Here's a challenge. Who will be the first to lay his hands on some of these Lithium Polymer cells and test them in slowfliers??
I know I would like to try them out, but so far I have not succeeded in finding someone who will sell them at realistic prices.
http://www.ulbi.com/polymer.html
http://www.panasonic.com/industrial_...m/new/pr18.htm

They can be found in a battery pack for Nokia mobile phones, but then you pay for the case as well ($69-$99) :-(

Epilot:

Have you tried Tadiran brand rechargeable lithiums? They work great and a 9 volt 800 mah pack only weighs 51 grams (9 volt 430 mah pack about 35 grams). From reading the specs I can't really see the advantage of these Lithium Polymer cells over Tadirans other than that they are environmentally friendly.

They don't list maximum discharge rates. More than likely your are limited to a few hundred mA. In fact life of the Ultrlife cells is listed as 300 cycles at C/2 rates. What kind of model will you fly on that kind of current? Did you also notice that the specified charge rate is C/2. This means about a 4 hour charge time for a full charge.

There's a lot of stuff on the internet. Most of it won't work for what we need. There are people looking for products that will work for us. They are easy to find.

Greg

Originally posted by greg morrison:
From reading the specs I can't really see the advantage of these Lithium Polymer cells over Tadirans other than that they are environmentally friendly.

Lots of good reasons:

They are less prone to suffer damage from overchargins (Li-ion cells scare the sh** out of me after a nasty experience)

Tadiran seems to have failed in attracting the mobile telecom wheras Lithium Polymer technology holds a lot of promise in this area. High production volumes = lower prices. They win = we win.

Besides, being environmentally friendly should be reason enough - our kids are going to inherit this earth :-)

Look at this article: http://www.eet.com/story/OEG20000908S0026

With that amount of investment these cells might just become useful to us one day. The technology is also being explored for possible use in electric cars so somewhere along the line they will probably be able to deliver the amps.

Windsurfer:

Have a good trip - we'll miss you on Saturday. From reading the specs. these batteries don't seem to offer the kind of performance Tadiran's do and wouldn't allow for longer flight times or the necessary discharge rates to run our small motors. For me there would be no reason to try/check them out at this point.

epilot:

Thanks for bringing these batteries to our attention. I hope I didn't seem like I was criticizing your post - I wasn't. We are all interested in new and potentially better power sources for eflight. The reason I mentioned Tadiran batteries (I also thought you might not be familar with them) is that they have a different chemistry than Li-ion cells and are meant to be recharged. They work fantastically well for sub 280 class applications offering unmatched duration for their weight and useable discharge rates for eflight. Until the day that they are no longer available or have been replaced by a superior lithium battery I will continue to use these cells as they are currently the best of their type for slow/micro eflight. I agree with you completely about the importance of using and endorsing environmentally friendly and safe products.

Greg

Hi Greg

I know the Tadiran cells well and I agree that they are the best bet for long flights at the moment. Some Nimh cells are even getting mighty close. I just wanted to point out what lies ahead of us.

These lithiums discharge at 5X the capacity that is about 5 amps. Who said they could not be discharged at our needs. I would be interested is trying.
John Moler

Hey! This is great stuff, these new polymer cells, but until they can give the same prices and current capacity as Tadrians, then the uses in our hobby remain untapped. We represent a fraction of the battery market and (by the demise of AR cells)not the viable market that this emerging technology is aimed at.The NiMH batts, while approaching Tadrians in duration, but not weight savings, are useless at below 48 degrees, something that you guys in the warmer climates need not fear, but in my area, cause at least a 50% capacity loss, whereas I can leave a Tadrian pack out overnight at 20 degrees and still fly it the next cold day with no noticeable losses except frozen fingers.If this polymer technology gets to cameras and their MOTOR drives, then we might soon see a battery we can afford and use.

A major benefit of these cells to their potential market is the light weight/sq" of their container. This allows light batteries of non-optimal (volumetricly speaking) shapes. This plus the inherently laminar nature of their construction (think about memo pads) will result in a lot of different sizes and shapes to be economically made rather than the AA, AAA sizes that dictate the thickness of consumer goods today.

So put your thinking caps on. What sort of aircraft designs could you do if you weren't limited to AA cell dimensions?

I wouldn't worry initially about current capacity. They'll need to eventually run equipment equivalent to at least AA alkalines, NiCD, NiMH and DL123s/CR2s to be successful in their intended markets.

I'm sure that it won't immediately replace whatever you're using now, it may never. But I'm sure someone will do some innovative thing with them at a higher price that will start others thinking.

As volume goes up, price will come down, but it won't be the modeling industry that drives this curve. Take advantage of the opportunities presented as they arise and
have fun!

jtm

I was not aware that NiMH batteries lost capacity at colder temperatures. Wow, that explains a few things. Ive been troubleshooting this one for a while!

YES. My first NiMH pack was a 700 maH AAA 8 cell pack that ran a geared 280 for 12 min in my living room and 3 minutes outside at 25 degrees. Drove me crazier than usual until I posted on this forum and w/ the help of many, we figured this out.What a great resource! Best Regards

Where does it say the Panasonic or Ultra Life LiIon cells can be discharged at 5C!? I must be missing something as I have never seen a LiIon cell capable of a sustained 5C discharge rate. LiIon Polymer (prismatic) cells are cheaper than LiIon cells but not as good at high rates of discharge. 2C is the max I've seen, and dared to test. Prismatic cells are great for portable devices, but I can hardly see a cell effecting the shape of a model, unless you talk about the enormous Saft LiIon cells.

Please correct me if I'm wrong.

How many chargers do you know of readily available that will charge LiIon cells? Of course this can be easily remedied and I know someone who is working on it, if there was a cell to use with it.

I'm up for new cell technology. In my opinion it is still pretty far away to be affordable for the average person.

LiIon cells have better energy densities than Tadirans. The problem is they are not as safe. As such they are not available to consumers as cells. 99% of LiIon cells out there are sold to OEM's and end up in assembled packs.

Tadirans don't handle over charge/discharge any better than LiIon but Tadirans won't catastophically fail(burn/explode).

I have heard of many stories that made me sick just thinking about it. Mostly modelers with little knowledge of LiIon characteristics taking chances they didn't understand.

One day it will be feasible. That day I will be driving an electric car with 300mi range, with a 30kUSD price tag.

Greg

Greg, now why do you use the Tadirans? For longer flight times. Why would you use the new polymers? For longer flight times.

Here is 5C.
UBC543483: 930 mAh Ultralife Polymer™ Rechargeable Cell


--------------------------------------------------------------------------------

System:
Polymer Rechargeable
Designation:
UBC543483
Maximum Dimensions:
5.4 mm thick x 34 mm wide x 83 mm long
Nominal Voltage:
3.8 volts. Ranges between 4.15 and 3.0 volts
Rated Capacity:
930 mAh @ C/5 Rate
Maximum Discharge:
2C Continuous; 5C Pulse
Discharge Profile:
The discharge profile of Polymer cells is flat at low current drains and sloping at higher current drains.
Energy:
3.5 Wh
Energy Density:
135 Wh/kg; 250 Wh/l
Weight:
26 grams
Cycle Life:
>300 Cycles @C/2 to 80% of initial capacity
Memory:
No memory effect
Operating Temp.:
-20°C to +60°C
Charging Temperature:
0°C to +45°C
Storage Temp.:
-40°C to +60°C
Self Discharge:
<10% per month
Charging:
Charge at a constant current at C/2. Hold at 4.15V until current declines to C/10.
Safety:
Built-in PTC. Meets UL Tests. Because the contents are solid, Polymer cells cannot leak. They are also safe if opened, as no metallic lithium is present. In addition, Polymer cells are extremely resistant to abuse from over-charging and discharging.
Environmental Factors:
Polymer cells are environmentally friendly. There are no toxic metals present, such as cadmium, lead, mercury, or nickel, and there are no restrictions on disposal.
Terminals:
Nickel tabs
Jacket:
Laminated foil
Form Factor:
Consisting of flat, flexible plates, Polymer cells are ideal for prismatic configurations. Minimal packaging and a high percentage of active materials enhance energy density.
Transportation:
With no metallic lithium present, Polymer cells have no transportation restrictions.