mkp007
100 mW
'
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/viewtopic.php?f=14&t=61672&start=175#p997783).
Reference Threads:
18650 Cell Packs:
Common pack design mistakes, how to avoid? https://endless-sphere.com/forums/viewtopic.php?f=14&t=84412
Spot Welding Copper Strips to 18650 Battery Cells https://endless-sphere.com/forums/viewtopic.php?f=14&t=84680
MultiStar Cell Packs:
Multistar High Capacity 6S 16000mAh https://endless-sphere.com/forums/viewtopic.php?f=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/viewtopic.php?f=14&t=84726#p1239597
So I would like to get everyone's perspective on this.
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/viewtopic.php?f=14&t=61672&start=175#p997783).
Reference Threads:
18650 Cell Packs:
Common pack design mistakes, how to avoid? https://endless-sphere.com/forums/viewtopic.php?f=14&t=84412
Spot Welding Copper Strips to 18650 Battery Cells https://endless-sphere.com/forums/viewtopic.php?f=14&t=84680
MultiStar Cell Packs:
Multistar High Capacity 6S 16000mAh https://endless-sphere.com/forums/viewtopic.php?f=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/viewtopic.php?f=14&t=84726#p1239597
So I would like to get everyone's perspective on this.