The best middle ground between Li-ion and Lipo is LiFePO4 cells.
A123s can do 70A continuously and 120A pulse. A 12S2P pack would be perfect. 38.4V nominal and 140A continuous discharge. 5000mAh is nothing special but it would be fine for most people. Guessing around 8 miles range.
I havenât personally tried A123âs but judging by there specs, they look like a better alternative than Li-ions
Boosted uses them and I also made a Boosted spec pack. I am not 100% sure about voltage sag but it still sagged a bit on hard acceleration but it was never an issue going up hills and such.
To match lipo specs, 2P a123 cells would work.
Iâm want to try them, just hard to find a place to source legit ones for a reasonable price. This is one thing I hate about buying non-lipo batteries. You never 100% know if youâre going to get legit ones or some counterfeit stuffâŚ
A123s are pretty easy to source. There are a bunch of overstock ones on eBay from accredited sellers.
Even my 300a Lipo pack sags a little. I donât know what it would take to eliminate sag completely.
Do you have any sellers you can recommend?
A 0ohm internal resistance cell that has a non thermal reaction.
Hereâs a good example on how to mitigate voltage sag and under performance on a li-ion battery
Budget: $300 Options: 60 NCR18650GA, 44 Sony VTC6. (I get the 500+ discount since we buy a ton of batteries for work.)
Possible configuration: 10S6P GA with max continuous draw of 60A 11S4P VTC6 with max continuous draw of 120A or temp cutoff of 80c
1KW load assumed.
1000/36v nominal / 6p = 4.62A/cell Now I can use Henrikâs website (Lygte) to find my actual nominal voltage at this power setting.
At 5A continuous, nominal voltage is closer to 3.48V 1000/(34.8*6) = 4.79A/cell So now we have nominal voltage and current draw for a continuous 1000W.
At this power setting, the cells have 3.2Ah of capacity. So total energy can be measured by: 3.48v3.2Ah60cells = 668Wh.
So I should be able to run roughly 40minutes at a constant 1000W. Which in reality is more like 35 (based on experience)
Same process can be done for the VTC6. 1000W/(39.64) = 6.31A @7A: nominal v= 3.58, capacity = 2.9Ah 1000W/(39.384) = 6.34A so weâre being a little conservative by using the 7A curve. Total energy = 3.582.940 = 415Wh Runtime @1000W: 25minutes.
So if you constantly pulled 1000W then the 10S6P would be the way to go as it has 50% more endurance.
Hereâs the upside to the VTC6s though. Your max power draw is capped at 2000W pulling 10A/cell with the GAs. Using VTC6, your max power draw is capped at 3000W pulling 20A/cell. In other words 50% more power.
So if you need endurance, 10S6P GA cells If you want power 11S4P VTC6s. You can most likely pull more power from both cells for short periods of time, but itâll most likely harm the life of your pack, (300 cycles, 80% capacity)
The same trade study can be done with LiPos and I would have done an example but I dont have data in front of me rn.
Cheers!
Good overview/calculations!
Just proves if the power demand is not as high, to go with bigger capacity pack but with less max power available.
This again brings us to the ââcalculationââ - prediction, on what the typical power demand might be in the situation - environment the eboard is gonna be used.
That part is pretty easy, for the air drag we can simplify and assume a 1m^2 frontal area and a 1Cd, and just calculate the torque on the wheel related to the grade and mass of the rider+board, the only factor missing is drivetrain and electric efficiency that can be guessed, or calculated using the motor parameters, but that is more complex, but the mechanical power/torque on the wheel that we need is easy
I actually have the exact cd for a human standing, sitting, etc⌠(Dont ask, aerospace engineering stuff lol) Will look it up when I get home
If from this we come up with a realistic energy use - demand calculation that would be great! Would make it possible to more realistically calculate max mileage, system max amps etcâŚ
But the raptor 2 can pull 120 amps with the Samsung 25r in a 10s4p (with manufacturers rating of 80 amp without impacting the cells life and you can still get 25 miles!!!
(Ps Iâm being sarcastic)
Nice, looking forward to it, i measure the frontal area in myself and was something like 0,7m^2, the cd i found various papers with modeling, but the numbers were far off from each other
If i have time i will plot it today so we can see whats happening
Just simply use my android app and make a video of it. There you can see the actual voltage, motor and battery amp draw, actual watts, speed and consumed, charged and average wh and ah. Then we can share the videos and have a much better picture what really happens to the VESC when we ride.
Here is a example how the video looks like then. this video is not modified. That is exactly the result you get. So you can record your ride and see the realtime data. You need a HM-10 bluetooth module for it which you can get here. https://de.aliexpress.com/item/HM-10-BLE-Bluetooth-4-0-CC2540-CC2541-Serial-Wireless-Module/32516357718.html?spm=2114.13010608.0.0.cbyTeS&detailNewVersion=&categoryId=400103
If you want to switch change the motor amps configuration you need to flash the VESC with my firmware as well. But to only watch the realtime data the standard firmware works as well.
Available in the Google Play store
or here
Windows BLDC-Tool, Modified Firmware, Ubuntu BLDC-Tool and Android app
More information you can read here. http://www.electric-skateboard.builders/t/extended-bldc-tool-with-watt-control-mode-ppm-cruise-control-and-individual-throttle-curve/12286
Experimenting only gets you so far if you donât understand the math/physics. You cannot get a full picture without understanding. Different setups with different sized people and different riding conditions should be taken into account and unless we have a model to explain things, you might as well just guess.
This is just the way I was taught to approach an engineering problem.
Edit: Youâd need a dyno to run an accurate experiment the way you show your video to get any relevant data.
It is pretty cool though
The good thing is you get the exact data for your board. So it helps to analyse and understand your own board. And you can also see how much of your time you are really drawing max or high amps. And i guess the most will be surprised. Another great thing is that we can also see the VESC max min motor and battery settings in the video. But that only works with my firmware.
Will give it a go next week once the build is completed
18650 GAâs