A lot depends on how much current you are drawing from each cell. At higher current levels the Samsung 40T will run for longer than the Molicel M50A (or Samsung 50G, 50E).
The capacity rating is measured when the cell is discharged at less than 1A. It doesn’t tell you how well the cell will perform when much above that.
The ultra-high capacity cells are a lot less efficient than the cells with higher current ratings (but lower capacity) and that low efficiency means their voltage sags a lot when used near or above their rating and that shortens their running time.
Thanks for the answer, that’s exciting.
Just for my better understanding, I have a continuous discharge of 70A the molicell efficiency is ok with 7P 140A battery max. but I have a discharge of 70A with the Samsung 50E with 7P 70A battery max they sonst go so long as if I am using the 40T. have I understood that correctly
I’m surprised how bad the 50E is vs. P42A in actual energy delivered.
You rate them as:
P42A: Total energy delivered down to 3.2V at 10A continuous = 12.4Wh
50E: Total energy delivered down to 3.2V at 10A continuous = 12.2Wh
Is it because the 50E is a pre-production sample? Did they get any better later on?
Seems like the 50E has to be discharged at something tiny like 5 amps to make it worth at all.
I’m not sure I understand you but here goes…
Using those 50E’s at 10A/cell will probably give you about the same range as using 40T’s. That discharge current level is around the crossover point where one will be a better performer than the other.
But since the 40T will be running at a lot lower than its rating that helps to ensure good overall life. I would recommend using the 40T for that reason.
No, they did not get better. That is how they perform. This is also typical behavior when using a cell at near or over its rating…any cell.
A big issue is that ultra-high capacity batteries have high internal resistance. That causes a lot of voltage sag so you reach the low voltage cutoff of your ESC sooner. This voltage sag can easily wipe out any advantage in capacity the 50E has over other cells.
The 50E is also one of the worst performing ultra-high capacity 21700’s, along with the 48G. TBH, and with no disrespect towards those who use it, I think it’s a terrible choice for esk8 use. Other cells like the 50E2, 50E3, M50A, and 50G hold their voltage up better and give you more running time. None of them are great performers above about 10A though.
Yes, the 50E is best used at only up to about 5A-7A. At above that the high-performance 4000mAh (approx.) cells like the P42A and 40T are a better choice due to their lower internal resistance (which means less voltage sag).
We all do it but comparing capacity specs is a terrible way to choose a cell unless you are discharging at only an amp or two. The “nominal” capacity spec is typically measured at under one amp and tells you very little about how the cell will perform at higher discharge levels.
I cant wait to see where the Tesla Model 3 cell fits into this lineup!
Yeah I am working on an opinion piece that goes into cell efficiency vs run time, and how that should determine how we select cells.
It’s pretty much just going to be a summary of a bunch of things that @Battery_Mooch has been saying for years, that I am only just recently learning since he has joined our community
Have you finalized that product? I’m looking for BMS to fit into 50mm x 154mm space and capable of 16s. can’t find any with vesc support or with Bluetooth at least.
We have a VESC BMS coming in next week. It will still take 2-3 more weeks until we will offer it on the website. 36*130mm, CAN linked to VESC motor controller, 18S capable.
Godawful app (and the fact that there’s another app in the first place besides vesc tool) and the fact that it might receive support from @janpom for the davega
It has tighter integration with the VESC ecosystem so there are some really nice features like soft roll-off of battery discharge as you approach cell under-voltage limits to protect you and your battery at the same time as opposed to the hard cut that a discharge BMS gives you. You can still have braking but the VESC can prevent you from over-discharging any of the sub-packs.
It also has some really nice tracking for pack capacity and we are working on more metrics to ascertain metrics of pack health and deterioration.
That is exactly the size I was proposing other developers - it just makes sense 