18650 / 21700 li-ion vs lipo reciever packs

[Atomic Skull]

What are the pros and cons of a high amp 18650 or 21700 2S receiver pack vs a lipo receiver pack?

[nightflyr]

A simple google search would yield you an explanation:
https://blog.grepow.com/lipo-vs-18650-battery/



https://www.protoolreviews.com/news/...battles/48042/


https://www.researchgate.net/publica...he_21700_Cells



https://www.dnkpower.com/advantages-...21700-battery/

[Atomic Skull]

None of those links has anything to do with 18650 receiver packs vs lipo receiver packs. They are about power tools and electric cars which have somewhat different requirements than what we need.

[JimJW]

The main drawback of the Li-Ion batteries is the high internal resistance relative to LiPo. So a high C Li-Ion is less than 10C where a low rated LiPo is closer to 30C, and really high C LiPos are 90-100C (whatever that really means...)

What that means is that the higher internal resistance will cause the receiver/servo voltage to sag more at peak demand.

That said if you had one of those fancy Supercapacitor backups and/or a really big Capacitor plugged into the Receiver bus, you might be able to keep the average RX current low enough at the battery...

[JimJW]

On top of all that, if you overload the cells then they can go up in a spectacular way... (think laptop batteries & airplanes)

Some cells have a built in current limiting circuit to address that issue.

[Ace Dude]

Fromeco has been selling Lithium Ion receiver battery packs specifically for giant scale RC aircraft applications since the early 2000s. Their packs/regulators were quite popular in the heli community. They even made a heli specific "Arizona" regulator. With HV servos regulators are a thing of the past.

I used their Relions and Arizona regulators for several years and they worked well. The only drawback to their Relions was the 1C charge rate and the limited size options (2s and 2s2p).

https://fromeco-scale-avionics-llc.myshopify.com/

[ticedoff8]

The question is not really "What are the pros and cons of a high amp 18650 or 21700 2S receiver pack".
It seems to be more related to "What are the pros and cons of a Li-ion vs. LiPo receiver packs."
I don't know.

I do know that my Spektrum iX12 transmitter uses 3 18650 format 10,200mAh Li-ion in parallel (1S3P) for power.
The original pack was a 1S3P Li-ion 6,000mAh pack.
But, I can only charge those Li-Ion at 2A maximum vs 10A for the 2S 3500mAh LiPo receiver pack in my nitros.
And, 1S is "rated" at 3.7v, so I would expect 7.4v for a 2S Li-Ion.

But, if they are really rated for a 2A C-rating, I would hesitate using them as a receiver pack.
On my BEC (Goblin 570), I log current spikes >15A on most flights

So... you decide.

BTW:

Fromeco has been selling Lithium Ion receiver battery packs specifically for giant scale RC aircraft applications since the early 2000s. Their packs/regulators were quite popular in the heli community. They even made a heli specific "Arizona" regulator. With HV servos regulators are a thing of the past.

Those would have been analog servos and/or the 1st generation of digital servos. Analog servos where weak compared to digital and the new HV digital servos suck down current at a far higher rate than a 1st gen digital or any LV analog servo used in a helicopter today.

[nightflyr]

Originally Posted by Atomic Skull

None of those links has anything to do with 18650 receiver packs vs lipo receiver packs. They are about power tools and electric cars which have somewhat different requirements than what we need.

Are you being obtuse, lazy or just difficult???
Or just posting for the sake of posting and sitting back as you usually do and see what becomes of your threads?

A 18650 battery is still a 18650 battery
Same to same for Lipo
Your dealing with size, weight, energy density, capacity, discharge rates and voltage sag.

Might try doing a google comparison on your own.
to find the answers.

[Dennis Everett]

one drawback is the lower voltage , servo wont have as much speed or torque .

[K2Freak]

Are you being obtuse, lazy or just difficult??

Please be tolerant, this was a serious question. There is much to be learned by many of us...

[Ace Dude]

Originally Posted by ticedoff8

BTW:Those would have been analog servos and/or the 1st generation of digital servos. Analog servos where weak compared to digital and the new HV digital servos suck down current at a far higher rate than a 1st gen digital or any LV analog servo used in a helicopter today.

The Relions are still being used today. Not all current HV digital servos are power hungry and giant scale fixed wing aircraft use far more servos than we do on our helicopters.

As always, size the power system based on the load requirements. Testing is actually quite trivial and the better cell manufacturers likely provide discharge curves for their cells under various loads.

IIRC Tesla is/was using 18650 cells in their cars so the cells have have a lot of potential in specific applications.

[Lastinch1]

Isn't Li-ion similar to Li-fe batteries , both have a low c discharge of around 10C & they both go flat suddenly at the end of cycle ?

Lipo has a high discharge rate and the charge cycle more predictable.

[Dennis P]

The Lithion cells come in many different configurations. As mentioned they are popular in giant scale aircraft today with 9-10 servos all with 500 plus oz of torque. The ones I run are rated at 20c so plenty of amperage for any heli. They are a much safer cell than a lipo and they are 7.2 volts so not really any lower than a lipo . They discharge similar to a lipo but can be run down without the internal damage like a lipo. The down fall when comparing them on the lithion side is the slower charge rate, on the lipo side is the more unstable chemistry and discharge damage. This is what Jeti uses in there receiver packs, Fromeco packs and many others are selling them. I sure have no complaint with them.

[Atomic Skull]

Originally Posted by JimJW

On top of all that, if you overload the cells then they can go up in a spectacular way... (think laptop batteries & airplanes)

Some cells have a built in current limiting circuit to address that issue.

No. 18650 cells have built in pressure relief vents to prevent that. lipo batteries are much more likely to explode than an 18650 cell.

Originally Posted by JimJW

The main drawback of the Li-Ion batteries is the high internal resistance relative to LiPo. So a high C Li-Ion is less than 10C where a low rated LiPo is closer to 30C, and really high C LiPos are 90-100C (whatever that really means...)

There now exist high output 18650 li-ion cells that can output 20a or 30a continuous and up to 100a burst. Many electric cars have batteries built out of hundreds of 18650 cells welded together. Tesla is one company that does this.

[Atomic Skull]

Originally Posted by Dennis P

The Lithion cells come in many different configurations. As mentioned they are popular in giant scale aircraft today with 9-10 servos all with 500 plus oz of torque. The ones I run are rated at 20c so plenty of amperage for any heli. They are a much safer cell than a lipo and they are 7.2 volts so not really any lower than a lipo . They discharge similar to a lipo but can be run down without the internal damage like a lipo. The down fall when comparing them on the lithion side is the slower charge rate, on the lipo side is the more unstable chemistry and discharge damage. This is what Jeti uses in there receiver packs, Fromeco packs and many others are selling them. I sure have no complaint with them.

That's the sort of information I was looking for.


I was thinking of using these:


https://www.imrbatteries.com/sony-mu...h-25a-battery/


The spec sheets state that after 500 charge cycles at 4 amps they will have lost about 30% of their capacity. I assume they will retain their capacity for longer if charged at 1c (2.5a) instead.

[Atomic Skull]

Just found these:


https://www.thunderheartreviews.com/...h-20a-big.html


https://alofthobbies.com/qb-26800-6800mah-37v.html


A 2S pack made from these would be 80x52x26 only slightly bigger that the 2200mah receiver packs I use now and over twice the capacity.

[Staub]

https://lygte-info.dk/review/batteri...een)%20UK.html

30 amps continuous with cell voltage not dropping below 3v. When I get around to I plan on making receiver pack out of these.

[JimJW]

Originally Posted by Atomic Skull

No. 18650 cells have built in pressure relief vents to prevent that. lipo batteries are much more likely to explode than an 18650 cell.

There now exist high output 18650 li-ion cells that can output 20a or 30a continuous and up to 100a burst. Many electric cars have batteries built out of hundreds of 18650 cells welded together. Tesla is one company that does this.

Yeah, they’ve fixed that problem in general...

You can’t compare a Tesla to what an RC pack is doing. Peak power for a Tesla is 615 kW. The battery is 100kWh. So a ‘ludicrous mode’ launch or whatever they’re calling, has a peak draw of about 6C. A LiPo doing the same trick could be 6kWh but wouldn’t have the same range (only 20 miles vs. 348)

By all means try it out if you can convince yourself it will work. Just be careful because some of the Li-Ion cells are overrated in not just capacity, but also in the maximum current. Stick with big brands (Panasonic / Sony / Samsung)

[Ace Dude]

Originally Posted by Staub

https://lygte-info.dk/review/batteri...een)%20UK.html

30 amps continuous with cell voltage not dropping below 3v. When I get around to I plan on making receiver pack out of these.

Those cells hold up well under a constant 30A load.

[JimJW]

Originally Posted by Ace Dude

Those cells hold up well under a constant 30A load.

Is that sarcasm? By the looks of it there is a voltage sag of 0.4 to 0.6 volts at 30 Amps. For a 2S pack that would be a drop of a full volt. The capacity also drops to 2250 mAh vs. the rates capacity of 2600 mAh a 14% loss.

The 18650 cells have come a long ways. Are they good enough, maybe they are...