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View Full Version : Li-Po vs. Li-Ion


JWN
09-24-2005, 05:10 PM
I know there is a difference between Lithium-Polymer and Lithium-Ion (though I'm not sure exactly what those differences are), but I know the two types are generally both referred to as Li-Po. However, I've seen warnings on several Great Planes chargers which state they are Lithium-Polymer only and not to be used with Lithium-Ion. So my question is, why are you not supposed to use Lithium-Ion batteries with these chargers?

Greg Covey
09-25-2005, 12:24 AM
John,

That is a good question.

Basically, it is the charge rate and discharge rate that differs between the two cell types. For the most part, any charger that works with Lithium Polymer cells will also work for Lithium Ion cells. I would recommend using a lower than 1C rate for charging Lithium Ion cells. Both cells use 4.2v as their charge voltage.

For the most part. Lithium Polymer cells can deliver much more current than Lithium Ion cells can deliver.

An exception to the 4.2v rule is Tadiran cells that use 3.6v as a maximum voltage.

timocharis
09-25-2005, 06:01 AM
There are two reasons to avoid Lithium Ion. First is, as already mentioned, a generally lower safe discharge rate. They're also a bit more violent when they overheat and pop. Because they can't tolerate high discharge rates they're more likely to flame out, and that makes them a bad risk in the air.

Not worth it; stay away.


Dave

HoverBovver
09-25-2005, 10:15 AM
Also because Li-Ion-Polymer batteries use a dry electrolyte (with a little gel added to enhance conductivity) rather than a liquid electrolyte as per Lithium-Ion batteries they do not require a hard case and are therefore lighter.

margotcopeland
09-25-2005, 12:01 PM
I use Li-Ion packs I make from cell or PDA batteries. Because Li-Ion batteries generally have 1-3C discharge rates, I use them in situations that require lower current. For example; a 1440 mAh pack can deliver enough to safely run motors that require about 3 amps continuous current...like an IPS/LPS/EPS 100 system or a Speed 300 motor with a 5x3 prop.

All of the same rules apply. Lithium charger only, don't let the cells run below 3 volts, charge at 1C or less, store and charge the batteries on a non-combustible surface, don't short the batteries.

Your best bet is to be cautious...if you can't be, stay away from the Lithium cells and stick with NiMH or NiCads.

JWN
09-25-2005, 10:56 PM
All very good information. I work for a computer company have have seen the results of a Lithium-Ion cell excursion. One such event left a hole in the middle of a very heavy wooden desk. Thanks guys!

GeraldRosebery
09-26-2005, 12:26 AM
[quote=JWN]I know there is a difference between Lithium-Polymer and Lithium-Ion (though I'm not sure exactly what those differences are), but I know the two types are generally both referred to as Li-Po. However, I've seen warnings on several Great Planes chargers which state they are Lithium-Polymer only and not to be used with Lithium-Ion. So my question is, why are you not supposed to use Lithium-Ion batteries with these chargers?[/quote

There is no reason at all. Just use a practical 0.3 C rate to charge LiION which I use in my transmitter (3 cells) - no regulator and for all flight packs (2 cells) through an MPI 6V regulator. The huge plus to using LiION for the transmitter and flight packs is that you charge them when you get home and they will still be ready to fly 3 months from now.

margotcopeland
09-26-2005, 04:06 AM
I just returned from a perfect Sunday's flying. My Dougsrc Micro Glider using an IPS setup with my 720mAh Li-Ion 7.2v packs...2 hours of flying with plenty more charge left, the packs barely warm to touch. I got the new Dell Axim packs at auction for 1.00 apiece...2 cells in each pack, plus the cost of wire and connector. It's nice when a plane works out :-)

Use them judiciously, and Li-Ion's can be quite an inexpensive way to fly. I've found that 1C works perfectly...no heat and a relatively fast charge. I don't happen to use a voltage regulator, when the motor begins to slow down, I land it.

Other's mileage may vary, but I'm relating actual experiences. As far as the chargers' warning not to charge Li-Ions, I can only think of two reasons, one is a higher than 1C charge rate, or a it's warning about not charging Li-Ion primary cells, which are non-rechargeable.

timocharis
09-26-2005, 05:06 AM
margot:

They may not have the .2v lower cutoff typical of LiIon. Note yours are nominal 7.2v rather than the typical 7.4v 2s LiPoly.

At least, that might be what they're concerned about. A .2v overcharge on an unbalanced Li-Ion probably could blow the pack. Anybody here know for sure?

The Hobbico QFC MkII charger handles them just fine (though it won't fully charge a LiPoly).


Dave North

margotcopeland
09-26-2005, 04:13 PM
Whoops, thanks Dave...have NiMH on the brain...sorry. They are 7.4 volt packs (cells are 3.7). I'm glad you pointed that out! I spent a weekend flying and making packs and not sleeping enough! I just came back from a morning run, and on an IPS setup with a 9070 prop, I got over 30 minutes of flying from a 7.4v 720mAh Li-Ion pack. Voltage at the end was 7.75v, pack not even warm...plenty of margin...(the sprinklers came on at the park <g>).

It really comes down to taking responsibility to learn for yourself what any type of Lithium pack can do, and, if you want to go the DIY route, to learn as much as you can. Just slapping Li-ion or Li-Poly cells together without balancing, static testing, and good "electrical hygiene" is inviting disaster. Start with short flights, check the pack after each flight, and increase flight times gradually and you'll be relatively safe.

And if you can't...don't.

Matt Kirsch
09-26-2005, 05:18 PM
Good advice.

Frankly, there isn't, or shouldn't be, any "VERSUS" discussion involving these cells. They're not interchangeable from a practical point of view. LiIon is only capable of 2-3C discharges for the most part, and you've got to scavenge them from old cell phone and laptop packs... LiPolys have seen all the development dollars over the last few years, so they're getting cheaper, they're getting lighter, they're capable of ever higher discharge rates, and they're getting safer. By comparison, LiIon is still in the dark ages.

Unless you want to experiment, and enjoy that sort of thing, there is absolutely no advangate to using LiIon technology.