be doing any acrobatics or using the throtle too much ... how much flight time when flying a nexstar select ?

[huayuhobby]

Normally flight time is related to the model fliying weight and the power system work current, and pilot operatiing habits.

[AEAJR]

Originally Posted by nits_physio

I wonder how much flight time one can get from a NiMH 8 cell, 3600 mAh battery and how durable they are ?

ESTIMATING BATTERY RUN TIME

CALCULATION METHOD

Note that a 1300 mAH pack = 1.3 AH pack


Capacity in AH / amp draw X 60 = minutes of run time.


m = mili which means 1/1000. Just to ways of expressing the same number.



1.3 AH / 8 amps = .1625 hours



.1625 X 60 = 9.75 minutes at 8 amps.


This assumes you use up all the useful battery capacity, not that you are running the battery to zero voltage. It also assumes that the battery can actually deliver its total rated capacity before the LVC, low voltage cut-off, kicks in to keep you from running it too low. See the end for more on this.


Normally you don't run at full throttle all the time. For mixed flying that is probably more like 15 minutes. I usually estimate mixed flying time at 150% of the calculation but your actual experience will differ based on how you fly.



When estimating useful flying time out of a pack, be conservative, then watch it over several flights to get your true number. This calculation is for planning purposes.


If you are sizing a power system for a plane, part of that sizing should include the duration of the battery pack.


QUICK ESTIMATE METHOD



Above is the more precise way to calculate run time. However I usually use this quick estimate method.

If the battery can delvier 1.3 amps for one hour then it can deliver 13 amps for 1/10 of an hour ( 6 minutes )

In this example, we are only drawing about 2/3 of that ( 8 amps) , so the run time will be about 1/3 longer than 6 minutes, about 8 minutes. Just a quick estimate method I use. Not as exact, just a quick approximation that I can do in my head.


However, your actual run time will vary by battery quality, how hard you are pushing the pack, the LVC setting on the ESC and how much time you spend at what throttle setting.


For example, if you run your 20C pack at 20C you will get greater voltage sag then if you run it at 10C. The greater voltage sag will cause you to hit the LVC sooner than if you run the same pack at 10C.




THE EFFECT OF C RATING ON PACK PERFORMANCE

While several battery packs may be "rated" at a given C rating we can see significant variation on how well they actually work at this rating. The higher priced, higher quality battery packs tend to be better at running at this extreme end of their abilty. The lower cost packs may not live up to that rating quite as well. But it can vary from brand to brand and pack to pack.

I typically don't plan to run my packs at greater than 80% of their stated C rating. So if that 1.3 AH pack I used in the example ( possibly a Radian pack for example ) is rated at 15C then you would expect it could run at 15 X 1.3 amps or 19.5 amps and maintain a good voltage of 10.5 to 11.1 Volts for most of its useful capacity. Well some can and some can't.

I would look at that pack and say that I would plan to never run it sustained at more than 15 amps. This would put less stress on the pack and give me more useful capacity in the range that I want.


If you are running in a situation where you only need full power for short bursts, like a 30 second full power climb followed by running most of the time at about 2/3 throttle, than the pack might handle 19.5 amps quite well for those short bursts.


Some packs have sustained ratings and peak ratings. I ignore the peak ratings.


To understand more on batteries see chapters 5 and 6.


EVERYTHING YOU WANTED TO KNOW ABOUT ELECTRIC POWERED FLIGHT
http://www.wattflyer.com/forums/showthread.php?t=31368

[kyleservicetech]

Originally Posted by nits_physio

I wonder how much flight time one can get from a NiMH 8 cell, 3600 mAh battery and how durable they are ?

What type of Nih cells? Sub "C" or "AA"? At any rate unless the cells are rated for high discharge currents, don't plan on running them to discharged in any time less then 10 or 15 minutes or so.

Nih cells that are not rated for very high discharge currents can have very significant voltage sags at high currents. A while back, I ran tests on a five cell 2700 Mah Nih RECEIVER "AA" type battery pack under load currents of 14 Amps. That battery pack quickly dropped below 3.6 Volts DC on a 4 cell pack. Quickly, like one or two seconds at 14 Amps.

FYI, the battery pack was virtually brand new. It was being used on a $$$$ wet turbine model full of digital servos. The pilot was lucky to have not lost his turbine model.

He went to a 2200 Mah LiFe pack that can put out 14 amps with little voltage sag.

I've got several models using the Hitec 645MG servos. The peak current drawn by those servos came out to about 2.1 amperes. Each.

For receiver power I NEVER go past about 50% capacity during any typical flight. That's so you have reserve power for one of those days when you're doing lots more acrobatics, or just when you have a bad day. As for motor battery packs, I don't go past about 60% discharge for the same reason.

[mred]

LiPo's are fantastic and easy to use. All you need to do is use them with a little common sense. Just like everything else in life, nothing is 100% safe, so take care and use them the way they were meant to be used and nothing bad will happen. Normal life out of a LiPo is about 500 cycles and if you take care of them, there is no reason they cannot reach this life span.

Someone said he thought the CellPro 4S added charge through the balance and not discharge. Well, the CellPro is not like any other charger. Since those are the only leads that get hooked up, there is little choice. Everything is done through the balance leads. To my way of thinking that is one of the best chargers on the market, because it will balance your battery every time you charge. Those chargers that hook up the main power leads along with the balance leads discharge through those leads, since the work is don't through the main leads.

I always charge at 1C regardless of the battery and how much it can take. They live longer that way and you don't have to worry about blowing one up because you forgot to change it back when you put a different battery on it. No matter what charger I use, I balance charge every time no matter what.

The capacity of a battery is figured from the 3V level to 4.2 volts. So a 2200MAh battery will give you 2200ma between 4.2v and 3v and at 3 volts the battery is considered discharged. it's not dead, but that is the full discharge. You should NEVER go below 3 volts per cell with a LiPo. If you do, you can sometimes bring it back up again. My Triton will give you an error if you try and charge this battery and will not go into charge. Some other chargers will do the same thing. This is how you charge that battery up. Put your charger on NiCad or NiMah and set the charge rate at 100ma. I would charge it for about 10 minuets and then take it off the charger and check that cell. It should now be over 3 volts, so you can put it back on the charger and charge it just like a LiPo should be charged and most of the time it will come back up to normal again. If it comes up to 4.2 volts and stays there like the other cells, then all is probably well with that battery. If it will not charge using a balance charge, then cycle it once and see if it will come up. If not, it's bad and needs to be disposed of properly.

When using a battery I try to not go past 80% of the capacity. For a 2200MAh battery, that is 1760. That will give you a little battery left just in case you really need it for some reason. I also NEVER go to LVC since I don't trust the ESC to be right. That is an easy way to go below 3 volts per cell. On some cheap ESC's, they will go down to 2.8 volts per cell for LVC and you can't change that. That voltage they are cutting off at is under load also, so it will read higher when you put your meter on it.

All in all, the modern LiPo's are great batteries and there is no need to fear them. Treat them with respect and they will serve you a long time. They give us great service and long life (unless they are really cheap ones) and they have a high output. What more could you ask? If you mistreat them, they will bite you and that is your fault.

Ed

[piercethesky]

Here is an insanely helpful tool a buddy of mine sent to me. Its a website with all sorts of lipo calculations and other tools as well. Hope this helps anyone in need! http://2bfly.com/tools/

(sorry if it has been posted before, havent had a chance to read the thread and wanted to post before I forgot!)

[xmech2k]

Thanks for that link! Good stuff there.

[barrosinc]

when a lipo 3S 1300mAh says charge up to 2C (2.6A right?) Should I use 2C, 1C or less?
I used 1C last night asi I read just two posts above, but the dude at the store said to use like 0,5C

[AEAJR]

Originally Posted by barrosinc

when a lipo 3S 1300mAh says charge up to 2C (2.6A right?) Should I use 2C, 1C or less?
I used 1C last night asi I read just two posts above, but the dude at the store said to use like 0,5C

my advice would be to charge at 1C when you are not in a rush. For example, if you are topping off your packs in your workshop the night before as you prep your things, charge at 1C.

If you are at the field and want to recharge to fly again, charge at 1.5 to 2C.

The higher the charge or dischate rate the more stress on the pack. So, if you don't need to rush it, let it charge a little slower.

That is my approach.

[road king 97]

We had one of our club members put his lipo in his pocket with his car keys ,it shorted out fast and caught his shorts on fire and burnt his leg a little before he could get it out. I put my lipos in my flight box with a piece of electrict tape over the ends of my deans conectors and i always watch them charge and never leave them alone. BTW i keep my lipos in old army surplus amo containers or i have a small cheap fire proof safe i bought .Helps me sleep better at night.

[mred]

The chemistry of the battery determines what it can be charged at. The older batteries were all 1C, so we didn't have any problems. With the newer ones, that charge rate goes up and it should be marked as to the max you can charge at. Now this is all find and dandy, but the higher charge rates are harder on the battery and will shorten the life of them some. It would be better overall to stick with the 1C rate unless you just have to have that fast charge and are not willing to wait an hour. While I have a couple of the newer batteries, I still use the 1C rate and have no problems with that. I buy more then one battery for a given plane if possible and then I can fly while one is charging. Not everyone wants to do that, so if you feel you really need to go with a faster charge, then yes, 2.6A is the max rate that battery can be charged at. Never go over that rate or bad things can happen.

Ed

[rcers]

Originally Posted by mred

The chemistry of the battery determines what it can be charged at. Ed

Actually I am not too sure the chemistry has changed much on most. I think it is the lower internal resistance IR of the cells that allow for this.

Mike