There seems to be more and more choice for cell-based electric bicycles batteries. For example, these 14s, 50AH monster that could potentially replace 4 Bonkas:
But the continuous discharge rate is only 70A… I guess the OpenPPG requires something that is closer to 150A, right?
Yeah the X4 needs to draw 150 continuous and close to 300 burst. I see 240 amps in the initial climb out. That’s not a short burst, it’s several minutes. Also my 4 Bonkas were $1,300CDN shipped.
Those e bike batteries have a nice, heavy, hard shell case that we don’t need and typically come with built in BMS which would be nice. Also they’ll probably last a lot more cycles.
There’s a great battery comparison write up you may want to check out if you haven’t already seen it, complete with a spreadsheet of various test results:
I was looking into building an 18650 pack for the X4. The biggest problem amp draw across standard nickel strips. You need to look into something like this to build it: Custom Power Lithium Battery Connector 6s8p 18650 21700 32650 Busbar Copper Nickel Copper Nickel Sheet - Buy 18650 21700 32650 Busbar Copper Nickel Plate Power Battery Pack Busbar Copper Copper Busbar Price,18650 Copper Nickel Busbar Copper Busbar Price,Copper Busbar Connector 18650 Busbars Copper Busbar For Li Ion Batteries Product on Alibaba.com
You also need to go 14s20p so not over work the pack. I actually bought Sony VTC6 15amp 3000mah to build one but then the 140 was teased, damnit! pack would be ~ 35-40lbs.
specs would have been:
14s20P (280 Sony VTC6 cells) 60ah
300a nominal 600peak up to 80c.
the problem with the ebike batteries usually are, is that they are not rated for such high amp draw.
they can use cheaper 18650 cells.
because of this drawback, I built my own 18650 battery pack,
I documented everything along the build process.
(note: I planned 15p first, but that was too little of capacity so I upgraded to 20p later. If I’d built a new system today, I’d go for 25P )
See it here: 13S15P Battery Pack Build
and then follow up here: Follow up post: Case for 13S20P Li-Ion Battery Pack
Reading your comments, it looks like you manage to get about 25 min without any thermal assist.
That’s about the same as I get with my 4 x 7s Bonkas (using a free flight canopy).
With thermal assist, my record so far is 1H30 (I hope to do much better once the rainy season is over).
If it’s to be believed… they show the cells as Samsung INR21700-50E. Looking that cell up on a different site show the specifications:
Model: INR21700-50E Size: 21700 Style: Flat Top Nominal Capacity: 5000mAh Continuous Discharge Rating: 9.8A Nominal Voltage: 3.6v Protected: No Rechargeable: Yes Approximate Dimensions: 20.25mm x 70.8mm Approximate Weight: 69g
The pack they show being rated
Maximum peak discharge current (A): 210A
Maximum Continuous Discharge Current (A): 70A
Cell Combination: 14 Series 10 Parallel
Cell Quantity (parallel x series): 140 pcs
They’re actually conservative on the max continuous discharge (70A vs 100A), and probably overly generous with the peak. From the cell we’re looking at a 2C rating which (52V X 50Ah = 2,600Watt-hour) puts this being capable of around 5,200 Watt. It’ll come up way short, unfortunately.