Data Complete Guide to Lithium Polymer Batteries and LiPo Failure Reports

[hoppy]

Originally Posted by Flyitall

I am sure this has been asked before, but is it OK to charge a Lipo just after it has been discharged, when it is still warm? For example, I fly my heli, drive back home and put the battery on charge after ten minutes or so. It is still warm to the touch.

Thanks in advance,

Gavin

Why do you charge it as soon as you get home?
Do you fully charge it at that time?

Warm <100F is OK.
If you are not going to be using the pack for days, I'd recommend only charging it halfway or between 3.85-4V/cell. That will extend the cycle life of the pack. When you are ready to fly again, charge it up the rest of the way.

[hoppy]

Originally Posted by dngo

Is there any sort of General view on how batteries perform?

Yes-

Try reading some of these:
http://www.rcgroups.com/forums/showp...85&postcount=6

I like http://homepage.mac.com/kmyersefo/ev...ng-e-power.pdf You can start on page 22.

[MerlinKing]

This my be out of topic, but how long a lithium polymer batteries may last? with a use of two or tree times a week.






Best Regards.

[dngo]

Originally Posted by hoppy

Yes-

Try reading some of these:
http://www.rcgroups.com/forums/showp...85&postcount=6

I like http://homepage.mac.com/kmyersefo/ev...ng-e-power.pdf You can start on page 22.

That second link is fantastic, thanks.
So would I be right in saying that I have a 11.1v 1200mah batt and I am getting 20min flight times, so my Set up is only drawing 3.6amps??(obviously not at full power.)

Which means I prob only need a 10 amp esc? Is that how it works?

[hoppy]

A 20 min flight time = a 3C draw. 60min/20min = 3 (1C draw will run a plane for 1 hour)
1200 x 3 = 3600ma
You have got this down pat.

You are correct - a 10A ESC would be just right, assuming full throttle currents are below 10A. This where a meter to measure current is needed.
IMO, a mandatory tool for electric flying in a wattmeter or ampmeter. It will pay for itself in short order by preventing damage to the motor/battery/ESC through over current applications.

Good job, you picked up on the principles very fast.

[dngo]

It is great, it will actually help me in choosing more batteries. I don't really need 20mins flight time. And it appears that more mah = more weight. So maybe even less mah, will make it fly easier and will in fact make up for lost flight time.. mmmm. I could get into this.
I don't suppose with these facts I could determine what the KV is of my motor? I guess with a tacho I could get close.

[hoppy]

What brand - model motor? Or is it home made?

You can use a thin disk in place of a prop with a 1/2" black stripe through the center to make it lok like a prop with a prop to find KV. Can't use a prop as that loads the motor and reduces the KV.

[dngo]

Thanks hoppy, it is a no name motor that came with a boat/plane thing I brought on ebay years ago. It looks identical to a bell type tower pro 2410-12T or 2408-21. I am unsure which one. Either way, with an 8x6 and 1200ma 3s I am getting 20mins flight time on my Nutball. So, it works, who cares what it is!

[acdcrocks4]

for some reason my charger has puffed two packs about 1 mm up and now to charger wont register them. the charger is one of theso cheap ones that come in begginer heli combos. it charges my two cells just fine but i dont know what to do

[Sir J David]

Hello!

I have a 3s lipo with one dead cell so I decided to test how it handles low temperature. I starded with one working cell at 4.17V and the other at 4.19V. After two weeks outdors with some nights around -5 degres celcius I measured the cells to exactly the same values as before.

(I have no idea how the lipo now differs under load)

I just wanted to share this information...

The lipo was a zippy flightmax 3s 2200mA 20C

EDIT: Now the lipo has been laying outdors on the ground for nine more days and nights it still holds the initial voltage while measuring it. We have had some cold nights now but still not below -10 degres celcius.

It will be intersting to see what happens when we go below -20...

/David

[MadCap231ex]

Guys and Gals,

If you have not already tried them, the G3 series Hyperion Lipo's rock!
They maintain a higher discharge voltage for a much longer time, are rated a true 30-35C, and also have a longer life cycle than older lipo cell chemistry.

And yes, they cost more than those cheap "Mega Hobby Mart" batteries, but you will go through two or three of the cheap ones to just one of the new G3's.

I run 3S and 4S 2200mAh G3 packs that far outlast my Hong Kong 2800mAh packs. They pretty much smoke my MaxAmp packs as well.

Pony up people!

[Sir J David]

I want to compare two brands of lipos. I want to maximize power output and see how well they work.

Can you give me some thoughts of how to set up a good lipo-test? How about connect a motor with some prop, give it maximum load and then measure current and voltage?

[AirChime]

I read the first post with a lot of interest and learned a lot. Thank you!

I'm relatively new to RC, and have been flying for the summer about an average of once per week with about 5 different batteries. Recently I noticed that two of them were hotter than normal after I landed and they had expanded noticably in size. If I touched them, they'd squish slightly. Is this considered a puffed lipo and is it no longer any good or a safety hazard? I've charged both of them and reused them without a problem.

If this is an issue, I'd like to learn how it happened so I can avoid ruining a battery in the future. My guess is that the C rating wasn't high enough for the plane. I'm mostly flying EDF jets with 1300mah and 1600mah 15C batteries. I have a multimetere but not a watt meter, but don't know what I'd be measuring to know if I were safe or not. Would simply getting a higher C rating solve the problem? I'm pretty sure the answer to that can't be given without knowing measurements. I'm all ears as far as what to do to be in the know.

Thanks in advance.

[davecrash]

Originally Posted by AirChime

I'm mostly flying EDF jets with 1300mah and 1600mah 15C batteries. I have a multimetere but not a watt meter, but don't know what I'd be measuring to know if I were safe or not. Would simply getting a higher C rating solve the problem? I'm pretty sure the answer to that can't be given without knowing measurements. I'm all ears as far as what to do to be in the know.

Thanks in advance.

A watts up meter IMHO is a must for anyone using LiPo's. This will tell you at a glance all the info you need to know about your setup. For longevity of battery life you shouldn't axceed 80% of the C rating. Your EDF jets should have some specs to tell you what the amp draw is. Your currant LiPo for example is 1300mah. this is 1.3 x 15 = 19.5amps max discharge rate.

[AirChime]

Originally Posted by davecrash

A watts up meter IMHO is a must for anyone using LiPo's. This will tell you at a glance all the info you need to know about your setup. For longevity of battery life you shouldn't axceed 80% of the C rating. Your EDF jets should have some specs to tell you what the amp draw is. Your currant LiPo for example is 1300mah. this is 1.3 x 15 = 19.5amps max discharge rate.

Hi Dave - thanks for the info. How does a Watt meter hook up to the system? Also, a 1300mah lipo at 20C would be 1.3 x 20 = 26 amps max discharge (right?), however are there any negative results that could be associated with using a battery that has a max amp draw that's way higher than what the system requires?