Help! Li-ion batteries instead of Li-Pos?

[MaxTheFliteFreak]

Hello, I recently discovered that Lithium Ion cells exel at long flight times for RC planes. I was doing some research before buying one, but got mixed results, so I hesitated to purchase one. Does anybody have any advice, warnings or even links for where I can buy one?
All input would be greatly appreciated!

 

[tamuct01]

Li-Ion batteries have a very high energy density, which is great for long flight times. However, they cannot deliver that energy as fast as Li-Po batteries. If you can match up the aircraft's max current draw very carefully to what the batteries can deliver then you can get long flight times. You will commonly see Li-Ion in use on smaller, very efficient aircraft designs. High-performance craft like drones or sport planes would be better with Li-Po.

 

[quorneng]

Max
On a like for like basis Li-ion are just a bit heavier than LiPo so ensuring a LI-ion battery is big enough to keep the max amp draw with their limit may result in a significant weight penalty. Any extra weight can eat into any duration advantage over LiPo. For a plane it is likely to be a finely balanced judgment.

 

[JasonK]

li-ions are generally higher energy density per weight, but have much lower max current draws.

for example you can get 3000mAh 2s li-ion pack at ~100g but will have a max current draw around 15-20A [IE 5-7C]
checking some of my lipos, I see around 20mah/g for one of them -> 150g to get to 3000mAh but it has a rating of 45C [so 135A]
another lipo [come cheapo that came with my kid's RC car] -> 66g for 1600mAh -> 25mah/g -> 120g to get 3000mAh with a rating of 30C [so 90A]

So for the examples I have, there is a meaningful weight savings using the li-ion packs, however the max current is really _low_ compared to the lipo.

Because of above, li-ions are best suited for endurance applications. if your not targeting 30+ minutes flight time, li-ions are probably the wrong choice.

 

[LitterBug]

I have been flying Li-Ion batteries in my Strix Nano Goblins for several years (since they were released 4-ish years ago). Like most have said, they are great for endurance flying and have limited "max current". Most Li-Ion batteries are in the 10-20 Amp max current range for batteries that are 1P. (1 cell in parallel). There are also larger packs that are 2P which are in the 20-40 Amp max current range. Li-Ion packs are usually built from 18650 battery cells which have a rough average weight of 50 grams per cell. This is pretty much regardless of MaH or Amp rating of the packs. Max usable MaH rating for an 18650 cell is roughly 3500 MaH. The higher the maximum Amperage output, the lower the MaH capacity. Roughly a pack with 10 Amp max current draw will have a capacity close to 3000-ish MaH. 20 Amp draw will be closer to 2000 MaH. There are trade offs for Maximum current capacity (Amps) verses maximum storage capacity (Mili Amp Hours). It has to do with the thickness of the plates inside the cells and the contact area. Any 18650 cells advertised greater than 3500 Mah (ie 5000+) are most likely bogus. There is only so much energy that can be packed into a finite amount of space.

I have 2S1P and 3S1P packs built for ReadyMadeRC and BuddyRC. The RMRC packs are rated in the 10-12 Amp max current range and have a MaH capacity of roughly 2900. The Buddy RC packs are rated at 20 Amps and have a capacity close to 2000 Mah. (capacities are measured useable capacity) I have flown close to an hour on the RMRC packs, and 35-40 minutes on the Buddy RC packs. Max current draw on the Nano Goblins is roughly 15 Amps. I see marked performance improvement by using the higher current Buddy RC packs, but at the expense of flight time. Flying line of sight, I prefer to have higher Current. Flying FPV, I prefer longer flight time.

These packs are newer versions of the ones I have and capacities and AMP ratings may be different due to the 18650 cells available when they were built:
2S1P
https://www.readymaderc.com/products/details/strix-power-stix-3200mah-2s-18650-li-ion-xt30
http://www.buddyrc.com/products/bud...tery-pack-with-xt30-connector-for-fight-drive
3S1P
https://www.readymaderc.com/products/details/strix-power-stix-3200mah-3s-18650-lithium-ion-xt30
http://www.buddyrc.com/products/bud...m-ion-li-ion-battery-pack-with-xt30-connector

Both BuddyRC and ReadyMade RC are very good places to get components from.

Cheers!
LitterBug

 

[MaxTheFliteFreak]

Thankyou to everyone who replied. I will take all of these things into consideration. שנה טובה!