rthorne

My Feedback: (29)

Hello Group:

A couple of us at our field are considering making the jumb to Litho Poly batteries for our glow powered, gas powered and electric powered planes.

The main advantage appears to be power to weight. You can get quite a bit more power with less weight. For example one of my 2700 mah nimh batteries (5 Cell 6v)weighs 6.8oz. A 2500mah two cell Litho Poly from Radical R/C weighs 3.5 oz or a 3300mah weighs 4.4oz.

I understand that Litho's require careful charging methods. There are a couple of good outfits selling chargers, Sirius, Astro, Triton ect ect.

What is the proper charge current for Litho Poly's? I've read a couple of things about charging:

- Never charge more than its capacity (C1)
- If you charge at C1 the life of the battery is reduced by 50%
- The best charge rate is C/10 which 10.5 to 11 hours of charge time (this is not a problem if you plan ahead)

What about internal resistance of Litho's. Are the newer Litho's dealing with this problem? I'm assuming yes since where going from a discharge rate of C1 to C3 and above with the new litho batteries on the market.

I listed the above to get a discussion going so I can make the decision on wether going to Litho's are worth the expense.

Scoubidou

My Feedback: (17)

Hello,
I was considering the lipo pack a few weeks ago for my 72'' Extra300 with gas engine. After reading many post on the danger of using them, i changed to go with li-ion pack. The li-poly are the future of our R/C hobby but presently, they are still experimental. You just have to read the first page of FMA direct!! The electric guys prefers li-poly because it can deliver 4C to 5C instead of 1 to 2C for li-ion. Li-ion pack are safer to charge because they have a PTC device to protect the user in case of overcharge and they are used in cell phone, lapbtop for many years. The li-poly can burn like hell if you overcharge them and do stupid things. Many people have reported fire in their house, car...

Here are some li-po supplier:
https://www.fmadirect.com/site/home.htm
http://www.lightflightrc.com/
http://www.batteriesamerica.com/newpage8.htm

Li-ion suppliers
http://www.duralitebatteries.com/

There is another forum explaining what to do with li-poly pack. You will find out many answers to your questions

http://www.rcgroups.com/forums/showt...hreadid=152536
Scou.

rthorne

My Feedback: (29)

Scou:

Thanks for the input and links.

GoeKeli

My Feedback: (18)

I am planning my next plane. I will use lipoly-ion. I have been flying lipoly 3 cells in my electric planes and they are amazing. My friend at the field uses 2 2000 mah on his DP extra and flys many many times. I already have a couple of small chargers so that is not a problem. The cells are not cheap and they need a reg. one for 6 and another 5.1 for the ignition. I am after the weight savings. The 2000 mah are really light! This is just the next logical step in power IMO. Nicads are great and so are nimh.

Joe

lsnover

My Feedback: (19)

Anybody see the new Kokams from FMA allowing discharge rates of up to 8C (12 amps)?

It looks like these packs are coming into thier own.

I'd like to use them in a small electric foam aerobatic plane.

FMAs Kokams peak at 1500mah capacity, I see. MisterBatteryAmerica has 2200mah packs now. These seem to be the same type pack. Anyone have any experience with these?

Regards,
Lee Snover

Fred Marks

Just about any technical question you might have is covered in the new Ap Note # 2, Kokam Li Po Systems at www.fmadirect.com. On the home page, click on Support, then scroll to Ap Notes to find Ap Note 2. The Ap Note will be kept current and, as questions arise, will be answered there. While you are at the home page, have a look at the Li Po Gallery where outstanding Li Po powered models are being added as they come in.

farrl

I have new kokam lithium poly battery. I was wondering if it comes fully charged or do I need to charge it before I use it ?

Shortman

My Feedback: (21)

Lithium Polymer batteries are many times stronger then Nicad, NiMH and Lithium Ion. The Li Polys can now handle 10-20C.

I know the new Thunderpower 2100mah 10.5C batteries can handle 20 amps CONTINUOUS and 40 amp bursts, any other type of battery only handles usually 1-5amps.

Lithium Polymer are used for their high discharge capabilities and there light weight. If you use them in a gas plane a battery will probably last you a month on a single charge[8D]

firegod2k

What does "C" mean? Does it have an equivilent to Amps ?
Thanks Rob

pettit

My Feedback: (23)

"C" is the battery capacity in milliamp hours.

Charging or discharging a 2000 milliamp battery, for example, no matter what technology, at a "C" rate, is 2000 milliamps per hour.

"2C" is adding or removing 2000 milliamps per hour from that 2000 mah battery, and so on...

s3nfo

My Feedback: (14)

Dick,

1C is adding or removing 2000 MaH per hour from that 2000 MaH battery, 2C is adding or removing 4000 MaH per hour from that 2000 MaH battery.
Musta been a brain fart.

smokingcrater

back to the original post...

1) correct, fire can result!
2) not proven. fast charging at 1c does reduce the life, but not much. lipos tend to be victims of time more then anything else. they only last 2 years or so, unless abused. the amount of use in that time doesn't have a huge affect. (this is a pretty general statement, especially considering lipos are very new technologies that change every day. my experience going back a couple years with lipos holds this true though, after about 2 years all my packs still kept most of their capacity, but their discharge capability went WAY down)
3) I wouldn't say it is best, anything under 1c is pretty much about the same as far as lifetime. you obviously need a dedicated lipo charger, this is VERY important!!!

cseb

Hi,

Some years have gone, but now I have a LiPo technical apsect post, and I found this topic.

I constructed a LiPo internal resistance measuring instrument. I provide every design documentation. If anyone is interested he can build his own, even a better version:
http://cseb.hu/lipo_rin

Regards,
Csaba