RC LiPo vs 18650 Cell High Power Packs

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mkp007   100 mW

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RC LiPo vs 18650 Cell High Power Packs

Post by mkp007 » Nov 20 2016 6:22pm

'
I know there is a ton of info deep in these threads about the pros and cons of building packs, and I want to specifically compare building a pack from an array of R/C LiPo packs and an array of 18650 cells. As we gather info and test results, I will update this post to summarize these pros and cons.

For comparison, I will choose the Turnigy Multistar 4S 16000mAh pack and Panasonic/Sanyo 18650GA cells. Let's say the goal is to get to 16S voltage and 64Ah energy with 150A capability. For the LiPo pack, you would need 4Sx4P array of 4S packs so 16 packs total. For the 18650 cells, you would need 16Sx20P for a total of 320 cells. The Multistar 4S 16Ah (MS-4S-16Ah) batteries are currently on sale for $50 so the total would be $800. The 18650GA cells are about $5/ea so that pack would be $1,600. The pack weight for the LiPo is 16*1.3kg = 20.8kg and for the 18650 cells 320*0.05kg*1.1= 17.6kg.

Performance Summary
Battery type: $/Wh, Wh/kg, Wh/L, Max Amps, Voltage Range
MS-4S-16Ah RC LiPo Pack: $0.21/Wh, 184Wh/kg, 411Wh/L, 320A, 16*(4.2-3.5)= 11.2V
18650GA Cell Pack: $0.39/Wh, 250Wh/kg, 550Wh/L, 180A, 16*(4.2-3.0)= 19.2V

MS-4S-16Ah RC LiPo Packs Pros: 1) No strip spot welding. 2) Performs very well under high loads with little voltage sag. 3) Dirt cheap right now ($0.21/Wh). 4) Capacity is in a tighter voltage range (4.2V to 3.5V) 5) capacity is not lost with higher loading (less internal resistance) 6) they run cooler under high loads
MS-4S-16Ah RC LiPo Packs Cons: 1) some consistency issues 2) damage tolerance 3) lifetime.

18650GA Cell Pros: 1) Up to 15% lighter weight for same energy stored (under low amp conditions) 2) Up to 10% smaller pack for same energy stored (under low amp conditions)
18650GA Cell Pros: 1) significant voltage sag under high loads. 2) significant capacity drop under high loads

Note: The 18650GA cell is not the highest amp rated cell out there but it is good. Even so, you need to add additional capacity to reduce the voltage sag and retain capacity. This skews the performance summary numbers above. I have tried to account for this a little by making the 18650 cell pack 20P giving it a little extra capacity but even this is probably not sufficient as each cell will draw 7.5A out of the rated 10A. As for the MS-4S-16Ah pack, each sub pack will only draw 37.5A which is 2.3C out of the 10C max rating. These packs have been tested to 3C and showed no loss in capacity (ref. https://endless-sphere.com/forums/viewt ... 75#p997783).


Reference Threads:
18650 Cell Packs:
Common pack design mistakes, how to avoid? https://endless-sphere.com/forums/viewt ... 14&t=84412
Spot Welding Copper Strips to 18650 Battery Cells https://endless-sphere.com/forums/viewt ... 14&t=84680

MultiStar Cell Packs:
Multistar High Capacity 6S 16000mAh https://endless-sphere.com/forums/viewt ... 14&t=63045


After researching building my pack from Panasonic/Sanyo 18650GA cells with plated copper strips, I decided to buy some of the Multistar 4S 16Ah battery packs for my initial testing. I got turned onto these when I was looking for a cheap power source to test my ESC, motor and prop. Here is a link to that: https://endless-sphere.com/forums/viewt ... 6#p1239597

So I would like to get everyone's perspective on this.
Last edited by mkp007 on Nov 21 2016 2:06am, edited 7 times in total.
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Re: RC LiPo vs 18650 Cell High Power Packs

Post by Hillhater » Nov 20 2016 7:00pm

You are certainly going to be resurecting a lot of prior discussion on this subject.
Basicly, RC has 2 main advantages....cost, and power potential (C rating) . Together with simplicity of assembly into various pack configurations.
...i guess that is 3 advantages ? :wink:
BUT.. The big disadvantage is a perception of fire risk !.. And low cycle life ! ( both arguable on sketchy info)
18650s have the advantage of better energy density (higher Whr/kg), higher cycle life and more robust packaging.
The choice really depends on the application.
For the test supply pack that you want , the Multistars are a realistic choice .
But if you were building a pack to power a device on a long range space probe....you wouldnt chose RCLipo ! 8)
...Now sit back and let the debate resume !
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mkp007   100 mW

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Re: RC LiPo vs 18650 Cell High Power Packs

Post by mkp007 » Nov 20 2016 7:19pm

Hillhater wrote:.....BUT.. The big disadvantage is a perception of fire risk !.. And low cycle life ! ( both arguable on sketchy info)....The choice really depends on the application........Now sit back and let the debate resume !
Much of the low cycle life posts I read were because they used the battery below 3.5V. Can't do that with these LiPo batteries. I'm very curious about the perception of fire risk. Again, was this because of misuse? Or is it a real problem with turnigy design and manufacturing? Maybe the cells are easier to damage is the primary concern as they don't have a hard candy shell. They kindof just melt in your hands. :o
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Re: RC LiPo vs 18650 Cell High Power Packs

Post by Hillhater » Nov 20 2016 7:25pm

If you search for threads on lipo fires (and 18650 fires !). You will find that the majority are the result of misuse, over charging, over discharging , poor assembly, shorting wiring etc etc...IE ..operator error.
There are however one or two unexplained incidents.
The weighting towards RC lipo, is possibly explained by the fact that it has been in use by hobbyists and Ebikers much longer than 18650s. Also RC hobbyists have a tendency to crash their aircraft , helecopters, cars etc...which is not good for long life !
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Re: RC LiPo vs 18650 Cell High Power Packs

Post by 999zip999 » Nov 20 2016 9:51pm

As posted before look up lipo fire. All batteries can catch fire.

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Re: RC LiPo vs 18650 Cell High Power Packs

Post by wesnewell » Nov 21 2016 12:48am

Rc lipo is all I use. I've never had a problem with it, other than shorting out my 100V pack once and blowing the connectors off the ends and putting a few holes in my fingers from the plasma blast. That same pack I ran for over 4 years and over 15K miles. When I retired it not long ago it still had ~90% capacity, but sag had increased somewhat. I don't think there's any difference in life cycle between it and ICR18650's, except I've read of many 18650 packs dying early because the cells just can't take high C rate discharges like rc lipo can. I never run my lipo below 10% soc and most times not below 20% soc. Other than that, they get no special treatment. I leave them in the 110F heat during the summer and and down to below freezing during the winter, The one thing I don;t do is leave them charged at full charge more than maybe over night every once in a while, but usually run the down to 4.1V per cell after a normal 4.2V charge per cell. I've bee waiting 6 years for something better and I haven't seen it yet. I run 10ah 24s packs and never pull more than 4C from them. Most times I run at 1C or less. And that's still ~1000W with a 24s pack.
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Re: RC LiPo vs 18650 Cell High Power Packs

Post by Punx0r » Nov 21 2016 4:03am

mkp007 wrote:'

MS-4S-16Ah RC LiPo Packs Pros: 2) Performs very well under high loads with little voltage sag.
I thought the multistars were, realistically, good for 3C discharge? I remember discounting them in favour of an 18650 pack on the basis of insufficient discharge. Regular RC LiCo is much better, but also much lower energy density than the multistars.

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